Cutinase and Other Lipolytic Esterases Protect Bean Leaves from Infection by Rhizoctonia solani

The results describe a novel activity of fungal cutinase, the protection of bean leaves from disease. Development of web blight symptoms on bean leaves infected with Rhizoctonia solani (AG-1) was prevented in the presence of cutinase purified from Venturia inaequalis. Instead of disease, small areas of tissue necrosis became visible, and the tissue in which the pathogen was restricted displayed strong autofluorescence beneath the inoculation sites. Mechanical wounding of the leaf surface had no effect on disease development and the permeability of the cuticle was not increased by cutinase action, indicating that surface wounding was not the cause for this novel activity of cutinase. A comparative study involving cutinase and other serine hydrolases revealed that the disease prevention resided in the lipolytic esterase activity rather than the cutinase activity. The pattern of expression of four pathogenesis-related (PR) protein genes provided no evidence for the modulation of known resistance responses of bean leaves in response to cutinase action. The protective mechanism of the esterase activity remains unknown.