DIVERSITY OF CUTINASES FROM PLANT-PATHOGENIC FUNGI - DIFFERENT CUTINASES ARE EXPRESSED DURING SAPROPHYTIC AND PATHOGENIC STAGES OF ALTERNARIA-BRASSICICOLA

The cutinase gene CUTAB1 of Alternaria brassicicola was disrupted by biolistic transformation of conidia with vector pDABC1, containing flanking regions of the cutinase gene fused to a selectable marker construct, Disruption of the cutinase gene had an impact on saprophytic stages of CUTAB1(-) mutants, The two isozymes cutinase A(c) and B-a, which are predominantly expressed by the wild-type strain during saprophytic growth on polymer cutin, were not expressed by respective mutants, and cutin was no longer utilized as a saprophytic carbon source, This correlation suggests a crucial role of CUTAB1 expression during saprophytic stages of the pathogen, Disruption of CUTAB1 had no significant effect on the pathogenicity and tissue specificity of CUTAB1(-) mutants, Although the two cutinase isozymes expressed by the wild-type strain under saprophytic growth conditions were not produced by CUTAB1(-) mutants in contact with polymer cutin, low levels of two serine hydrolases with molecular weights of 31 and 19 kDa were specifically induced and expressed, The mixture of these hydrolases exhibited cutinase activity, The same hydrolases were expressed by both the wildtype strain and CUTAB1(-) mutants during early stages of host infection, In contrast, the gene products of the cutinase gene CUTAB1 with crucial functions in saprophytic stages were not detected on host surfaces inoculated with the wild-type strain. The results suggest that different cutinases evolved with important functions in either saprophytic or pathogenic stages of the pathogen.