Bensulfuron-methyl, often abbreviated BSM, belongs to the sulfonylurea class of herbicides that work by inhibiting acetolactate synthase, or ALS, a pivotal enzyme in plants. ALS catalyzes key steps in the biosynthesis of the branched-chain amino acids valine, leucine, and isoleucine. When the enzyme is blocked, protein synthesis stalls, cell division halts, and the plant ultimately dies. This lethal mechanism is precisely what makes BSM so valuable as a selection agent in plant transformation. After new genetic material is delivered into plant cells via Agrobacterium, biolistics, or other methods, only those cells carrying a resistance gene, typically a mutated ALS gene such as Als1 or Als2 first identified in soybean, can survive exposure to the herbicide. Everything else perishes, leaving researchers with a population enriched for transgenic tissue.

Remarkably, BSM is potent at extraordinarily low concentrations, halting the growth of non-transgenic explants at levels below one micromolar. That potency, however, is a double-edged sword. Even modest degradation of the compound in the aqueous environment of tissue culture medium could allow non-transformed plants, known as escapes, to slip through the selection sieve. Escapes are not a trivial nuisance. They consume greenhouse space, reagents, analyst time, and money, and they inflate the apparent failure rate of transformation experiments. In large operations where media plates containing BSM are routinely prepared in bulk and stored in the dark at four degrees Celsius for two to three weeks before use, any slow decay of the active ingredient would be a serious quality-control problem.

The chemistry of BSM degradation gave the team reason for concern. Sulfonylurea herbicides are known to break down through two principal pathways: chemical hydrolysis and photolysis. Previous work had shown that BSM is relatively stable under neutral and alkaline conditions but hydrolyzes faster in acidic environments, with the cleavage occurring at the carbon-nitrogen bond between the sulfonylurea bridge and the acetyl group. Plant tissue culture media typically sit at a mildly acidic pH of around 5.6, a range that favors this hydrolytic mechanism. Light exposure adds a second threat, since photodegradation of sulfonylureas in aqueous solution is well documented. The stage seemed set for storage to erode the herbicide’s power, yet no one had quantified the effect under realistic laboratory conditions.

To settle the question, the researchers developed a quantitative analytical workflow combining liquid chromatography tandem mass spectrometry with a biological assay. They prepared a semi-solid medium called SoyE1 0.3BSU, dispensed sixty-four milliliters into standard petri dishes, and stored the plates under a matrix of conditions ranging from the mundane to the extreme. Small agar plugs were punched from the plates and extracted with acetonitrile, and the resulting extracts were analyzed on a Sciex QTrap 5500 mass spectrometer coupled to an ultra-performance liquid chromatography system. The method targeted the protonated BSM precursor ion at a mass-to-charge ratio of 411.26 and monitored a characteristic product ion at 149.00, with quantification performed against a serial dilution standard curve using the Skyline software package. Recovery of BSM from freshly prepared plates was estimated at eighty-five percent, and control plates lacking BSM showed no interfering signals, confirming that the measurement reflected the herbicide itself rather than background noise from other media components.

In parallel, the team ran a bioassay using wild-type Nicotiana benthamiana, a tobacco relative prized in plant research for its rapid growth and ease of handling. Seedlings were transplanted onto plates that had endured each storage condition, and after six days the researchers photographed the plates and computed total leaf area using the Easy Leaf Area image-analysis software. Because BSM stunts the growth of susceptible plants, larger leaf areas signaled weaker herbicide activity. Nine seedlings per plate and three plates per condition provided replication, and statistical comparisons were made using linear models with Sidak-adjusted p-values at a confidence level of 0.05.

The results were strikingly reassuring for standard practice. Plates stored for one week at four degrees Celsius, whether in complete darkness or under five hours of daily light at 170 micromoles per square meter per second, showed no significant loss of BSM and no reduction in herbicidal efficacy. Even more notably, plates held for a full three weeks at four degrees Celsius in twenty-four hours of darkness, treatment H in the study’s design, remained statistically indistinguishable from freshly prepared controls in both mass spectrometric abundance and bioassay performance. In other words, the common walk-in cold-room storage that transformation facilities rely on does not meaningfully degrade the selection agent, at least over the storage windows typically used.

The picture changed dramatically when the researchers pushed the conditions toward the harsh end of the spectrum. Plates stored for two weeks at twenty-three degrees Celsius with five hours of daily light lost roughly forty percent of their BSM content. Three weeks at twenty-three degrees Celsius under continuous light at 170 micromoles per square meter per second cut the herbicide to about half of the control level. The most punishing treatment, a greenhouse exposure of approximately twenty-five degrees Celsius with a sixteen-hour photoperiod and a blazing light intensity near 6,400 micromoles per square meter per second, produced the greatest degradation of all, and the tobacco seedlings grown on those plates more than doubled their leaf area relative to controls. A similarly severe decline appeared in plates that had already been used for soybean tissue culture for two weeks in a growth chamber at twenty-three degrees Celsius with sixteen hours of light at 1,100 micromoles per square meter per second, suggesting that most BSM loss occurs during the transformation process itself rather than during storage, and that uptake of the herbicide by plant explants may contribute to the depletion.

The study also exposed an instructive gap between the two measurement approaches. The mass spectrometry data detected moderate declines in BSM, such as the fifty percent reduction after three weeks of continuous room-temperature light, that the tobacco bioassay failed to register as statistically significant improvements in leaf area. The seedling assay, while simple and visually intuitive, appears too blunt an instrument to resolve partial losses of the active ingredient. The authors suggest that future work should employ a more sensitive indicator species and aim to define a precise threshold of herbicide concentration below which transformation efficiency is compromised, which would tell facilities exactly when plates must be replaced with fresh selection media.

