The research, led by Guowei Yang, Yinlu Deng, and colleagues at Zhejiang University, focused on two cytorhabdoviruses: rice stripe mosaic virus (RSMV), a pathogen of rice in the genus Betacytorhabdovirus, and tomato yellow mottle-associated virus (TYMaV), an Alphacytorhabdovirus studied in the model plant Nicotiana benthamiana. Plant rhabdoviruses are a substantial group, comprising at least 269 species across 12 genera in the family Rhabdoviridae. Most produce bullet-shaped or bacilliform virions wrapped in a lipid envelope and are transmitted by sap-feeding hemipteran insects such as leafhoppers, planthoppers, aphids, and whiteflies in a persistent-propagative manner. Their genomes encode five conserved structural proteins—nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), and the large polymerase (L)—plus a movement protein belonging to the 30K superfamily.

During replication, the viral RNA is encapsidated by N in association with P and L to form nucleocapsids, which previous work has established as the minimal infectious units for cell-to-cell movement. The movement protein interacts with N and P to redirect these nucleocapsids through plasmodesmata. Separately, the M protein condenses nucleocapsids into tightly coiled complexes and drives budding through G-enriched host endomembranes, producing enveloped particles that accumulate in the lumen of the nuclear envelope in nucleorhabdoviruses or the endoplasmic reticulum in cytorhabdoviruses. Whether these endomembrane-trapped virions are simply terminal assembly products or active participants in vascular trafficking has been a long-standing open question, particularly because plant rhabdovirus particles have never been observed within or around desmotubules, the ER-derived tubes that thread through plasmodesmata.

To address this, the team first mapped the spatial distribution of RSMV in infected rice using immunofluorescence staining of cryosections with an N protein-specific monoclonal antibody. In both leaf and stem sections, viral antigens were predominantly localized to vascular tissues, including xylem and phloem-associated regions, surrounding parenchyma and bundle sheath cells, and, in leaves, hypodermal sclerenchyma. Strong fluorescence appeared in infected samples while healthy controls showed none, confirming assay specificity. However, immunofluorescence could not resolve the structural form of the virus at these sites, so the researchers turned to transmission electron microscopy (TEM) on ultrathin resin-embedded sections.

The TEM results were striking. Mature enveloped RSMV virions, roughly 50 to 60 nanometers in diameter, accumulated abundantly in xylem parenchyma cells surrounding mature vessel elements, often arranged in orderly arrays within enclosing vesicle-like membranes that occupied a substantial portion of the cytoplasmic space. More remarkably, bacilliform particles with or without an enclosing membrane were detected within the lumens of mature xylem vessels themselves—hollow, dead conduits that have undergone programmed cell death and lost all cytoplasmic contents. Such particles appeared in 5 of 46 vessel-containing fields examined. Because fixing and detecting material inside these large lumens is technically difficult, the observation is all the more significant. The team also found membrane-enclosed mature virions in sclerenchyma cells that retain little cytoplasm, suggesting that RSMV particles can persist through advanced stages of cellular autolysis.

To corroborate these ultrastructural findings, the researchers collected xylem sap from the stems and roots of infected rice plants using vacuum infiltration and centrifugation, taking care to exclude cytoplasmic contamination with a glucose-6-phosphate dehydrogenase activity assay. Immunoblotting with antisera raised against purified RSMV virions detected four major protein bands in stem sap whose migration patterns matched the N, P, M, and G structural proteins of purified virions; root sap showed distinct G and M signals. Negative-stain TEM of concentrated sap then revealed bacilliform particles approximately 65 nanometers in diameter with morphology characteristic of plant rhabdovirus virions, the slightly larger apparent size reflecting differences in sample preparation and staining. Together, these data demonstrate that intact enveloped virions, not just soluble proteins or nucleocapsids, are present in the xylem translocation stream.

The phloem told a parallel story. In infected rice stems, the team identified sieve element–companion cell complexes containing virus particles, using sieve element plastids and pore-plasmodesmal units as diagnostic landmarks. Bacilliform particles consistent with mature enveloped RSMV virions were observed within both companion cells and sieve elements, with most virions in sieve elements occurring in clusters enclosed by vesicle-like membranes. Virions were found in 8 of 62 sieve element-containing fields. The same pattern held in the second pathosystem: in TYMaV-infected N. benthamiana, enveloped virions were detected in immature vessel elements that still retained residual cytoplasm, in fully differentiated vessel elements with patterned wall thickening and no protoplasmic contents, and in phloem sieve elements with or without an evident surrounding vesicle. Across the observations, enveloped virions appeared in at least 3 immature vessels, 7 mature vessels, and 6 sieve element-containing fields.

