The interaction between Arabidopsis and Xanthomonas campestris pv. campestris (Xcc) provides a useful model system to identify components that are involved in incompatible interactions of this phytopathogen and cruciferous plants. We have previously described a new gene from Arabidopsis thaliana, ECS1 (formerly CXC750), which showed an ecotype-specific expression pattern, although homologous sequences are present in the genomes of all ecotypes tested. Interestingly, ECS1 mRNA transcripts were only detected in ecotypes which showed the resistant phenotype against Xcc race 750. Subsequent genetic studies with F-3 progeny of a cross between a Xcc750 resistant ecotype (Col-0) and a Xcc750 sensitive ecotype (Oy-0) revealed segregation of the ECS1(RNA)-phenotype away from the Xcc750 susceptible phenotype in one out of 16 F3 families. In addition, transformation of Xcc750 sensitive plants that did not express ECS1, with a constitutively transcribed ECS1 gene, did not lead to the resistant phenotype in the transgenic plants. From these results we conclude that ECS1 is not a Xcc750 resistance gene, but the genetic data indicate that ECS1 is linked to a locus influencing resistance to Xcc750. ECS1 was localized to YACs 3H12 and 12F3 of the CIC library, which map to chromosome 1. Subcellular localization of the gene product indicated that the ECS1 protein is associated with the plant cell wall. Further molecular investigation of 10 ecotypes revealed the utility of ECS1 as a new marker for chromosome 1, which is detectable by RFLP PCR or expression analysis.
