The research, led by Tolga Bozkurt and colleagues at Imperial College London together with collaborators including Chih-Horng Kuo, Erh-Min Lai, Jiorgos Kourelis, and Lida Derevnina, positions AS109 as what the authors describe as an accessible and versatile chassis for functional genomics in non-model crops. The significance of that claim lies in the widening gap it addresses. Modern genomics generates candidate genes at a pace that far outstrips the capacity of stable transformation to test them, particularly in crop species where regeneration protocols are slow, expensive, or simply unavailable. A transient expression system that works across families would allow researchers to move from hypothesis to experimental validation in days rather than seasons.

Agrobacterium-mediated transfer works by exploiting the natural ability of certain soil bacteria to smuggle DNA into plant cells. In transient expression, the delivered construct is not integrated into the genome in a heritable way; instead, it drives temporary production of a protein of interest, typically within two to five days of infiltration. This makes the technique ideal for testing protein localization, reconstituting signaling pathways, screening for molecular recognition events, and dissecting host-pathogen interactions. But host range has always been the constraint. The canonical laboratory strains, derived largely from Agrobacterium tumefaciens isolates, perform well in Nicotiana species and a handful of other solanaceous hosts, while many legumes, brassicas, and other crops respond poorly, if at all, to infection by these strains.

The PLOS Biology team systematically evaluated AS109 across diverse dicot species spanning multiple taxonomic families and found that the engineered Rhizobium strain mediated efficient transient expression where conventional strains faltered. The breadth of the host range is the headline result, but the consistency matters just as much: across the species tested, AS109 outperformed commonly used laboratory agrobacterial strains, suggesting that the advantage is not a niche adaptation to one or two unusual hosts but a general property of the strain’s interaction with plant tissue.

To demonstrate what a broad-host-range chassis makes possible, the researchers built a suite of functional assays in faba bean (Vicia faba), a legume of global agricultural importance that has long lacked accessible rapid assay tools. The assays covered protein localization, allowing researchers to see where a candidate protein travels within faba bean cells; RNA interference-mediated gene silencing, enabling targeted knockdown of endogenous genes to test function; cell-surface elicitor recognition screens, which reveal whether a plant’s immune receptors can detect molecules characteristic of invading pathogens; and nucleotide-binding leucine-rich repeat receptor, or NLR, activation, the intracellular immune signaling events that trigger programmed cell death upon effector recognition.

The fifth assay in the suite pushes into infection cell biology at the host-pathogen interface, the frontier where plant immunity research increasingly operates. Using live-cell imaging approaches refined in model solanaceous systems, researchers can now watch, in faba bean cells, how pathogens attempt to suppress defenses and how resistance proteins respond in real time. Bringing this capability to a non-model crop transforms faba bean from a species studied mainly through forward genetics and field trials into one amenable to the same mechanistic cell biology that has accelerated discovery in Arabidopsis and Nicotiana benthamiana.

Among the most consequential demonstrations is the cross-family transferability of disease-resistance genes. NLR proteins are the intracellular immune receptors that plants use to detect pathogen effectors, and engineering broad-spectrum resistance increasingly depends on moving NLRs between species. The team showed that both singleton NLRs and sensor-helper NLR pairs—two-member systems in which one receptor perceives the pathogen effector and a partner propagates the signal—originating from the Solanaceae retain their effector recognition and cell death activity when transferred into faba bean. In practical terms, this means a researcher can take a resistance gene characterized in potato or tomato and, within days, test in faba bean whether it recognizes the corresponding effector and mounts the appropriate immune response.

That result has implications well beyond faba bean. Sensor-helper NLR pairs are architecturally complex, requiring coordinated expression and physical interaction, so their successful reconstitution in a distantly related legume suggests that the cellular machinery supporting NLR signaling is more conserved across families than pessimistic assessments had assumed. For crop protection, the AS109 platform offers a rapid pre-screen: before committing years to stable transformation of a candidate resistance gene into a crop, breeders and biotechnologists can evaluate its recognition specificity and signaling competence in a transient assay, triaging candidates that would otherwise consume resources without delivering durable resistance.

The study also speaks to a structural problem in plant science. Research infrastructure has concentrated on a small number of model species, so the tools, protocols, and reference strains are optimized for them, while orphan crops and regionally important staples lag behind. The authors frame AS109 as bridging the gap between hypothesis generation and experimental validation across diverse plant species, and the phrase captures a genuine bottleneck. As genome assemblies and gene annotations accumulate for crops such as faba bean, the limiting step is no longer identifying candidate genes but testing what they do. A chassis that accepts diverse hosts converts that bottleneck from a multi-year transformation cycle into an experiment of days.

What remains to be seen is how the community adopts and extends the platform. The authors present AS109 as accessible, and its performance across families suggests immediate utility for labs working on legumes and other previously underserved dicots. Monocots, which include the cereal crops that supply the majority of human calories, present distinct barriers to Agrobacterium-mediated transfer and were not the focus of this study, so the broad-host-range claim is best understood within the dicot lineage it demonstrates. Even so, for the families it covers, the arrival of a strain that reliably outperforms standard laboratory agrobacteria across species boundaries redefines what a routine experiment in crop biology can look like—moving functional genomics for non-model crops closer to the speed and flexibility that model systems have long enjoyed.

Subject of Research: Broad-host-range Rhizobium rhizogenes-mediated transient expression for functional genomics in diverse crop species

Article Title: A broad-host-range Rhizobium rhizogenes strain enables transient expression across diverse crop species

Article References: King, F., Lopez-Agudelo, J. C., Stephens, C., Aung, M. H., Ibrahim, T., Yuen, E. L. H., Chen, A., Eilmann, N., Jenkins, S., Vuolo, C., Swee, Y.-N., Liu, W.-J., Bruty, S., Toghani, A., Kuo, C.-H., Lai, E.-M., Kourelis, J., Derevnina, L., Wu, C.-H., & Bozkurt, T. (2026). A broad-host-range Rhizobium rhizogenes strain enables transient expression across diverse crop species. PLOS Biology, 24(10), e3004010. https://doi.org/10.1371/journal.pbio.3004010

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004010

Keywords: Rhizobium rhizogenes, transient expression, Agrobacterium, faba bean, functional genomics, NLR receptors, plant immunity, crop biotechnology, gene silencing, host-pathogen interface, disease resistance, non-model crops

The plant immune system operates through two interconnected layers that function as an integrated defense network rather than as separate pathways. Pattern-triggered immunity, or PTI, is initiated when pattern-recognition receptors at the cell surface detect pathogen-associated molecular patterns. This recognition activates mitogen-activated protein kinase cascades and stimulates the biosynthesis of salicylic acid, a key immune phytohormone. Salicylic acid accumulation promotes the redox-dependent monomerization of NPR1, allowing it to enter the nucleus, where it partners with TGA transcription factors to activate defense genes such as PR1, PR2 and RBOHD. Effector-triggered immunity, or ETI, is mounted when intracellular nucleotide-binding leucine-rich repeat receptors, known as NLRs, detect specific pathogen effectors. ETI potentiates the reactive oxygen burst through RBOHD, facilitates the assembly of EDS1/PAD4/ADR1 helper complexes and amplifies salicylic acid-dependent transcriptional reprogramming, ultimately triggering localized cell death and systemic acquired resistance. Far from being redundant, the two layers form a continuum: PTI provides the foundation for ETI activation through shared signaling components, while ETI enhances PTI by increasing transcript levels of pattern-recognition receptors and their signaling partners.

