Mechanisms of recognition in dominant R gene mediated resistance.

One branch of plant innate immunity is mediated through what is traditionally known as race-specific or gene-for-gene resistance wherein the outcome of an attempted infection is determined by the genotypes of both the host and the pathogen. Dominant plant disease resistance (R) genes confer resistance to a variety of biotrophic pathogens, including viruses, encoding corresponding dominant avirulence (Avr) genes. R genes are among the most highly variable plant genes known, both within and between populations. Plant genomes encode hundreds of R genes that code for NB-LRR proteins, so named because they posses nucleotide-binding (NB) and leucine-rich repeat (LRR) domains. Many matching pairs of NB-LRR and Avr proteins have been identified as well as cellular proteins that mediate R/Avr interactions, and the molecular analysis of these interactions have led to the formulation of models of how products of R genes recognize pathogens. Data from multiple NB-LRR systems indicate that the LRR domains of NB-LRR proteins determine recognition specificity. However, recent evidence suggests that NB-LRR proteins have co-opted cellular recognition co-factors that mediate interactions between Avr proteins and the N-terminal domains of NB-LRR proteins.