Characterization of Fusarium graminearum pectic enzymes secreted in liquid culture and during wheat infection

Fusarium graminearum (teleomorph Giberella zeae) causes important diseases in cereals, like wheat, barley and maize. During the infection process this fungus produces mycotoxins and secretes several cell wall degrading enzymes (CWDEs) which could have a role in host colonization. Among CWDEs, we analyzed pectic enzymes produced in liquid culture and during wheat infection. In culture, activity of endo-polygalacturonase (endo-PG) resulted much greater than that of pectin lyase (PNL). Two endo-PGs are secreted and they exhibit different pH range and optimum: one of them, named PG1, has an optimum pH of 5.0 and is inactive at pH 8.0; the second one, named PG2, has an optimum pH of 7.0 and is still active at pH 8.0. Gene expression analysis performed by real time RT-PCR (qRT-PCR) and enzyme activity data showed that, in liquid culture, PG1 was more expressed than PG2. The expression of pg1 and pg2 genes during the infection of wheat spikes was compared to that of pnl gene, encoding a pectin lyase, and xylA gene, encoding an endo-xylanase. This latter gene was later expressed than pg and pnl genes, but its expression resulted higher. To clarify the importance of F. graminearum endo-PGs in the infection process we performed transformation-mediated gene disruptions. A phenotypic characterization of these mutants will be presented.