The decisive experiment came from reverse genetics. The researchers constructed TYMaV-ΔM:RFP, an infectious clone in which the matrix protein gene was replaced with a red fluorescent protein reporter while a green fluorescent protein reporter was retained. In diluted agroinoculation assays designed to test cell-to-cell movement, the mutant behaved essentially like the wild type: isolated fluorescent single cells appeared at 6 to 7 days post inoculation and foci expanded to roughly 12 cells on average by 10 days for both viruses. Immunoblotting showed GFP accumulating to slightly higher levels in mutant-infected tissues, likely because the M protein normally suppresses viral RNA synthesis. Yet negative-stain and immunogold TEM revealed that the mutant failed to assemble any detectable mature virions; gold labeling was distributed over viral material lacking recognizable virion morphology rather than decorating intact particles.

When the researchers inoculated plants under conditions permitting systemic infection, the phenotypes diverged dramatically. Wild-type TYMaV spread extensively, producing systemic GFP fluorescence from about 10 days post inoculation followed by typical mottling and leaf distortion in upper leaves, and systemically infecting 59 of 60 plants by 21 days. The M deletion mutant, by contrast, produced no systemic fluorescence or symptoms in any of 60 inoculated plants throughout the observation period. Deletion of the matrix gene thus abolished long-distance movement completely while leaving local cell-to-cell propagation intact—a phenotype that directly links virion morphogenesis to vascular dissemination.

Integrating these results, the authors propose a model in which enveloped virions serve as a major mobile entity for rhabdovirus systemic trafficking through both vascular conduits. For xylem-mediated movement, nucleocapsids colonize metabolically active immature xylem precursor cells or xylem parenchyma, where replication and envelopment occur; subsequent programmed cell death and autolysis then release assembled virions into the hollow vessel lumen for upward transport in the transpiration stream. For phloem-dependent movement, virions assembled in companion cells may be loaded into sieve elements through dilated pore-plasmodesmal units, or nucleocapsids may invade undifferentiated sieve element precursors before maturation, with the abundant membrane-enclosed virion bundles in sieve elements favoring in situ envelopment. The envelope may also protect nucleocapsids from hydrolytic enzymes abundant in vascular sap, mirroring the reliance of many positive-sense RNA viruses on intact coat proteins for stable phloem transport. The model does not exclude nucleocapsids as a less-efficient alternative—M or G deletion mutants of the nucleorhabdovirus sonchus yellow net virus retain limited systemic infectivity at roughly 9 to 14 percent of wild-type levels—but the complete block in TYMaV-ΔM:RFP underscores the importance of mature virions. The findings carry implications beyond the plant as well: because hemipteran vectors feed on both phloem and xylem sap, and successful insect acquisition requires intact virions whose surface glycoprotein mediates entry into midgut cells, virions resident in both conduits may provide dual sources for transmission between plants.

Subject of Research: Vascular long-distance movement mechanisms of enveloped plant rhabdoviruses

Article Title: Potential contribution of enveloped virions to long-distance movement of plant rhabdoviruses

Article References: Yang, G., Deng, Y., Liu, Q., Lin, W., Wang, J., Xie, L., & Li, Z. (2026). Potential contribution of enveloped virions to long-distance movement of plant rhabdoviruses. Frontiers in Microbiology, 17, Article 1994490. https://doi.org/10.3389/fmicb.2026.1994490

Image Credits: AI Generated

DOI: 10.3389/fmicb.2026.1994490

Keywords: plant rhabdoviruses, enveloped virions, xylem, phloem, sieve elements, vessel elements, rice stripe mosaic virus, tomato yellow mottle-associated virus, matrix protein, systemic movement, transmission electron microscopy, reverse genetics

A research team led by Ruifeng Guo and Yonglin Wang of Beijing Forestry University, together with colleagues at the Beijing Academy of Agriculture and Forestry Sciences and the United States Department of Agriculture, set out to map the microbial communities living inside smoke tree branches. The researchers sampled twelve trees, six healthy and six diseased, separating each branch into two distinct compartments: the outer epidermis, or bark, and the inner xylem, the vascular tissue that transports water. From each tree they collected branches in three health states: branches from completely healthy trees, symptomless branches from diseased trees, and the visibly diseased branches themselves. Using amplicon sequencing of bacterial 16S rRNA and fungal ITS regions, they generated a detailed census of the endophytic microbiota inhabiting each tissue type.

