The role of cutinase and its impact on the pathogenicity of Colletotrichum truncatum

Abstract

The phytopathogenic fungus, Colletotrichum truncatum infects and colonises chili fruit through direct penetration of the cuticle. The cutinase gene of C. truncatum (CtCut1), a cutin degrading enzyme was identified, cloned and shown to be essential in breaching the cuticle of chili fruit. The expression of CtCut1 gene was studied through RNA-mediated gene silencing and its impact on fungal pathogenicity was demonstrated. The vector, pAA1 encoding a hairpin RNA of GFP and CtCut1 was constructed and transformed into C. truncatum pathotype F8-3B (virulent strain). F8-3B-pAA1 transformants exhibited reduced patterns of infection with one isolate having a 45.8% reduction in cutinase activity (reduction in CtCut1 transcript) in comparison to the wild type. Importantly, CtCut1-deficient strains were unable to infect detached chili and soybean hosts as efficiently as the wild type. There was a delay in the infection period by the transformants. Nevertheless, artificial wounding of the cuticle enabled these F8-3B-pAA1 transformants to infect and colonise host tissues, resulting in typical anthracnose disease lesions. Coupled with microscopy, these data suggested that the defect in pathogenicity was likely due to a failure in penetration of the host cutin. Knowledge of the plant-fungal interactions arose from the development of a fungal transformation system for C. truncatum and implementation of RNAi technology. This technology thus provides an alternative genetic tool for studies of gene function, particularly of essential pathogenicity genes.