Low molecular weight acids differentially impact Fusarium verticillioides transcription

Fusarium verticillioides is both an endophyte and pathogen of maize. During growth on maize, the fungus often synthesizes the mycotoxins fumonisins, which have been linked to a variety of diseases, including cancer in some animals. How F. verticillioides responds to other fungi, such as Fusarium proliferatum, Aspergillus flavus, Aspergillus niger, and Penicillium oxalicum, that coinfect maize, has potential to impact mycotoxin synthesis and disease. We hypothesize that low molecular weight acids produced by these fungi play a role in communication between the fungi in planta/nature. To address this hypothesis, we exposed 48-h maize kernel cultures of F. verticillioides to oxalic acid, citric acid, fusaric acid, or kojic acid and then compared transcriptomes after 30 min and 6 h. Transcription of some genes were affected by multiple chemicals and others were affected by only one chemical. The most significant positive response was observed after exposure to fusaric acid which resulted in >2-fold upregulation of 225 genes, including genes involved in fusaric acid synthesis. Exposure of cultures to the other three chemicals increased expression of only 3-15 genes. The predicted function and frequent co-localization of three sets of genes support a role in protecting the fungus from the chemical or a role in catabolism. These unique transcriptional responses support our hypothesis that these chemicals can act as signaling molecules. Studies with gene deletion mutants will further indicate if the initial transcriptional response to the chemicals benefit F. verticillioides.