AflT, a MFS transporter-encoding gene located in the aflatoxin gene cluster, does not have a significant role in aflatoxin secretion

Abstract

The aflT gene resides between the polyketide synthase gene pksA and the P450-encoding cypA gene in the aflatoxin gene cluster of Aspergillus parasiticus. It is a single copy gene in the genome of A. parasiticus SRRC 2043 and SU-1 and was also found at the same relative position in the genome of Aspergillus flavus isolates. The predicted AFLT protein contained 14 transmembrane domains and had various degrees of the amino acid identity (34–56%) to fungal transporters belonging to the major facilitator superfamily. Targeted deletion of aflT in A. parasiticus SU-1 yielded transformants that were morphologically similar to SU-1. These aflT-deleted mutants produced and secreted aflatoxins comparable to the parental strain although they lost the production of the aflT transcript. Real-time RT-PCR analysis showed that the expression of aflT was controlled neither by the aflatoxin pathway-specific activator AFLR nor by the co-activator AFLJ, which differed from the regulation of the aflatoxin biosynthetic genes pksA, nor1, ver1, and omtA. The FadA-dependent G-protein signaling pathway previously shown to govern aflatoxin biosynthesis and sporulation plays a role in the regulation of aflT expression.