The bZIP Protein MeaB Mediates Virulence Attributes in Aspergillus flavus

LaeA is a fungal specific virulence factor of both plant and human pathogenic fungi. Transcriptional profiles of laeA mutants have been successfully exploited to identify regulatory mechanisms of secondary metabolism in fungi; here we use laeA mutants as tools to elucidate virulence attributes in Aspergillus flavus. Microarray expression profiles of Delta laeA and overexpression laeA (OE::laeA) were compared to wild type A. flavus. Strikingly, several nitrogen metabolism genes are oppositely mis-regulated in the Delta laeA and OE:: laeA mutants. One of the nitrogen regulatory genes, the bZIP encoding meaB, is up-regulated in Delta laeA. Significantly, over-expression of meaB (OE:: meaB) phenocopies the decreased virulence attributes of a Delta laeA phenotype including decreased colonization of host seed, reduced lipase activity and loss of aflatoxin B1 production in seed. However, a double knock-down of laeA and meaB (KD::laeA, meaB) demonstrated that KD:: laeA, meaB closely resembled Delta laeA rather than wild type or Delta meaB in growth, aflatoxin biosynthesis and sclerotia production thus suggesting that meaB does not contribute to the Delta laeA phenotype. MeaB and LaeA appear to be part of regulatory networks that allow them to have both shared and distinct roles in fungal biology.