Expression of cercosporin toxin biosynthetic gene cluster in wild type and cercosporin deficient mutant isolates of Cercospora canescens

Abstract

Many phytopathogenic cercospora spp. synthesize the photoactivated phytotoxin cercosporin which are couses many plant disease. Cercosporin is a photosensitizing compound (M.E. Daub, 1982). When activated by light, it absorbs light energy, converting it to an electronically activated (triplet) state, which reacts with oxygen molecules via either electron or energy transfer to generate reactive oxygen species such as superoxide and singlet oxygen. Cercosporin has been shown to produce both singlet oxygen and superoxide in vitro, but the major toxicity of cercosporin to the cells is dependent on the production of singlet oxygen (Daub and Hangarter, 1983) that destructively reacts with lipids, proteins, and DNA. Exposure of plant cells and tissues to cercosporin results in peroxidation of the membrane lipids, leading to membrane breakdown and death of the cells (Daub and Briggs, 1983) and this membrane damage allows for leakage of nutrients into the leaf intercellular spaces, allowing for fungal growth and sporulation.

Key words: Cercospora; inoculation; inoculum; mung bean; spores.