Real-time quantitative analysis of carbon catabolite derepression of cellulolytic genes expressed in the basidiomycete Phanerochaete chrysosporium

Abstract

Production of cellulolytic enzymes, such as cellobiohydrolases (CBH) and cellobiose dehydrogenase (CDH), by the basidiomycete Phanerochaete chrysosporium is significantly repressed in glucose-containing media; this is known as carbon catabolite repression. We have analyzed the glucose concentration dependence of transcript numbers of the cellulolytic genes (cel6A, cel7D, and cdh) and beta-glucosidase gene (bgl3A) by means of real-time quantitative reverse transcriptase polymerase chain reaction to investigate the roll of carbon catabolite derepression in these gene expression. When the mycelium of P. chrysosporium grown in glucose culture was transferred to media containing various concentrations of glucose (0-5,000 microM), the expression levels of cel6A, cel7D, and cdh were drastically influenced by glucose, whereas no significant change was observed in bgl3A. The numbers of transcripts of cel6A, cel7D, and cdh increased exponentially during incubation for 6 h in the culture without glucose, and the rates of increase were 2.1 times per hour for cel6A transcripts and 2.7 times per hour for cel7D transcripts. Moreover, derepression of cel6A and cel7D was delayed (by 1.6 and 0.6 h, respectively) when the culture contained 50 microM glucose compared with that in the absence of glucose, suggesting that the promoter activities of cel7D and cel6A are distinct under conditions of carbon catabolite derepression.