Identifying genes induced by ferulic acid and dependent on transcription factor ChAP1 in Cochliobolus heterostrophus
Ferulic acid (FA) belongs to a group of phenolics widespread in plants, which are perceived by the necrotrophic maize pathogen C. heterostrophus as a stress signal. The mechanisms of signaling and toxicity are unknown. We used RNAseq to follow the transcriptome in response to short (30 min) exposure to 0.5-2 mM FA. Differentially expressed genes related to metabolism of phenolics, major facilitator family transporters and acetyl CoA metabolism were prominent among the many differential transcripts. Since FA promotes nuclear retention of the redox-sensitive transcription factor ChAP1 without up-regulating genes for oxidant tolerance, we are identifying specific ChAP1-dependent FA targets. Comparing the transcriptome of ∆chap1 and WT showed 819 genes that were significantly differentially expressed, at a pvice-versa. Interestingly, the annotation of some of these genes suggests that they might participate in the regulation of the PCD, like ankyrin domain containing protein and a NACHT nucleoside triphosphatase domain protein. In contrast, others like a major facilitator superfamily member and a gene annotated as "AMP-dependent synthesis" are positively regulated by ChAP1. In response to FA, the fungus apparently operates two mechanisms to cope with this stress. Transcriptomics indicate that there is a balance or competition between them. One is a defense pathway in which the fungal cell can overcome the stress by removing and metabolizing FA, and the other is a PCD pathway. The transcription factor ChAP1 has an important role in determining the balance between defense and PCD.