The research, led by Jinfeng Qi and Jianqiang Wu of the Kunming Institute of Botany at the Chinese Academy of Sciences, addresses a stubborn bottleneck in plant functional genomics. Terpene synthases, or TPSs, are the enzymes that convert linear prenyl diphosphate substrates into the enormous diversity of terpenoid structures found across the plant kingdom. The traditional approach to determining what a given TPS produces involves expressing the gene in bacteria such as Escherichia coli and analyzing the products. But bacterial systems come with well-known liabilities: they cannot perform the eukaryotic post-translational modifications that may be essential for enzyme activity, high-level expression often drives misfolded proteins into insoluble inclusion bodies, and the prokaryotic cellular environment lacks the chaperones and folding machinery needed to keep some plant enzymes soluble and active. Generating stable transgenic maize lines to bypass these problems is expensive and slow, given the crop’s recalcitrance to transformation.

Protoplasts—plant cells stripped of their walls by enzymatic digestion—offer an attractive alternative. Exogenous DNA can be delivered into protoplasts by polyethylene glycol-mediated transfection, driving transient expression of genes of interest within 24 to 48 hours. Maize protoplasts have already proven useful for promoter analysis, protein interaction studies, and investigating nonvolatile defensive metabolites such as benzoxazinoids. But nobody had shown whether they could support the study of volatile terpene biosynthesis, which poses a distinct analytical challenge: the products evaporate, making detection and quantification far more delicate than measuring water-soluble compounds. The new work demonstrates that, with the right combination of growth conditions, culture parameters, and extraction chemistry, maize protoplasts can indeed become miniature terpene factories whose output is readily captured and measured.

The first obstacle the team faced was a genuine biological paradox. Protocols for isolating stable maize protoplasts typically call for etiolated seedlings grown in complete darkness, because the large central vacuoles characteristic of skotomorphogenic cells maintain high turgor pressure and help the naked cells survive the mechanical stresses of centrifugation and pipetting. However, light is a critical environmental cue for terpenoid metabolism: it drives plastid development and the accumulation of farnesyl diphosphate, the C15 precursor of sesquiterpenes. When the researchers compared seedlings grown in darkness with those given one, two, three, or eight days of dim light at 4.25 micromoles per square meter per second, they found that the partially greened seedlings accumulated dramatically more precursor and product. After methyl jasmonate treatment, the greenish seedlings released 2.7-fold more (E)-α-bergamotene and 3.8-fold more (E)-β-farnesene than etiolated controls, and farnesyl diphosphate levels rose up to 5.9-fold with eight days of light exposure. The compromise—eight days of dim light—balanced cellular robustness with metabolic competence, resolving what the authors call the light paradox.

Leaf anatomy added a second layer of optimization. The maize leaf is a developmental gradient running from the division-active basal meristem to the fully mature tip. Protoplasts isolated from the base and middle of the second leaf showed excellent integrity and transfection efficiencies above 90 percent with an enhanced green fluorescent protein reporter, but a substantial fraction of protoplasts from the leaf tips ruptured after transfection. The likely explanation lies in cellular architecture: in mature tip cells, the central vacuole has fragmented into smaller vacuoles and the cytoplasm is packed with chloroplasts, undermining osmotic stability and mechanical strength. The base and middle regions of greenish seedling leaves were therefore selected for all subsequent experiments, underscoring how developmental stage alone can make or break a protoplast protocol.

Detecting the volatile products required its own series of refinements. The team compared direct overnight headspace adsorption with solid-phase microextraction against a strategy in which protoplasts are first lysed and extracted with an organic solvent. Extraction with n-hexane or n-pentane vastly outperformed direct adsorption, and n-pentane was chosen for its lower toxicity and greater volatility. The final workflow concentrates the extract, heats it to 65 degrees Celsius to drive volatiles into the headspace, and captures them on a polydimethylsiloxane solid-phase microextraction fiber before gas chromatographic analysis on a Shimadzu GC-2014 system. Culture conditions mattered as well: a nutrient-rich medium supplemented with sucrose, glucose, and Murashige and Skoog salts supported higher terpene accumulation than the standard W5 solution, sealed containers and darkness outperformed light and open vessels, and larger culture volumes helped—in 50-milliliter headspace tubes, (E)-β-farnesene levels ran 60 percent higher than in 2-milliliter tubes.

