Fresh R. ambiguum leaves were collected at an elevation of 3,291 meters in Gongga Mountain National Nature Reserve in Sichuan, China, and a corresponding voucher specimen was deposited at the West China Subalpine Botanical Garden in Dujiangyan under voucher number 2019-GG-015. DNA was extracted with a modified CTAB method and sequenced on an Illumina HiSeq X Ten platform. The project generated 8 gigabases of paired-end reads, corresponding to an estimated sequencing depth of about 18-fold, which the authors compared with the approximately 650-megabase size reported for most Rhododendron genomes.

The researchers assembled the reads with MIRA and NOVOplasty, using the published chloroplast genomes of R. × pulchrum and R. calophytum as references. Annotation was performed with CpGAVAS and supplemented by manual curation and BLAST gene verification. The completed R. ambiguum chloroplast genome was deposited in GenBank under accession OR455462. The assembly was circular and quadripartite, spanning 207,478 base pairs: two inverted repeats of 47,249 base pairs each, a large single-copy region of 110,367 base pairs and a small single-copy region of 2,613 base pairs.

The R. ambiguum genome contained 110 unique genes, comprising 77 protein-coding genes, 29 transfer RNA genes and four ribosomal RNA genes. Sixteen genes were duplicated in the inverted repeats, and overall GC content was 35.8%. Fourteen genes contained introns: 10 protein-coding genes and four transfer RNA genes. The ycf3 gene contained two introns, while the annotated-gene table also marked rps12 as trans-spliced. These features followed the typical organization reported for many terrestrial plant chloroplast genomes, although the assembled sequence was larger than the 120,000–160,000-base-pair range cited for a typical angiosperm chloroplast genome.

Comparisons across the 18 Rhododendron genomes revealed extensive variation in gene order and in the boundaries of the large single-copy, small single-copy and inverted-repeat regions. Eleven species had genomes near 200,000 base pairs and relatively small small-single-copy regions. R. simsii, R. latoucheae and R. × pulchrum had shorter total genomes, although R. simsii possessed a 69,783-base-pair small-single-copy region. R. molle and R. huadingense had the longest large single-copy regions and shortest inverted repeats, while R. kawakamii and R. datiandingense differed markedly in regional lengths and gene arrangement. Across all 18 genomes, total length ranged from 146,941 base pairs in R. × pulchrum to 230,777 base pairs in R. kawakamii. The authors cautioned that mapping or annotation differences could also contribute to unusual structural patterns.

Sliding-window analysis of 11 species with similar genome structures, using 600-base-pair windows and 200-base-pair steps, identified four highly variable non-coding regions with nucleotide-diversity values of at least 0.095: trnI-rpoB, ndhE-psaC, rpl32-ndhF and rrn16S-trnI. The first two were located in the large single-copy region, rpl32-ndhF in the small single-copy region and rrn16S-trnI in an inverted repeat. Non-coding regions were more variable than coding regions in this dataset. The R. ambiguum genome also contained 76 simple sequence repeats, including 69 mononucleotide, six dinucleotide and one trinucleotide repeat. Fifty-nine were in intergenic regions, and none was detected in the small single-copy region.

Codon analysis across the 18 genomes identified a general preference for codons ending in A or U. Relative synonymous codon-usage values ranged from 0.317 for CGC to 2.17 for UUA, with UUA preferentially used for leucine. Selection-pressure estimates were calculated for 53 shared protein-coding genes. Among 42 genes for which an applicable nonsynonymous-to-synonymous substitution ratio, or Ka/Ks ratio, was obtained, 38 had ratios below 1 and the mean was 0.496. Four genes—cemA, rps4, rpl16 and rpl14—had estimated ratios above 1. These were interpreted by the authors as signs of positive selection, rather than as direct measurements of adaptive function.

Bayesian inference based on shared protein-coding genes divided the sampled Rhododendron species into three broad clades, with node values reported as approximately 1 for nearly all nodes. Analyses of both shared genes and complete chloroplast genomes placed R. ambiguum near R. concinnum. However, the two datasets produced inconsistent topologies, and relationships among Rhododendron subgenera remained unresolved. The authors associated much of this uncertainty with the placement of subgenus Tsutsusi and noted that natural hybridization, introgression and intermediate morphologies complicate taxonomic identification within the genus.

The study provides a complete chloroplast-genome resource for R. ambiguum and identifies variable regions that may serve as candidate markers in future phylogenetic analysis. Its comparative scope was limited to 18 Rhododendron chloroplast genomes, with V. bracteatum, V. macrocarpon and V. uliginosum added as outgroups, and the phylogenetic results did not establish a genus-wide topology. Genome mapping and annotation may influence some apparent structural differences, while the Ka/Ks estimates do not directly demonstrate the causes of selection. The assembled sequence and associated datasets are available through the NCBI Bioproject and GenBank accession OR455462.

Subject of Research: Comparative chloroplast genomics and phylogeny of Rhododendron species

Article Title: The complete chloroplast genome of Rhododendron ambiguum and comparative genomics of related species

Article References: Ma, W. B., Ou, Y., Dayananda, B., Ji, H. J., & Yu, T. (2024). The complete chloroplast genome of Rhododendron ambiguum and comparative genomics of related species. Comparative Cytogenetics, 18, 143-159. https://doi.org/10.3897/compcytogen.18.119929

Image Credits: AI Generated

DOI: 10.3897/compcytogen.18.119929

Keywords: Rhododendron ambiguum, chloroplast genome, comparative genomics, phylogenetics, plant molecular biology, Rhododendron, Bayesian inference, DNA barcoding, codon usage, selection pressure, complete, chloroplast

The researchers combined the 25 newly assembled chloroplast genomes with 36 previously reported genomes retrieved from the NCBI database. Across the resulting dataset, genome sizes ranged from 151,073 to 154,259 base pairs. The genomes retained a typical quadripartite structure and showed high conservation in gene content, with 112 unique genes, as well as in gene organization, guanine–cytosine content and intron composition. Inverted-repeat boundaries, amino-acid composition and codon usage were also highly similar among species, while simple sequence repeats showed a moderate degree of variation.

Maximum-likelihood phylogenetic analyses supported the division of Gnaphalieae into the two subtribes Relhaniinae and Gnaphaliinae and placed the Relhania clade as the earliest-diverging lineage in the chloroplast tree. The analysis did not recover several large genera—including Gnaphalium, Anaphalis, Pseudognaphalium and Helichrysum—as monophyletic. The backbone of the Filago–Leontopodium–Antennaria–Gamochaeta, or FLAG, clade received only weak support, contrasting with earlier topologies based on nuclear ITS and ETS data. The authors characterized this difference between chloroplast and nuclear evidence as cytonuclear discordance and said both sources of data would be needed for accurate taxonomic inference in rapidly radiating lineages.

The findings and limitations summarized here are based on the supplied abstract of an accepted research article that the publisher states remains subject to further edits. The chloroplast dataset covers 61 species rather than the approximately 2,100 species estimated to occur in the tribe, and its phylogenetic signal was not uniform across the group. The reported non-monophyly and weak support should therefore be interpreted as results of this chloroplast-based analysis rather than as a definitive revision of Gnaphalieae taxonomy.

Subject of Research: Comparative chloroplast genomics and phylogenetic relationships in the plant tribe Gnaphalieae

Article Title: Comparative chloroplast genomics of Gnaphalieae (Asteraceae)

Article References: Abdullah, & Heidari, P. (2026). Comparative chloroplast genomics of Gnaphalieae (Asteraceae). BMC Plant Biology. https://doi.org/10.1186/s12870-026-10004-y

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10004-y

Keywords: Gnaphalieae, Asteraceae, chloroplast genomes, comparative genomics, phylogenetics, maximum likelihood, cytonuclear discordance, taxonomy, Comparative, chloroplast, genomics, scientific research

Amorphophallus is an economically and ornamentally important genus in the arum family, Araceae. Traditional identification is challenging because members of the genus show pronounced morphological plasticity, and the timing of leaf and flower emergence can also be separated. The study therefore used chloroplast-genome comparisons to investigate genome structure, codon usage bias and phylogenetic relationships, including the placement of Amorphophallus among other sampled Araceae.