Despite this sophistication, engineered resistance faces formidable obstacles. The foremost is the growth-defense trade-off: while timely immune activation is crucial for survival, mistimed or constitutive immune responses can lead to autoimmunity and severe growth penalties. Introducing a new resistance gene therefore requires precise regulation at the DNA, mRNA and protein levels. Immune recognition itself is vulnerable, as pathogens continuously evolve to evade or suppress plant defenses. The rice gene Xa23, for example, encodes an executor resistance protein activated by the transcription activator-like effector AvrXa23 of the bacterial blight pathogen, yet mutant variants of AvrXa23 have already evolved to bypass recognition by Xa23. Genetic variation among plant species further limits the transferability of immune receptors, because recipient plants may lack essential helper receptors or compatible signaling components. These constraints, the review argues, highlight the urgent need for innovative strategies that repurpose immune switches to bypass both evolutionary and physiological limitations.

At the transcriptional level, epigenetic modifications offer reversible and context-dependent control of resistance gene expression. Whole-genome sequencing in common bean has shown that nearly half of all NLR genes are methylated, with roughly 90 methylated NLRs targeted by 24-nucleotide small interfering RNAs and exhibiting reduced expression consistent with RNA-directed DNA methylation. In rice, the allelic inhibitor PigmS antagonizes the resistance protein PigmR through heterodimerization, and RNA-directed DNA methylation controls its tissue-specific expression: the PigmS promoter is hypermethylated and silenced in leaves but hypomethylated in pollen, allowing expression where immunity would compromise yield. Similarly, the resistance gene Xa21G harbors 5-methylcytosine modifications in its promoter that maintain transcriptional silence, and artificial demethylation restores expression and confers resistance to bacterial blight. Methylation can also act positively: methylation of the Pib promoter enhances its inducible expression upon infection by the rice blast fungus. The authors propose a synthetic epigenetic on/off switch that fuses DNA demethylases such as ROS1 with pathogen-inducible promoters, so that bacterial blight infection would relieve methylation-mediated silencing at the Xa21G promoter and induce resistance gene expression precisely when needed.

Pathogen effectors themselves can be turned into tools for transcriptional engineering. During ETI, transcription activator-like effectors from Xanthomonas recognize and bind effector-binding elements in the promoters of executor resistance genes such as Xa23, Xa7, Xa10 and Xa27 in rice, and Bs3 in pepper, thereby activating transcription and inducing cell death. Synthetic pathogen-inducible promoters exploit this specificity by multimerizing minimal effector-responsive elements, typically 12 to 24 base pairs in length, upstream of a core promoter. In one striking example, a combinatorial promoter module comprising ten effector-binding elements was designed to target ten distinct isolates of the bacterial blight and bacterial streak pathogens, and a 220-base-pair DNA cassette was inserted into the TATA-box region of the Xa23 promoter using genome editing, conferring resistance to both diseases. In potato, the synthetic blight-inducible promoter 2×S-4×D-NpCABE combined with the Avr3a allele has generated transgenic lines with significantly enhanced resistance to Phytophthora infestans, the late blight pathogen. The natural salicylic acid-responsive PR-1a promoter has been engineered by inserting jasmonic acid-responsive elements, enabling a single gene to confer resistance to both necrotrophic and biotrophic pathogens. CRISPR activation technology extends this approach further, allowing pathogen-inducible promoters to drive fusion proteins composed of dead Cas9 and transcriptional activators that target the promoters of resistance genes in tomato and common bean.

Pathogens also deliver transcriptional repressors, and this vulnerability can be repurposed. Fungal and oomycete effectors such as MoHTR1 and MoHTR2 from Magnaporthe oryzae, and CRN108 and Avh23 from Phytophthora sojae, bind cis-regulatory elements in host promoters to suppress defense gene expression. Introducing such elements into the promoters of susceptibility genes using genome editing would downregulate their expression upon pathogen infection, thereby enhancing resistance. The authors propose integrating CRISPR interference, in which pathogen-inducible promoters drive dead Cas9 combined with guide RNAs, to enable tunable repression of susceptibility genes such as the rice SWEET13, whose partial downregulation confers resistance to multiple pathogens without yield penalty. AI-driven direct promoter editing, combining deep learning for promoter sequence analysis with multi-omics approaches, enables the precise deletion of cis-regulatory elements to fine-tune gene expression and balance the growth-defense trade-off. Computational models for de novo design of regulatory DNA are also advancing rapidly: the deep learning model PhytoExpr, trained on 600,000 genes from 17 plant species coupled with over 6,000 matched transcriptomes, can design novel regulatory sequences with experimentally validated biological activity. Future targets could include vascular-specific elements for diseases like bacterial wilt and Huanglongbing, epidermis-specific elements that promote cuticle thickening, and senescence-specific elements activated during fruit ripening to prevent postharvest diseases.

Post-transcriptional mechanisms provide additional layers of control. Small RNA pathways regulate immunity by silencing mRNAs: in Arabidopsis, siRNAs produced at the RPP5 locus mediate cosuppression of SNC1 and neighboring resistance genes, preventing constitutive immune activation, while in rice, miR168 targets AGO1, and overexpression of miR168 increases disease susceptibility whereas expression of a target mimic enhances resistance and improves yield. miR160a confers broad-spectrum resistance to rice blast, bacterial blight and sheath blight by suppressing multiple auxin response factor genes. Beyond intracellular regulation, plants transport specific small RNAs into pathogens such as Botrytis cinerea via exosome-like vesicles to silence virulence genes, a natural cross-kingdom RNA interference adapted into spray-induced, host-induced and microbe-induced gene silencing strategies. Artificial microRNA systems using endogenous miRNA backbones have been engineered to target viral genes, and the authors suggest that hairpin RNA or artificial microRNA constructs directed against susceptibility genes such as OsSWEET14 in rice, TaMlo in wheat or DMR6 in tomato, expressed under pathogen-inducible promoters, could provide broad-spectrum resistance. Alternative splicing offers another switch: the Arabidopsis RPS4 gene undergoes pathogen-induced alternative splicing upon recognition of the AvrRps4 effector, the potato RB gene switches from a non-functional isoform during normal growth to a functional transcript upon infection, and the tobacco N gene fine-tunes antiviral immunity through virus-triggered inclusion of a 70-base-pair mini-exon. CRISPR-mediated knock-in of pathogen-inducible splicing elements could engineer synthetic splicing events that generate highly active immune receptor isoforms upon infection, while alternative polyadenylation, observed in all 72 resistance genes profiled in Arabidopsis, could be redirected by genome editing to shift transcript isoforms toward variants with increased abundance of immunity-related proteins.