Promoter choice and cofactor supply further sharpened the system’s sensitivity. When the maize gene ZmTPS10 was expressed from the maize ubiquitin promoter, protoplasts accumulated more (E)-α-bergamotene and (E)-β-farnesene than when the cauliflower mosaic virus 35S promoter drove the same gene. Spraying the mother plants with methyl jasmonate eight hours before protoplast isolation—an approach the authors describe as in planta priming—boosted terpene accumulation in subsequently transfected protoplasts more than tenfold compared with untreated controls, exploiting the intact plant’s metabolic machinery to enrich precursors rather than adding expensive, hydrolysis-prone farnesyl diphosphate directly to the medium. Because all terpene synthases carry a conserved DDxxD domain that binds magnesium, the researchers also tested whether adding 10 millimolar magnesium ions to the culture medium would help. It did: bergamotene rose 2.7-fold and farnesene 2.0-fold, confirming that cofactor availability limits ZmTPS10 activity inside the transfected cells.

To show that the platform extends beyond single-enzyme biochemistry, the team used it to interrogate transcriptional regulation. A previous study had identified ZmMYC2a, a basic helix-loop-helix transcription factor in the jasmonate signaling pathway, as a positive regulator of (E)-α-bergamotene and (E)-β-farnesene biosynthesis. Overexpressing ZmMYC2a in maize protoplasts significantly elevated both volatiles relative to a green fluorescent protein control, demonstrating that the system can resolve regulatory layers as well as catalytic function. The authors argue that the high efficiency of multi-plasmid co-transfection opens the door to reconstructing entire defense signaling cascades—receptor to kinase to transcription factor to structural gene—inside a single batch of cells. Because maize protoplasts provide a homologous cellular environment with the correct cofactors, membranes, and post-translational modification machinery, the resulting data should carry higher physiological fidelity than results from heterologous bacterial or yeast systems.

The implications reach well beyond one crop. Graminaceous staples such as wheat and sorghum share maize’s stubborn resistance to genetic transformation, and a rapid protoplast-based assay could serve as an efficient shortcut for functional gene studies across these species, with potential extension to other non-model plants through optimization of osmotic regulators, enzyme cocktails, and ionic conditions. Ecologically, the stakes are considerable: maize terpene volatiles recruit parasitoid wasps against fall armyworm and other pests above ground, attract entomopathogenic nematodes against the western corn rootworm below ground, and even directly damage the peritrophic matrix of lepidopteran midguts. By shrinking the timeline for assigning function to the roughly 30 TPS genes in the maize genome—about half of which still lack confirmed products—this system promises to accelerate the discovery of defensive chemistry that could inform breeding programs and crop synthetic biology for years to come.

Subject of Research: A maize protoplast transfection system for analyzing the biosynthesis and regulation of volatile terpenoid defense compounds

Article Title: A maize protoplast transfection system for studying the biosynthesis of volatile terpenoids

Article References: Qi, J., Li, M., Hu, Z., Li, R., Li, J., Zhang, M., Ma, C., & Wu, J. (2026). A maize protoplast transfection system for studying the biosynthesis of volatile terpenoids. Crop Health, 4(1), Article 13. https://doi.org/10.1007/s44297-026-00076-5

Image Credits: AI Generated

DOI: 10.1007/s44297-026-00076-5

Keywords: maize, protoplast transfection, terpene synthases, volatile terpenoids, ZmTPS10, methyl jasmonate, plant defense, ZmMYC2a, solid-phase microextraction, secondary metabolism, crop biotechnology, protoplast

The problem begins with how C. asiatica is currently sourced. Wild harvesting remains the dominant supply model, and the review documents staggering variability: centelloside content in wild populations fluctuates up to five- to ten-fold depending on geography, environment, and harvest timing. Because the plant naturally favors swamp and marsh ecosystems, wild-collected material faces elevated risks of heavy metal contamination, pathogen exposure, and adulteration. Field surveys in Peninsular Malaysia found significant accumulation of cadmium, copper, nickel, lead, and zinc in wild-harvested gotu kola, with estimated daily intakes suggesting potential lead toxicity risk from plants gathered at polluted sites. Standards bodies such as the World Health Organization expect high-quality herb to contain at least two percent triterpene saponins, while the European Scientific Cooperative on Phytotherapy reports saponin and sapogenin content ranging from one to eight percent—a spread that makes quality control a persistent headache for phytopharmaceutical manufacturers.