Researchers sequenced, assembled and annotated chloroplast genomes from A. pendulus, A. glaucophyllus, A. fornicatus, A. macrophyllus, A. titanum and A. hewittii using the PacBio Revio platform. When combined with data from 10 additional species, the dataset covered 16 Amorphophallus taxa. Their chloroplast genomes ranged from 152,492 to 185,810 base pairs and displayed the characteristic quadripartite structure, with the study treating differences in genome size, inverted-repeat regions and gene regions as part of the comparative analysis.

Structural variation was detected in the inverted-repeat regions of several genomes. Expansion of this region occurred in A. macrophyllus and A. glaucophyllus, while contraction was found in A. fornicatus. The comparison also identified the chloroplast gene accD as a highly variable region, with a reported nucleotide diversity value of Pi = 0.1217. These results show that the sampled genomes share a broad structural pattern while differing in specific regions relevant to comparative analysis.

The researchers also assessed codon usage across the 16 chloroplast genomes. Codons showed a bias toward sequences ending in A or U rather than G or C, and the analysis identified natural selection as the predominant driving force behind this pattern. Despite variation among species, six codons were classified as optimal in all 16 Amorphophallus species, indicating a common set of preferred codons within the sampled group. The analysis therefore characterized both shared codon-usage features and differences among individual taxa.

Only C-to-U base-editing events were detected in the chloroplast genomes of the 16 species. In other words, the reported editing pattern was directional within this dataset: cytosine-to-uracil changes were observed, but the analysis did not identify the corresponding U-to-C events. The findings add another layer to the comparison of chloroplast genomes, alongside genome-size variation, inverted-repeat changes and codon-usage bias.

One of the study’s most direct identification results came from its search for an informative DNA barcoding region. The researchers identified the genomic segment spanning 80,401–81,200 base pairs as an optimal barcoding window for the sampled species. Five diagnostic loci within that window could discriminate all 16 Amorphophallus species examined. This finding is specific to the comparative sample used in the study and provides a molecular marker for distinguishing the included taxa.

Phylogenetic reconstruction recovered all sampled Amorphophallus species as a monophyletic group, which the researchers divided into three major clades: Continental Asia I, Continental Asia II and Southeast Asia. The Southeast Asia clade contained A. fornicatus, A. pendulus, A. hewittii and A. titanum. The Continental Asia II clade included A. glaucophyllus, A. macrophyllus, A. konjac, A. krausei, A. albus and A. kachinensis. Continental Asia I comprised A. coaetaneus, A. tonkinensis, A. yunnanensis, A. kiusianus, A. muelleri and one accession that was not identified to species.

Within the wider Araceae sample, Symplocarpus was sister to the remaining sampled members of the family. Amorphophallus was most closely related to Syngonium, Xanthosoma, Zomicarpella and Caladium. Together, the chloroplast analyses provide a comparative account of structural evolution, codon usage and lineage relationships in 16 Amorphophallus species, while the five-locus barcoding window offers a sequence-based means of discriminating the taxa included in the study. The authors identify species identification, germplasm conservation and molecular breeding as areas supported by these findings.

Subject of Research: Comparative chloroplast genomics of structure, codon usage and phylogeny in 16 Amorphophallus species

Article Title: Comparative chloroplast genomics in Amorphophallus: revealing codon usage patterns and phylogenetic clades across 16 species

Article References: Shi, H., Lu, Q., Qi, Y., Yang, M., Zhao, M., Gao, P., Huang, F., Zhao, J., Li, L., & Yu, L. (2026). Comparative chloroplast genomics in Amorphophallus: revealing codon usage patterns and phylogenetic clades across 16 species. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09945-1

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09945-1

Keywords: Amorphophallus, chloroplast genomes, comparative genomics, codon usage bias, plant phylogenetics, DNA barcoding, genome structure, Araceae, base editing, species identification, Comparative, chloroplast

The Zingiberaceae, the ginger family, is the largest lineage in the order Zingiberales, with more than 57 genera and over 1,600 species spread across tropical and subtropical Asia. It includes some of humanity’s most familiar spices and medicines: ginger, turmeric, cardamom, galangal, and white ginger. Within this sprawling family, Amomum has long stood out for its value as a spice and its extensive use in traditional remedies across Southeast Asia, where its species have served as substitutes for true cardamom. But despite this importance, the genus has been a taxonomic headache. Species identification relies heavily on inflorescence characteristics that bloom only once or twice a year, and morphological convergence has repeatedly blurred the boundaries between Amomum and its close relatives.

Previous molecular studies had already confirmed that Amomum, as traditionally circumscribed, was paraphyletic, meaning it excluded some of its own descendants. A comprehensive taxonomic revision by de Boer and colleagues in 2018 resurrected three old genera, Conamomum, Meistera, and Wurfbainia, and described three new ones, Epiamomum, Lanxangia, and Sundamomum, within the broader Amomum complex. That revision updated the list of Amomum species in Peninsular Malaysia to 28 species spread across five genera. Yet even with this framework in place, species-level relationships among Peninsular Malaysian taxa remained poorly resolved, particularly where morphological convergence is common and herbarium specimens with both vegetative and reproductive material are scarce.

To break through this impasse, researchers turned to chloroplast phylogenomics, a powerful approach that exploits the relatively conserved structure and slower mutation rates of chloroplast genes to resolve evolutionary relationships. The team collected fresh flowering material of seven Amomum species from type localities across Peninsular Malaysia, including sites at Batu Caves in Selangor, the Forest Research Institute Malaysia, Penang Hill, and the Penang Botanic Gardens. Each species was represented by two biological replicates, and tissues were harvested at equivalent developmental stages during the flowering season between March and April 2022, always between 8 and 10 in the morning, to ensure comparability.

The sequencing effort generated approximately 170 gigabytes of raw RNA data. From the transcriptome assemblies, the researchers identified 85 chloroplast protein-coding genes, of which 43 complete genes were retained for analysis after excluding short or incomplete sequences. The concatenated length of these genes ranged from 27,414 to 27,500 base pairs across the seven species, with GC content between 37.4 and 38.0 percent, a figure characteristic of the AT-biased plastid genomes of monocots. Codon position analyses revealed purifying selection at the first codon position, stronger evolutionary constraint at the second, and relaxed selection at the third, where synonymous substitutions accumulate more freely and contribute to evolutionary plasticity.

Beyond raw sequence data, the study also examined chloroplast gene expression profiles across species. A hierarchical clustering heatmap of normalized expression values revealed distinct species-specific transcriptional signatures. Most strikingly, the species Amomum elan formed a separate cluster entirely, with genes such as ycf68, ycf4, rpl33, and rps14 showing their highest expression levels in this species, while Amomum aculeatum and Amomum trilobum generally displayed lower expression across the same genes. Meanwhile, Amomum trilobum and Amomum testaceum clustered closely together, suggesting similar plastid gene regulation. These patterns hint at lineage-specific functional divergence in chloroplast biology that may reflect adaptation to different ecological niches or regulatory changes accumulated over evolutionary time.

