Interactions between water activity and temperature on the Aspergillus flavus transcriptome and aflatoxin B₁...

Effects of Aspergillus flavus colonization of maize kernels under different water activities (a_w; 0.99 and 0.91) and temperatures (30, 37°C) on (a) aflatoxin B₁ (AFB₁) production and (b) the transcriptome using RNAseq were examined. There was no significant difference (p=0.05) in AFB₁ production at 30 and 37°C and 0.99 a_w. However, there was a significant (p=0.05) increase in AFB₁ at 0.91 a_w at 37°C when compared with 30°C/0.99 a_w. Environmental stress effects using gene ontology enrichment analysis of the RNA-seq results for increasing temperature at 0.99 and 0.91 a_w showed differential expression of 2224 and 481 genes, respectively. With decreasing water availability, 4307 were affected at 30°C and 702 genes at 37°C. Increasing temperature from 30 to 37°C at both a_w levels resulted in 12 biological processes being upregulated and 9 significantly downregulated. Decreasing a_w at both temperatures resulted in 22 biological processes significantly upregulated and 25 downregulated. The interacting environmental factors influenced functioning of the secondary metabolite gene clusters for aflatoxins and cyclopiazonic acid (CPA). An elevated number of genes were co-regulated by both a_w and temperature. An interaction effect for 4 of the 25 AFB₁ genes, including regulatory and transcription activators occurred. For CPA, all 5 biosynthetic genes were affected by a_w stress, regardless of temperature. The molecular regulation of A. flavus in maize is discussed.