Extracellular Amylase Is Required for Full Virulence and Regulated by the Global Posttranscriptional Regulator RsmA in Pathovar .

As with many phytopathogenic bacteria, the virulence of pv. , the causal agent of black rot disease in cruciferous plants, relies on secretion of a suite of extracellular enzymes that includes cellulase (endoglucanase), pectinase, protease, and amylase. Although the role in virulence of a number of these enzymes has been assessed, the contribution of amylase to pv. virulence has yet to be established. In this work, we investigated both the role of extracellular amylase in pv. virulence and the control of its expression. Deletion of (here renamed ), a putative amylase-encoding gene from the genome of pv. strain 8004, resulted in a complete loss of extracellular amylase activity and significant reduction in virulence. The extracellular amylase activity and virulence of the mutant could be restored to the wild-type level by expressing in trans. These results demonstrated that is responsible for the extracellular amylase activity of pv. and indicated that extracellular amylase plays an important role in pv. virulence. We also found that the expression of is strongly induced by starch and requires activation by the global posttranscriptional regulator RsmA. RsmA binds specifically to the 5'-untranslated region of transcripts, suggesting that RsmA regulates directly at the posttranscriptional level. Unexpectedly, in addition to posttranscriptional regulation, the use of a transcriptional reporter demonstrated that RsmA also regulates expression at the transcriptional level, possibly by an indirect mechanism.