Proteome analysis of Xanthomonas citri subsp. citri protein extract with elicitor activity on Arabidopsis thaliana

Extensive research is currently going on in different research centers of the world to find new elicitors from microorganisms and their related receptors from different plants. Comprehensive knowledge about these elicitors and their cognate receptors could be used for development of transgenic plants displaying resistant against plant pathogens. As a crude protein extract of Xanthomonas citri subsp. citri (Xcc) has strong elicitor activity on Arabidopsis, in this study protein extracts of this bacterium were prepared and fractionated and a semi-purified sample displaying elicitor activity was analyzed by LC-MS/MS. About 60 different proteins were detected in the analyzed sample. Among the detected proteins, only three were similar to the elicitor activity observed in a protein extract of Xcc bacterium: cspA (cold shock protein A), csrA (carbon storage regulator protein A) and an unknown conserved hypothetical protein from the DUF1456 protein family. This protein is soluble in water and it has no bacterium membrane-targeting sequence as determined by PSORTB and SOSUI analysis, suggesing with high probability that it is a cytoplasmic protein.