Lack of aflatoxin production byAspergillus flavus is associated with reduced fungal growth and delayed expression of aflatoxin pathway genes

Abstract

Aflatoxins, produced byAspergillus flavus andAspergillus parasiticus, are the most toxic fungal secondary metabolites that contaminate agricultural commodities such as peanuts, cotton and maize. Understanding the underlying mechanisms of crop resistance to fungal infection is an important step for plant breeders to develop better and improved crop varieties for safe production of human food and animal feed. Infection studies have identified a resistant (R) peanut line, GT-C20, which is able to decrease aflatoxin contamination. The mycelial growth ofA. flavus NRRL3357 on the R peanut line was much lower than that on the susceptible (S) peanut line, Tifrunner. Besides reducing fungal growth, the R line compared to the S line inhibited aflatoxin production completely. Real-time RT-PCR assays of both the R and S lines infected byA. flavus showed that expression of five aflatoxin biosynthetic pathway genes, theaflR regulatory gene and theaflD,aflM,aflP andaflQ structural genes, was not reduced but was significantly delayed on the R line. The results suggested that resistance factors of the R line acted negatively onA. flavus growth and also altered fungal development. The dysfunction in development changed the timing and the pattern of aflatoxin gene expression, which in part renderedA. flavus unable to produce aflatoxins.