Diversity of Cutinases from Plant Pathogenic Fungi: Different Cutinases Are Expressed during Saprophytic and Pathogenic Stages of Alternaria brassicicola. Chenglin Yao. Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456 U.S.A. Wolfram Koller. Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456 U.S.A. MPMI 8:122-131. Accepted 1 November 1994. Copyright 1995 The American Phytopathological Society.

The cutinase gene CUTABI of Alternaria brassicicola was disrupted by biolistic transformation of conidia with vector pDABCl, 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 Ac and Ba, which are predominantly expressed by the wild-type strain during saprophylic 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 CUTABI expression during saprophytic stages of the pathogen. Disruption of CUTABI had no significant effect on the pathogenicity and tissue specificity of CUTABI- mutants. Although the two cutinase isozymes expressed by the wild-type strain under saprophytic growth conditions were not produced by CUTABI- 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 wild-type strain and CUTABI- mutants during early stages of host infection. In contrast, the gene products of the cutinase gene CUTABI 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.