Towards the determination of exact interaction mechanisms between the tomato immune receptor Ve1 and the fungal effector Ave1

Recognition of pathogen effectors, small secreted molecules that facilitate host colonization, represents the basis for plant resistance against well-adapted pathogens. In tomato, the Ve1 gene confers resistance against race 1 strains of the vascular wilt pathogen V. dahliae. Ve1 encodes a surface-localized leucine-rich repeat (LRR) receptor-like protein (RLP), which recognizes the recently identified secreted V. dahliae effector Ave1. Immunopurification of affinity-tagged Ave1 transiently co-expressed with HA-tagged Ve1 in tobacco showed that the receptor protein co-purifies with Ave1, indicating an interaction between the pathogen effector and the immune receptor. A mutational screen of extracellular solvent-exposed residues across the LRR domains within the C1 region of Ve1 showed that stable Ve1 mutant alleles of the two consecutive LRR regions LRR3-LRR8 and LRR20-LRR23 were compromised in their HR-inducing activity when co-expressed with Ave1. Accordingly, when challenged with race1 V. dahliae, transgenic Arabidopsis plants carrying the non-functional Ve1 alleles displayed symptoms similar to inoculated non-transgenic controls. These results suggest that Ve1 functionality is determined by two distinct clusters of LRR domains that may be involved Ave1 perception. Despite the fact that further mutational analyses in combination with biochemical methodologies can be employed to further elucidate the interaction between the receptor and the effector proteins, structural information will greatly enhance our ability to improve those strategies.