The hexY genes of Erwinia carotovora ssp carotovora and ssp atroseptica encode novel proteins that regulate virulence and motility co-ordinately

Mutations located in a new gene, hexY, in Erwinia carotovora ssp. carotovora (Ecc) and ssp. atroseptica (Eca) cause strong upregulation of production of exoenzyme virulence factors and motility, The hexY gene encodes a novel 14.4 kDa protein with no known homologues. The hexY mRNA transcript has an unusually long (525 bp) 5' untranslated region, which may be important for post-transcriptional regulation. An elevated level of transcription of two exoenzyme genes, pelC and celV, was observed in the HexY mutant background, The levels of cellulase and protease in a HexY mutant were independent of the presence of PGA, suggesting a role for HexY in the induction of these enzymes seen upon PGA addition. Electron microscopy revealed that HexY cells were hyperflagellated, perhaps contributing to the hypermotility phenotype of this mutant. The HexY mutant M5 exhibited enhanced maceration capacity on potato tubers. Therefore, the hexY gene and its gene product may define another level of regulation of virulence determinants in Ece and Eca.