Translational regulation exploits the fact that pathogens suppress cap-dependent translation during infection. Purine-rich R-motifs in the 5-prime untranslated regions of many resistance gene transcripts drive cap-independent translation, allowing sustained synthesis of defense proteins when decapping enzymes would otherwise promote mRNA decay. The barley RNA-binding protein La1 specifically recognizes the R-motif and promotes translation of defense-related transcripts, enhancing antiviral immunity. Upstream open reading frames, or uORFs, act as translational brakes: the Arabidopsis TBF1 contains two uORFs that impede ribosomes under normal conditions, but upon pathogen infection ribosomes bypass the uORFs, enabling rapid TBF1 synthesis. The transgenic cassette ProTBF1::uORFTBF1-AtNPR1 confers broad-spectrum disease resistance in rice without compromising yield, and CRISPR-mediated truncation of the uORF in OsTBF1 enables rice to maintain stable yields while achieving broad-spectrum resistance. The CRISPR-aTrE-uORF system constructs different uORF types to fine-tune translation levels precisely, offering heritable control of disease resistance without introducing foreign DNA.

At the post-translational level, the recognition surfaces of immune receptors represent the most direct switches. Structure-guided mutagenesis and domain swapping within the leucine-rich repeat domains of wheat receptors Sr33 and Sr50 have redirected recognition specificity to new pathogen effectors without triggering autoimmunity, and high-throughput mutagenesis of the tomato Tm-2² LRR domain produced variants conferring robust resistance to both tomato brown rugose fruit virus and tobacco mosaic virus. Integrated domains such as the heavy-metal-associated module in NLRs like RGA5 and Pik-1 directly recognize pathogen effectors, and structure-guided mutagenesis of the Pikp HMA domain yielded mutants that acquired recognition of additional effector variants. Nanobody-fused NLRs create artificial immune receptors capable of recognizing defined antigens, while the directed evolution technique GRAPE, which mimics natural evolution in planta, successfully evolved the integrated domain of Pikm-1 to recognize six distinct Avr-Pik variants of the rice blast fungus. Protein cleavage provides a modular cleavage-release switch: replacing the protease cleavage site of the decoy kinase PBS1 with the site recognized by a viral protease conferred resistance to the corresponding virus, and engineered cleavage-activated NLRs carrying cleavage sites for six conserved viral proteases confer resistance to over 100 types of viruses in tobacco, soybean and Arabidopsis.

The review concludes that resistance gene engineering is transitioning from time-consuming cloning from limited genetic resources to a new phase of rational design facilitated by immune switches, high-quality pan-genomes, multi-omics datasets and AI-driven protein design. Single-cell and spatial transcriptomics, ribosome profiling, cross-linking mass spectrometry and cryo-electron microscopy are deepening mechanistic understanding of how switches operate, while AlphaFold-Multimer predictions of effector-NLR interfaces closely match experimental structures. Yet the authors caution that pathogen population dynamics must be monitored continuously, since resistance genes targeting individual effectors often follow a boom-and-bust cycle, as demonstrated when the stem rust race Ug99 rapidly overcame resistance conferred by Sr31 in East African wheat. A novel endogenous sentinel strategy proposes engineering plant endophytes that express effectors in response to generic pathogen-induced signals such as reactive oxygen species, triggering effector-triggered immunity in a generalized manner and decelerating pathogen adaptive evolution. By integrating real-time pathogen population monitoring with engineered immune switches, the authors argue, crop disease resistance can be transformed from a passive to an active strategy, enabling precise and durable disease control aligned with the goals of sustainable agriculture.

Subject of Research: Plant immunity engineering

Article Title: Exploiting plant immune “switches” for resistance engineering

Article References: Wu, B., Xu, K., Bashir, A., Han, X., Sun, Q., Sun, P., Wang, G.-F., Milne, R. J., Zhang, M., Yang, L., Xu, G., & Li, G. (2026). Exploiting plant immune “switches” for resistance engineering. Stress Biology, 6(1), Article 32. https://doi.org/10.1007/s44154-026-00306-4

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00306-4

Keywords: plant immunity, disease resistance, CRISPR, NLR receptors, gene editing, crop protection, synthetic biology, food security, AI protein design, salicylic acid, Exploiting, plant

To appreciate why this matters, it helps to understand how plants normally defend themselves. Plants rely heavily on nucleotide-binding and leucine-rich-repeat immune receptors, known as NLRs, which come in three main subclasses: Toll/interleukin-1 receptor domain-containing NLRs (TNLs), coiled-coil domain-containing NLRs (CNLs), and RESISTANCE TO POWDERY MILDEW 8-like CC domain-containing NLRs (RNLs). These intracellular receptors detect pathogen effectors, the molecules pathogens deliver into host cells to promote infection, and activate defense responses that often include a localized cell death called the hypersensitive response. The problem is that a single NLR typically recognizes only a limited number of effectors from specific pathogens, which means the resistance it confers is usually narrow in spectrum. Worse still, pathogens can rapidly evolve to evade recognition by altering or discarding the effectors that betray them.

Plant breeders and biotechnologists have therefore invested heavily in engineering NLRs with broader recognition capabilities. Approaches such as domain swapping, decoy engineering, integrated domain engineering, and structure-guided, random or targeted mutagenesis have all been developed to expand the range of effectors a receptor can detect. Yet these methods carry significant drawbacks. NLRs modified by mutagenesis or domain shuffling can acquire deleterious autoimmune phenotypes, firing off defensive responses in the absence of any pathogen and stunting the plant. Even when they work, they can be sidestepped by rapid pathogen evolution in the field. Decoy engineering, exemplified by the well-studied PBS1/RPS5 system in which the protease cleavage site of the decoy protein PBS1 is modified so that diverse pathogen proteases can trigger RPS5-mediated resistance, requires engineering both a decoy protein and its cognate NLR. Many crops lack RPS5 or analogous receptors, constraining the approach’s applicability.

