Mutational analysis of the Arabidopsis RPS2 disease resistance gene and the corresponding Pseudomonas syringae avrRpt2 avirulence gene

Plants have evolved a large number of disease resistance genes that encode proteins containing conserved structural motifs that function to recognize pathogen signals and to initiate defense responses. The Arabidopsis RPS2 ge ne encodes a protein representative of the nucleotide-binding site-leucine- rich repeat (NBS-LRR) class of plant resistance proteins. RPS2 specifically recognizes Pseudomonas syringae pv. tomato strains expressing the avrRpt2 gene and initiates defense responses to bacteria carrying avrRpt2, includin g a hypersensitive cell death response (HR). We present an in planta mutage nesis experiment that resulted in the isolation of a series of rps2 and avr Rpt2 alleles that disrupt the RPS2-avrRpt2 gene-for-gene interaction. Seven novel avrRpt2 alleles incapable of eliciting an RPS2-dependent HR all enco de proteins with lesions in the C-terminal portion of AvrRpt2 previously sh own to be sufficient for RPS2 recognition. Ten novel rps2 alleles were char acterized with mutations in the NBS and the LRR, Several of these alleles c ode for point mutations in motifs that are conserved among NBS-LRR resistan ce genes, including the third LRR, which suggests the importance of these m otifs for resistance gene function.