POLYGALACTURONASES AND PATHOGENESIS OF SCLEROTINIA-SCLEROTIORUM

The pectinolytic system from Sclerotinia sclerotiorum is composed of m ultiple enzymatic isoforms and its polygalacturonase system is encoded by a multigene family. Isoenzyme multiplicity renders this fungus abl e to hydrolyze the pectic components of plant cell walls in order to p enetrate its hosts. Synthesis of these polygalacturonases is sequentia l and regulated: inducible by pectic polymers, repressed by glucose or constitutive. During sunflower cotyledon infection, this phytopathoge nic fungus secretes multiple polygalacturonase isoenzymes of exo- and endo-type mode of action. This production was confirmed by enzyme assa y and exopolygalacturonase immunorevelation. Gene expression analysis by RT-PCR revealed that genes encoding neutral endopolygalacturonases were highly expressed since the beginning of plant necrosis. This resu lts suggest that these polygalacturonases could play a primordial role in pectic degradation and tissue maceration during pathogenesis cause d by S. sclerotiorum.