The new strategy sidesteps many of these limitations with a deceptively simple design. The engineered receptor is a chimeric protein built from three components: a flexible polypeptide linker fused to the N-terminus, a pathogen-derived protease cleavage site (PCS), and an autoactive NLR (aNLR). Autoactive NLRs are modified versions of normal receptors carrying amino acid substitutions at specific sites that mimic the activation normally induced by pathogen effectors. In the chimeric construct, the N-terminal fused polypeptide, which can include small tags such as HA, suppresses the activity of the autoactive receptor, holding it firmly in an off state. When a pathogen invades and secretes its protease, the enzyme cleaves the PCS, releasing the free autoactive NLR, which then triggers a powerful and broad-spectrum resistance response. The pathogen’s own enzymatic arsenal thus becomes the fuse that lights the plant’s defensive bomb.

The researchers validated the system using potyviruses as a model, a choice with enormous practical significance because this family includes some of the most devastating crop viruses in the world, all of which carry highly conserved NIa proteases. The team fused the conserved Potato Virus Y (PVY) protease cleavage site, YEVHHQ↓A, to the N-terminus of the autoactive CNL Tm-2², creating a chimeric protein designated HA-PCS^PVY-aTm-2². When co-expressed with PVY NIa in Nicotiana benthamiana leaves, these redesigned CNL proteins induced cell death, and immunoblotting assays using anti-HA antibodies confirmed that PVY NIa cleaved the chimeric protein in planta, releasing the free autoactive receptor. Transgenic Nicotiana benthamiana plants expressing the chimeric receptor showed cell death upon transient expression of the PVY protease and, crucially, complete resistance against multiple potyviruses, including PVY, Turnip mosaic virus (TuMV), Pepper mottle virus (PepMoV), chilli veinal mottle virus (ChiVMV) and Plum pox virus (PPV).

The results became even more impressive when the researchers swapped in a different receptor class. Replacing the autoactive CNL with the autoactive RNL AtNRG1.1, producing HA-PCS^PVY-aAtNRG1.1, induced what plant pathologists call extreme resistance: transgenic T1 plants infected with virus strains such as PPV and PepMoV showed no visible hypersensitive lesions and no detectable viral RNA in systemic leaves. Extreme resistance represents the strongest form of antiviral immunity, in which viral replication is shut down so completely that even the molecular hallmarks of infection disappear. That a single engineered receptor could deliver this level of protection across multiple, evolutionarily distinct potyviruses underscores the power of targeting a conserved enzymatic function rather than a variable effector molecule.

The system’s specificity, however, proved to be a double-edged sword that the researchers then turned to their advantage. When challenged with Tobacco etch virus (TEV), whose NIa protease recognizes a distinct cleavage site, ENLYFQ↓G, that differs from the XXVXXQ↓A(G/S) consensus motif and from the PVY site used in the engineered receptors, the redesigned receptors failed to confer resistance. To close this gap, the team generated an innovative construct, HA-PCS^TEV-PCS^PVY-aAtNRG1.1, containing tandem protease cleavage sites for both TEV and PVY. This receptor was confirmed to be cleaved by both proteases, triggering cell death in response to either, and transgenic plants carrying it showed either extreme or complete resistance against PVY, TEV and four other tested potyviruses. This tandem PCS design overcomes the limitation of tying a receptor’s recognition specificity to a single pathogen’s protease, significantly expanding the resistance spectrum against evolutionarily divergent viruses.

Demonstrating that the concept transfers from a model plant to a crop was the next critical test, and the researchers turned to the soybean–soybean mosaic virus (SMV) pathosystem. They constructed HA-PCS^SMV-aAtNRG1.1, incorporating the SMV NIa cleavage site ESVSLQ↓S. Co-expression assays and immunoblots confirmed that the chimeric receptor was cleaved by the SMV protease in plants. Most tellingly, T1 transgenic soybean plants inoculated with SMV-eGFP showed no infection symptoms and no detectable viral RNA, while growing normally and displaying normal agronomic traits. The absence of any observable growth penalty is particularly noteworthy, because a trade-off between growth and defense is a common pitfall in disease-resistant plants: immune receptors that are chronically active or easily triggered typically divert energy from yield. A receptor that stays silent until a pathogen’s protease appears should, in principle, avoid this cost.

Writing in Stress Biology, the commentators argue that this strategy delivers four transformative advantages over current approaches. First, it is straightforward, requiring modification of only a single NLR receptor gene rather than the concurrent engineering of a decoy protein and its cognate receptor. Second, it applies across diverse receptor types, including CNLs and RNLs, and across multiple plant species, with a single engineered receptor conferring resistance against phylogenetically related pathogens; a receptor incorporating the conserved PVY cleavage site could in theory protect against roughly 110 potyviruses. Third, resistance durability is enhanced, because resistance breakdown would generally require loss-of-function mutations in the pathogen’s protease, and proteases are essential enzymes whose loss is lethal to the pathogen. Fourth, transgenic plants achieved high-level resistance against multiple viruses with no obvious growth penalty under greenhouse conditions. The commentators further note that the approach could extend to cross-kingdom pathogens that secrete proteases, including bacteria, oomycetes, fungi and nematodes, and that CRISPR-Cas genome editing could be integrated to modify endogenous NLR genes directly, circumventing the need for transgenic procedures altogether.

Important questions remain before the technology reaches farmers’ fields. The commentators ask whether the approach will perform under natural agricultural conditions rather than the greenhouse, and whether unintended autoactivation could occur in the absence of target pathogens. Abiotic stresses such as drought, heat or physical injury, or infection by non-target pathogens, might induce plant proteases that are not typically active; if these share sequence similarity with the engineered cleavage site, they could incidentally cleave the receptor and trigger chronic immune activation, suppressing growth and yield. There is also the question of whether excessive tandem cleavage sites might induce steric hindrance or misfolding of the NLR protein, or whether an extended N-terminus of more than eight amino acids might interfere with NLR-mediated resistance. These issues warrant in-depth investigation in future studies. Even so, the conceptual leap is unmistakable: by converting pathogen-essential proteases into suicide switches that activate plant immunity, this molecular decoy design offers a compelling blueprint for next-generation, broad-spectrum and durable disease resistance, fortifying the foundations of sustainable agriculture as pathogen evolution and climate change intensify the pressures on global food security.

