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

Abstract

Aflatoxins, produced by Aspergillus flavus and Aspergillus 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 of A. 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 by A. flavus showed that expression of five aflatoxin biosynthetic pathway genes, the aflR regulatory gene and the aflD, aflM, aflP and aflQ 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 on A. flavus growth and also altered fungal development. The dysfunction in development changed the timing and the pattern of aflatoxin gene expression, which in part rendered A. flavus unable to produce aflatoxins.

Genotypic Regulation of Aflatoxin Accumulation but Not Aspergillus Fungal Growth upon Post-Harvest Infection of Peanut (Arachis hypogaea L.) Seeds

“…Although our in vitro data is consistent with field studies in regard to aflatoxin resistance of ICG 1471, additional field and laboratory studies are needed to define the resistance mechanisms for this genotype. GT-C20 was previously reported to limit A. flavus fungal growth and inhibit aflatoxin production [ 33 ], which is contrary to our findings. Both our field and in vitro studies demonstrated the high susceptibility of GT-C20 to A. flavus fungal growth and aflatoxin production.…”

“…ICG 1471 also is drought tolerant [ 31 ]. GT-C20 is a Chinese cultivar [ 32 ] reported to retard A. flavus fungal growth and prevent aflatoxin production [ 33 ]. C76-16 is a drought tolerant USDA breeding line with field aflatoxin resistance [ 34 ].…”

Integrated small RNA and mRNA expression profiles reveal miRNAs and their target genes in response to Aspergillus flavus growth in peanut seeds

“…Two cultivated peanuts, including GT-C20 and Tifrunner, were obtained from Shandong Center of Crop Germplasm Resources, Jinan, China, and the voucher specimens were deposited in the Shandong Center of Crop Germplasm Resources. The resistance of GT-C20 and Tifrunner to A. flavus has ever been reported in previous studies [76]. The A. flavus strain (AF-Wh2014) isolated from peanut was kindly provided by lab of Prof. Boshou Liao, Oil Crops Research Institute of Chinese Academy of Agricultural Sciences.…”