Different from vertebrates, plants rely solely on their innate immune system to defend against pathogens. This system involves nucleotide-binding leucine-rich repeat receptors (NLRs) located on both the plasma membrane and intracellular space. These receptors play a crucial role by directly or
indirectly sensing pathogen effector proteins and inducing effector-triggered immunity. Nevertheless, our current understanding of the molecular mechanisms and interactions that orchestrate this immune response remains limited.
This study focuses on the wheat coiled-coil (CC)-NLR (CNL) protein Sr33, which provides strainspecific resistance against Puccinia graminis f. sp. tritici, the pathogen responsible for stem rust disease. To gain better understanding of its function, Pichia pastoris expression system was used to produce recombinant full-length Sr33 protein for both structural and functional studies.
Many extensively studied NLRs require interaction with effectors to initiate their assembly into activated complexes known as resistosomes. In contrast, we report that Sr33 expressed and purified readily forms a pentameric state in the absence of its cognate effector, as demonstrated by mass
photometry and size-exclusion chromatography coupled with multiple-angle light scattering (SECMALS) analysis. This unique observation hints at a potential novel mechanism absent of any known effector involvement. By employing cryo-electron microscopy (Cryo-EM) to analyze the protein
complex, our aim is to decipher the intricate molecular interactions of this unique CNL receptor.
In essence, this 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.