The sequencing data revealed that Verticillium wilt profoundly reshapes the internal microbial world of the tree. Bacterial communities in diseased xylem actually showed higher Shannon diversity than in healthy xylem, suggesting that infected trees may recruit additional microorganisms as a defensive response. Fungal communities told the opposite story: diversity dropped significantly in the epidermis and xylem of diseased branches. Principal coordinate analysis and permutational multivariate analysis of variance confirmed that disease status significantly altered community composition in nearly every compartment. Critically, when the researchers re-ran their analyses after excluding V. dahliae sequences, the pattern held, meaning the pathogen’s influence on the fungal community extended well beyond its own abundance. Quantitatively, disease explained roughly 40 percent of the variation in fungal communities but only about 11 percent in bacterial communities, indicating that fungi are far more sensitive to the wilt epidemic than bacteria.

To probe the stability of these communities, the team constructed co-occurrence networks linking microbial taxa based on correlated abundances. The fungal networks in diseased branches had fewer connections, fewer negative correlations, and markedly lower robustness when nodes were removed in simulations of species extinction. Both diseased and symptomless branches from infected trees showed elevated vulnerability, meaning the loss of a single taxon could disproportionately collapse network efficiency. Fungal networks proved consistently more fragile than bacterial ones, echoing earlier findings in pepper stems and olive roots where disease also destabilized fungal assemblages. This loss of connectivity, a form of microbial dysbiosis, suggested that wilt disease does not merely add a pathogen to an otherwise intact community; it actively dismantles the ecological architecture that keeps endophytes in check.

Within this destabilized landscape, one genus stood out. Differential abundance analysis and random forest classification both identified Botryosphaeria as a top biomarker of diseased branches, enriched alongside Verticillium itself. Linear correlation analysis showed that the relative abundance of Verticillium was positively and significantly associated with Botryosphaeria, with an R-squared of 0.47, while it was negatively correlated with Alternaria and Cladosporium. The team isolated a strain of Botryosphaeria dothidea from infected branches and found that it showed no antagonistic activity against V. dahliae in culture, ruling out simple competition. Spatially, the two fungi occupied different niches: B. dothidea concentrated in the bark while V. dahliae dominated the xylem. Field collections from four Beijing districts reinforced the association, with both fungi recovered together from 37 percent of 76 diseased branch samples and V. dahliae alone from 63 percent.

The decisive test came in the greenhouse. When smoke tree seedlings were inoculated with B. dothidea alone, nothing happened; the trees stayed healthy. When they were inoculated with V. dahliae alone, characteristic wilt symptoms appeared. But when seedlings received V. dahliae first and B. dothidea second, wilting was dramatically more severe than with either pathogen alone. Quantitative PCR revealed the mechanism behind this synergy: V. dahliae biomass was unchanged by the presence of its partner, but B. dothidea biomass surged in co-inoculated plants. In other words, the vascular pathogen was not simply teaming up with an equal partner; it was unlocking the door for a latent endophyte to multiply and inflict damage it could never achieve on its own.

Physiological and histochemical assays traced how the trees lost their ability to resist the second invader. Catalase and peroxidase, the antioxidant enzymes that scavenge reactive oxygen species during immune responses, were most active in plants challenged with V. dahliae alone and lowest in co-inoculated plants. Malondialdehyde content and relative conductivity, both markers of cell membrane damage, peaked in co-inoculated seedlings. DAB staining showed that V. dahliae infection drove substantial hydrogen peroxide accumulation, while trypan blue staining revealed extensive cell death, and microscopy documented solid blockage of xylem vessels. Together these results indicated that the first infection had already crippled the tree’s defense system before the second fungus even arrived.

