Abstract
Colletotrichum higginsianum is a fungal pathogen that infects a wide variety of cruciferous plants causing important crop losses. We have used map-based cloning and natural variation analysis of 19 Arabidopsis ecotypes to identify a dominant resistance locus against C. higginsianum. By analyzing natural variations, we found that alleles of RRS1 from susceptible ecotypes contain SNPs that may affect the encoded protein. Furthermore, two susceptible mutants, rrs1-1 and rrs1-2, were identified by screening a T-DNA-tagged mutant library for the loss of resistance to C. higginsianum. The screening identified an additional susceptible mutant (rps4-21) which has a 5 bp deletion in the neighboring gene, RPS4-Ws, a well-characterized R gene that provides resistance to Pseudomonas syringae pv. tomato strain DC3000 expressing avrRps4 (Pst-avrRps4). The rps4-21/rrs1-1 double mutant exhibited similar susceptibility levels to C. higginsianum as the single mutants. We also found that both RRS1 and RPS4 are required for resistance to Ralstonia solanacearum and Pst-avrRps4. Thus RPS4-Ws and RRS1-Ws function as a dual resistance gene system that prevents infection by three distinct pathogens.