Beyond the immediate findings, the research opens a path toward smarter formulation of selection media. Because hydrolysis is a dominant breakdown pathway, the authors speculate that oil-in-water emulsion formulations, in which the active ingredient remains dissolved in an organic phase and shielded from water, could slow degradation. Additives offer another avenue: humic and fulvic acids have been shown to increase the photostability of BSM on dry soil, and ultraviolet absorbers such as riboflavin or 3-(4-methylbenzylidene) camphor have been used in pharmacology to stabilize structurally related compounds like the antibiotic sulfacetamide. Monitoring known breakdown products by mass spectrometry could further illuminate which degradation routes dominate under laboratory conditions. For now, the practical message is clear and welcome: refrigerated, dark storage of BSM-containing media is safe for at least three weeks, but laboratories should keep selection plates far from bright light, warm rooms, and greenhouse benches if they want their herbicide to keep doing its job. The mass spectrometry method described here, robust and reproducible with an eighty-five percent recovery rate, gives plant biotechnology facilities a ready-made quality-control tool to verify that their selection media remain as lethal to non-transgenic tissue as the day they were poured.

Subject of Research: Degradation of the herbicide bensulfuron-methyl in plant tissue culture medium under different storage conditions

Article Title: Impact of storage conditions on the degradation pattern of bensulfuron-methyl in plant tissue culture medium

Article References: Beam, K., Pinter, T. B. J., Cieszewski, P., Wu, P., Elumalai, S., & Rigoulot, S. B. (2025). Impact of storage conditions on the degradation pattern of bensulfuron-methyl in plant tissue culture medium. Discover Biotechnology, 2(1), Article 6. https://doi.org/10.1007/s44340-025-00014-1

Image Credits: AI Generated

DOI: 10.1007/s44340-025-00014-1

Keywords: bensulfuron-methyl, plant tissue culture, herbicide degradation, acetolactate synthase inhibitor, plant transformation, selectable marker, mass spectrometry, LC-MS/MS, sulfonylurea, Nicotiana benthamiana, bioassay, media storage

The receptor in question, named RCSP, belongs to the TNL family of plant immune proteins, which carry a Toll-interleukin-1 receptor, or TIR, domain alongside a nucleotide-binding region and a leucine-rich repeat array. TNL receptors are famous in plant pathology for recognizing pathogen effectors and triggering a localized cell death response that walls off infection. What makes RCSP remarkable is its target: rather than a bacterial or oomycete effector, it responds to CSPs delivered by phloem-feeding insects such as aphids and the brown planthopper Nilaparvata lugens. Previous work from the same group had shown that recognition of a salivary effector by RCSP promotes effector-triggered immunity and systemic resistance in the model plant Nicotiana benthamiana, causing the insects to induce dwarfism in the plant as part of a defensive response. The new study asks how, at the level of atoms and residues, this recognition actually works.

The answer, it turns out, involves three departures from the canonical TIR domain playbook. First, the RCSP-TIR domain carries a deletion of nine amino acids in the loop connecting beta-strand B and alpha-helix B, a region known as the BB-loop. Second, it contains an insertion of eight amino acids in the loop between alpha-helices 5 and 6, the alpha5alpha6-loop. Third, the glutamate residue that normally serves as a key catalytic component in TIR enzymatic chemistry is replaced by glutamine, an E87Q substitution. Each of these changes would be expected to compromise the standard functions of a TIR domain, and indeed the researchers found that the BB-loop deletion disrupts the canonical NAD+-binding pocket and prevents the standard tetramerization that many TIR domains use to become active enzymes.

That loss of conventional architecture raises an obvious puzzle: if RCSP cannot form the usual tetramer or bind NAD+ in the usual way, how does it signal at all? The team turned to AlphaFold3 and DMFold structure prediction to find out. Their modeling revealed a striking compensatory mechanism: the alpha5alpha6-loop insertion creates a novel protein-protein interface that stabilizes an atypical tetrameric architecture. In other words, the receptor appears to have traded its ancestral assembly interface for a new one, built from an inserted loop, that restores the multimeric state needed for activity. This kind of structural re-engineering, in which one evolutionary change offsets another, offers a vivid example of how immune receptors can diversify while preserving function.

The enzymatic story is equally unconventional. TIR domains in plants and animals are known to act as NAD+ cleaving enzymes, and this activity underlies their ability to drive cell death signaling. Molecular docking combined with site-directed mutagenesis indicated that RCSP may utilize a noncanonical NAD+-binding pocket and depends on a pair of catalytic residues, aspartate 86 and glutamine 87, to mediate what the authors describe as weak cell death. The dual-residue dependence is notable because the canonical glutamate is absent; glutamine at position 87, the very residue that replaced it, appears to be part of the catalytic machinery rather than a silent placeholder. The weak cell death phenotype also fits the biology of insect defense, where a measured response may be more useful than the explosive hypersensitive reaction typical of microbial pathogen recognition.

To place these findings in context, it helps to recall what is known about TIR domain signaling more broadly. Seminal work published in Science in 2019 demonstrated that animal and plant TIR domains cleave NAD+ in cell death pathways, and subsequent structural studies of proteins such as SARM1 in animals illuminated how NADase activity is regulated. In plants, activated TNL receptors assemble into large resistosome complexes, as visualized for ZAR1 and ROQ1, and signal through helper NLR proteins that function as calcium-permeable channels. The EDS1 family of proteins, together with SAG101 and NRG1, forms a coevolved module that mediates cell death signaling downstream of TIR-domain receptors. RCSP presumably plugs into this downstream framework in Nicotiana benthamiana, but its upstream activation mechanism, as the new study shows, is built on a distinctly nonstandard scaffold.