Transcriptome sequencing provided the molecular explanation. In V. dahliae-infected branches, 2,800 predicted genes were significantly downregulated and 1,871 were upregulated compared with controls. Among the downregulated set, 394 genes in a single expression cluster were tied to plant defense, including disease resistance genes, protein kinases, jasmonic acid-responsive factors, chitinase-binding proteins, terpenoid synthases, cellulose synthases, protease inhibitors, redox regulators, and transcription factors. KEGG enrichment showed that hormone signal transduction, phenylpropanoid biosynthesis, MAPK signaling, brassinosteroid and monoterpenoid biosynthesis, and benzoxazinoid production were all significantly suppressed. Gene ontology analysis likewise flagged reduced transmembrane receptor kinase activity and compromised cell wall and cytoskeleton components. B. dothidea-infected branches showed a strikingly similar transcriptional signature, with the same defense and hormone pathways downregulated, confirming that both fungi exploit overlapping vulnerabilities in the host.

The study reframes B. dothidea, long recognized as a worldwide latent pathogen of woody plants that waits for drought, wounds, or stress before striking, as an opportunistic accomplice whose pathogenicity is triggered by another microbe rather than by abiotic stress alone. It also adds smoke tree wilt to a growing list of plant diseases, from grafted grapevine decline to soybean root rot, in which co-infection produces symptoms far worse than the sum of the parts. For forest managers, the practical implications are significant: because the two fungi occupy different tissues, control strategies may need to pair fungicides with measures that boost overall host vigor, keeping the latent bark dweller in its harmless endophytic state. The researchers are already testing plant immune activators in smoke tree plots to see whether shoring up the tree’s own defenses can break the deadly synergy, offering hope that the red hills of Beijing can be protected not by attacking one pathogen, but by managing the entire microbial community within the tree.

Subject of Research: Synergistic co-infection of smoke trees by Verticillium dahliae and the latent bark fungus Botryosphaeria dothidea

Article Title: The bark latent fungus Botryosphaeria dothidea exacerbates branch dieback following the infection with Verticillium dahliae

Article References: Guo, R., Li, Y., Tang, C., Zhao, Y., Wang, M., Qiao, G., Klosterman, S. J., & Wang, Y. (2026). The bark latent fungus Botryosphaeria dothidea exacerbates branch dieback following the infection with Verticillium dahliae. Stress Biology, 6(1), Article 13. https://doi.org/10.1007/s44154-026-00288-3

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00288-3

Keywords: Verticillium dahliae, Botryosphaeria dothidea, smoke tree, Cotinus coggygria, Verticillium wilt, plant microbiome, endophytes, co-infection, branch dieback, xylem, RNA-seq, forest pathology

Gypsum soils are a botanical paradox. They are chemically peculiar, dominated by calcium sulfate, often low in the nutrients most plants crave, and physically punishing, drying out rapidly and offering little organic matter. Yet across the world’s arid regions, from the Chihuahuan Desert of North America to the Iberian Peninsula and the steppes of Central Anatolia, a remarkable guild of specialist plants has evolved to exploit these barren landscapes. What makes gypsum substrates especially fascinating to botanists is that many gypsophytes are strict endemics, confined to outcrops that may span only a few hillsides. Linum mucronatum subsp. gypsicola is a textbook example, restricted to gypsum-marl hills in northwestern Türkiye, where its survival strategies have remained largely unexplored until now.

The research team deployed an unusually comprehensive analytical arsenal. Light microscopy and scanning electron microscopy, or SEM, were used to chart the internal architecture of the plant’s roots, stems, and leaves at resolutions down to the micrometer scale. To go beyond structure alone, the researchers coupled the electron microscope with energy-dispersive X-ray analysis, known as SEM-EDX, which maps the elemental composition of tissues point by point. This was complemented by multi-elemental analyses of the plant’s vegetative parts and a full suite of soil chemical analyses from the collection site, allowing the team to compare what the substrate offers against what the plant actually accumulates. The approach links form to function in a way that few single-technique studies can achieve.

The anatomical findings paint a picture of a plant built for drought. In the roots, the researchers documented a strongly developed secondary xylem layer, the water-conducting tissue that thickens as woody plants mature. A robust secondary xylem provides both mechanical anchorage in crumbly, erodible gypsum-marl slopes and an expanded hydraulic network for scavenging scarce water from a substrate that sheds moisture quickly. Equally telling was the stem: its pith region, the soft central core found in many herbaceous plants, was markedly narrowed. A reduced pith conserves resources and may limit water loss through internal tissues, while lending the stem a tougher, more drought-resistant profile suited to arid exposure.

