The
Ptr1 (
Pseudomonas tomato race 1) locus in
Solanum lycopersicoides confers resistance to strains of
Pseudomonas syringae pv. tomato expressing AvrRpt2 and
Ralstonia pseudosolanacearum expressing RipBN. Here we describe the identification and phylogenetic analysis of the
Ptr1 gene. A single recombinant among 585 F2 plants segregating for the
Ptr1 locus was discovered that narrowed the
Ptr1 candidates to eight nucleotide‐binding leucine‐rich repeat protein (NLR)‐encoding genes. From analysis of the gene models in the
S. lycopersicoides genome sequence and RNA‐Seq data, two of the eight genes emerged as the strongest candidates for
Ptr1. One of these two candidates was found to encode
Ptr1 based on its ability to mediate recognition of AvrRpt2 and RipBN when it was transiently expressed with these effectors in leaves of
Nicotiana glutinosa. The ortholog of
Ptr1 in tomato and in
Solanum pennellii is a pseudogene. However, a functional
Ptr1 ortholog exists in
Nicotiana benthamiana and potato, and both mediate recognition of AvrRpt2 and RipBN. In apple and Arabidopsis, recognition of AvrRpt2 is mediated by the Mr5 and RPS2 proteins, respectively. Phylogenetic analysis places
Ptr1 in a distinct clade compared with
Mr5 and
RPS2, and it therefore appears to have arisen by convergent evolution for recognition of AvrRpt2.
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