Sliding-window analysis of nucleotide diversity identified clear hotspots of sequence polymorphism. The ndhJ gene region exhibited the highest nucleotide diversity, followed by elevated values near psbT, psbZ, and rps14. These loci could serve as molecular markers for species differentiation and evolutionary research, filling a critical gap in a group where traditional DNA barcoding has struggled. Conversely, genes such as rbcL, psbA, and atpI, which perform essential photosynthetic or housekeeping functions, remained highly conserved with minimal variability, reducing their effectiveness in distinguishing species-level variation. The contrast between hypervariable and conserved regions highlights the dynamic evolutionary forces shaping the Amomum chloroplast genome.

For the phylogenetic reconstruction, the team combined their transcriptome-derived sequences with 93 related taxa downloaded from NCBI GenBank and two outgroups, Hedychium coronarium and Roscoea humeana. Bayesian inference and maximum likelihood analyses, both based on 43 concatenated chloroplast genes totaling 28,794 aligned positions, recovered two major well-supported clades. Clade A primarily comprised species from the genera Zingiber and Kaempferia, while Clade B contained the Amomum-Alpinia complex, including representatives of Amomum, Wurfbainia, Lanxangia, and Alpinia. All seven Peninsular Malaysian species fell within Clade B, though their positions within it varied considerably.

The most consequential finding concerns Amomum trilobum. In both the Bayesian and maximum likelihood trees, this species showed a closer association with the Wurfbainia lineage than with the core Amomum-Alpinia cluster, suggesting that its transfer to Wurfbainia may be warranted pending further taxonomic evaluation. Similarly, Amomum uliginosum and Amomum testaceum, previously transferred to Wurfbainia, resolved within the Wurfbainia lineage, supporting the 2018 taxonomic revision. Meanwhile, Amomum curtisii, Amomum elan, and Amomum smithiae clustered together with strong support, forming a sister lineage to two Alpinia species. These placements collectively affirm the paraphyletic nature of Amomum as traditionally circumscribed and reinforce the recognition of segregate genera within the broader complex.

The study provides the first transcriptome-derived chloroplast phylogenomic framework for Peninsular Malaysian Amomum, demonstrating that even partial plastome data recovered from RNA sequencing can recover robust phylogenetic patterns where complete plastomes are unavailable. The identification of hypervariable loci such as ndhJ, psbT, and rps14 offers promising candidates for future barcoding and phylogeographic studies, while the species-specific expression profiles of genes like rps14, rpl33, and ycf68 suggest potential functional shifts that merit further investigation. As genomic datasets expand and taxon sampling broadens, the evolutionary history of this charismatic ginger lineage is finally coming into focus, one chloroplast gene at a time.

Subject of Research: Chloroplast phylogenomics of Amomum s.l. in Peninsular Malaysia reveals paraphyly and species-level evolutionary relationships within Zingiberaceae.

Article Title: Comprehensive plastid phylogenomics reveal the phylogeny of Amomum s.l. ( Zingiberaceae ) from Peninsular Malaysia

Article References: Fareed, F. S., Singaram, N., Abdul Malek, A. Z., Hashim, A. M., Sam, Y. Y., & Hin, O. I. (2026). Comprehensive plastid phylogenomics reveal the phylogeny of Amomum s.l. (Zingiberaceae) from Peninsular Malaysia. PhytoKeys, 276, 151-174. https://doi.org/10.3897/phytokeys.276.192768

Image Credits: AI Generated

DOI: 10.3897/phytokeys.276.192768

Keywords: phylogenomics, chloroplast, Zingiberaceae, Amomum, Peninsular Malaysia, RNA sequencing, taxonomy, Wurfbainia, nucleotide diversity, ginger family, Comprehensive, plastid

The bypass in question is known as GOC, an acronym drawn from its three components: glycolate oxidase, oxalate oxidase, and catalase. In earlier work by collaborators, constitutive expression of these three enzymes in chloroplasts enhanced biomass in rice and potato, apparently by short-circuiting photorespiration and raising the CO2 concentration around Rubisco. The logic behind the new experiment was elegant. Rather than running the bypass all the time, which carries metabolic costs when water is plentiful, the researchers placed the three transgenes under the control of drought-inducible promoters, so the pathway would spin up only when water scarcity made photorespiration most punishing. The goal was to increase CO2 around Rubisco precisely under stress and thereby improve the drought tolerance of rice.

At the transcript level, the design worked spectacularly. Under drought stress, messenger RNA from all three transgenes was strongly induced, reaching levels tens of times higher than the endogenous control gene used for comparison. By every conventional molecular metric, the synthetic pathway had been activated. The promoters fired, the chloroplast transit peptides were in place, and the cell was flooded with instructions for building the three enzymes. If gene expression stopped at transcription, this would have been a textbook success story for inducible metabolic engineering.

But the story collapsed at the next level of the central dogma. When the team measured the corresponding proteins, neither glycolate oxidase, oxalate oxidase, nor catalase accumulated in proportion to their transcripts. The enzymatic activities told the same tale: under drought, and even more strikingly under abscisic acid or osmotic treatment, the activities remained at wild type levels or actually decreased. Abscisic acid is the hormone that orchestrates drought responses in plants, and osmotic treatment mimics the cellular dehydration that drought causes, so these assays probed the same stress program from different angles. In every case, the massive transcript induction decoupled from any functional protein accumulation.

The phenotypic consequences followed directly. Transgenic lines showed no improved tolerance to drought or osmotic stress compared with wild type plants. Under osmotic stress, the engineered lines actually exhibited greater membrane damage than their unmodified counterparts, an unexpected and unwelcome result. Membrane damage is a standard readout of cellular injury under water stress, so the bypass not only failed to protect the plants but appeared to leave them more vulnerable. Without functional enzymes in the chloroplast, the synthetic pathway existed only as a blueprint, and the plants paid the price of carrying the transgenes without receiving any benefit.

Why would a cell transcribe genes at extraordinary rates yet fail to produce the proteins? The authors propose two converging bottlenecks. The first is a stress-activated blockade of chloroplast protein import. Chloroplast-targeted enzymes are synthesized in the cytosol as precursor proteins bearing N-terminal transit peptides, and they must be threaded through the TOC-TIC translocon complexes in the chloroplast envelopes. Recent work has identified a chloroplast ubiquitin ligase system, sometimes called CHLORAD, that tags envelope and imported proteins for ubiquitin-mediated degradation, allowing the cell to regulate chloroplast proteome composition from outside. The researchers suggest that drought and its hormonal signals may activate a CHLORAD-like mechanism that degrades or blocks incoming precursor proteins, so the enzymes are made and then destroyed, or never admitted at all.

The second bottleneck is translational capacity. The GOC bypass requires the coordinated production of three separate chloroplast-targeted enzymes, each competing for ribosomes, chaperones, and import machinery. Under stress, the cell globally represses protein synthesis to conserve resources, prioritizing survival proteins over growth. Multiple transgenes induced simultaneously under such conditions may simply overwhelm the diminished translational and import capacity, so none of them reaches functional accumulation. The combination of an import blockade and insufficient translation would explain why transcripts soared while proteins and activities flatlined.

The implications reach far beyond this single experiment. Stress-inducible expression is an increasingly popular strategy in synthetic biology for crops, because constitutive expression of engineered pathways can carry fitness costs when the pathway is not needed. Inducible promoters promise to spend the metabolic budget only when it matters. Yet this study delivers a cautionary empirical note: transcript induction alone does not guarantee protein synthesis or delivery to the chloroplast. A pathway that looks switched on at the RNA level may be entirely dark at the protein level, and the disconnect is invisible unless researchers verify protein accumulation and enzymatic activity under the exact stress conditions the pathway is meant to serve.