The leaves revealed perhaps the most striking adaptations of all. Microscopic examination showed a high stomatal density and, crucially, an amphistomatic structure, meaning stomata, the adjustable pores that regulate gas exchange, are present on both the upper and lower leaf surfaces. While amphistomy can increase photosynthetic capacity in high-light environments, it also demands tight regulation to prevent catastrophic water loss, and its combination with other xeromorphic traits suggests a finely balanced compromise between carbon gain and water conservation. The team also observed a well-organized arrangement of palisade parenchyma cells, the elongated photosynthetic cells packed beneath the upper epidermis, paired with a thin and loose spongy parenchyma below. This layered configuration maximizes light capture in intense steppe sunlight while the airy spongy tissue facilitates rapid internal gas diffusion, an arrangement frequently seen in plants of open, sun-baked habitats.

Beyond the anatomy, the elemental analyses clarified how the plant handles the unusual chemistry of its substrate. By quantifying macro- and micronutrients in the vegetative tissues and comparing them with soil measurements, the researchers showed how L. mucronatum subsp. gypsicola responds to substrate-derived nutrients, detailing the accumulation patterns that support its development on gypsum. The findings align with a growing international literature suggesting that gypsum specialists manage distinctive nutritional strategies, including notable accumulation of sulfur, an element abundant in calcium sulfate soils, and the capacity to gather excess nutrients as a constitutive buffer against the impoverished, grazed, and eroding landscapes they inhabit. Rather than merely tolerating gypsum chemistry, the flax appears to actively exploit it.

The study’s significance extends beyond a single species. Gypsum ecosystems host some of the most specialized floras on Earth, and understanding the mechanisms of plant survival on these substrates has become a priority for evolutionary ecologists. Recent comparative work has shown that gypsophiles from different continents often converge on similar elemental profiles, hinting at deep, repeatable solutions to the gypsum problem. By adding a micromorphological dimension, the Turkish team’s work connects that chemical story to physical structure, showing how water-conducting tissues, stomatal architecture, and photosynthetic cell arrangement work in concert with mineral accumulation to produce a genuinely integrated survival strategy.

There is also a conservation dimension. Endemic gypsophytes are inherently vulnerable: their restricted ranges, specialized habitat requirements, and the pressures of grazing, quarrying, and land-use change make them acutely sensitive to disturbance. Previous assessments of Turkish endemic Linum taxa have flagged conservation concern for several species in the genus. Documenting the precise anatomical and physiological requirements of L. mucronatum subsp. gypsicola provides a scientific foundation for protecting both the plant and its fragile gypsum habitat, since a specialist locked to a particular substrate cannot simply be transplanted elsewhere if its hills are degraded or destroyed.

Methodologically, the study also demonstrates the power of pairing SEM-EDX with conventional microscopy in plant science. The technique, increasingly used in medicinal plant research and comparative anatomy, allows researchers to visualize tissue architecture and elemental distribution simultaneously, revealing relationships that would be invisible to either method alone. As climate change intensifies aridity across the Mediterranean and Central Asian steppes, the adaptations documented in this unassuming flax, from its reinforced xylem to its dual-surface stomata, may inform broader efforts to understand, and perhaps even emulate, how plants cope with drought and marginal soils.

For now, the humble L. mucronatum subsp. gypsicola stands as a quiet marvel of evolutionary engineering, a plant that turned a geological curse into a biological refuge. Its gypsum hills, once dismissed as wasteland, are revealed as laboratories of adaptation, where every narrowed pith and densely packed stoma tells a story of survival refined over millennia. The research, supported by the TUBITAK 2209 Research Project Support Programme for Undergraduate Students, underscores how much remains to be learned from the world’s extreme habitats, and how the smallest plants often carry the biggest lessons about resilience on a changing planet.

Subject of Research: Anatomical and phytochemical adaptations of the endemic gypsophyte Linum mucronatum subsp. gypsicola to gypsum soils in Türkiye

Article Title: Micromorphological and phytochemical traits of the gypsophyte Linum mucronatum subsp. gypsicola (Linaceae) from Türkiye

Article References: Kayabaş Avşar, A., Polat, I., Abduljabbar Abdullah Allaw, H., Keçeli, T., & Çiçek, N. (2026). Micromorphological and phytochemical traits of the gypsophyte Linum mucronatum subsp. gypsicola (Linaceae) from Türkiye. Plant Biosystems, 160(4), Article 221. https://doi.org/10.1007/s44473-026-00235-0

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00235-0

Keywords: gypsophyte, gypsum soils, Linum mucronatum, Linaceae, plant anatomy, SEM-EDX, stomata, xylem, drought adaptation, endemic plants, Türkiye, Plant Biosystems