Subject of Research: Engineering autoactive NLR immune receptors with pathogen protease cleavage sites to confer broad-spectrum plant disease resistance

Article Title: Enemy’s arsenal backfires: pathogen proteases detonate broad-spectrum plant immunity via engineered NLRs

Article References: Liu, S., Jing, Y., & Chen, J. (2026). Enemy’s arsenal backfires: pathogen proteases detonate broad-spectrum plant immunity via engineered NLRs. Stress Biology, 6(1), Article 20. https://doi.org/10.1007/s44154-026-00296-3

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00296-3

Keywords: plant immunity, NLR receptors, protease cleavage site, potyvirus, autoactive NLR, disease resistance, crop biotechnology, NIa protease, extreme resistance, CRISPR-Cas, soybean mosaic virus, hypersensitive response

To appreciate why this matters, it helps to understand how plants normally sense attack. Plants deploy two layers of immune surveillance. The first relies on pattern recognition receptors at the cell surface, which detect generic molecular signatures of microbes. The second, more powerful layer operates inside the cell and depends on intracellular receptors called NLRs, short for nucleotide-binding leucine-rich repeat proteins. NLRs recognize the effectors, virulence proteins that adapted pathogens inject into host cells to suppress defense, and when they do, they trigger effector-triggered immunity, or ETI. This response is famously robust and durable, and it is often marked by a rapid, localized cell death at infection sites known as the hypersensitive response, which sacrifices a few cells to wall off the invader. Intriguingly, some NLRs that mediate antiviral immunity confer extreme resistance without any visible cell death at all. Genetic studies stretching back decades have shown that the majority of classical plant disease resistance genes encode NLR proteins, which is precisely why they have been prized targets for breeders trying to protect staple crops from devastating epidemics.

Structural biology has transformed what is possible with these receptors. Cryo-electron microscopy and biochemical work in recent years revealed that upon effector recognition, activated NLRs assemble into large multi-protein complexes called resistosomes. In the case of the two major sensor classes, CNLs, which carry a coiled-coil domain, and helper NLRs of the RESISTANCE TO POWDERY MILDEW 8-like class, known as RNLs, these resistosomes insert themselves into the plasma membrane and form calcium-permeable channels. The resulting influx of calcium ions into the cell acts as a second messenger that ignites the ETI program. A landmark finding came from the study of an autoactive RNL variant, AtNRG1.1 carrying a D485V substitution, which mimics the activated state and spontaneously oligomerizes into functional calcium channels even without a pathogen cue. Researchers also discovered that the pore-forming activity of CNLs and RNLs depends on a short N-terminal helix within their N-terminal domains, and, crucially, that fusing extra protein sequences to the N-terminus can physically block their ability to trigger immunity. That observation planted the seed for the new engineering strategy.

The design logic is elegant. Wang and colleagues constructed chimeric autoactive NLRs, or aNLRs, by taking an autoactive CNL or RNL and fusing to its N-terminus a blocking peptide linked through a pathogen-originated protease cleavage site, abbreviated PCS. Under normal growing conditions, the blocking peptide suppresses the receptor’s autoactivity, so the plant grows normally with no wasteful immune activation or stunting. Upon infection, proteases secreted or released by the pathogen cleave the PCS, the blocking peptide falls away, and the now-liberated aNLR oligomerizes into calcium-permeable channels, launching a potent immune response exactly where and when it is needed. The pathogen, in effect, pulls the trigger on its own destruction. Because the switch is flipped by an enzymatic activity the pathogen must deploy rather than by recognition of a specific molecular shape, the system sidesteps the evolutionary arms race that usually undermines single-resistance-gene deployments.

The practical demonstrations were striking. The team incorporated a cleavage site, designated PCS-PVY with the sequence YEVHHQ followed by the scissile bond, that is targeted by the NIa proteases encoded by more than 110 potyviruses, a vast virus family that includes some of agriculture’s worst enemies. Transgenic tobacco plants expressing the engineered autoactive form of the CNL Tm-2², tagged as aTm-2², or the autoactive RNL AtNRG1.1, tagged as aAtNRG1.1, each fused behind the PCS-PVY module, displayed complete or extreme resistance against multiple potyviruses. The researchers then broadened the resistance spectrum further by tandemly integrating PCS-PVY with PCS-TEV, the cleavage site for the NIa protease of tobacco etch potyvirus, allowing a single receptor to respond to proteases from an even wider range of viral attackers. Critically, the strategy was not confined to one species: transgenic soybeans expressing an aAtNRG1. construct carrying a soybean mosaic virus-specific cleavage site, PCS-SMV, achieved complete resistance to soybean mosaic virus, a devastating global pathogen responsible for significant yield losses in one of the world’s most important legume crops.

What sets aNLR engineering apart from earlier attempts to reprogram plant immunity is its simplicity and generality. Most current NLR engineering strategies focus on sensor NLRs, trying to alter which effectors they recognize by mutating or swapping domains within the leucine-rich repeat region or in integrated decoy domains that make direct contact with effectors. These approaches demand detailed structural knowledge of NLR-effector complexes, require labor-intensive site-directed modifications at binding interfaces, and carry the constant risk of triggering deleterious autoimmunity if the modifications go wrong. An alternative tactic uses the PBS1 decoy system, in which cleavage of the PBS1 protein by the bacterial effector AvrPphB activates the guard NLR RPS5; substituting different cleavage sites into PBS1 can redirect RPS5 activation toward other pathogens. But that trick only works in plants that naturally possess a similar PBS1-guarding NLR pairing, limiting its portability across species.

The aNLR approach, by contrast, needs only a single autoactive CNL or RNL that tolerates being silenced by an N-terminal fusion, plus a short blocking peptide and a cleavage site to govern activation. Because activation depends on protease cleavage rather than specific effector binding, using a conserved cleavage site recognized by proteases from many related pathogens, or stringing several sites together, readily yields broad-spectrum resistance. Since proteases are ubiquitous among pathogens and pests of every kind, the authors argue the same chassis could, in principle, be retargeted against virtually any pathogen or even insect by simply swapping the cleavage site, potentially extending protection across kingdom boundaries from viruses to fungi to bacteria. Durability is another built-in advantage: if the protease that processes the cleavage site is essential for the pathogen’s virulence or infection cycle, then any mutation that prevents cleavage would simultaneously cripple the pathogen itself, making escape mutations costly or lethal. The pathogen is trapped between an immune response it triggers and a virulence factor it cannot afford to change.

There are also reasons to expect the platform to travel well across the crop universe. CNLs and RNLs are widespread among crop species, and the calcium-channel activity that emerges when they form resistosomes is a conserved mechanism, so the strategy does not depend on the particular genetic background of a recipient cultivar in the way that effector-recognition engineering often does. The editorial’s authors additionally point out that aNLR engineering can be combined with CRISPR/Cas genome editing, allowing breeders to remodel endogenous CNL or RNL genes directly in elite varieties, conditioning their autoactivity in place rather than introducing transgenes. That prospect matters enormously for deployment, because it could compress the years of backcrossing that conventional resistance breeding requires and avoid some of the regulatory and consumer complications associated with transgenic crops, depending on jurisdiction and the exact editing outcome.