For the broader community engineering photorespiratory bypasses and other chloroplast metabolic modules, the message is that the chloroplast envelope is not a passive doorway. It is an actively regulated gate that stress can slam shut, and the cytosolic translation apparatus is a shared, rationed resource that drought repossesses. Future designs may need to consider bypassing the cytosolic import route altogether, for example by expressing bypass enzymes directly inside chloroplasts through chloroplast transformation, or by engineering resistance to stress-activated degradation systems. Protein-level verification under target stress conditions, the authors argue, is not an optional confirmation but an indispensable step for anyone building inducible metabolic pathways in chloroplasts.

The study, led by Haiyan Teng and colleagues at Yichun University in China and supported by the Jiangxi Provincial Natural Science Foundation, was published as an open access research article in BMC Plant Biology. Its value lies less in a successful crop improvement than in a precise mapping of where an engineering strategy failed, and why. In the race to make photosynthesis more efficient under a drying climate, knowing that the last mile of gene expression, the journey from transcript to functional chloroplast enzyme, can be severed by the very stress the pathway is meant to conquer, may redirect the entire field toward designs that survive that journey.

Subject of Research: Plant Biotechnology

Article Title: Transcript-protein decoupling of chloroplast targeted enzymes in a stress inducible GOC photorespiratory bypass in rice

Article References: Teng, H., Liu, Z., Wang, R., Shen, X., & Li, J. (2026). Transcript-protein decoupling of chloroplast targeted enzymes in a stress inducible GOC photorespiratory bypass in rice. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09975-9

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09975-9

Keywords: rice, chloroplast, photorespiration, GOC bypass, drought stress, transcript-protein decoupling, protein import, synthetic biology, Transcript-protein, decoupling, targeted, enzymes

The two populations immediately caught the attention of the research team, led by Xin Tan and Zhikun Wu of Guizhou University of Traditional Chinese Medicine, together with colleagues from the Kunming Institute of Botany and partner institutions. Both plants bear deeply lobed leaves and distinctly inflated calyces with a flattened base, features that place them squarely within sect. Auganthus. Yet their overall appearance is conspicuously different from every previously described member of the section, a mismatch that raised an urgent question: were these unusual populations merely variants of known species, or did they represent evolutionary lineages that science had never catalogued?

Karst regions, with their dramatic terrain of soluble limestone, sinkholes, and isolated rock outcrops, are famous for strong habitat heterogeneity, meaning that sharply different microhabitats can exist within very small distances. Evolutionary biologists widely consider this patchiness a crucial mechanism underlying species differentiation, particularly for rapidly radiating groups such as the Primulaceae. In such landscapes, populations separated by a cliff face or a dry ridge can experience different light, moisture, and soil chemistry, and over generations these differences can drive divergence. The discovery of two candidate new primroses in these provinces fits this pattern well, and it highlights how much undocumented diversity may still be sheltered in China’s fragmented karst habitats.

To resolve the plants’ identities, the team combined classical morphological analysis with comparative chloroplast genomics. The chloroplast genome, typically around 150,000 base pairs in flowering plants, evolves in a way that makes it ideal for tracing relationships among closely related species. The researchers assembled the chloroplast genomes of the two putative new species alongside those of known sect. Auganthus members and constructed a phylogenetic tree, the branching diagram that shows how lineages are related. In the analysis, the two new species clustered together with all known species of the section, confirming their membership in the group while also revealing their distinct positions within it.

The comparative genomic work went beyond simple tree building. The team performed analyses of boundary contraction and expansion, examining the borders between the large single-copy, small single-copy, and inverted repeat regions of the chloroplast genome, whose shifting boundaries are a well-known source of structural variation. They also carried out a global comparison using mVISTA, a visualization tool that aligns whole genomes to show conserved and variable blocks, and a diversity site analysis to pinpoint regions of high nucleotide diversity among species. These technical approaches together allowed the researchers to see exactly where the genomes of the new species differed from their relatives.

One of the most concrete findings concerns the inverted repeat regions, often abbreviated as IR regions, which are duplicated segments of the chloroplast genome. The IR region lengths of the two putative new species measured 25,403 base pairs and 25,710 base pairs respectively. Differences of this kind in IR length are more than trivia; they reflect structural rearrangements that can help distinguish species and illuminate the evolutionary history of a lineage. Combined with sequence-level differences, such structural data strengthen the case that the two populations are genuinely independent evolutionary units rather than minor variants.

The diversity site analysis detected seven highly variable hotspots across the chloroplast genomes. These hotspots, concentrated in intergenic regions, include the spacers psbI–trnS-GCU, trnS-GCU–trnG-UCC, and trnT-GGU–psbD, as well as the genes accD and ycf1, all of which exhibited high nucleotide diversity among the species examined. Intergenic spacers tend to accumulate mutations faster than coding sequences because they face fewer functional constraints, making them powerful markers for species-level discrimination. The identification of these hotspots is valuable beyond the current study, since such variable regions can serve as DNA barcodes for future surveys of Primula diversity across the region.

Morphology provided the complementary half of the evidence. Each of the two putative new species possesses distinct characteristics that set it apart from its closest relatives, and the paper provides detailed morphological comparisons with closely related species. The plants were named according to their distribution localities: Primula shibingensis, from Shibing, and Primula longmenshanensis, from the Longmen Mountains area. The formal authorship of the names, J.L.Gu & Z.K.Wu, sp. nov., follows the conventions of botanical nomenclature, and the descriptions include information on the distribution ranges and conservation status of both species, an essential step for plants known only from restricted karst localities.

Based on the combined morphological and phylogenetic evidence, the researchers concluded that both newly discovered species are recognized as new to science. The study, published open access on 16 October 2026 and citable under the DOI 10.1186/s12870-026-10039-1, was supported by the National Natural Science Foundation of China and several provincial programs, including the Young Top-notch Talents Program of Yunnan Province and the Guizhou Provincial Science and Technology Project. The work exemplifies how modern genomics can transform a curious field observation into a rigorous species description.

For conservationists, the message is bittersweet. Karst ecosystems in southwestern China are among the planet’s great hotspots of narrow-endemic plants, yet they face pressures from habitat degradation and climate change. Documenting species such as Primula shibingensis and P. longmenshanensis is the first step toward protecting them, because a species that has not been formally described cannot be assessed, listed, or conserved. As chloroplast genome sequencing becomes faster and cheaper, botanists expect more hidden lineages to surface from these ancient limestone terrains, each one a reminder that the inventory of life on Earth is still being written.

Subject of Research: Plant Genetics

Article Title: Comparative chloroplast genomics reveal two new species of Primula sect. Auganthus (Primulaceae) from the karst regions of China: Primula shibingensis and P. longmenshanensis

Article References: Tan, X., Wu, Y., Jiang, X., Gu, J., Jiang, M., Yang, L., Ye, Q., Liu, J., Zhou, W., & Wu, Z. (2026). Comparative chloroplast genomics reveal two new species of Primula sect. Auganthus (Primulaceae) from the karst regions of China: Primula shibingensis and P. longmenshanensis. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10039-1

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10039-1

Keywords: chloroplast genome, Primula, karst, new species, phylogenetics, Primulaceae, China, biodiversity, Comparative, chloroplast, genomics, reveal

The review begins with a principle that has governed plant nutrition for decades. Essentiality means that the absence of even one essential plant nutrient element renders growth or reproduction impossible. By convention, the essentials for plant nutrition include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, zinc, manganese, copper, boron, chlorine, molybdenum, nickel, and, to the extent that it is accepted as an essential mineral element, cobalt. On a dry-weight basis, the elements derived from air and water, namely carbon, hydrogen and oxygen, account for roughly 94 to 96 percent of plant biomass. The primary macronutrients make up about 2 to 3.5 percent, the secondary macronutrients about 0.5 to 1.5 percent, and the micronutrients less than 0.1 percent of dry mass. Despite their small share, the authors emphasize, these elements sustain light harvesting, water oxidation, electron transport, ATP and NADPH production, the carbon reactions, and the integration of photosynthesis with the metabolism of the whole plant.