The pathogens in question are a select group of bacteria that have made the plant vascular system their exclusive home. Xylella fastidiosa colonizes the xylem, the water-transport network of the plant, while Spiroplasmas, Phytoplasmas and Liberibacters confine themselves to the phloem, the sugar-rich tissue that distributes photosynthetic products. These bacteria cannot move between plants on their own. They depend on piercing-sucking insects, mostly hemipterans such as leafhoppers, planthoppers, spittlebugs and psyllids, whose needle-like stylets penetrate directly into the vascular tissues. In doing so, the insects ingest sap along with any microbes it contains and later deposit the bacteria into new hosts. Intriguingly, within the insect suborder Sternorrhyncha, only psyllids are known to transmit bacterial pathogens, while aphids and whiteflies, their close relatives, are primarily virus carriers.

The economic stakes are enormous. Citrus huanglongbing, or HLB, caused by the psyllid-transmitted Liberibacter species, has cut citrus yields in Florida by 74 percent since its detection there in 2005. In Italy, Xylella fastidiosa triggers olive quick decline syndrome, a disease that has killed millions of olive trees in the southern region of Puglia. Genetic analysis traced that outbreak to a Central American introduction of the pathogen around 2008, and phylogenetic work suggests the bacterium actually arrived in Europe as early as 1993. Xylella infects more than 700 plant species, including grape, in which it causes Pierce’s disease, and almond and citrus, where it produces leaf scorch and variegated chlorosis. The review also highlights the recent recognition of Xylella taiwanensis as a distinct species rather than a subspecies of X. fastidiosa.

Each pathogen has evolved a distinctive lifestyle suited to its vascular niche. Xylella, a Gram-negative bacterium related to Xanthomonas albilineans, uses Type IV pili to twitch its way through the nutrient-poor xylem, secreting cell wall-degrading enzymes such as polygalacturonase and endoglucanases to dissolve the pit membranes that separate adjacent vessels. It then forms sticky biofilms, anchored by extracellular polysaccharides and adhesins, that physically obstruct water flow. The resulting drought stress, stomatal closure and reduced photosynthesis eventually kill the plant. Spiroplasmas, by contrast, are helical, wall-less bacteria of the class Mollicutes that swim by propagating kinks along their bodies. Spiroplasma citri, discovered in 1970 and the first vector-borne bacterium ever cultured, causes citrus stubborn disease, while S. kunkelii produces maize stunt and S. phoeniceum infects periwinkle.

Phytoplasmas are stranger still. First observed in 1967 as mycoplasma-like organisms in infected phloem, they remain unculturable in the laboratory, forcing researchers to rely on DNA extracted from infected plants and on 16S rRNA gene sequencing for classification. Lacking both cell walls and flagella, they cannot produce the classic molecular patterns that plant immune receptors normally detect, and they appear to elicit immune responses through internal patterns instead. Their most dramatic effects are developmental: infected plants produce witches’ brooms, dense clusters of stunted twigs, or phyllody, in which flowers transform into leafy structures. These deformities prevent normal reproduction and turn the plant into a breeding ground for both the pathogen and its vectors. Phytoplasmas compensate for their lack of motility genes by using their immunodominant membrane protein to bind plant actin, apparently hitching rides through the host’s own cytoskeletal transport system.

The Liberibacters tell an evolutionary story of their own. Six species share a common ancestor, and genome analysis suggests the non-pathogenic Liberibacter crescens gave rise to the pathogenic Candidatus Liberibacter lineages. The pathogenic species are fastidious and unculturable, likely because their highly reduced genomes lack genes for thiamine and essential amino acids that L. crescens retains. Candidatus Liberibacter asiaticus is the primary HLB agent, transmitted by the Asian citrus psyllid Diaphorina citri, while Ca. L. solanacearum exists as at least six haplotypes: A and B, spread by the potato psyllid Bactericera cockerelli, cause zebra chip disease of potato, named for the dark streaks that appear in tubers after frying, and haplotypes C, D and E, carried by the carrot psyllid B. trigonica, attack umbelliferous crops.

