Different from vertebrates, plants rely exclusively on their innate immune system to defend against pathogens. Adapted pathogens secrete virulent factors, known as effectors, into the host cells to overcome the PAMP-triggered immunity (PTI). In response, plants evolved intracellular nucleotide-binding leucine-rich repeat receptors (NLRs) that recognise pathogen effectors either directly or indirectly, initiating the effector-triggered immunity (ETI). Upon effector recognition, NRLs assemble into oligomeric complexes called resistosomes, which are crucial for activating ETI and generating resistance or a hypersensitive response that limits pathogen spread. However, the precise molecular interactions orchestrating these immune responses remains limited.
This study investigates two distinct pathogen effector-plant receptor interactions. First, we examine the flax (Linum usitatissimum) toll/interleukin-1 receptor (TIR) domain-containing NLR (TNL) protein L6, which recognises the AvrL567 effector protein and confers resistance against the flax rust fungus (Melampsora lini). We have expressed and purified recombinant full-length L6 and confirmed through mass-photometry and negative-stain electron microscopy that L6 recognises AvrL567, triggering resistosome formation. The assembled L6 resistosome exhibits NAD+ catalytic activity, generating secondary metabolites essential for downstream immune signalling. We are currently using cryo-electron microscopy (Cryo-EM) to elucidate the interaction underlying effector-receptor recognition and resistosome architecture.
Second, we are investigating a distinct class of flax rust fungi effector that targets multiple TNLs to prevent resistosome formation and suppress downstream signalling. This immune evasion mechanism remains largely uncharacterised. Using L6 and M receptors from flax, we aim to define the molecular basis for effector-mediated TNL inhibition.
In essence, the project predominantly entails fundamental research, serving as the foundation for building strategies aimed at developing effective and durable resistance in crop plants by shedding light on the molecular basis of plant immunity.