To understand why, it helps to revisit the architecture of photosynthesis. Two pigment-protein systems embedded in the thylakoid membrane of the chloroplast, Photosystem I and Photosystem II, mediate light absorption, excitation energy transfer, primary photochemistry, electron transfer, the oxidation of water, and the reduction of NADP+ to NADPH. In addition to electron transfer, several membrane complexes release protons into the thylakoid lumen, generating a proton gradient that is exploited by ATP synthase to produce ATP. The NADPH and ATP are then used to convert carbon dioxide into carbohydrates via the C3 and C4 pathways, packing energy into sugar bonds. Each of these steps depends on specific elements. Magnesium sits at the center of every chlorophyll molecule, both in the antenna complexes that harvest sunlight and in the reaction-center chlorophylls of Photosystems I and II that drive electron transfer from water to NADP+. Manganese and calcium form the Mn4CaO5 cluster of Photosystem II, the site of water splitting and oxygen evolution. Iron and sulfur together build the iron-sulfur clusters of the cytochrome b6f complex, Photosystem I and ferredoxin, while copper is the redox cofactor of plastocyanin, the mobile carrier that transfers electrons from the cytochrome b6f complex to Photosystem I.

The air- and water-derived elements play roles that go beyond serving as the molecular framework of substrates and products. Carbon is the backbone of all organic molecules, and in plants it is primarily acquired from atmospheric carbon dioxide, which diffuses into leaves through stomata and serves as the inorganic carbon source for the Calvin-Benson-Bassham cycle. But the bicarbonate ion is also a critical cofactor of Photosystem II, regulating the photosynthetic electron transport chain. Hydrogen and oxygen make up the water that is split during water oxidation, the core of oxygenic photosynthesis because it generates molecular oxygen. Furthermore, the hydrogen ions released during water oxidation and other steps play essential roles in generating the pH gradient across the thylakoid membrane that leads to ATP production. The stoichiometry is demanding: the fixation of six carbon dioxide molecules via the Calvin-Benson-Bassham cycle, corresponding to the synthesis of one glucose equivalent, requires 18 ATP and 12 NADPH molecules, while the oxidation of two water molecules at Photosystem II supplies four electrons that drive the formation of two NADPH molecules and a proton-motive force sufficient to synthesize up to three ATP molecules.

Nitrogen occupies a special place among the macronutrients because its influence on photosynthesis does not saturate the way most mineral nutrients do. Leaf nitrogen content shows an approximately proportional relationship with photosynthetic capacity across a wide physiological range, a relationship that arises because a large fraction of nitrogen is invested directly in the photosynthetic apparatus within the leaf, particularly in rubisco and the thylakoid proteins of the electron transport chain. The capacity for electron transport in the chloroplast is directly proportional to cytochrome f content, and nitrogen assimilation is integral to carbon assimilation. Nitrogen is a constituent of amino acids, proteins, chlorophyll, nucleic acids, NADPH and ATP, and it is a building block of the enzymes of the Calvin-Benson-Bassham cycle. Nitrogen use and allocation differ substantially between C3 and C4 plants, a distinction with consequences for how crops respond to fertilization under different climates.

Phosphorus and potassium complete the primary macronutrient picture with distinct technical roles. Phosphorus is a constituent of inorganic phosphate and of the key energy-transfer molecules NADP, NADPH, ADP and ATP, and it is embedded in the thylakoid membrane as phospholipids. Under phosphorus deficiency, the photosynthetic electron transport chain is disrupted, ATP synthase activity is restricted, and carbon dioxide fixation is reduced, linking phosphorus to both the light reactions and the carbon reactions. Potassium, meanwhile, is involved in transmembrane transport and enzyme activation. Ion transporters and potassium channels are integrated into the thylakoid, where a potassium channel activates plastoquinone and a potassium/hydrogen antiporter stimulates electron transport. Energy conversion may be affected by modulation of acidification through thylakoid and lumen potassium and chloride channeling. Potassium also facilitates carbon dioxide diffusion into chloroplasts and is involved in the transport of photosynthates throughout the plant.

The secondary macronutrients and micronutrients reveal how tightly the light and carbon reactions are coupled through metal chemistry. Calcium is part of the Mn4CaO5 cluster required for water oxidation and oxygen evolution, and it is implicated, by still unknown mechanisms, in the regulation of electron transfer and carbon reaction proteins. Magnesium is required for key Calvin-Benson-Bassham cycle enzymes and for rubisco activation, and all reactions involving ATP require magnesium ions. Sulfur is associated with iron in the Rieske iron-sulfur protein of the cytochrome b6f complex and is part of several Photosystem I components and ferredoxin, and it is a component of methionine and cysteine, two amino acids central to photosynthetic protein complexes. Zinc is a cofactor of the copper/zinc superoxide dismutase and carbonic anhydrase, contributing to carbon metabolism. Boron is required for the regulation of carbohydrate metabolism in the carbon reactions. Molybdenum is present in four metalloenzymes that catalyze redox reactions in plants, particularly those involved in nitrogen assimilation, and it improves chloroplast configuration and increases chlorophyll content. Chlorine, in the form of chloride ions, is required for Photosystem II activity and is involved in the regulation of proton transfer during water oxidation, acting as an essential micronutrient for Photosystem II photoassembly and photosynthetic oxygen evolution. Nickel and cobalt play indirect roles, mainly as cofactors of the nickel/cobalt transporter-permease NiCo-PIC1, which transports ferrous iron through the inner membrane of the chloroplast, and cobalt is a chaperone of copper in the copper/zinc superoxide dismutase.

The authors also stress that elements work as teams within protein complexes, and that these team relationships are equally essential. Iron and sulfur partner in a Rieske protein. Calcium and manganese partner in the Mn4CaO5 cluster and again in lectins. Cobalt, zinc and copper cooperate in the copper/zinc superoxide dismutase. Iron, nickel and cobalt cooperate in NiCo-PIC1. Metal transporter families, including ABC, CAX, CCX, CDF/MTP, ECA, HMA, NRAMP, OPT, VIT and ZIP, enable the uptake and movement of these nutrients, and transporters coordinate the interplay of compounds, metals and metalloids that regulate the acquisition, distribution and efficient utilization of essential plant nutrients. Close to a third of all known enzymes are associated with the metal elements calcium, magnesium, iron, manganese, zinc, copper, nickel and cobalt, and these elements are required for the activity of their respective metalloenzymes. The activity of cobalt in chloroplast functions, the authors note, supports its classification as an essential element, and like nickel its optimal foliar dose may be in the nanomolar range.

Signaling and crosstalk emerge as the connective tissue that directs the metabolic pathways of photosynthates such as sugars. Recent work summarized in the review shows that signaling between nitrogen, phosphorus, sulfur, zinc and iron may involve complex crosstalk processes in response to nutrient deficiency, and that dynamic nutrient signaling networks connect sugar, nitrate and phosphate in controlling molecular pathways. Carbon and nitrogen assimilation are integrated processes, and co-application of elevated carbon dioxide with nitrogen promotes the synthesis of nitrogenous products key to growth, while molybdenum plays key roles in nitrogen assimilation. Several enzymes in the path of carbon are activated by the reduction of disulfide bonds on conversion, in light, of ferredoxin reduced in Photosystem I to a thiol signal, meaning that the light and carbon reactions employ sulfur to transmit signals in the process of photosynthesis. Deficiencies of secondary fertilizers such as calcium, magnesium and sulfur in lateritic and leached acid soils are growing concerns for farm production precisely because these minerals are vital to photosynthesis. Where a deficiency of any element is diagnosed, supplementation by foliar applications is recommended, and because the light reactions of photosynthesis are measured in picoseconds, nutrients cannot be drawn up from roots in the soil to the shoot with such rapidity, making foliar placement at the site of the photosynthetic processes potentially important.

