Expression of exo-polygalacturonases in Botrytis cinerea

The pathogenic fungus, Botrytis cinerea, causing gray mold disease in a variety of plant species, secretes at least four polygalacturonases (PGs), cell wall degrading enzymes. Among them, we prepared polyclonal antibody against purified 66-kDa exo-PG in rabbit. Immunoblot analysis revealed that the antibody recognized two exo-PGs, 66 kDa and 70 kDa in molecular mass, secreted from B. cinerea cultured in the medium containing citrus pectin as a carbon source. By immunohistochemical analysis, the expression of exo-PGs was identified in cucumber leaves inoculated with spores of B. cinerea. The exo-PGs were observed 9 h after inoculation, and the amount of exo-PGs increased with time in the leaves. The exo-PGs were induced by polygalacturonic acid as well as its monomer, galacturonic acid, in vitro. The expression of 66-kDa exo-PG (exo-PG I) increased with time of culture, while 70-kDa exo-PG (exo-PG II) was transiently expressed soon after the start of culture. Therefore, exo-PGs might play an important role in pathogenesis at an early stage of infection as well as in tissue maceration of host plant.