The evolutionary analysis adds another layer of interest. By surveying RCSP-TIR homologs across plant genomes, the researchers classified them into four distinct clades, with evidence highlighting Solanaceae-specific adaptations. This pattern suggests that the structural innovations seen in RCSP are not one-off accidents but part of a broader, family-wide diversification within the nightshade lineage, the group that includes tobacco, tomato, potato and pepper. Such lineage-specific expansion of atypical TIR domains could reflect an ongoing evolutionary dialogue with phloem-feeding insects, whose CSP effectors are conserved across aphids and planthoppers. If plants in this family have repeatedly reworked their TIR domains to detect these proteins, it would imply that CSP recognition has been a persistent selective pressure.

CSPs themselves are an intriguing class of effectors. Originally named for their putative roles in insect chemoreception, they are small, conserved proteins found in the saliva of phloem-feeding insects. Proteomic surveys of aphid and planthopper saliva have repeatedly identified them among secreted proteins, and functional studies have shown that some CSPs can modulate plant defenses. One aphid CSP, SmCSP4, has been reported to stimulate salicylic acid-mediated defense responses in wheat by interacting with a transcription factor. The fact that the same protein family can function as both a virulence factor and a trigger of immunity, depending on the host genotype, underscores the double-edged nature of effector biology: what is a weapon in a susceptible plant becomes a molecular signature in a plant carrying the right receptor.

The broader significance of this work lies in expanding the known repertoire of what plant immune receptors can recognize and how they can be built. Most research on NLR receptors has focused on microbial pathogens, and the structural biology of resistosomes has largely been worked out in that context. Herbivorous insects cause enormous agricultural losses, and the global burden of pests on major food crops is well documented, yet the molecular mechanisms by which plants detect insect attack have remained comparatively opaque. RCSP provides one of the clearest examples to date of a conventional NLR scaffold being repurposed for insect effector recognition, and it does so through structural changes, a deleted loop, an inserted loop and a swapped catalytic residue, that would have been difficult to predict from sequence alone.

For crop improvement, the implications are tantalizing. If the structural determinants of CSP recognition can be pinned down precisely, as this study begins to do with its docking and mutagenesis data, then engineering RCSP-like receptors or their recognition specificities into crop species could offer a route to durable resistance against aphids and planthoppers. The finding that weak cell death, mediated by an atypical catalytic mechanism, suffices for signaling also hints that immune outputs can be tuned, which matters because overly aggressive cell death can damage plant tissue. Much remains to be resolved, including the exact geometry of the noncanonical NAD+-binding pocket and how CSP binding allosterically activates the receptor, but the study establishes a compelling framework. A plant receptor has been caught in the act of reinventing itself, and the reinvention is aimed squarely at the insects that would eat the plant.

Subject of Research: Structural and catalytic mechanisms by which insect chemosensory protein effectors activate the atypical plant TNL immune receptor RCSP

Article Title: The insect effector CSPs activate an atypical plant TNL immune receptor

Article References: Rao, W., Li, T., Yang, J., Zhu, L., Zhao, W., & Ma, T. (2026). The insect effector CSPs activate an atypical plant TNL immune receptor. Plant Cell Reports, 45(10), Article 291. https://doi.org/10.1007/s00299-026-03972-w

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03972-w

Keywords: plant immunity, chemosensory proteins, TNL receptor, TIR domain, RCSP, insect effectors, brown planthopper, aphids, NAD+ cleavage, Nicotiana benthamiana, effector-triggered immunity, plant-insect interaction

S-palmitoylation, also called S-acylation, is the covalent attachment of a saturated 16-carbon palmitate to a cysteine residue through a thioester bond. Unlike other lipid modifications, the thioester linkage is intrinsically unstable, which makes the modification reversible and dynamically regulated by two antagonistic enzyme families: palmitoyl acyltransferases (PATs), which carry a conserved DHHC catalytic motif and add palmitoyl groups, and depalmitoylases, which hydrolyze the thioester bond and strip acyl groups away. In humans, 23 PATs have been identified and many are implicated in disease, but the enzymology of S-acylation in plants remains comparatively underexplored. Arabidopsis encodes 24 PATs with distinct subcellular localizations, and S-palmitoylated proteins have been catalogued in rice, maize and soybean, yet validated enzyme-substrate pairs in plant-virus systems have been scarce, limiting mechanistic insight into how this modification shapes infection.

The research team, led by Yan Xie and Xueping Zhou of Zhejiang University together with colleagues, began by establishing where TYLCCxV C4 resides inside plant cells. When C4 fused to green fluorescent protein was expressed in N. benthamiana leaf cells, fluorescence accumulated predominantly at the cytoplasm and plasma membrane, with weak nuclear signal. Subcellular fractionation experiments reinforced the picture: C4 co-sedimented with a plasma membrane marker in the membrane-enriched pellet fraction, while free GFP stayed in the soluble supernatant. Bioinformatic prediction tools suggested that C4 lacks a transmembrane domain but carries two candidate lipid modifications, N-myristoylation at glycine 2 and S-acylation at cysteine 4, hinting that a fatty anchor rather than a hydrophobic helix might explain the membrane association.

To test that hypothesis directly, the researchers deployed the biotin-switch assay, a technique in which hydroxylamine selectively cleaves thioester bonds and the newly freed cysteines are tagged with biotin for detection. A strong S-acylation signal appeared in hydroxylamine-treated samples of C4 but not in untreated controls. Quantitative mass spectrometry using Q-Exactive liquid chromatography-tandem mass spectrometry then pinpointed the modification to cysteine 4. When the team substituted that cysteine with serine, generating a mutant called C4(C4S), the S-acylation signal vanished entirely. The consequences were striking: the mutant redistributed to the cytoplasm and nucleus, and its protein accumulation collapsed to roughly a tenth of wild-type levels, even though semi-quantitative RT-PCR showed that transcript abundance was unchanged. Treating plants with 2-bromopalmitate, a chemical inhibitor of palmitoylation, produced the same dual effect, driving C4 out of the membrane and reducing its steady-state abundance without touching its mRNA.