Caveats remain, as they always do between a Nature paper and the field. The published demonstrations cover potyviruses in tobacco and soybean mosaic virus in soybean, and extending the platform to other pathogen classes, other crops, and real-world field conditions will require further validation, as will careful agronomic assessment to confirm that the silenced receptors impose no yield penalty and that immune activation is properly contained at infection sites. Nonetheless, the conceptual leap is hard to overstate. Instead of chasing every new pathogen strain with a new resistance gene, breeders could deploy a universal immune tripwire that any pathogen must spring in order to attack, and that it cannot disarm without losing its own virulence. If that vision holds up, the engineering of autoactive NLRs may well be remembered as a turning point in the long war between farmers and the pathogens that pursue their harvests, offering durable, broad-spectrum protection built from the plant’s own deepest immune machinery.

Subject of Research: Engineering of autoactive NLR immune receptors for broad-spectrum and durable disease resistance in crops

Article Title: Engineering of autoactive NLRs: a big step toward breeding crops with durable and broad-spectrum resistance

Article References: Wang, Y., & Xiao, S. (2025). Engineering of autoactive NLRs: a big step toward breeding crops with durable and broad-spectrum resistance. Advanced Biotechnology, 3(3), Article 24. https://doi.org/10.1007/s44307-025-00079-3

Image Credits: AI Generated

DOI: 10.1007/s44307-025-00079-3

Keywords: plant immunity, NLR receptors, autoactive NLRs, effector-triggered immunity, resistosome, broad-spectrum resistance, potyvirus, soybean mosaic virus, protease cleavage site, crop breeding, CRISPR, disease resistance

The receptors in question belong to the nucleotide-binding leucine-rich repeat family, the workhorse intracellular immune sensors of plants. NLR proteins carry a modular architecture: a variable N-terminal signalling domain, a central nucleotide-binding domain that acts as a molecular switch, and a C-terminal leucine-rich repeat domain that serves as the recognition module. In the resting state, the receptor is autoinhibited, folded upon itself. When the leucine-rich repeat domain perceives, directly or indirectly, the presence or activity of a pathogen effector protein, the switch flips, the receptor oligomerises into a resistosome, and a cascade of defensive responses follows, often culminating in a localised cell death that walls off the invader.

The trouble with engineering these receptors has always been the recognition surface. Leucine-rich repeats are exquisitely tuned by evolution to particular effector proteins, and their binding interfaces are diffuse, conformationally dynamic and poorly tolerant of casual mutation. Attempts to retune an existing NLR to recognise a new effector have met with limited success, because the coupling between recognition and activation is idiosyncratic to each receptor. Natural diversity, meanwhile, is finite. When a pathogen delivers an effector for which no plant in the gene pool carries a matching sensor, breeders have no card to play. This is the gap that synthetic receptors are designed to close.

The new approach sidesteps the problem of retuning natural recognition surfaces by building the sensing module afresh. Advances in de novo protein design, accelerated by deep-learning structure prediction tools such as AlphaFold and by generative design methods demonstrated over the past several years, allow researchers to specify a protein binder with a chosen shape and interaction profile and then compute an amino acid sequence that should fold into it. Rather than asking an existing NLR to learn a new partner, the strategy designs a synthetic binder against a defined pathogen effector and wires that binder into an immune receptor scaffold, so that effector binding triggers the conserved activation machinery of the NLR.

Wiring is the crux. A binder that merely sticks to an effector accomplishes nothing unless binding is mechanically transduced into receptor activation. The engineering challenge is therefore one of allostery: the designed recognition domain must be coupled to the nucleotide-binding switch such that the receptor sits stably in its off state in the absence of pathogen, yet flips decisively when the effector is present. Getting this balance wrong in either direction is costly. A receptor that fires without its ligand would impose autoimmune damage and yield penalties, while one that fails to respond leaves the plant defenceless. The design-build-test cycle must therefore evaluate both specificity and the absence of spontaneous activation.

This is where the second half of the strategy, evolution in vivo, earns its place. Computational design produces starting points, not finished products; predicted interfaces routinely require empirical optimisation. Directed evolution, in which libraries of receptor variants are generated and screened for the desired activity, has already proven its worth in plant immunity. Previous work showed that natural NLRs can be turned into robust sensors of specific effectors through targeted mutagenesis of their recognition domains, and that such engineered receptors can be deployed in crops. The synthetic pipeline extends this logic: rather than evolving a natural receptor toward a new specificity, researchers evolve a designed receptor toward reliable function, screening variants in planta for strong responses to the target effector and no response to plant proteins.

The significance of combining these steps is that each compensates for the other’s weakness. De novo design offers unlimited starting diversity, unconstrained by what nature has provided, but its predictions are imperfect. Directed evolution offers empirical optimisation with exquisite sensitivity to function, but it needs a plausible starting scaffold to improve upon. Designed receptors give evolution a head start; evolution gives design its final polish. The result, as the Nature Plants commentary describes it, is on-demand design and refinement of resistance genes: a workflow in which a pathogen effector of agricultural concern can be identified, a synthetic receptor raised against it in silico, and functional variants selected in plants within a timeframe that conventional breeding cannot approach.

The broader context makes the timing notable. Structure prediction has matured to the point that protein complexes and designed binders can be modelled with remarkable fidelity, and generative protein design has produced functional enzymes, sensors and therapeutics in other domains. Plant immunology, meanwhile, has accumulated a detailed mechanistic understanding of how NLRs activate, including structural snapshots of resistosomes that reveal how effector perception is coupled to signalling. The convergence of these threads is what makes synthetic immune receptors plausible now, when the same attempt even five years ago would have lacked both the design tools and the mechanistic template.

There are, of course, substantial hurdles between a working prototype and a deployed resistance gene. Pathogens evolve; an effector targeted by a synthetic receptor can mutate its surface, and durable resistance may require stacking multiple sensors or targeting effectors whose function the pathogen cannot easily relinquish. Regulatory frameworks for crops carrying designed genes, and public acceptance of them, remain open questions. There is also the matter of scale: each new effector target demands its own design and evolution campaign, and the reliability of the pipeline across diverse effector families has yet to be demonstrated broadly. The commentary’s authors, writing from a laboratory with deep roots in plant immunity research, frame the advance as the opening of a route rather than its completion.

Even so, the conceptual shift is hard to overstate. Plant immunity has until now been a scavenging enterprise, drawing on variation that pathogens and plants co-authored over millions of years. If synthetic receptors can be designed against arbitrary pathogen proteins and matured by directed evolution in planta, the defensive repertoire of crops becomes a matter of engineering choice rather than evolutionary inheritance. For a world in which plant diseases claim a substantial share of harvests and climate change keeps redistributing pathogen pressure, the ability to write a resistance gene to order, and to have it refined in the very organisms it will protect, marks a genuine inflection point in how humanity arms its crops.

