Differential Expression Pattern of Heat Shock Protein Genes in Toxigenic and Atoxigenic Isolate of Aspergillus flavus

Aflatoxin biosynthesis in Aspergillus flavus requires coordinated expression of regulatory and structural genes. Aflatoxin production is optimum at 24-30°C and inhibition occurs at temperature higher than 35°C. Chaperones or heat-sock proteins are involved in processing of cellular protein and heat-stress induced protein, hence, we studied the genes encoding for heat-shock proteins under the influence of temperature (30°C vs. 37°C). A. flavus isolates, aflatoxigenic (MTCC9367) and atoxigenic (MTCC11580) were grown in glucose minimal salt broth for 24 hours for expression profile of selected genes using quantitative real-time PCR. We monitored the expression profile of genes encoding for heat-shock proteins (hsp98, hsp90, hsp70 and hsp60) and regulatory gene of aflatoxin biosynthesis pathway aflR. We found the similar trend for heat-shock proteins gene expression except hsp70 in aflatoxigenic and atoxigenic isolates of A. flavus. Expression for hsp70 was found to be upregulated at 30°C (vs 37°C)in atoxigenic isolate (P<0.001) of A. flavus in comparison of toxigenic (P<0.05) isolate. Since, heat-shock proteins are involved in protein folding and conformational stability of cellular proteins to maintain the biological activity, our data on transcripts encoding for heat-shock proteins suggested it may influence the aflatoxin biosynthesis process in A. flavus.