The functional stakes became clear in infection experiments. When C4 or the palmitoylation-deficient C4(C4S) was expressed from a potato virus X vector, plants receiving wild-type C4 developed systemic upward leaf curling and stem elongation by 14 days post-inoculation, while plants receiving the mutant showed only mild chlorotic symptoms indistinguishable from the empty-vector control. Western blots confirmed that C4 protein levels and PVX coat protein accumulation were comparable across treatments, ruling out differences in expression or vector fitness. More importantly, the team engineered an infectious TYLCCxV clone carrying the same C4S mutation. Plants inoculated with the mutant virus developed dramatically milder symptoms than those infected with wild-type TYLCCxV, and Southern blot analysis revealed weak viral DNA signals at 15 days that diminished further by 30 days. S-acylation of a single cysteine, in other words, is a major determinant of geminiviral pathogenicity and accumulation.

Having established that the modification matters, the researchers went hunting for the enzymes that control it. Screening four candidate palmitoyl acyltransferases from N. benthamiana with a yeast split-ubiquitin assay, they found that NbPAT4 and NbPAT6 interacted with C4. They focused on NbPAT4 and confirmed the interaction in plant cells using bimolecular fluorescence complementation, which reconstituted yellow fluorescent protein signal at the cytomembrane, and co-immunoprecipitation, which pulled down NbPAT4 specifically with C4 but not with free GFP. Genetic evidence followed: in CRISPR-generated NbPAT4 knockout plants, TYLCCxV induced only mild leaf curling and accumulated less viral DNA, whereas plants overexpressing NbPAT4 developed more severe symptoms, including vein swelling and leaf clustering, and carried higher viral loads. Biotin-switch measurements placed the enzyme at the chemistry itself: C4 S-acylation levels fell to about half of wild type in knockout plants and rose to nearly double in overexpression lines.

Palmitoylation is a two-way street, so the team also screened 19 candidate depalmitoylases, including four acyl-protein thioesterases and fifteen alpha/beta hydrolase domain-containing proteins, for interactors of C4. Only one emerged: NbABHD6, a 274-amino-acid enzyme containing a conserved alpha/beta hydrolase domain with a catalytic triad of serine 147, aspartate 212 and histidine 241, mirroring the architecture of the mammalian ABHD17 family. Yeast split-ubiquitin, bimolecular fluorescence complementation and co-immunoprecipitation all confirmed a specific interaction with C4. Functionally, co-expression of NbABHD6 reduced C4 S-acylation levels to roughly 0.6 of control values and cut C4 protein accumulation by half, again without altering transcript levels. When the three catalytic residues were simultaneously mutated to alanine, the resulting NbABHD6(mSDH) mutant still bound C4 but lost all ability to reduce its S-acylation or abundance, demonstrating that the depalmitoylase activity, not mere physical association, drives the effect.

The fate of depalmitoylated C4 proved to be destruction by the ubiquitin-proteasome system. Treatment with the proteasome inhibitor MG132 increased C4 accumulation, while inhibitors of autophagy, E64d and 3-methyladenine, had no effect, indicating that C4 is normally turned over through the 26S proteasome. When NbABHD6 was co-expressed, C4 levels dropped sharply in vehicle-treated leaves, but MG132 partially rescued the protein, and the catalytically dead mutant had no such effect. The authors note that even with the proteasome blocked, NbABHD6 still reduced C4 below control levels, hinting at additional regulatory mechanisms consistent with C4’s multifunctional nature. They also observed that NbABHD6 did not markedly change C4’s membrane localization, likely because the myristoylation site at glycine 2 provides a second, independent lipid anchor, a reminder that subcellular localization alone cannot reliably report S-acylation status.

The findings sit within a growing appreciation that S-acylation is a battleground in plant-microbe encounters. Rice stripe virus disrupts the S-palmitoylation of host Remorin 1 and shunts it into autophagy; potato mop-top virus hijacks the acylated stress sensor HIPP26 for long-distance movement; and the C4 protein of beet severe curly top virus uses its own S-acylation to engage the receptor kinase CLAVATA 1. In mammals, an elegant palmitoylation cycle on STAT3, catalyzed by DHHC7 and reversed by APT2, governs inflammatory signaling, illustrating how dynamic acylation can act as a molecular switch. The new study extends this logic to plant antiviral immunity and, notably, identifies only the second defined plant depalmitoylase-viral substrate pair, after the recent report that Arabidopsis ABAPT3 targets the C4 protein of beet severe curly top virus.

The authors frame their results as a host-pathogen enzymatic tug-of-war aligned with the recently proposed concept of apoplastic interactive balance. Early in infection, TYLCCxV exploits the host’s own S-acylation machinery: NbPAT4 palmitoylates C4, anchoring it at the plasma membrane, stabilizing the protein and amplifying viral accumulation. The plant counters by deploying NbABHD6, whose depalmitoylase activity destabilizes C4 and channels it into proteasomal degradation, suppressing infection. The equilibrium between these opposing enzymes sets the stoichiometry of C4 acylation and, with it, the trajectory of disease. Open questions remain, including whether C4 recruits specific E3 ubiquitin ligases and how S-acylation crosstalks with myristoylation, phosphorylation and ubiquitination. But the identification of NbPAT4 and NbABHD6 as antagonistic regulators offers a concrete enzymatic axis, and potentially a target for engineering crop resistance to one of agriculture’s most damaging virus families.

