NsdC and NsdD Affect Aspergillus flavus Morphogenesis and Aflatoxin Production

The transcription factors NsdC and NsdD are required for sexual development inAspergillus nidulans . We now show these proteins also play a role in asexual development in the agriculturally important aflatoxin (AF)-producing fungusAspergillus flavus . We found that both NsdC and NsdD are required for production of asexual sclerotia, normal aflatoxin biosynthesis, and conidiophore development. Conidiophores innsdC andnsdD deletion mutants had shortened stipes and altered conidial heads compared to those of wild-typeA. flavus . Our results suggest that NsdC and NsdD regulate transcription of genes required for early processes in conidiophore development preceding conidium formation. As the cultures aged, the ΔnsdC and ΔnsdD mutants produced a dark pigment that was not observed in the wild type. Gene expression data showed that although AflR is expressed at normal levels, a number of aflatoxin biosynthesis genes are expressed at reduced levels in bothnsd mutants. Expression ofaflD ,aflM , andaflP was greatly reduced innsdC mutants, and neither aflatoxin nor the proteins for these genes could be detected. Our results support previous studies showing that there is a strong association between conidiophore and sclerotium development and aflatoxin production inA. flavus.