Subject of Research: Engineering synthetic plant NLR immune receptors through de novo protein design and directed evolution in planta

Article Title: Plant immune receptors built in silico and evolved in vivo

Article References: Jones, J. D. G., & Zhao, H. (2026). Plant immune receptors built in silico and evolved in vivo. Nature Plants. https://doi.org/10.1038/s41477-026-02398-2

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02398-2

Keywords: plant immunity, NLR receptors, de novo protein design, directed evolution, synthetic biology, crop disease resistance, pathogen effectors, protein engineering, plant biotechnology, resistance genes, AlphaFold, resistosome

The blast fungus is the most serious disease of cultivated rice, and its reach is expanding. First detected in wheat in Brazil in the 1980s, the pathogen has since spread to parts of Asia and Africa, where it now threatens cereal harvests that millions of people depend upon. Although blast is not currently present in the United Kingdom, researchers caution that a changing climate could eventually allow it to threaten cereal production in northern Europe as well. That combination of global spread and environmental change is precisely why the John Innes Centre team describes their work as a potential intervention against what they call the worst fungal disease of cereals.

To understand why the new findings matter, it helps to look at how the pathogen attacks. Like many plant pathogens, Magnaporthe oryzae inserts small proteins known as effectors into the cells of leaves and stems. Once inside, these effectors manipulate the host’s cellular machinery to suppress defences and promote disease. Plants, in turn, have evolved intracellular immune receptors that can detect these foreign molecules and trigger an immune response. That response typically involves localised cell death around the site of infection, a dramatic but effective sacrifice that cuts off the pathogen’s route to spreading through the rest of the plant.

For more than three decades, the dominant characters in this molecular arms race have been a class of receptors called nucleotide-binding and leucine-rich repeat receptors, or NLRs. A considerable body of research has placed NLRs at the forefront of our understanding of how plants mount immune responses to blast and other diseases. But in recent years, scientists studying cereal crops have increasingly turned their attention to a second, newer class of intracellular immune receptors known as tandem kinase proteins, or TKPs. These receptors, first characterised in cereals, appear to operate differently from NLRs, and their full potential has only begun to be explored.

What caught the attention of Professor Mark Banfield, a group leader at the John Innes Centre and an author of the study, was a structural feature that some TKPs share with certain NLRs: an integrated Heavy Metal Associated domain, abbreviated HMA. Previous research had shown that these HMA domains are important for recognising pathogen effectors and for mounting an immune response. If the domain acts as the molecular docking site for effectors, Banfield reasoned, then deliberately altering the amino acids at that binding interface could create novel recognition specificities, effectively reprogramming the receptor to catch effectors it would never notice naturally. That, he suggests, could open a new frontline for plant defence.

To test that idea, the team turned to structural biology. Using biophysical analysis and crystallography, they resolved at high resolution the structural interaction between HMA domains and effectors from the blast pathogen. The structures revealed that HMA domains function as biological baits within TKPs, luring pathogen effectors into a binding interaction. When the effector takes the bait, the receptor is activated and the plant’s immune response follows. Seeing the interface in atomic detail gave the researchers exactly the map they needed: they could see which residues on the HMA domain contact the effector and therefore which positions to target when engineering new binding properties.

The engineering itself delivered the study’s most striking result. Guided by the structural knowledge, the researchers successfully modified TKP immune receptors so that they acquired dual specificity, binding to effectors associated with infection of both wheat and barley. Such broad recognition rarely occurs in nature, where receptors tend to be tuned to particular pathogen molecules. Demonstrating that a cereal immune receptor can be redesigned to respond to multiple effectors simultaneously is a powerful indication that TKPs are amenable to bioengineering, and it sets the stage for work on the many TKPs that have recently been discovered in diverse cereal crops. In principle, the approach could allow scientists to custom-engineer disease resistance receptors that respond to several effectors at once, making it much harder for the pathogen to escape detection.

It is important to note that these proof of principle experiments were carried out in protoplasts, individual wheat cells used as surrogates for whole plant tissue. The next stage for the group is to translate the findings from these surrogate assays into glasshouse plants, where the engineered receptors must function within intact immune systems and provide genuine protection against infection. Dr Daniel Yu, the first author of the study, said the work shows that this new class of resistance proteins is amenable to engineering purposes, and that tools previously used to engineer NLR receptors may also work with this new class. That continuity with established methods could accelerate progress considerably, since the plant science community already has decades of experience in manipulating NLRs.

The structural understanding of effector-receptor binding may also be amplified by other emerging technologies. Precision breeding and artificial intelligence approaches could help researchers design novel specificities into HMA domains more rapidly and accurately than trial-and-error screening would allow. Machine learning tools trained on protein structures are increasingly capable of predicting how changes at a binding interface will alter molecular recognition, and combining such predictions with the crystallographic data from this study could compress the design cycle for new disease resistance genes from years to months.

Perhaps the most strategically significant aspect of the work lies in the relationship between the two receptor classes. Professor Banfield noted that NLRs and TKPs are probably activated in different ways, which opens the possibility of more robust immunity in the field because breeders would not be putting all their eggs in one basket. Further down the road, he suggested, techniques may allow genes encoding TKPs and NLRs to be stacked together against the same disease, producing what he described as a super-resistant crop. Because the two receptor classes would trigger immunity through different mechanisms, it is likely to be substantially more difficult for the pathogen to evolve around the combined defence. For a fungus that already claims enough rice each year to feed 60 million people and is steadily extending its range into wheat and barley, that kind of layered, engineered resistance may be exactly the intervention global food security requires.

Subject of Research: Bioengineering of tandem kinase plant immune receptors to broaden recognition of cereal blast fungus effectors

Article Title: Can this biotech innovation halt the destructive march of a cereal killer?

Article References: Can this biotech innovation halt the destructive march of a cereal killer?. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: blast fungus, Magnaporthe oryzae, tandem kinase proteins, NLR receptors, HMA domain, plant immunity, wheat, rice, barley, effector recognition, bioengineering, food security

The first line of defence is mounted by pattern recognition receptors, or PRRs, which sit at the cell surface and detect conserved microbial molecules known as microbe-associated molecular patterns. These include bacterial flagellin, the translation factor EF-Tu, fungal chitin and bacterial peptidoglycan. When a PRR such as the flagellin receptor FLS2 binds its ligand, it recruits a co-receptor kinase called BAK1, forming an active receptor complex that triggers a cascade of phosphorylation events. Structural studies over the past decade have revealed the atomic details of these interactions, showing how ligand binding induces dimerization and allosteric activation of the kinase domains. The review emphasizes that receptor-like proteins, which lack an intracellular kinase domain, rely on partner kinases such as SOBIR1 and BAK1 to transduce signals, and that recent work has clarified how these complexes assemble and activate downstream pathways.