Subject of Research: Reversible S-palmitoylation of the geminiviral C4 protein and its regulation by host palmitoylation enzymes during plant-virus interaction

Article Title: Reversible S-palmitoylation of C4 protein encoded by TYLCCxV orchestrates geminiviral pathogenesis

Article References: Xie, Y., Zhao, M., Liu, X., Yan, J., Yang, W., Chen, Y., Yang, M., Wang, X., Fu, S., & Zhou, X. (2026). Reversible S-palmitoylation of C4 protein encoded by TYLCCxV orchestrates geminiviral pathogenesis. Stress Biology, 6(1), Article 35. https://doi.org/10.1007/s44154-026-00308-2

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00308-2

Keywords: S-palmitoylation, geminivirus, C4 protein, TYLCCxV, palmitoyl acyltransferase, depalmitoylase, NbPAT4, NbABHD6, Nicotiana benthamiana, plant-virus interaction, 26S proteasome, post-translational modification

The motivation behind the study was practical. Cas13 depends on a short guide RNA to find its target, but the team had previously discovered that these guides can silence transcripts even when the Cas13 protein is absent, a phenomenon they termed guide-induced gene silencing, or GIGS. This Cas13-independent silencing appears to hijack the plant’s endogenous RNA interference pathway, which processes small RNAs and uses them to direct silencing complexes to complementary sequences. Similar guide-only effects have been observed in human cell lines and mosquito cells, suggesting that Cas13-independent silencing is a widespread feature of eukaryotic cells rather than a plant-specific quirk. For biotechnologists, this is a problem: silencing that runs through RNAi rather than Cas13 is harder to control and more prone to off-target effects, undermining the precision that makes Cas13 attractive in the first place.

The researchers’ initial hypothesis was elegant in its simplicity. Plant viruses face relentless pressure from host RNAi, the primary antiviral defense in plants, and in response nearly all characterized plant viruses encode viral suppressors of RNAi, or VSRs. These specialized proteins neutralize the silencing machinery through diverse mechanisms, including sequestering small interfering RNAs so they cannot assemble into active RISC complexes, or directly interacting with core RNAi components such as Dicer-like proteins, Argonautes, and RNA-dependent RNA polymerases. The team reasoned that if they co-expressed a VSR alongside Cas13 and its guide, the VSR would mop up the RNAi-mediated, Cas13-independent silencing while leaving the Cas13 protein itself untouched. The result would be clean, Cas13-dependent transcript knockdown free of background noise.

Reality proved messier. The team tested two well-characterized VSRs: HcPro, the helper component protease from Turnip mosaic virus (TuMV), and P19 from Tomato bushy stunt virus (TBSV). Their assay system used Nicotiana benthamiana leaves infiltrated with Agrobacterium carrying the relevant constructs, with a GFP-expressing TuMV as the target. A multiguide construct carrying three targeting sequences against the TuMV genome effectively reduced viral accumulation, visible as diminished GFP fluorescence, in both Cas13-independent and Cas13-mediated assays when a GUS control protein was co-expressed. But when HcPro was substituted for GUS, the picture changed dramatically. HcPro suppressed the expected Cas13-independent silencing, consistent with its known anti-RNAi function, yet it also crippled Cas13-mediated targeting, restoring GFP fluorescence to levels comparable to controls in which no targeting occurred at all.

The quantitative data underscored how potent this interference is. Western blotting and densitometric analysis showed that HcPro expression restored GFP accumulation by approximately 20 percent in the Cas13-independent assays, but produced a nearly sixfold increase in GFP accumulation when Cas13 was present. P19 told the same story: co-expression increased GFP accumulation by 33 percent in Cas13-independent assays and by 78 percent in Cas13-mediated assays. Control experiments confirmed that the effect was specific to targeting guides rather than a general effect on viral accumulation, and RT-PCR verified that Cas13 transcripts were present only in the Cas13-mediated assays, ruling out contamination as an explanation. Both suppressors, in other words, were not merely dampening background RNAi but actively dismantling the CRISPR effector’s ability to silence its target.

To determine whether this anti-Cas13 activity was limited to viral RNA or represented a broader antagonism of Cas13 function, the researchers turned to an endogenous plant transcript. They targeted phytoene desaturase, or PDS, a gene whose silencing produces a visually distinctive photobleaching phenotype and whose transcript levels can be measured precisely by quantitative PCR. When GUS was co-expressed with a PDS-targeting multiguide and Cas13, PDS transcripts dropped by roughly 60 percent. When HcPro or P19 was co-expressed instead, PDS transcript levels remained statistically indistinguishable from those seen with a non-targeting guide. Northern blotting with a PDS-specific probe independently confirmed that the transcript was stabilized in the presence of the viral suppressors. The inhibitory effect, therefore, extends beyond antiviral contexts to general mRNA targeting, establishing HcPro and P19 as genuine antagonists of Cas13 interference.

The mechanistic key came from a mutant. HcPro suppresses RNAi by binding and sequestering small interfering RNAs, preventing the assembly of active RISC complexes, and this binding depends on amino acids in the protein’s central domain. The AS9 mutations, previously characterized in HcPro, abolish siRNA-binding activity without destroying the protein outright. When the team expressed wild-type HcPro alongside Cas13 and the PDS-targeting guide, Cas13-mediated silencing was blocked as before. But the HcPro AS9 mutant failed to inhibit Cas13-mediated silencing, and PDS transcripts were knocked down just as efficiently as in the GUS controls. This result ties HcPro’s anti-CRISPR activity directly to its RNA-binding, silencing-suppression function, and points to a plausible mechanism: both RNAi and Cas13 rely on short guide RNAs complexed with a protein effector, and a suppressor that sequesters small double-stranded RNAs indiscriminately will intercept Cas13 guide RNAs just as readily as viral siRNAs.

