The Gram-positive bacterium Clavibacter michiganensis subsp. sepedonicus is the causal agent of bacterial wilt and ring rot of potato. So far, only two
proteins have been shown to be essential for virulence, namely a plasmid-encoded
cellulase CelA and a hypersensitive response-inducing
protein. We have examined the relative expression of CelA and eight putative
virulence factors during
infection of potato and in liquid culture, using quantitative real-time PCR. The examined putative virulence genes were celB, a
cellulase-encoding gene and genes encoding a
pectate lyase, a xylanase and five homologues of the Clavibacter michiganensis subsp. michiganensis
pathogenicity factor Pat-1 thought to encode a
serine protease. Six of the nine assayed genes were up-regulated during
infection of potato, including celA, celB, the xylanase gene, and two of the pat genes. The
pectate lyase gene showed only slightly elevated expression, whereas three of the five examined pat genes were down-regulated during
infection in potato. Interestingly, the two up-regulated pat genes showed a noticeable sequence difference compared to the three down-regulated pat genes. These results reveal several new
proteins that are likely to be involved in Clavibacter michiganensis subsp. sepedonicus pathogenicity.