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

Effects of Aspergillus flavus colonization of maize kernels under different water activities (a(w); 0.99 and 0.91) and temperatures (30, 37 degrees C) on (a) aflatoxin B-1 (AFB(1)) production and (b) the transcriptome using RNAseq were examined. There was no significant difference (p = 0.05) in AFB(1) production at 30 and 37 degrees C and 0.99 a(w). However, there was a significant (p = 0.05) increase in AFB(1) at 0.91 aw at 37 degrees C when compared with 30 degrees 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 degrees C and 702 genes at 37 degrees C. Increasing temperature from 30 to 37 degrees C at both a(w) levels resulted in 12 biological processes being upregulated and 9 significantly down regulated. Decreasing a(w) at both a(w) 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, and temperature. An interaction effect for 4 of the 25 AFB(1) 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.