A team led by Jian-Feng Li at Sun Yat-sen University in Guangzhou, working with collaborators at South China Agricultural University, the Chinese University of Hong Kong and the University of Macau, identified two paralogous chitinases in the model plant Arabidopsis thaliana that they named MIC1 and MIC2. Both genes are induced by chitin and by other microbe-associated molecular patterns, including the bacterial flagellin-derived peptide flg22 and the elongation factor Tu-derived peptide elf18. Both proteins are secreted into the apoplast, the fluid-filled space outside the plant cell membrane where fungal contact first occurs, and both possess direct antifungal activity in vitro, breaking down chitin in the fungal cell wall itself. On the surface, the two enzymes look like redundant copies of the same tool.

The resemblance is deceptive. When the researchers generated CRISPR/Cas9 knockout mutants, the two paralogs pulled in opposite directions. Plants lacking MIC1 became markedly more resistant to the grey mould pathogen Botrytis cinerea and to the vascular wilt fungus Verticillium dahliae, while plants lacking MIC2 became more susceptible. The team also showed that the single mutants and the mic1 mic2 double mutant grow normally under standard conditions, which means the antagonistic effects of these enzymes are specific to immune outcomes rather than general developmental defects. The picture that emerged is of two enzymes with the same substrate but opposing roles in tuning the immune response.

The key to this antagonism lies in the products of chitin digestion. Chitin is a polymer of N-acetylglucosamine units, conventionally abbreviated NAG, and the length of the oligomers released by hydrolysis determines their biological meaning. Using high-performance liquid chromatography to track the fate of defined chitin oligomers, the researchers found that MIC2 cleaves long chitin chains into intermediate fragments, principally NAG4 to NAG6, which are precisely the sizes that plant chitin receptors recognize as immunogenic elicitors. These fragments activate mitogen-activated protein kinase signalling, a canonical early readout of chitin-triggered immunity, and pretreatment with NAG4 primed Arabidopsis leaves for enhanced resistance against B. cinerea. MIC2, in other words, is an alarm bell: it chews the fungal wall in a way that generates the molecular signals that rally the plant’s defenses.

MIC1 does the opposite. Rather than stopping at immunogenic intermediates, MIC1 processes chitin all the way down to NAG2 dimers and NAG1 monomers, fragments that are too short to activate receptor signalling. In seedling assays, exogenous chitin normally inhibits root growth, a visible manifestation of constitutive chitin signalling, and MIC1 is the enzyme responsible for preventing this self-inflicted damage. When the researchers tested additional Arabidopsis chitinases from other clades, they found that the MIC1-like degradation pattern, exemplified by the clade IV enzyme chitIV1, is functionally conserved, and that deleting whole clusters of MIC1-like genes reproduced the chitin-hypersensitive growth phenotype. MIC1 and its relatives therefore act as a molecular off-switch, extinguishing the growth-inhibitory signal once the immune alarm has sounded.

What makes one enzyme stop at immunogenic fragments while its near-identical paralog grinds chitin to dust? The answer, uncovered through a combination of mass spectrometry, PNGase digestion assays and site-directed mutagenesis, is N-glycosylation, the attachment of sugar chains to asparagine residues of secreted proteins. Both MIC1 and MIC2 carry N-glycans, and these modifications are not decorative: glycosylation-deficient variants of either protein failed to be secreted efficiently into the apoplast, and a glycosylation-deficient MIC2 could no longer complement the enhanced susceptibility of mic1 mic2 double mutants to B. cinerea. Glycosylation is thus required for these enzymes to reach their site of action at all.

But one glycan does far more than ensure secretion. Mass spectrometry mapped three N-glycosylation sites on MIC1 and two on MIC2, and the decisive difference came down to a single residue: asparagine 137 in MIC1. When the researchers swapped variable segments between the two proteins to create chimeric enzymes, the exchange that transferred the MIC1 region containing Asn137 into MIC2 converted MIC2 into a MIC1-like enzyme, digesting NAG7 into more dimers and monomers and fewer immunogenic pentamers and tetramers. Conversely, the corresponding chimeric version of MIC1 lost its characteristic band shift and behaved more like MIC2. In complementation tests, the chimeric MIC2 carrying the MIC1 glycosylation region partially suppressed chitin-induced growth inhibition, whereas wild-type MIC2 did not, and it slightly increased susceptibility to B. cinerea instead of restoring resistance. Removing the Asn137 glycan from MIC1 converted it into a MIC2-like enzyme, demonstrating that this one sugar attachment dictates the chitinolytic specificity of the entire protein.

