RPS2, AN ARABIDOPSIS DISEASE RESISTANCE LOCUS SPECIFYING RECOGNITION OF PSEUDOMONAS-SYRINGAE STRAINS EXPRESSING THE AVIRULENCE GENE AVRRPT2

A molecular genetic approach was used to identity and characterize pla nt genes that control bacterial disease resistance in Arabidopsis. A s creen for mutants with altered resistance to the bacterial pathogen Ps eudomonas syringae pv. tomato (Pst) expressing the avirulence gene avr Rpt2 resulted in the isolation of four susceptible rps (resistance to P. syringae) mutants. The rps mutants lost resistance specifically to bacterial strains expressing avrRpt2 as they retained resistance to Ps t strains expressing the avirulence genes avrB or avrRpm1. Genetic ana lysis indicated that in each of the four rps mutants, susceptibility w as due to a single mutation mapping to the same locus on chromosome 4. Identification of a resistance locus with specificity for a single ba cterial avirulence gene suggests that this locus, designated RPS2, con trols specific recognition of bacteria expressing the avirulence gene avrRpt2. Ecotype Wu-0, a naturally occurring line that is susceptible to Pst strains expressing avrRpt2, appears to lack a functional allele at RPS2, demonstrating that there is natural variation at the RPS2 lo cus among wild populations of Arabidopsis.