Effects of catechol on growth, antioxidant enzyme activities and melanin biosynthesis gene expression of <i>Rhizoctonia solani</i> AG-1 IA

Abstract

Rhizoctonia solani AG-1 IA is one of the most important fungal pathogens that causes severe yield losses in rice-growing regions worldwide. Catechol (1, 2-benzenediol) is a natural catecholamine which can induce melanization of fungi and contribute to enhanced virulence and fungal resistance to diverse environments. In this study, the effects of catechol on growth, activities of antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), glutathione S-transferase (GSH-ST), glutathione peroxidase (GSH-PX) and glutathione reductase (GR), as well as expression of melanin biosynthesis genes in R. solani AG-1 IA, were evaluated by culturing the fungus in catechol-containing nutrient media. The results showed that the activities of CAT, POD, SOD, GSH-ST, GSH-PX and GR were decreased in the presence of 12.5–50 μg mL−1 catechol, while GSH-PX activity was significantly increased (by 310%) in the presence of 50 µg mL−1 catechol. The growth rates of R. solani AG-1 IA on potato dextrose agar (PDA) containing catechol were significantly decreased, whereas the pathogenicity to rice of R. solani AG-1 IA cultured on PDA containing different concentrations of catechol was enhanced when compared with the catechol-free control. Quantitative RT-PCR results showed that the expression of four melanin biosynthesis genes, i.e. protein tyrosine phosphatase (Ptp), chorismate mutase (Cm), peroxidase (Per) and phenol hydroxylase (Ph), was significantly down-regulated in R. solani AG-1 IA cultured in catechol-containing PDB at 100 µg mL−1. These results suggest that catechol was utilized by the fungus to synthesize melanin, and it could also induce the activities of antioxidant enzymes and melanization in R. solani AG-1 IA. Our results provide strong evidence to support the view that melanin contributes to virulence directly through fungal antioxidant defence systems in which melanization is induced by oxidative stress.