A Major Facilitator Superfamily Transporter Contributes to Ergot Alkaloid Accumulation but Not Secretion in Aspergillus leporis

Abstract

Ergot alkaloids are fungal natural products with important roles in agriculture and medicine. We used heterologous expression and gene knockout approaches to investigate potential roles for the product of a major facilitator superfamily transporter gene (easT) recently found in an ergot alkaloid biosynthetic gene cluster in Aspergillus leporis. A strain of Aspergillus fumigatus previously engineered to accumulate lysergic acid, but which did not convert the precursor agroclavine to lysergic acid efficiently or secrete lysergic acid well, was chosen as an expression host for easT. Expression of easT in this strain resulted in accumulation of significantly more pathway intermediates but no detectable lysergic acid. Secretion of ergot alkaloids was reduced in the easT-expressing strain. EasT localized to discrete vesicle-like structures in the cytosol of A. fumigatus, with no localization detected in the plasma membrane. When easT was knocked out in A. leporis, accumulation of lysergic acid amides was reduced relative to the wild type. There was no negative effect on secretion of ergot alkaloids in the knockout mutant. The data indicate that easT encodes a product that contributes to accumulation of ergot alkaloids, perhaps by transporting intermediates between cellular compartments, but does not have a significant role in secreting ergot alkaloids.