Engineered Plant Immune Receptors Turn Viral Proteases Into Suicide Switches

Plant scientists have unveiled a strikingly elegant strategy that turns the very weapons pathogens rely on into the trigger for their own destruction. A recent study, highlighted in a commentary published in the journal Stress Biology by Shan Liu, Yanping Jing and Jian Chen of Jiangsu University, describes how a new class of engineered immune receptors can convert pathogen-secreted proteases into molecular switches that detonate a broad-spectrum defensive response. The approach, first demonstrated by Wang and colleagues in a study published in Nature, represents what the commentators call a paradigm shift in plant immune engineering: instead of teaching plants to recognize specific enemies, it exploits a common weapon that enemies cannot easily abandon. The moment a virus uses its own protease to cleave the engineered receptor’s blocking site, it unknowingly opens what the commentary vividly describes as its own tomb.

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