The review closes with a forward-looking argument for agriculture and for the transfer of photosynthesis-related technologies to the field. When treating crops with plant growth regulators, nitrogen input plays integral roles in carbon partitioning, and co-application of essential plant nutrient elements with regulators such as methyl-alpha-D-mannopyranoside, a plant growth regulator for photosynthesis, were found to enhance yields as compared to nutrient controls, with a recognized role for manganese and calcium in the lectin cycle. Lectins have roles in the carbon reactions of photosynthesis, the sugar code and cell signaling, and ongoing studies of the plant lectome may lead the field toward glycomimetics, molecules that emulate the structure and function of natural glycans, which the authors suggest could improve the efficiency of photosynthesis. The authors recommend further investigations, especially for cultivated plants, by means of biocuration and genetic tools including transcriptomics, metabolomics, proteomics, genomics, epigenomics, ionomics and lipidomics, seeking information about the specificity of metalloenzymes to corresponding organelles such as chloroplasts, peroxisomes and vacuoles. They also point to silicon as a beneficial mineral whose interactions with photorespiration and with essential and beneficial elements may indicate a critical role. For now, the message is clear: photosynthesis depends on the presence of essential mineral elements at their sites of action, for the most part in the leaves and green stems of crop plants, and securing their sufficiency is inseparable from securing the energy transformation on which all green plants, and the food systems built upon them, ultimately rely.

Subject of Research: The roles of essential nutrient elements in the light and carbon reactions of photosynthesis

Article Title: The essential nutrient elements in photosynthesis

Article References: Shevela, D., & Nonomura, A. (2026). The essential nutrient elements in photosynthesis. Frontiers in Photobiology, 4, Article 1817712. https://doi.org/10.3389/fphbi.2026.1817712

Image Credits: AI Generated

DOI: 10.3389/fphbi.2026.1817712

Keywords: photosynthesis, essential nutrients, mineral nutrition, chloroplast, Photosystem II, Photosystem I, macronutrients, micronutrients, metalloproteins, electron transport, crop productivity, plant signaling

The story begins with the mutant phenotype itself. Seedlings carrying the yll mutation in the homozygous state show a dramatic reduction in chlorophyll content, the green pigment complexes that harvest light in the chloroplast. Their photosystem II, the protein complex at the heart of the light reactions of photosynthesis, performs poorly, and the plants do not survive past the seedling stage. Because the trait is recessive, plants inheriting only one copy of the mutation look perfectly normal, which is exactly the pattern that makes such mutants so useful for genetic analysis. Chlorophyll-deficient mutants have long served as entry points for dissecting chloroplast biology in crops, and soybean, one of the world’s most important oilseed and protein crops, has relatively few such well-characterized loci.

To find the gene responsible, the researchers turned to classical genetic mapping, but at high resolution. By following the inheritance of molecular markers across segregating populations, they narrowed the yll locus to a remarkably small stretch of DNA: a 165-kilobase interval on chromosome 10. In the reference soybean genome annotation known as Wm82.a6.v1, that interval contains just two genes. This is the kind of genetic compression that mapping projects dream of, because it converts a genome-wide search of tens of thousands of genes into a two-horse race.

Of the two genes in the interval, one emerged as the clear frontrunner. Glyma.10G090700, which the authors designate GmPAO7, encodes a protein annotated as a polyamine oxidase, an enzyme of the PAO1-like family. Several independent lines of evidence converged on it. First, the gene is expressed in leaves, the tissue where the phenotype manifests. Second, its transcript abundance is reduced in yll seedlings compared with their normal siblings. Third, and most strikingly, the mutant plants carry a reproducible splicing defect: a 110-base-pair intron between the first and second exons of the gene is retained in the mature messenger RNA instead of being excised.

The consequences of that retained intron are severe. In molecular terms, the extra sequence introduces a premature termination codon, a stop signal that halts protein synthesis far earlier than it should. Computational prediction suggests that instead of the annotated 500-amino-acid PAO1-like protein, the mutant would produce a truncated peptide of only 32 amino acids. That fragment would lack both of the domains that define the enzyme’s function: the flavin amine oxidase domain and the NAD(P)-binding domain. In other words, if the prediction holds, the mutant plants would be effectively devoid of a functional GmPAO7 protein.

The splicing evidence was verified the old-fashioned way, by direct sequencing. The researchers amplified the relevant region of the gene’s complementary DNA by RT-PCR and read the sequence of the products. Wild-type plants showed the normally spliced transcript, with the intron cleanly removed and the first exon joined directly to the second. Homozygous mutant plants showed the intron-retained sequence. Heterozygous plants, carrying one normal and one mutant copy, displayed overlapping splice forms, with sequencing chromatograms showing mixed signals downstream of the splice junction, consistent with both transcript types being present. The authors are careful to note that this qualitative assay demonstrates the presence of the aberrant transcript but does not establish the relative proportions of the splice forms in any genotype.

To understand what the mutation does to the plant more broadly, the team performed RNA sequencing on mutant and wild-type sibling seedlings at the same developmental stage. The comparison revealed widespread expression differences, with significant enrichment of genes involved in photosynthesis, chloroplast function, and redox metabolism. A protein-protein interaction network built from the differentially expressed genes, using the STRING database with a confidence threshold of 0.700, retained a connected core of 304 nodes and 3,278 predicted interactions, organized into modules covering photosynthesis and chloroplast function, ribosome and translation, RNA processing, redox metabolism, and protein folding. Supplementary heatmaps also documented changes in transcription factor families including MYB, NAC, WRKY, bHLH, ERF/AP2, and bZIP, as well as in genes associated with the major plant hormones: auxin, gibberellin, cytokinin, abscisic acid, and ethylene.

Here the authors exercise an important caution. Because yll seedlings are severely chlorotic and developmentally compromised, the transcriptomic differences they observe cannot be taken as a clean readout of the gene’s primary function. A dying, yellow seedling is a very different biological system from a healthy green one, and many of the expression changes may simply reflect the downstream consequences of a failing chloroplast rather than direct regulatory effects of the candidate gene. The profiles are best interpreted, the authors write, as the transcriptomic state associated with the phenotype. This distinction matters, and it is the kind of nuance that separates careful candidate-gene studies from overreach.

Complementary evidence came from the electron microscope. Transmission electron microscopy of mutant leaves revealed chloroplast ultrastructural abnormalities: grana, the stacked membrane structures where photosystem II concentrates, were poorly developed, and the thylakoid membranes were disorganized. These defects are entirely consistent with the reduced chlorophyll content and impaired photosystem II performance measured physiologically. But as the authors point out, ultrastructural observations, while suggestive, do not by themselves functionally validate the candidate gene. They describe the cellular wreckage without proving which genetic wrench caused it.

That proof remains the outstanding task. Glyma.10G091000, the second gene in the 165-kilobase interval, has not been excluded, and the authors are explicit that functional complementation, introducing a normal copy of GmPAO7 into the mutant to see whether it rescues the phenotype, or the identification of an independent allele of the same gene, will be required to establish causality. They also flag a tempting but untested hypothesis: a connection between polyamine oxidase activity, polyamine metabolism, and reactive oxygen species. Polyamine oxidases are known to participate in redox reactions that can generate hydrogen peroxide, and such a pathway could plausibly tie a defective oxidase to chloroplast damage and cell death. But the authors did not measure PAO enzyme activity, polyamine concentrations, or reactive oxygen species levels in this study, so that link remains a hypothesis to be tested, not a finding.