Cultivation has not solved the problem either. The review highlights a paradox familiar to anyone working with medicinal plants: more biomass does not mean more medicine. Unlike conventional crops where yield predicts output, C. asiatica can produce lush growth while delivering disappointingly dilute metabolite profiles. Multiple factors shape both growth and centelloside accumulation, including cultivation system, propagation method, light regime, genotype, soil type, farming practice, and even the ploidy status of planting material. Researchers exploring aquaponics, co-cultivation with the root endophyte Piriformospora indica, and polyhouse cultivation of rooted cuttings have reported cultivar-specific differences and dynamic metabolite trends, reinforcing the need for extensive genotypic screening before any field program can deliver consistent quality.

This is where plant tissue culture enters the picture. Callus cultures initiated from leaves, petioles, and nodal segments using auxins such as 2,4-dichlorophenoxyacetic acid and naphthaleneacetic acid, often paired with cytokinins like benzylaminopurine, have reliably produced triterpenoid- and flavonoid-rich biomass. Cell suspension cultures and hairy root cultures—induced through transformation with Agrobacterium rhizogenes—have emerged as the most scalable platforms because they grow rapidly in liquid media, remain genetically stable, and do not require exogenous hormones. Notably, Baek and colleagues demonstrated that petiole-derived hairy roots produced 1.4 times more triterpenoids than leaf-derived lines, a reminder that even the choice of starting explant can decisively shape biosynthetic output. In suspension cultures, asiaticoside accumulation peaked at 1.7-fold above baseline between 21 and 25 days of culture.

The heart of the review is a systematic comparison of elicitation strategies, and the numbers are striking. Methyl jasmonate, the field’s workhorse elicitor, increased asiaticoside by 494 percent in cell suspensions, by 5.6- to 71-fold in hairy roots, and by 69-fold in callus, depending on genotype and treatment conditions. Coronatine delivered 116 milligrams per gram dry weight of madecassoside in elicited hairy roots at day 14 post-elicitation—one of the highest absolute yields ever reported. But the authors issue a crucial warning about the so-called fold-increase paradox: a two-fold rise from a 20 milligram per gram baseline yields 40 milligrams per gram, which is pharmaceutically far more relevant than a 50-fold rise from 0.1 milligrams per gram yielding just 5. Tetraploid hairy roots responded more dramatically to methyl jasmonate than diploid lines, likely because their untreated controls were extremely low to begin with. Heavy metal elicitors such as cadmium and lead could drive 24- and 49-fold increases in asiaticoside and madecassoside respectively, but the authors dismiss these as unusable for pharmaceutical production because of phytotoxicity and contamination risk.

Among biotic elicitors, the toolkit is expanding rapidly. Yeast extract delivered a 3.5-fold boost in asiaticoside, chito-oligosaccharide achieved a five-fold increase in hairy roots at 30 parts per million, and pectin raised asiaticoside content by 31 percent in callus cultures. Endophytic symbionts add another layer of sophistication: Piriformospora indica colonization triggered a 2.5-fold increase in asiaticoside through activation of root-associated stress responses, while rhizobacteria such as Azospirillum and Pseudomonas promote triterpenoid biosynthesis by stimulating jasmonic acid and ethylene signaling pathways. Combined elicitor treatments—methyl jasmonate plus salicylic acid, or coronatine plus methyl jasmonate—consistently outperform single agents, suggesting synergistic activation of jasmonate- and salicylate-dependent signaling, though optimal ratios and staged application sequences remain largely untested.

Beyond elicitation, the review maps several emerging enhancement strategies. Precursor feeding with squalene at 2.5 micromolar boosted total triterpenoids 3.1-fold to 57.53 milligrams per gram dry weight, while higher concentrations triggered feedback inhibition—a classic concentration-dependent regulatory signature. Pyruvic acid supplementation increased triterpenoids 1.9-fold with preferential enhancement of madecassoside. Cell permeability enhancement through ultrasound-assisted extraction has proven remarkably effective: optimized conditions yielded 83.14 milligrams per gram of asiatic acid and 19.71 milligrams per gram of asiaticoside, and combining ultrasound with natural deep eutectic solvents pushed asiaticoside recovery to 229.92 milligrams per gram. Reversible electroporation could theoretically enable repeated, non-destructive metabolite harvesting from viable cultures, transforming batch processes into semi-continuous bioreactor-compatible systems—though this remains untested in C. asiatica.