Structural modelling with AlphaFold showed that MIC1 and MIC2 are highly similar in sequence and fold, with their catalytic glutamates aligned and their glycosylation sites positioned on surface loops, including the Loop III region implicated in substrate handling in GH19 family chitinases. The Asn137 glycan apparently reshapes the local architecture of the catalytic cleft in a way that changes how many NAG units the enzyme removes per cleavage event. This is a remarkable example of post-translational modification acting as a functional diversification code: two genes born of duplication, nearly interchangeable in sequence, are sorted into opposing immune roles by a single covalently attached oligosaccharide. The authors describe this as an N-glycosylation code governing the functional specialization of paralogous chitinases.

The implications extend well beyond Arabidopsis. A bioinformatic survey revealed that MIC1-like chitinases are widespread across the plant kingdom, and the Asn137-equivalent residue is highly conserved among MIC1 orthologs from different Arabidopsis ecotypes. The team turned to rice, the world’s most important staple crop, and generated CRISPR knockout mutants of the rice ortholog OsMIC1. The osmic1 mutants showed enhanced resistance to rice blast and to bacterial blight, the latter an intriguing bonus suggesting the mechanism is not strictly antifungal, while their grain length, grain width and thousand-grain weight remained indistinguishable from wild-type plants. Like their Arabidopsis counterparts, however, osmic1 seedlings did exhibit chitin-induced root growth inhibition, confirming that the dampening function of OsMIC1 is conserved.

For breeders, this is the rare kind of result that points directly at a molecular target. Fungal pathogens destroy a substantial fraction of global crop yields each year, and conventional resistance breeding often trades yield for defense. The MIC1/MIC2 system suggests a third path: tune the enzymatic processing of a universal pathogen-derived signal so that immunity is amplified without the growth penalty that constitutive immune signalling imposes. Editing or selecting variants of MIC1-like chitinases, or manipulating the glycosylation machinery that controls them, could in principle produce crops that detect and respond to fungal attack more vigorously while growing as if no pathogen were present. A single sugar on a single asparagine, it turns out, may hold the balance between feast and famine in the plant kingdom.

Subject of Research: N-glycosylation-dependent functional divergence of paralogous plant chitinases balancing immunity and growth

Article Title: N-glycosylation code diversifies paralogous chitinases to balance plant immunity and growth

Article References: Li, C., Lin, X.-X., Tian, L., Sun, W., Liu, J., Liu, Q., Du, Y., Jiang, X., Liang, Z., Deng, Y. Z., Au, S. W. N., Wan, J.-B., & Li, J.-F. (2026). N-glycosylation code diversifies paralogous chitinases to balance plant immunity and growth. Nature Plants. https://doi.org/10.1038/s41477-026-02420-7

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02420-7

Keywords: chitinases, N-glycosylation, plant immunity, chitin signalling, Arabidopsis thaliana, MIC1, MIC2, growth-defense trade-off, fungal resistance, rice breeding, apoplast, CRISPR

The commentary centers on a study by Zhang and colleagues published in Molecular Plant, which examined how the gaseous signaling molecule hydrogen sulfide, or H2S, influences the balance between immunity and development in rice. Hydrogen sulfide has long been recognized as a versatile player in plant physiology. It promotes seed germination by activating antioxidant enzymes and MAPK signaling pathways, enhances photosynthetic efficiency by upregulating photosynthetic enzymes and light signaling responses, and suppresses chlorophyll degradation to delay senescence. Under abiotic stresses such as heavy metal contamination, drought, heat, cold, and salinity, H2S bolsters resilience through enhanced antioxidant activity, protection of the photosynthetic apparatus, regulation of sulfur metabolism, and crosstalk with phytohormones. It also participates in defense against pathogens and herbivores by inducing pathogenesis-related gene expression, modulating glutathione metabolism, and interacting with hormone signaling networks.