Once a PRR is activated, a receptor-like cytoplasmic kinase called BIK1 is released from the receptor complex and phosphorylates a remarkable range of targets. BIK1 directly activates the NADPH oxidase RbohD, driving a burst of reactive oxygen species that reinforces cell walls and signals to neighbouring cells. It also regulates calcium channels, including CNGCs and OSCA1.3, allowing cytosolic calcium concentrations to rise rapidly. This calcium influx is not merely a byproduct; it is a central hub of immune signalling. Calcium-dependent protein kinases decode the calcium signature and phosphorylate transcription factors and metabolic enzymes, while calcium-activated metacaspases release immunomodulatory peptides from damaged cells. The review highlights how this spatiotemporally controlled calcium symphony, as one group of researchers has described it, links pattern recognition to gene expression, stomatal closure and the production of antimicrobial compounds.

The second branch of plant immunity operates inside the cell. Intracellular nucleotide-binding leucine-rich repeat receptors, or NLRs, detect pathogen effectors, the virulence proteins that pathogens inject into host cells to suppress pattern-triggered immunity. The gene-for-gene concept, articulated by Harold Flor in the 1970s, predicted that for every resistance gene in the plant there is a corresponding avirulence gene in the pathogen. Decades of work have vindicated this idea at the molecular level. Some NLRs directly bind effectors, while others act as guards or decoys, monitoring host proteins that effectors modify. Integrated domains, which are fusions of host target mimics into the NLR architecture, allow single receptors to sense effectors that manipulate specific host processes. The review traces this conceptual evolution from the cloning of the first NLR genes in the 1990s to the recent explosion of structural biology that has revealed how these receptors work.

The most striking recent discovery in this field concerns resistosomes. When certain NLRs recognize their cognate effectors, they do not simply change shape; they oligomerize into large, ordered complexes that function as channels or enzymes. The ZAR1 resistosome, for example, forms a pentameric calcium-permeable channel in the plasma membrane, flooding the cytosol with calcium and triggering cell death at the infection site. Helper NLRs of the NRC and ADR1 families form hexameric resistosomes with similar channel activity, while TIR-domain-containing NLRs act as NAD-cleaving enzymes that produce small signalling molecules. Recent work has shown that helper NLR resistosome clusters assemble upon activation of sensor NLRs, and that a wheat CCG10-NLR receptor forms an octameric resistosome. These structures represent a remarkable convergence with animal immunity, where inflammasomes perform analogous functions, and they explain how a single molecular recognition event can be amplified into a full-scale defensive response.

Perhaps the most important conceptual shift in recent years is the recognition that pattern-triggered immunity and effector-triggered immunity are not separate pathways but mutually reinforcing branches of a single system. Studies published in 2021 demonstrated that PRR signalling is required for full NLR-mediated resistance, and that activation of TIR signalling boosts pattern-triggered responses. The EDS1-PAD4-ADR1 node, a complex of lipase-like proteins and helper NLRs, mediates both branches, providing a molecular bridge between cell surface and intracellular perception. This mutual potentiation means that a plant that has already mounted a pattern-triggered response is primed to respond more vigorously to effector recognition, and vice versa. The review argues that this integration explains why plants with compromised PRR function are often more susceptible to disease even when they possess functional NLR genes.

But immunity is expensive. Uncontrolled activation of PRRs or NLRs causes stunted growth, autoimmunity and reduced seed yield, a phenomenon known as the growth-defence trade-off. Plants have evolved multiple mechanisms to keep immune signalling in check. Negative regulators such as the protein phosphatase PP2C38 dephosphorylate BIK1, while ubiquitin ligases control BIK1 protein homeostasis. The BAK1 co-receptor is shared between immune receptors and the brassinosteroid growth receptor BRI1, creating a molecular competition between defence and growth signalling. BIK1 inversely modulates these two pathways, promoting immunity while suppressing brassinosteroid responses. Membrane nanodomains physically separate immune and growth receptor complexes, even when they share signalling components. The review also describes how phytosulfokine signalling, mediated by the receptor PSKR1, balances growth and defence in the rhizosphere, and how transcription factors such as BZR1 mediate trade-offs at the gene expression level.

Environmental conditions add another layer of complexity. Temperature, light and humidity all modulate immune responses. Elevated temperatures can suppress NLR-mediated resistance, but recent work has identified CBP60g family transcription factors as key determinants of temperature sensitivity, offering a route to climate-resilient immunity. Light quality matters too: the blue-light receptor CRY1 acts as a switch that balances photosynthesis and defence, while phytochromes regulate salicylic acid and jasmonic acid pathways in rice. High humidity dampens salicylic acid signalling and NPR1 function, promoting disease, and daily humidity oscillations entrain the circadian clock to influence plant physiology. The microbiome also plays a role, with rhizosphere bacteria suppressing local root immune responses through pH modulation, and leaf microbiota influencing autoimmunity in Arabidopsis. The review presents a schematic model of these interplays, emphasizing that immunity cannot be understood in isolation from the environment.

The practical implications are profound. Understanding the mechanisms of immune receptor activation and regulation opens the door to engineering disease-resistant crops with optimized fitness. Researchers have transferred PRRs between plant families to confer broad-spectrum bacterial resistance, stacked multiple PRRs in potato against Phytophthora infestans, and used reverse engineering of FLS2 to expand recognition of evasive flagellin epitopes. NLR engineering has progressed from single amino acid mutations that expand effector recognition to designer receptors with novel specificities, nanobody fusions that redirect NLRs to new targets, and interfamily co-transfer of sensor and helper NLR pairs. Genome editing of susceptibility genes has produced multipathogen resistance without agronomic penalty, and inducible overexpression of transcription factors such as Ideal Plant Architecture1 improves both yield and disease resistance in rice. Machine learning and AlphaFold-guided design are now being applied to predict effector targets and redesign immune proteins. The review concludes that the next frontier lies in combining these engineering strategies with a deep understanding of growth-defence balance, so that crops can be made both resistant and productive in a changing climate.

Subject of Research: Mechanisms of pathogen perception, immune signalling and growth-defence balance in plant immunity

Article Title: Mechanisms and balanced regulation of plant immunity

Article References: Chai, J., Wang, Y., & Wang, Y. (2026). Mechanisms and balanced regulation of plant immunity. Nature Reviews Molecular Cell Biology. https://doi.org/10.1038/s41580-026-01009-4

Image Credits: AI Generated

DOI: 10.1038/s41580-026-01009-4

Keywords: plant immunity, pattern recognition receptors, NLR receptors, resistosomes, calcium signalling, growth-defence trade-off, effector recognition, immune receptor engineering, BIK1, BAK1, PTI, ETI