The findings resonate with a broader story about anti-CRISPR proteins. Bacteriophages long ago evolved proteins that disable bacterial CRISPR-Cas immunity, through mechanisms ranging from blocking PAM recognition to mimicking crRNA structure, and recent work has identified anti-CRISPR factors specific to RNA-targeting Cas13 systems. Plant viruses have almost certainly never encountered selective pressure from bacterial CRISPR-Cas systems, yet this study shows they already possess Cas13-inhibitory capacity as a byproduct of their anti-RNAi arsenal. Intriguingly, previous reports of successful Cas13-mediated virus resistance in plants often targeted the viral suppressor sequences themselves, which may have skewed the arms race toward the plant by limiting VSR protein accumulation. Guides directed against HcPro provided stronger TuMV interference in the team’s earlier work than guides against other regions of the viral genome, and other studies found that targeting viral open reading frames other than VSRs yielded weaker resistance.

There is an important caveat, and it concerns timing. A previous study reported that transgenic potato plants expressing Cas13 targeting the Potato virus Y coat protein resisted PVY infection effectively, seemingly contradicting the idea that VSRs can defeat Cas13 during infection. But that same line lost its resistance under mixed infections with PVY plus Potato virus X or Potato virus S, which carry their own heterologous suppressors. In stably transformed plants, Cas13 and its guide are present before the virus arrives, allowing the Cas13-crRNA complex to form and strike early, before suppressors accumulate. In the transient assays of the new study, Cas13, guide, and VSR are delivered simultaneously, giving the suppressor a window to accumulate and block complex formation. The authors suggest that any scenario reducing Cas13-crRNA accumulation, whether through stress, developmental regulation, or co-infecting viruses, could similarly compromise resistance. The sobering takeaway is that plant viruses did not evolve to counter Cas13, yet they may already be primed to overcome engineered CRISPR-Cas13 antiviral defenses through suppressors refined over millions of years of warfare with RNAi, and viral variants with enhanced Cas13-inhibiting function could be selected in the field.

Subject of Research: Inhibition of CRISPR-Cas13-mediated RNA targeting by plant viral suppressors of RNA interference

Article Title: Plant viral suppressors HcPro and P19 inhibit CRISPR-Cas13-mediated transcript interference

Article References: Sharma, V. K., Marla, S., & Cook, D. E. (2026). Plant viral suppressors HcPro and P19 inhibit CRISPR-Cas13-mediated transcript interference. Stress Biology, 6(1), Article 69. https://doi.org/10.1007/s44154-026-00339-9

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00339-9

Keywords: CRISPR-Cas13, viral suppressors of RNAi, HcPro, P19, guide-induced gene silencing, RNA interference, Turnip mosaic virus, Tomato bushy stunt virus, anti-CRISPR, plant virology, transcript engineering, Nicotiana benthamiana

The research, conducted by Hasan Zeitooni and Masoud Shams-Bakhsh at Tarbiat Modares University in Tehran together with Rosa Lozano-Durán of Eberhard Karls University Tübingen, the Max Planck Institute for Plant Breeding Research, and the GreenRobust Cluster of Excellence, was published in Virology Journal. Because PYLCV was only recently identified and assigned to the genus Pylecuvirus as the species Pylecuvirus petroselini, essentially nothing was known about how its individual proteins behave inside plant cells. The team set out to fill that gap by focusing on C4, a protein of just 85 amino acids whose biological activities and cellular distribution had remained entirely uncharacterized.

The investigation began with comparative sequence and bioinformatic analysis of the PYLCV C4 protein. Even at only 85 residues, the protein carries an impressive collection of candidate targeting features. The computational screen identified a predicted N-terminal myristoylation motif—a lipid attachment signal that in many viral and cellular proteins anchors them to membranes—a putative palmitoylation site that could reinforce membrane association, motifs potentially related to nuclear trafficking including nuclear localization signals and a nuclear export signal, and a chloroplast transit peptide that could direct the protein into plastids. Such a combination of targeting determinants in a protein this small hints at a multifaceted role during infection, consistent with the pleiotropic effects that C4 proteins from related geminiviruses exert on their hosts.

To test these predictions experimentally, the researchers turned to confocal microscopy. They fused the C4 protein to green fluorescent protein and expressed the construct in plant tissue, allowing them to track exactly where the protein accumulates within the cell. The imaging revealed that PYLCV C4–GFP localizes prominently to the plasma membrane, the boundary between the cell interior and its surroundings, and also accumulates in two additional compartments: the nucleus, where many geminivirus proteins carry out their manipulations of host gene expression and cell cycle control, and the chloroplasts, the photosynthetic organelles that are frequent targets of viral effectors.

A key experiment followed from the predicted myristoylation motif. N-myristoylation is a covalent modification in which a myristoyl lipid group is attached to a glycine residue at position two of the protein, a process that typically requires the removal of the initiator methionine and is essential for membrane anchoring. By substituting the glycine at position 2, the team created a mutant form of C4 and examined its localization. The result was striking: loss of Gly2 strongly reduced the plasma membrane association of the C4–GFP fusion and, at the same time, increased the chloroplast-associated signal. This finding supports an important role for the Gly2-containing N-terminal region in directing the protein to the cell periphery, and it suggests a competitive relationship between targeting pathways—when Gly2-dependent membrane association is disrupted, chloroplast targeting becomes more prominent. In other words, the same short protein can be routed to different destinations depending on whether its lipid modification site is intact.

Localization studies alone cannot establish pathogenicity, so the researchers next asked what happens when the protein is produced in plants at physiological relevance. They expressed PYLCV C4 from a potato virus X–based vector in Nicotiana benthamiana, a widely used experimental host in plant virology. PVX is an RNA virus whose genome can be engineered to carry additional sequences, providing a convenient system to test whether a heterologous protein induces symptoms. The outcome was dramatic. Plants expressing PYLCV C4 developed severe developmental alterations, including mosaic patterns, yellowing, leaf curling, stem deformation, and in the most extreme cases, plant death. Critically, these symptoms arose without any change in PVX RNA accumulation, demonstrating that the damage was caused by the C4 protein itself rather than by an alteration in the vector virus’s replication. This separation of protein effect from viral accumulation is a hallmark of a genuine pathogenicity determinant.

