Xv4-vrxv4: A new gene-for-gene interaction identified between Xanthomonas campestris pv. vesicatoria race T3 and the wild tomato relative Lycopersicon pennellii

Strains of tomato race 3 (T3) of Xanthomonas campestris pv. vesicatoria eli cit a hypersensitive response (HR) in leaves of Lycopersicon pennellii LA71 6. Genetic segregation of the resistance exhibited ratios near 3:1 in F-2 p opulations, which confirmed that a single dominant gene controlled the inhe ritance of this trait. With the aid of a collection of introgression lines, restriction fragment length polymorphism, and cleaved amplified polymorphi c sequence markers, the resistance locus was located on chromosome 3 betwee n TG599 and TG134. An avirulence gene named avrXv4 was also isolated by mob ilizing a total of 600 clones from a genomic DNA library of the T3 strain 9 1-118 into the X. campestris pv. vesicatoria strain ME90, virulent on L. pe nnellii. One cosmid clone, pXcvT3-60 (29-kb insert), induced HR in resistan t plants. The avirulent phenotype of pXcvT3-60 was confirmed by comparing g rowth rates in planta and electrolyte leakages among transconjugants carryi ng a mutated or intact clone with the wild-type T3 strain 91-118. A 1.9-kb DNA fragment contained within a 6.8-kb active subclone was sequenced and wa s determined to carry an open reading frame of 1,077 bp. The predicted AvrX v4 protein exhibits high similarity to members of an emerging new family of bacterial proteins from plant and mammalian pathogens comprising AvrRxv, A vrBsT, YopJ, YopP, AvrA, and YL40.