Regulation by carbohydrates of the sequential in vitro production of pectic enzymes by Botrytis cinerea

Abstract

Cultures of Botrytis cinerea in a basal salt medium supplemented with different pectin-related polysaccharides (French bean cell walls; citrus pectin; sodium polygalacturonate) as the only carbon source were examined daily for polygalacturonase activity, type of pectic enzymes present, and mycelial growth. Total polygalacturonase activity and number of enzymes detectable were influenced by type and concentration of the substrate and by the conidial concentration at which the cultures were started. A consistent sequence in the production of pectic enzymes was found. The polygalacturonase PG2 was always the first enzyme present in the culture filtrates and was followed by a number of polygalacturonase and pectinesterase isoenzymes. PG2 was also found in ungerminated conidia. Its production is the expression of a constitutive gene as it was independent of the presence of the substrate and strictly correlated with fungal growth. D-Galacturonic acid at 2 mM induced the production of some of the pectic enzymes. At 10 mM and above, however, it repressed PG2 and the subsequent production of the whole pectic isoenzyme complex, indicating a feedback repression. The results suggest that the pectic isoenzymes produced by B. cinerea constitute a coordinated catabolic pathway for the complete degradation of pectic polysaccharides.