The genomic era is now catching up with the chemistry. A haplotype-resolved genome assembly published in The Crop Journal confirmed that CaCYP716C11 catalyzes the conversion of 23-hydroxyursolic acid to asiatic acid, and identified CaUGT73CL69 as a glucosyltransferase that converts asiatic acid and madecassic acid to their respective monoglucosides. Tandem duplicate clusters of CaUGT73 genes on chromosome 8 reveal that gene duplication and neofunctionalization have shaped the plant’s glycosylation capacity. Earlier transcriptomic work flagged CaHDR1, CaIDI2, and CaβAS1 as key regulators, while UGT73AH1 and the glycosyltransferases CaUGT73C7 and CaUGT73C8 appear to catalyze the rate-limiting steps that assemble the characteristic sugar chains of asiaticoside and madecassoside. Yet the review’s authors caution that transcript abundance establishes correlation rather than causation, and no peer-reviewed study has yet reported CRISPR/Cas9-mediated editing of centelloside biosynthetic genes in this species.

Scale-up remains the field’s stubborn bottleneck. A 5-liter stirred bioreactor achieved 60.08 milligrams per gram dry weight of asiaticoside with optimized agitation and aeration, while a Plantform temporary immersion system combined with methyl jasmonate elicitation delivered centelloside levels 2.8-fold higher than elicited shake flasks—and 12.2-fold higher than untreated controls. A twin-bottle temporary immersion system more than tripled biomass compared to conventional semi-solid culture, though it did not quantify centellosides. Hairy root cultures, despite their biosynthetic promise, resist scale-up because their dense branching architecture and sensitivity to mechanical stress limit mass transfer. The review identifies mist reactors, wave-mixed bioreactors, and low-shear stirred tanks as untested but promising alternatives. On the translational front, preliminary estimates suggest bioreactor production only becomes economically competitive when centelloside yields exceed 5 percent dry weight and process volumes surpass 500 liters—thresholds that current elicited cultures approach but rarely achieve.

Perhaps the most forward-looking suggestion concerns extracellular vesicles. Membrane-bound nanoparticles secreted by C. asiatica cell cultures have recently been characterized and shown to carry high levels of polyphenols, reduce intracellular reactive oxygen species, suppress pro-inflammatory genes such as COX2, and promote skin repair by inhibiting tyrosinase activity and upregulating barrier-related genes including filaggrin and aquaporin-3. These vesicles outperformed conventional cell culture extracts in stability, cellular uptake, and precision. Because centellosides are packaged during vesicle biogenesis from the endomembrane system, elicited suspension cultures may serve as a platform for generating centelloside-enriched vesicles directly—skipping the extraction step entirely. Combined with the review’s proposed research framework, which prioritizes complete pathway elucidation, enzyme characterization, and systems-level regulatory mapping before engineering intervention, the picture that emerges is one of a field standing at an inflection point: the biological machinery is increasingly understood, the culture platforms are proven, and the remaining gaps—functional validation of candidate genes, standardized elicitor dosing, and validated industrial-scale bioprocesses—are now clearly defined targets rather than open questions.

Subject of Research: Centelloside biosynthesis enhancement in tissue cultures of Centella asiatica

Article Title: Advancements on centelloside biosynthesis in tissue cultures of Centella asiatica (L.) Urban

Article References: Hundare, A., & Joshi, N. (2026). Advancements on centelloside biosynthesis in tissue cultures of Centella asiatica (L.) Urban. Discover Plants, 3(1), Article 396. https://doi.org/10.1007/s44372-026-00867-8

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00867-8

Keywords: Centella asiatica, centellosides, asiaticoside, madecassoside, plant tissue culture, hairy root cultures, elicitation, methyl jasmonate, bioreactor, metabolic engineering, CRISPR, extracellular vesicles