What has remained poorly understood, however, is how H2S fits into the growth-defense trade-off itself. The resource constraint hypothesis, one of the most prevalent explanations for this trade-off, holds that plants possess finite energy and materials, so any reallocation toward defense necessarily diminishes what is available for growth. Yet accumulating evidence suggests that plants do not simply passively divide a fixed budget. Instead, they actively regulate the balance through a sophisticated, multi-layered regulatory network in which hormone crosstalk plays a central role, supplemented by microRNAs and non-coding RNAs, epigenetic regulation, and post-translational modifications of key transcription factors and NLR immune receptors. The new work adds an unexpected layer to this network: a redox-controlled structural transition of a single metabolic enzyme.

Zhang and colleagues began with a simple observation: applying H2S externally to rice plants improved their resistance to two devastating bacterial pathogens, Xanthomonas oryzae pv. oryzicola and Xanthomonas oryzae pv. oryzae, the causal agents of bacterial leaf streak and bacterial blight respectively. The treatment triggered the release of hydrogen peroxide, a burst of reactive oxygen species, and the expression of defense genes. But there was a cost. The same treatment stunted root elongation and impaired the development of lateral roots, a textbook manifestation of the growth-defense trade-off. The question became how the plant could harness the defensive benefits of H2S while avoiding its developmental penalties.

The answer lay in a protein called OsCBSX3, a rice protein containing a cystathionine beta-synthase domain. CBS domain-containing proteins are homologs of enzymes known from mammals, where they catalyze the condensation of cysteine and homocysteine to form cystathionine and H2S. The researchers showed that OsCBSX3 positively regulates rice resistance to both Xoc and Xoo, and that this protective function depends on its ability to produce hydrogen sulfide. Crucially, like other CBS domain-containing proteins, OsCBSX3 exists in two distinct structural states within the plant: a monomeric form and an oligomeric form. When bacteria infect the plant, monomeric OsCBSX3 shifts into the oligomeric state, and this oligomer can enter the chloroplast, the energy-producing organelle of the cell.

The functional importance of this structural conversion was demonstrated through genetics. An oligomerization-deficient mutant of OsCBSX3 showed impaired H2S production, compromised resistance against Xanthomonas oryzae, and defective chloroplast localization. In other words, the ability of the protein to assemble into its multi-subunit form is not a structural curiosity but the very mechanism by which the plant ramps up sulfide-based signaling during an attack. The oligomeric state is the immune-active state, and the monomeric state is the quiet, growth-compatible state.

To understand how this toggle is itself controlled, the team searched for proteins that physically interact with OsCBSX3 and identified two partners: OsTrxZ, a member of the thioredoxin family of redox proteins, and OsPsbO, the manganese-stabilizing protein of photosystem II. The picture that emerged is elegantly self-regulating. Upon pathogen infection, PsbO binds to OsCBSX3 and promotes its monomer-to-oligomer transition, elevating H2S generation and thereby enhancing disease resistance. But once H2S levels rise too high, a second interaction takes over: TrxZ competes with PsbO for binding to OsCBSX3 and reduces the protein back to its monomeric form. This monomerization curtails further H2S synthesis, alleviating the overaccumulation of the gas and its detrimental impacts on growth and development. The system thus functions as a negative feedback loop, with the signal itself, H2S, triggering the shutdown of its own production.

The significance of this finding extends beyond rice pathology. As Pu and colleagues emphasize in their commentary, the study provides the first evidence that H2S plays a coordinating role in plant growth-defense trade-offs and reveals the underlying mechanism. It also overturns a long-standing assumption about how plants make hydrogen sulfide in the first place. Until now, H2S production in plants was attributed almost exclusively to cysteine desulfurization enzymes, namely L-cysteine desulfhydrase and D-cysteine desulfhydrase. The demonstration that a CBS domain protein catalyzes H2S synthesis in plants fills a genuine gap in the field and suggests that the enzymology of sulfide signaling is more diverse than previously appreciated. It also illustrates a universal strategy for managing the growth-defense trade-off: rather than changing gene expression wholesale, the plant dynamically tunes the metabolic activity of a single enzyme by switching its oligomeric state.

