The minimal gene set member msrA, encoding peptide methionine sulfoxide reductase, is a virulence determinant of the plant pathogen Erwinia chrysanthemi

Peptide methionine sulfoxide reductase (MsrA), which repairs oxidized prote ins, is present in most living organisms, and the cognate structural gene b elongs to the so-called minimum gene set [Mushegian, A. R. & Koonin, E. V., (1996) Proc. Natl. Acad. Sci. USA 93, 10268-10273]. In this work, we repor t that MsrA is required for full virulence of the plant pathogen Erwinia ch rysanthemi. The following differences were observed between the wild-type a nd a MsrA(-) mutant: (i) the MsrA(-) mutant was more sensitive to oxidative stress; (ii) the MsrA- mutant was less motile on solid surface; (iii) the MsrA(-) mutant exhibited reduced virulence on chicory leaves; and (iv) no s ystemic invasion was observed when the MsrA(-) mutant was inoculated into w hole Saintpaulia ionantha plants. These results suggest that plants respond to virulent pathogens by producing active oxygen species, and that enzymes repairing oxidative damage allow virulent pathogens to survive the host en vironment, thereby supporting the theory that active oxygen species play a key role in plant defense.