Several fungi penetrate host tissue directly through the cuticle. The structural polymer of plant cuticle is cutin, a polyester composed of C16 and C18 fatty acids that covers the aerial parts of plants and acts as a barrier to direct penetration. However, on contact some fungi produce inducible cutinase enzymes that extracellularly degrade cutin by hydrolyzing the ester linkages. A role of cutinase in fungal pathogenesis was obtained by studying the infection of papaya fruit by Mycosphaerella (Dickman et al., 1989). The fungus infected papaya fruit only if the skin of the fruit was mechanically breached before applying spores. However, transformation of a Mycosphaerella sp. (Ascomycotina) that lacked the ability to produce cutinase with the Fusarium (Anamorphici) cutinase gene, resulted in the production of cutinase in transformants. The severity of lesions in transformant was correlated with the cutinase activity and including antibodies against Fusarium cutinase with spore inoculum prevented infection.
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