For breeders, the practical implications are considerable. OsCBSX3, PsbO, and OsTrxZ together constitute a module of potential targets for engineering disease resistance in rice, one of the world’s most important staple crops feeding billions of people. The commentary’s authors are careful to note, however, that the goal is not simply to maximize H2S production. Concentration thresholds must be optimized so that resistance is deployed on demand, avoiding the excessive growth inhibition that would erode any yield advantage gained from disease resistance. They point to precise gene editing techniques, including the use of pathogen-inducible promoters that would activate the defense module only when a threat is detected, as a plausible route to achieving this kind of calibrated immunity.

The work also reframes how scientists think about trade-offs in general. The resource constraint hypothesis remains valid as a broad principle, but the OsCBSX3 story shows that plants possess dedicated molecular machinery for actively arbitrating between growth and defense, rather than merely suffering the consequences of a fixed budget. A gaseous signal, a photosynthetic protein, a thioredoxin, and a metabolic enzyme form a self-correcting circuit that boosts immunity during infection and quietly stands down when the danger has passed or when the cost to the plant becomes too great. Understanding such circuits in rice may well presage similar discoveries in other crops, opening a path toward plants that no longer have to choose between thriving and surviving.

Subject of Research: Hydrogen sulfide signaling and the growth-defense trade-off in rice

Article Title: Growth or immunity? OsCBSX3’s molecular toggle decides

Article References: Pu, M., Liu, S., Xie, Y., & Chen, J. (2025). Growth or immunity? OsCBSX3’s molecular toggle decides. Crop Health, 3(1), Article 18. https://doi.org/10.1007/s44297-025-00057-0

Image Credits: AI Generated

DOI: 10.1007/s44297-025-00057-0

Keywords: rice, hydrogen sulfide, OsCBSX3, growth-defense trade-off, plant immunity, Xanthomonas oryzae, chloroplast, thioredoxin, PsbO, oligomerization, disease resistance breeding, plant signaling

The research team, led by scientists at the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences together with colleagues from Yangzhou University, Tibet University, and the Xizang Academy of Forest, conducted a multi-year in-situ experiment at a field site on the plateau. Rather than simulating future climate in a greenhouse, the researchers manipulated temperature and precipitation directly in the natural ecosystem, using open-top warming chambers and altered rainfall treatments applied to intact plots. This design allowed them to observe how two dominant alpine desert species, Ajania tibetica and Ceratoides compacta, responded to realistic combinations of warming and added water over multiple growing seasons, integrating responses across physiology, growth, and genome-wide gene expression.

The two species, though growing side by side in the same harsh environment, turned out to be running fundamentally different biological playbooks. Ajania tibetica adopted what the researchers describe as a conservative strategy. When temperatures rose, this plant suffered oxidative stress and its growth was inhibited, and remarkably, this happened regardless of whether additional water was available. Even the relief of increased precipitation, which one might expect to buffer the harm of warming, could not rescue A. tibetica from the damaging effects of higher temperatures. Something deeper than water availability was constraining its capacity to cope, and that something turned out to be written in its transcriptome.

To dissect that constraint, the team developed a metric they call the physiological-transcriptomic decoupling index, or PTDI. The concept is elegant: it measures how much a plant changes its gene expression in relation to how much it actually gains physiologically. In A. tibetica, the PTDI was high, revealing a metabolically costly mismatch. Under warming, the plant massively upregulated genes involved in ribosome biogenesis, the energy-intensive process of building the cellular machinery for protein synthesis, yet this enormous transcriptional investment produced negligible physiological benefits. In effect, the conservative species was spending its limited energy budget on an expensive repair and rebuilding program that failed to translate into growth or improved stress tolerance, a molecular equivalent of running to stand still.

Ceratoides compacta told a completely different story. This species pursued an opportunistic strategy, characterized by a lower PTDI and enhanced growth under the experimental warming and altered precipitation conditions. Rather than escalating a costly molecular emergency response, C. compacta maintained its physiological performance with minimal transcriptional volatility, changing relatively few genes while achieving meaningful gains in biomass. The researchers traced this efficiency to a molecular network centered on heat shock proteins, the cellular guardians responsible for maintaining proteostasis, the proper folding, function, and turnover of the proteome. By keeping its existing proteins stable and functional under heat stress, C. compacta avoided the need for wholesale transcriptional restructuring, preserving resources that could instead be channeled into growth.