Even with those caveats, the study is a textbook example of how modern crop genetics proceeds. A lethal phenotype is captured, mapped to a small genomic interval, and a candidate is prioritized by triangulating expression data, transcript abundance, and a concrete molecular lesion, in this case an intron-retention event that would demolish the encoded protein. If GmPAO7 is confirmed, it would add a new entry to the short list of genes whose disruption produces chlorophyll-deficient, seedling-lethal phenotypes in soybean, and it would spotlight alternative splicing, a process often overlooked in crop mutation screens, as a source of catastrophic developmental defects. It would also raise broader questions about what polyamine oxidation contributes to chloroplast maintenance in one of the world’s staple legumes. For now, the strongest candidate stands accused, the evidence is circumstantial but coherent, and the decisive experiment, complementation, is the next act in a story that began with a handful of yellow seedlings that never made it out of the seedling tray.

Subject of Research: Fine mapping and candidate gene analysis of a soybean yellow-leaf lethal mutant implicating aberrantly spliced polyamine oxidase gene GmPAO7

Article Title: Fine mapping of yll prioritizes aberrantly spliced Glyma.10G090700 (GmPAO7) as the strongest candidate in a soybean yellow-leaf lethal mutant

Article References: Chen, L., Feng, J., Ning, J., Shi, X., Wu, X., Che, X., Li, Z., Yu, Z., Wang, X., Chen, Q., Sun, H., Guo, Y., Liu, L., Ma, Z., Li, H., Lin, J., & Zhao, J. (2026). Fine mapping of yll prioritizes aberrantly spliced Glyma.10G090700 (GmPAO7) as the strongest candidate in a soybean yellow-leaf lethal mutant. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10015-9

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10015-9

Keywords: soybean, yellow-leaf lethal mutant, GmPAO7, polyamine oxidase, intron retention, alternative splicing, chloroplast, chlorophyll deficiency, fine mapping, candidate gene, RNA-seq, photosystem II

The story began when researchers spotted an unusual plant in a barley population treated with ethyl methane sulfonate, or EMS, a chemical mutagen that has been a workhorse of plant genetics since the 1950s. EMS sprinkles random point mutations throughout the genome, and when one of them disrupts a gene involved in chloroplast development, the result can be a plant with abnormal leaf coloration. The mutant in question, derived from the two-rowed winter barley cultivar Igri, displayed white stripes of varying intensity—some seedlings were nearly albino, while others bore only a few narrow white streaks. Crucially, unlike complete albinos, which die as seedlings because they cannot photosynthesize, variegated plants survive and set seed, making them ideal subjects for genetic analysis.

Under the microscope, the difference between green and white tissue was dramatic. Transmission electron microscopy of 14-day-old seedlings revealed that chloroplasts in the white sectors were significantly smaller than their healthy counterparts, still carrying prolamellar bodies—structures typical of immature plastids—and lacking the well-organized stacks of thylakoid membranes, called grana, that house the photosynthetic machinery. In other words, chloroplast biogenesis had stalled in the white sectors at an early stage of development. But the mutant held another surprise: after six months in the greenhouse, the white stripes gradually turned yellow, and electron microscopy showed that some plastids in these aging sectors had developed thylakoids and small grana. Chloroplast development, it seemed, could partially recover as the plant matured.

To dissect the inheritance of the trait, the team crossed the mutant with two green-fruited wild-type cultivars, Alraune and Igri, generating several large mapping populations. Reciprocal crosses produced similar proportions of variegated offspring regardless of which parent was the mutant, ruling out maternal or cytoplasmic inheritance and confirming that the trait is encoded in the nucleus. The segregation ratios in the second generation told an even more interesting story: they fit a 1:15 ratio, the classic signature of two recessive genes acting in duplicate dominant epistasis. In plain terms, a plant becomes variegated only if it is homozygous for the mutant allele at both loci simultaneously; a single functional copy of either gene is enough to keep the leaves green.

Mapping the two loci required a combination of modern genomic tools. The researchers used genotyping-by-sequencing on hundreds of F3 plants to build a linkage map, then applied interval mapping to pinpoint the regions associated with variegation. Two major loci emerged, one on chromosome 2H and one on chromosome 3H, which the team named Variegated 4 (var4) and Variegated 5 (var5), following barley gene-naming conventions. Neither interval overlapped with the regions previously linked to other barley variegation mutants such as albostrians, luteostrians or grandpa1.a, confirming that this was an entirely new genetic system. Because the intervals were initially enormous—spanning hundreds of millions of base pairs—the team turned to whole-genome resequencing of variegated and green progeny from a backcross to Igri to narrow the search.

The resequencing strategy exploited a key feature of EMS mutagenesis: it almost always converts cytosine to thymine or guanine to adenine. By filtering the thousands of polymorphisms in each interval for those with predicted moderate or high effects on proteins, and by requiring that the variants segregate correctly with the phenotype across six striped and twenty-four green plants, the researchers whittled each interval down to five candidate genes. At the var4 locus, one candidate stood out: a gene homologous to NBR1 in Arabidopsis, which encodes a selective autophagy receptor. In Arabidopsis, NBR1 recognizes photodamaged chloroplasts and directs their degradation through a microautophagy-like process, and it also regulates the levels of TOC proteins, the import machinery that controls which nuclear-encoded proteins enter the chloroplast. In the barley mutant, a glycine residue just sixteen amino acids upstream of the zinc finger domain is replaced by an aspartic acid—a negatively charged substitution that could distort the domain’s orientation and impair its binding efficiency.

At the var5 locus, the strongest candidate is a gene encoding a DNAJ-domain protein, a co-chaperone that works with HSP70 chaperones to keep chloroplast proteins properly folded. DNAJ proteins recognize unfolded or misfolded substrates and deliver them to HSP70s, which either refold them or route them to Clp proteases for degradation. In the mutant, a highly conserved serine—one present in 284 of 326 related proteins across monocots—is replaced by the bulky, hydrophobic phenylalanine within one of the protein’s two DUF3444 domains, a radical change likely to compromise function. Although the NBR1-like receptor and the DNAJ co-chaperone do not appear to interact directly, both sit at the heart of chloroplast proteostasis: the constant cycle of protein import, folding, assembly and degradation that keeps the organelle’s roughly 3,000 proteins—about 90 percent of them encoded in the nucleus and imported from the cytosol—in working order.

The epistasis now makes biological sense through a threshold model, echoing ideas developed for the classic Arabidopsis var2 mutant, in which a related protease partially compensates for the loss of its partner. Each of the two barley mutations, on its own, may inflict only a mild dent in proteostasis—too subtle to disturb chloroplast development. Together, however, the combined defects could push the system below a functional threshold, causing chloroplast biogenesis to collapse in some cells while others, perhaps by chance or through compensatory gene expression, recover sufficiently to stay green. The partial recovery observed in older plants fits this picture too: because the plastid proteome changes with developmental stage, the demands on proteostasis may ease over time, allowing some plastids in the formerly white sectors to resume development and turn yellow rather than staying white.

The researchers are careful to note that functional confirmation is still required. Only one of the ten candidate mutations is a predicted loss of function; the rest are amino acid substitutions with milder expected effects, which may be precisely why two loci had to combine before a phenotype appeared. Regulatory variants in non-coding regions, which the analysis did not exhaustively cover, cannot yet be ruled out, and finer mapping in populations where one locus is fixed will help confirm or refute the candidates. Still, the study delivers something genuinely new: a first glimpse of digenic control of chloroplast-deficient variegation, and a pair of candidate genes that tie the phenomenon to protein quality control inside the chloroplast. For a trait that has fascinated botanists for decades, the striped barley mutant suggests that sometimes it takes two wrongs—not one—to paint a leaf.