Given that many geminivirus C4 proteins function as suppressors of RNA silencing—a cornerstone of the plant antiviral immune response—the team also examined whether PYLCV C4 interferes with post-transcriptional gene silencing, or PTGS. They employed standard silencing suppression assays, monitoring both local and systemic silencing of a reporter transgene in N. benthamiana, including the well-known 16c line that carries a green fluorescent protein transgene used to visualize silencing spread. Under the conditions tested, PYLCV C4 did not behave as a strong suppressor of local or systemic PTGS. However, the researchers observed a possible delay in the spread of GFP silencing in 16c plants, leaving open the possibility that the protein has a subtle or context-dependent effect on silencing mobility rather than a robust suppressor activity of the kind seen with classic viral silencing suppressors.

The combination of results paints a picture of a compact but multifunctional protein. PYLCV C4 is a membrane-associated factor whose N-terminal lipidation motif governs its subcellular distribution, with an apparent routing switch between the plasma membrane and the chloroplasts controlled by a single glycine residue. When expressed in plants, it is sufficient to cause severe developmental perturbation on its own, echoing the symptoms associated with the natural disease. At the same time, its weak apparent activity as a silencing suppressor distinguishes it from some of its homologs in other geminivirus genera, suggesting that different C4 proteins may achieve pathogenicity through overlapping but non-identical mechanisms.

These findings carry broader implications for understanding geminivirus evolution and host manipulation. The family Geminiviridae encompasses many genera, and their C4/AC4 proteins have diversified while retaining core functions as symptom determinants. Comparative analysis across these genera, as undertaken here with a dataset of C4/AC4 and C3 protein homologs from twelve genera, helps place PYLCV within that evolutionary landscape. The discovery that a single point of lipidation—the glycine at position two—acts as a switch between membrane and chloroplast targeting offers a mechanistic handle for future studies dissecting how subcellular localization translates into developmental reprogramming. It also raises questions about which host proteins C4 engages at each destination, whether chloroplast-associated C4 contributes to the yellowing symptoms typical of the disease, and whether nuclear accumulation supports interactions with cell cycle regulators.

As the first experimental characterization of any PYLCV protein, this work establishes a framework for future mechanistic studies of how a recently emerged geminivirus interacts with its hosts. The methodology—combining comparative sequence analysis, confocal microscopy, site-directed mutagenesis, heterologous expression, and silencing assays—provides a template that can now be extended to the virus’s remaining proteins and to PYLCV’s interactions with parsley and experimental model hosts. For a pathogen family whose members continue to emerge and recombine at alarming rates, understanding the molecular toolkit of each new virus is an essential step toward anticipating and managing the diseases they cause.

Subject of Research: Functional characterization of the C4 pathogenicity protein of parsley yellow leaf curl virus

Article Title: Characterization of the C4 protein encoded by parsley yellow leaf curl virus

Article References: Zeitooni, H., Lozano-Durán, R., & Shams-Bakhsh, M. (2026). Characterization of the C4 protein encoded by parsley yellow leaf curl virus. Virology Journal. https://doi.org/10.1186/s12985-026-03309-9

Image Credits: AI Generated

DOI: 10.1186/s12985-026-03309-9

Keywords: geminivirus, PYLCV, C4 protein, myristoylation, plasma membrane, chloroplast, Nicotiana benthamiana, potato virus X, pathogenicity, gene silencing, symptom determinants, plant virology

The new system, described in the journal Crop Health, is built around commercially available one-liter opaque plastic hydroponic pots with matching lids, each costing approximately 0.30 US dollars. A hole roughly half a centimeter in diameter is drilled in the center of each lid to cradle the seedling stem while the roots descend into the nutrient solution. Smaller auxiliary holes accommodate plastic sticks and clips that prop up plants as they grow, preventing tilting in mature specimens. The pots themselves are opaque, a detail with real practical consequences: by blocking light from reaching the solution, they suppress algal growth, which otherwise fouls hydroponic systems and adds cleaning labor. Because the pots can be cleaned, disinfected, and reused across experiments, the long-term cost of the platform drops even further. Crucially, no pumps, circulating reservoirs, or aeration devices are required at any point in the workflow.

The cultivation protocol begins on germination trays filled with perlite moistened with a half-strength modified Hoagland solution, or MHS, a complete nutrient formulation containing major ions such as nitrate, potassium, calcium, magnesium, and phosphate together with a full complement of micronutrients including boron, manganese, zinc, copper, molybdenum, and cobalt, buffered at a pH of 5.8 to 6.0. Seeds are surface-sterilized with a sodium dichloroisocyanurate solution containing Tween-20 before sowing, and seedlings germinate under controlled conditions at 24 degrees Celsius with a 16-hour light, 8-hour dark photoperiod and 60 to 70 percent relative humidity. After 15 days on the trays, seedlings are transferred into the hydroponic pots. The perlite clinging to the roots is gently rinsed away in water to minimize transplant damage, and the young plants are kept under low light for their first two days in the system to reduce shock. Early on, the solution fully submerges the roots; as the root system matures, the level is lowered so the liquid occupies only about three-quarters of the pot volume. This seemingly minor adjustment is one of the system’s most important engineering decisions, because it leaves the basal portions of the roots exposed to air and provides enough passive oxygenation to eliminate the need for artificial aeration altogether.

Nutrient management under the system is deliberately minimal. The solution is first replaced one month after transplanting, and thereafter renewed every two weeks, a schedule the authors found sufficient to sustain healthy growth without pH corrections or intermediate top-ups in most cases. The simplicity translates directly into labor savings compared with setups that demand frequent solution changes, continuous pH monitoring, and mechanical aeration. The researchers first optimized the platform with Nicotiana benthamiana, a mainstay of plant molecular biology prized for its amenability to transient transformation, grafting, and virus-induced gene silencing, and then expanded their tests across a striking taxonomic breadth.

