Characterization and expression of Fusarium graminearum endo-polygalacturonases in vitro and during wheat infection

This study investigated the expression and characterization of two polygalacturonases (PG1 and PG2) of Fusarium graminearum during infection of wheat spikelets; after purification, these were demonstrated to be products of two unique endo - pg genes annotated in the genome database of F. graminearum . Both genes (Fgpg1 and Fgpg2) were expressed in vitro and during spike infection. PG1 had a greater specific activity, with a maximum at pH 5–7, was largely secreted in liquid culture and clearly detectable in the infected ovary tissue. PG2 was more active at pH 7–7.8, was poorly secreted in liquid culture and faintly detectable in infected ovaries. Both PG-encoding genes were maximally expressed 24 h after wheat spikelet infection, paralleling the expression of a pectin lyase (Fgpnl1) gene; they anticipated the expression of a xylanase gene (FgxylA) that was induced only 48 h after infection with a maximum at 96 h. These data strongly indicate F. graminearum -secreted PG activity at an early stage of wheat infection.