Characterization and expression ofFusarium graminearumendo-polygalacturonasesin vitroand during wheat infection

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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.

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