Direct interaction of resistance gene and avirulence gene products confers rice blast resistance

Rice expressing the Pi‐ta gene is resistant to strains of the rice blast fungus, Magnaporthe grisea, expressing AVR‐Pita in a gene‐for‐gene relationship. Pi‐ta encodes a putative cytoplasmic receptor with a centrally localized nucleotide‐binding site and leucine‐rich domain (LRD) at the C‐terminus. AVR‐Pita is predicted to encode a metalloprotease with an N‐terminal secretory signal and pro‐protein sequences. AVR‐Pita176 lacks the secretory and pro‐protein sequences. We report here that transient expression of AVR‐Pita176 inside plant cells results in a Pi‐ta‐dependent resistance response. AVR‐Pita176 protein is shown to bind specifically to the LRD of the Pi‐ta protein, both in the yeast two‐hybrid system and in an in vitro binding assay. Single amino acid substitutions in the Pi‐ta LRD or in the AVR‐Pita176 protease motif that result in loss of resistance in the plant also disrupt the physical interaction, both in yeast and in vitro. These data suggest that the AVR‐Pita176 protein binds directly to the Pi‐ta LRD region inside the plant cell to initiate a Pi‐ta‐mediated defense response.