Non-host Resistance Induced by the Effector XopQ Is Widespread within the Genus and Functionally Depends on EDS1.

Most Gram-negative plant pathogenic bacteria translocate effector proteins (T3Es) directly into plant cells via a conserved type III secretion system, which is essential for pathogenicity in susceptible plants. In resistant plants, recognition of some T3Es is mediated by corresponding resistance () genes or R proteins and induces effector triggered immunity (ETI) that often results in programmed cell death reactions. The identification of genes and understanding their evolution/distribution bears great potential for the generation of resistant crop plants. We focus on T3Es from pv. (), the causal agent of bacterial spot disease on pepper and tomato plants. Here, 86 lines mainly of the genus were screened for phenotypical reactions after -mediated transient expression of 21 different effectors to (i) identify new plant lines for T3E characterization, (ii) analyze conservation/evolution of putative genes and (iii) identify promising plant lines as repertoire for gene isolation. The effectors provoked different reactions on closely related plant lines indicative of a high variability and evolution rate of potential genes. In some cases, putative genes were conserved within a plant species but not within superordinate phylogenetical units. Interestingly, the effector XopQ was recognized by several spp. lines, and infection assays revealed that XopQ is a host range determinant in many species. Non-host resistance against and XopQ recognition in required , strongly suggesting the presence of a TIR domain-containing XopQ-specific R protein in these plant lines. XopQ is a conserved effector among most xanthomonads, pointing out the XopQ-recognizing R as candidate for targeted crop improvement.