The contrast between these two modes carries profound implications for how we think about stress biology. Much of plant molecular research has focused on the magnitude of gene expression changes, on how many genes switch on or off under stress. This study reframes the question: the quality and economy of a transcriptional response may matter more than its scale. A high-cost repair mode, in which a plant frantically rebuilds its protein synthesis machinery in response to damage, can consume resources that a low-cost maintenance mode, anchored in proteostasis control, would leave available for reproduction and growth. In an environment where every calorie counts, transcriptomic efficiency, not transcriptomic drama, appears to determine adaptive success.

At the ecosystem scale, these findings sketch out a potential reshuffling of life on the plateau. The authors suggest that opportunistic species like Ceratoides compacta may outcompete conservative species like Ajania tibetica under future warmer and wetter climate scenarios, potentially driving significant shifts in alpine desert community structure. Such shifts would ripple far beyond the plants themselves. Alpine deserts of the Qinghai-Xizang Plateau anchor grazing economies, regulate water flows into major Asian river systems, and store carbon in fragile soils. If the dominant species composition changes, the ecosystem services these landscapes provide could change with them, making it essential to predict which species will thrive and which will fade as the climate continues to warm.

The methodological rigor of the work deserves emphasis. Conducting a multi-year manipulation experiment at high elevation on the Tibetan Plateau is logistically formidable, requiring sustained maintenance of field infrastructure in one of the most remote environments on Earth. The researchers combined physiological and biochemical trait measurements with genome-wide expression profiling and network analysis, using weighted gene co-expression network approaches whose statistical properties they carefully validated. By integrating physiological trajectories with transcriptomic data across treatments and species, they were able to move from correlation to a mechanistic account of why one species grew and the other stalled. The PTDI framework itself may prove a valuable export, offering researchers studying other ecosystems a quantitative way to ask whether a plant’s molecular response is efficient or wasteful.

There is also a sobering conservation dimension. A. tibetica’s plight illustrates that some species may possess no physiological escape route from warming, no matter how water availability changes. Its conservative strategy, presumably honed over evolutionary time in a colder and more stable climate regime, becomes a liability in a warmer world, locking the plant into a cycle of oxidative stress and stunted growth. Conservation planning for high-altitude ecosystems has often focused on range shifts, the idea that species will simply move upslope as conditions warm. This study adds a molecular warning: some species may be transcriptionally incapable of capitalizing on the new conditions even where they remain, and their decline may be written in gene expression long before it becomes visible at the population level.

As the planet’s high-altitude and high-latitude ecosystems warm faster than the global average, the lessons from the Qinghai-Xizang Plateau will resonate far beyond it. The growth-defense trade-off is one of the oldest concepts in ecology, but this research shows that its resolution is orchestrated at the level of the transcriptome, in the competing economies of ribosome construction and protein maintenance. Whether a plant faces the future with an expensive repair manual or a quiet, efficient toolkit may decide not just its own survival, but the face of entire communities. For the alpine deserts of the Tibetan Plateau, and perhaps for stressed ecosystems everywhere, the future may belong less to the plants that react loudest and more to those that respond with the quiet discipline of molecular efficiency.

Subject of Research: Growth-defense trade-offs and transcriptomic plasticity in alpine desert plants of the Qinghai-Xizang Plateau under climate change

Article Title: Transcriptomic efficiency shapes growth-defense trade-offs in alpine desert plants under climate change

Article References: Gan, L., Yang, Z., Wang, S., Meng, F., Liu, Y., & Dorji, T. (2026). Transcriptomic efficiency shapes growth-defense trade-offs in alpine desert plants under climate change. Genome Biology. https://doi.org/10.1186/s13059-026-04282-w

Image Credits: AI Generated

DOI: 10.1186/s13059-026-04282-w

Keywords: alpine desert, Qinghai-Xizang Plateau, climate change, growth-defense trade-off, transcriptomic plasticity, heat shock proteins, proteostasis, ribosome biogenesis, Ajania tibetica, Ceratoides compacta, plant stress responses, Genome Biology