To assess species compatibility, the team grew seven representative species side by side in hydroponics and conventional soil: the dicotyledonous cucumber, tomato, soybean, and N. benthamiana, and the monocotyledonous rice, wheat, and maize. Shoot length was tracked at 10, 20, and 35 days after transfer, with dry biomass measured at the final time point. The results favored hydroponics for several of the dicots. Ten days after transfer, cucumber and soybean shoots were 69 percent and 63 percent longer, respectively, than their soil-grown counterparts, an advantage maintained throughout the cultivation period. N. benthamiana nearly doubled its shoot length relative to soil-grown plants by day 35, and the shoot dry weights of hydroponic cucumber, soybean, and N. benthamiana were all significantly greater than those of soil-grown controls. Tomato was the exception among the dicots, with soil-grown plants reaching heights 32 percent greater after 35 days, although shoot dry weights did not differ significantly between the two systems, indicating that total biomass accumulation was comparable even if internodal elongation differed.

The monocots told a more cautious story. Rice, wheat, and maize showed no obvious differences in shoot length relative to soil-grown plants during the first 20 days after transfer, but as cultivation continued they progressively developed chlorosis and weak growth. The team attempted to rescue performance by testing half-strength, full-strength, and double-strength nutrient solutions, yet leaf yellowing persisted. The authors therefore conclude that the current system supports early-stage monocot growth but is not yet suitable for long-term monocot cultivation, and they suggest that formulations supplying nitrogen as ammonium or as mixed ammonium and nitrate, along with alternative iron sources and pH adjustments, may be needed to close that gap. The honest recognition of this limitation gives the work practical credibility: the platform is presented as a broadly capable dicot system rather than a universal solution.

Beyond the seven directly compared species, four additional plants, Arabidopsis thaliana, cultivated tobacco, potato, and the medicinal legume Astragalus membranaceus, all grew healthily in the system. In total, eight dicotyledonous species were cultivated successfully, and four of them, N. benthamiana, Arabidopsis, soybean, and tomato, completed their entire life cycles and produced mature seeds entirely within the hydroponic setup. The full-cycle result is particularly notable for Arabidopsis, a species often considered difficult to grow hydroponically, and it means researchers can now carry a plant from germination to seed set without ever touching soil, opening the door to experiments in which root-zone conditions are controlled from cradle to grave.

The functional demonstrations extend well beyond simple cultivation. In transient expression assays, hydroponically grown N. benthamiana leaves expressing the RUBY reporter, which produces a visible red pigment, and the enhanced green fluorescent protein showed transformation efficiency comparable to soil-grown plants. Tomato grafting succeeded in both systems, with all nine graft attempts taking under each condition, supporting the system’s use in studies of systemic signaling and metabolite transport. The parasitic weed dodder, Cuscuta australis, established infections on hydroponic hosts just as readily as on soil-grown plants, providing a clean platform for host–parasitic plant interaction studies. Perhaps most compelling is the system’s performance in root exudate work, a field where soil is a hopeless confound. The researchers collected exudates from phosphorus-starved N. benthamiana and found that the concentrated exudates triggered germination in up to 76 percent of broomrape (Phelipanche aegyptiaca) seeds, a rate closely matching that induced by the synthetic strigolactone analog GR24, confirming that the platform captures biologically meaningful strigolactone signaling under nutrient stress.

Stress physiology experiments further showcased the platform’s precision. Thirty-day treatments of nitrogen deficiency, phosphorus deficiency, and 200 millimolar salt stress produced distinct, quantifiable phenotypes in N. benthamiana: salt stress severely suppressed height and cut chlorophyll content by roughly half, nitrogen starvation drove strong leaf yellowing and a 50 percent reduction in shoot biomass, and phosphorus deficiency reduced biomass by 32 percent while actually stimulating root elongation, a classic foraging response. Quantitative PCR confirmed that the expression of marker genes for nitrogen starvation (NRT1.1, NR, AMT1;1), phosphorus starvation (PHO2, PHR1, SPX1), and oxidative salt stress (SOD1-1, SOD1-2, CAT1) tracked the treatments faithfully. Wounding experiments added another layer: mechanical damage to hydroponically grown leaves and roots rapidly induced the jasmonic acid biosynthesis genes AOC and AOS, and root wounding triggered measurable accumulation of jasmonic acid and its bioactive conjugate JA-isoleucine within 30 minutes, demonstrating that even fast-moving hormonal signaling can be resolved in this system.

The authors argue that the combination of negligible cost, effortless assembly, reusability, and freedom from aeration equipment makes this platform a practical tool for laboratories with limited resources, and the breadth of validated applications, from root physiology and stress assays to grafting, parasitic plant interactions, exudate collection, and transient gene expression, suggests it could become a quiet workhorse across plant biology. For a field in which the price of entry has often been measured in specialized hardware and hours of maintenance, a 30-cent pot that can carry a plant from seed to seed is a refreshingly democratic proposition, and one that many laboratories are likely to adopt within the year.

Subject of Research: A low-cost, reusable hydroponic system for multi-species plant cultivation and root biology research

Article Title: A versatile, low-cost, and reusable hydroponic system for the cultivation of plants of various species

Article References: Zhang, J., Zhang, X., Qian, M., & Wu, J. (2026). A versatile, low-cost, and reusable hydroponic system for the cultivation of plants of various species. Crop Health, 4(1), Article 21. https://doi.org/10.1007/s44297-026-00084-5

Image Credits: AI Generated

DOI: 10.1007/s44297-026-00084-5

Keywords: hydroponics, plant science, Nicotiana benthamiana, Arabidopsis thaliana, soybean, tomato, root exudates, abiotic stress, parasitic plants, jasmonic acid, grafting, soilless cultivation