Subject of Research: Digenic epistatic control of leaf variegation and chloroplast proteostasis in an EMS-mutagenized barley line

Article Title: Leaf variegation in a barley EMS mutant is controlled by two epistatic mutations

Article References: Pidon, H., Nagireddy, S. R., Melzer, M., Himmelbach, A., & Stein, N. (2026). Leaf variegation in a barley EMS mutant is controlled by two epistatic mutations. Theoretical and Applied Genetics, 139(11), Article 305. https://doi.org/10.1007/s00122-026-05370-y

Image Credits: AI Generated

DOI: 10.1007/s00122-026-05370-y

Keywords: barley, leaf variegation, chloroplast biogenesis, epistasis, EMS mutagenesis, proteostasis, NBR1, DNAJ, autophagy, genetic mapping, whole-genome resequencing, chloroplast

The research team, led by Yusheng Wang and Cunyu Zhou of Yangtze University together with colleagues at Huazhong University of Science and Technology, the Wuhan Botanical Garden of the Chinese Academy of Sciences, and Southwest Minzu University, assembled complete mitochondrial genomes from nine accessions of D. fruticosa and one accession of D. glabra. Rather than relying on short-read sequencing, which often struggles with the repetitive architecture of plant mitogenomes, the team used PacBio HiFi long reads, a technology that produces highly accurate reads long enough to span the complex repeats that make plant mitochondrial DNA notoriously difficult to assemble. When combined with two previously published accessions, the dataset encompassed twelve complete mitogenomes, providing an unusually rich comparative resource for a single plant genus.

The assembled genomes ranged in size from 263,889 to 294,600 base pairs, a span of roughly thirty thousand base pairs that underscores how variable mitochondrial genomes can be even among closely related individuals of the same species. Despite this size variation, the overall architecture proved remarkably stable. Guanine-cytosine content was conserved across all twelve accessions, and the core gene set remained essentially unchanged: thirty protein-coding genes, three ribosomal RNA genes, and between seventeen and eighteen transfer RNA genes. This combination of a stable functional core with a fluctuating genome size is a hallmark of plant mitochondrial evolution, where most of the size differences arise not from changes in gene content but from the gain and loss of non-coding sequence, repeats, and foreign DNA.

Codon usage analysis added another layer to the picture. Across all twelve mitogenomes, the researchers detected a clear preference for codons ending in A or U, a pattern consistent with the nucleotide composition biases that characterize many plant mitochondrial genomes. Such preferences matter beyond mere bookkeeping: they influence translational efficiency, the evolution of synonymous sites, and the choice of markers for phylogenetic reconstruction. For researchers hoping to use mitochondrial genes to untangle relationships within Dasiphora and among its relatives in the Rosaceae, knowing which codons and which genes carry the strongest compositional signals is essential groundwork.

Perhaps the most visually striking findings came from the repeat analysis. The team catalogued abundant simple sequence repeats and dispersed repeats scattered throughout the genomes, including a set of reverse repeats that appear to be specific to the D. glabra lineage. In plant mitochondria, large repeats are not passive passengers; pairs of repeats can recombine with one another, flipping genome segments, generating alternative genomic conformations, and occasionally triggering structural rearrangements. The presence of lineage-specific reverse repeats in D. glabra suggests that this species may harbor distinct recombination dynamics, potentially shaping its mitochondrial genome architecture in ways that differ from D. fruticosa even though the two species share a recent common ancestor.

The study also documented extensive traffic of DNA between the cell’s three genome-containing compartments, a phenomenon that has fascinated plant genomicists for decades. The researchers identified multiple chloroplast-derived fragments embedded within the mitochondrial genomes, evidence of DNA flowing from the plastid into the mitochondrion over evolutionary time. They also detected large nuclear mitochondrial DNA segments, known as NUMTs, in which mitochondrial sequence has been transferred into the nucleus. Strikingly, D. glabra harbored especially large mitochondrial-derived segments, indicating that the scale of inter-compartmental DNA transfer can differ substantially even between sister species. These transfers are more than curiosities; they can disrupt genes at insertion sites, inflate genome size, and complicate phylogenetic analyses by mixing signals from different compartments.

To gauge how much raw evolutionary variation the mitogenomes contain, the team measured nucleotide diversity across the genomes. The analysis pinpointed several highly variable mitochondrial genes as well as a set of hypervariable intergenic regions in the plastid genomes. Such variable loci are exactly what population geneticists and conservation biologists need: they serve as fine-grained markers for tracking gene flow, identifying population structure, and reconstructing the demographic history of species that colonized high-altitude habitats. For a genus like Dasiphora, whose members occupy fragmented alpine landscapes sensitive to climate change, a menu of variable markers is a practical tool for future monitoring and conservation work.

Phylogenetic trees built from the mitochondrial genomes and, separately, from the plastid genomes told a consistent and intriguing story: D. glabra was consistently placed within the D. fruticosa clade rather than as a clearly diverged sister lineage. This result echoes the reticulate, or network-like, evolutionary history that nuclear data had previously suggested for the pair, and it raises questions about how species boundaries are maintained, or blurred, in this group. Whether the pattern reflects recent divergence, incomplete lineage sorting, or historical hybridization cannot be settled by organellar genomes alone, but the congruence between mitochondrial and plastid signals strengthens the case that the two species are separated by a very shallow evolutionary divide.

Collinearity analysis, which aligns the genomes to one another to detect shared blocks of sequence, revealed high structural conservation across the twelve mitogenomes, punctuated by localized rearrangements. In other words, the overall gene order and large-scale architecture have been preserved, but specific regions have been shuffled, inverted, or repositioned, likely through the repeat-mediated recombination described above. This mosaic of conservation and local disruption is characteristic of plant mitochondrial genomes, which evolve slowly at the sequence level yet can reorganize their structure abruptly. Documenting where those breakpoints occur in Dasiphora provides a baseline for future comparisons with other Rosaceae genera and for studying the mechanisms that drive mitochondrial genome rearrangement in plants.

The significance of this work extends well beyond two shrubs. Dasiphora fruticosa is an ecologically important species across vast tracts of the Northern Hemisphere’s mountainous terrain, and it serves as a model for studying adaptation to cold, high-radiation environments. By delivering the first complete mitogenomic dataset for the genus, the study fills a conspicuous gap in the genomic resources available to plant scientists and lays a foundation for research into how organellar genomes contribute, or fail to contribute, to high-altitude adaptation. The work was supported by China’s National Key Research and Development Program, the Chinese Academy of Sciences’ Light of West China Program, the Second Tibetan Plateau Scientific Expedition and Research program, and the China Postdoctoral Science Foundation, reflecting the strategic importance of alpine ecosystem research in the region. As long-read sequencing becomes routine, studies of this kind are transforming plant mitochondria from genomic backwaters into front-line systems for exploring how genomes move, merge, and evolve inside the cell, and the shrubby cinquefoils of the world’s mountains have now joined that conversation.

Subject of Research: Comparative mitochondrial genomics of the alpine shrubs Dasiphora fruticosa and D. glabra

Article Title: Comparative mitogenomics of Dasiphora fruticosa and D. glabra: insights into genome structure, inter-organellar DNA transfer, and evolutionary dynamics

Article References: Wang, Y., Zhou, H., Jiang, Z., Wang, M., Wang, H., Zhang, H., & Zhou, C. (2026). Comparative mitogenomics of Dasiphora fruticosa and D. glabra: insights into genome structure, inter-organellar DNA transfer, and evolutionary dynamics. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09452-3

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09452-3

Keywords: Dasiphora, mitochondrial genome, mitogenomics, DNA transfer, chloroplast, NUMTs, repeats, phylogeny, nucleotide diversity, alpine plants, Rosaceae, PacBio HiFi