ECOLOGICALLY-SOUND PEST, WATER AND SOIL MANAGEMENT STRATEGIES FOR NORTHERN GREAT PLAINS CROPPING SYSTEMS
Location: Agricultural Systems Research Unit
Title: Effects of Basidiomycete Laccase on Cercosporin
Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 23, 2009
Publication Date: July 1, 2009
Citation: Caesar, T., Lartey, R.T., Solberg Rodier, L.L., Caesar, A.J. 2009. Effects of Basidiomycete laccase on Cercosporin. Journal of Plant Pathology. 91(2):347-355.
Interpretive Summary: Leaf spot disease caused by the fungus Cercospora is most noted for its economic impact on sugar beet production. The toxin produced by Cercospora, called cercosporin, generates under light harmful oxygen radicals and superoxide causing disruption of the plant cells. We demonstrate that the enzyme laccase, secreted by Basidiomycete fungi can decrease the toxicity of cercosporin, decreasing mortality of living cells, such as bacteria. In laboratory studies, we have shown that lesions were apparent on sugar beet leaves exposed to cercosporin under light after 48 h, but leaves exposed to cercosporin and laccase showed visibly less damage. The feasibility to apply laccase in the field as an environmentally safe strategy to control cercosporin leaf spot is discussed.
Cercosporin is a perylenequinone pigment produced by fungi in the genus Cercospora which under light generates reactive oxygen species causing membrane damage and mortality of living cells. Our objectives were to evaluate the effects of laccase, a lignolitic copper-containing enzyme on the temporal evolution of the UV-visible spectrum of cercosporin and to demonstrate that laccase can reduce cercosporin toxicity toward living cells. Cercosporin from Cercopsora beticola and Cercospora hayi was treated with laccase from basidiomycete fungi (Pleurotus ostreatus and Trametes versicolor) in the dark and under constant light. Under these conditions the absorbance of the cercosporin decreased at 220, 279 and 295-500 nm within 10 min of reaction with laccase from either P. ostreatus or T. versicolor, indicating that basidiomycete laccase can induce changes in UV-visible spectra of cercosporin. The LIVE/DEAD® Bac LightTM VIABILITY kit and fluorescent microscopy showed more viable E. coli cells after incubation under light with cercosporin and laccase than with cercosporin alone. Lesions were apparent on sugar beet leaves exposed to cercosporin under light after 48 h, but leaves exposed to cercosporin and laccase showed visibly less damage. Furthermore, air-borne microorganisms can grow on cercosporin-producing C. beticola cultures with laccase added under light, but cercosporin-producing cultures without laccase appeared to inhibit their growth. These data suggests that laccase from basidiomycete fungi can decrease the toxic effect of cercosporin toward microorganisms and plant tissue.