Central to the review is the molecular arms race between these bacteria and plant immunity. Plants deploy pattern recognition receptors that detect bacterial flagellin and other pathogen-associated molecular patterns, triggering a first line of defense. Bacteria strike back with effector proteins. Phytoplasma effectors are among the best characterized: SAP05 hijacks the host 26S proteasome to degrade SPL and GATA transcription factors, promoting lateral shoots and sterile flowers; SAP11 and related proteins degrade TCP transcription factors to stimulate bud growth; SAP54 converts flowers into leaf-like structures; and SRP1 from rice orange leaf phytoplasma impairs chlorophyll precursor biosynthesis, producing yellow leaves that attract leafhoppers. Liberibacter effectors are equally sophisticated. CLas secretes SDE15 to target the programmed cell death regulator CsACD2, SDE1 to suppress papain-like cysteine proteases, and SDE3 and SDE4405 to manipulate autophagy, while the effector CLas4425 undermines salicylic acid signaling. For CLso, the effector Lso-HPE1 disrupts the tomato ubiquitin-proteasome system, and CKC_05701 suppresses programmed cell death and reactive oxygen production.

The relationship between pathogen and vector is just as intricate. Xylella is unique among these bacteria in forming biofilms in the foregut of its sharpshooter and spittlebug vectors, a semi-persistent, non-circulative association. It degrades chitin and uses adhesins such as XadA1 and XadA2, which bind strongly to chitin and cellulose, to anchor itself in the insect’s feeding apparatus. The phloem-limited bacteria, by contrast, establish persistent, circulative relationships: they cross the insect gut epithelium, survive in the hemolymph and eventually reach the salivary glands for reinoculation. Spiroplasma citri uses adhesion proteins including P89 and ScARPs for receptor-mediated endocytosis, and its phosphoglycerate kinase interacts with insect actin to promote colonization. Phytoplasmas enter insect cells through clathrin-mediated endocytosis, and their antigenic membrane proteins form complexes with insect microfilaments that determine vector specificity.

Liberibacters manipulate their psyllid hosts in remarkable ways. CLas localizes along the actin cytoskeleton of D. citri gut cells, and roughly 95 percent of its genes are active during gut colonization. In adult psyllids, CLas triggers apoptosis in the gut, which may reduce their transmission capacity, whereas nymphs show no such response and transmit more efficiently. CLso takes a preemptive approach: it induces expression of the anti-apoptotic gene IAPP5.2 early in infection, suppressing gut cell death to facilitate its own acquisition. The two zebra chip haplotypes provoke distinct immune responses in the potato psyllid, with CLsoB repressing apoptosis and achieving higher titers and more efficient transmission. Even insect symbionts matter: Wolbachia correlates positively with CLas titer in D. citri, and psyllids lacking Wolbachia acquire and transmit CLso less efficiently, suggesting microbiome-based control strategies.

The three-way interplay culminates in pathogen-driven manipulation of plant chemistry to recruit vectors. Phytoplasma effectors dampen jasmonic acid signaling and increase leafhopper fecundity, while SAP54 makes infected plants more attractive to leafhopper females. CLas induces citrus to release specific volatiles that deceptively attract D. citri and alters metabolite emissions to shift vector preference. Current management leans on insecticides and antibiotics, including oxytetracycline and streptomycin, approved by the U.S. EPA for Florida citrus, with trunk injection proving more efficient than foliar sprays. Promising alternatives include antimicrobial peptides such as nisin, which disrupts the Xylella lipid bilayer, and MaSAMP, a heat-stable peptide from HLB-resistant Microcitrus that both kills CLas and primes plant immunity. The authors point to CRISPR/Cas9 gene editing, plant immunomodulators such as salicylic acid analogues and GABA supplementation, and even light-engineering technologies as future directions. But with many of these pathogens still unculturable and genetically intractable, the review’s central message stands: cracking the bacterium-insect-plant triangle is the essential next step toward protecting global food security.

Subject of Research: Interactions among insect vectors, bacterial plant pathogens and host plants

Article Title: Bacterial vector-borne plant diseases: global issues caused by three-way interactions

Article References: Huang, Y., Hao, J., & Tang, X. (2025). Bacterial vector-borne plant diseases: global issues caused by three-way interactions. Crop Health, 3(1), Article 10. https://doi.org/10.1007/s44297-025-00049-0

Image Credits: AI Generated

DOI: 10.1007/s44297-025-00049-0

Keywords: Xylella fastidiosa, huanglongbing, Liberibacter, phytoplasma, Spiroplasma, insect vectors, psyllids, leafhoppers, plant immunity, effector proteins, phloem, xylem