Pseudomonas syringae pv. tomato (Pst), the causal agent of bacterial speck in tomato, is a model for understanding plant-pathogen coevolution. Within this pathosystem, the emergence of race 1 has traditionally been interpreted as a direct adaptive response to the development of Pto/Prf-mediated resistance in tomato. While race 0 strains are recognized through the type III effectors AvrPto and AvrPtoB, race 1 strains evade this immune surveillance by losing, mutating, or silencing these de