Genotypic and Phenotypic Versatility of Aspergillus flavus during Maize Exploitation

Abstract

Aspergillus flavus is a cosmopolitan fungus able to respond to external stimuli and to shift both its trophic behaviour and the production of secondary metabolites, including that of the carcinogen aflatoxin (AF). To better understand the adaptability of this fungus, we examined genetic and phenotypic responses within the fungus when grown under four conditions that mimic different ecological niches ranging from saprophytic growth to parasitism. Global transcription changes were observed in both primary and secondary metabolism in response to these conditions, particularly in secondary metabolism where transcription of nearly half of the predicted secondary metabolite clusters changed in response to the trophic states of the fungus. The greatest transcriptional change was found between saprophytic and parasitic growth, which resulted in expression changes in over 800 genes in A. flavus. The fungus also responded to growth conditions, putatively by adaptive changes in conidia, resulting in differences in their ability to utilize carbon sources. We also examined tolerance of A. flavus to oxidative stress and found that growth and secondary metabolism were altered in a superoxide dismutase (sod) mutant and an alkyl-hydroperoxide reductase (ahp) mutant of A. flavus. Data presented in this study show a multifaceted response of A. flavus to its environment and suggest that oxidative stress and secondary metabolism are important in the ecology of this fungus, notably in its interaction with host plant and in relation to changes in its lifestyle (i.e. saprobic to pathogenic).

Discovery and confirmation of genes/proteins associated with maize aflatoxin resistance

“…Some other genes have also been found to affect either fungal growth or infection of the host, such as α-amylase (Woloshuk et al, 1997) and alkaline protease ). In addition, many other studies have focused on the expression of A. flavus genes during saprophytic growth to parasitism or during infection of maize kernels (Reese et al, 2011;Reverberi et al, 2013). Reverberi et al (2013) found that at least one member of a Pth11p-like protein receptor family is strongly up-regulated in inoculated maize kernels.…”

<i>Aspergillus flavus</i> Secondary Metabolites: More than Just Aflatoxins

“…Subsequent to this, the examination of other SM gene clusters using customized microarrays were reported 8,29,49,50) . An early effort at this was by Georgianna et al 8) whereby a collection of microarray data from 28 different treatments was used to comprehensively associate cluster expression patterns depending on treatment and environmental conditions.…”

“…In 2013, Reverberi et al 49) examined 24 SMURF-identified gene clusters that were described to be up or down regulated in two separate comparisons. In the first, A. flavus grown in liquid media with and without autoclaved maize kernels indicated up regulation of what is now known to be the gene clusters producing a pyrazinone (cluster 11), aflatrem (cluster 15), leporins (cluster 23), and down regulation of the AF (cluster 54) cluster.…”

Resistance to Aspergillus flavus in maize and peanut: Molecular biology, breeding, environmental stress, and future perspectives

“…In addition, detoxifying enzymes such as glutathione-S-transferase (GST) and pathogenesis-related proteins such as PR-10 can also be used to screen for pathogen resistance or abiotic stress tolerance based on their respective biological activities [15,55,56]. Genomic and proteomic expression studies during the infection process have indicated that oxidative stress tolerance is vital to adaptive changes in fungal biology during infection [57]. Additional studies have also shown that maize lines with known resistance to drought and aflatoxin contamination are more recalcitrant to oxidative stress due to more stably expressed antioxidant components than susceptible lines [25].…”