Dual functions of AreA, a GATA transcription factor, on influencing ganoderic acid biosynthesis in Ganoderma lucidum

Nitrogen metabolism repression (NMR) has been well studied in filamentous fungi, but the molecular mechanism of its effects on fungal secondary metabolism has been generally unexplored. Ganoderic acid (GA) biosynthesis in Ganoderma lucidum differs between ammonia and nitrate nitrogen sources. To explain the functions of NMR in secondary metabolism, AreA, which is a core transcription factor of NMR, was characterized in G. lucidum. The transcription level of AreA was dramatically increased (approximately 4.5-folds), with the nitrate as the sole nitrogen source, compared with that with ammonia as the source. In addition, the expression of related genes involved in NMR was changed (upregulated of MeaB and downregulated of Nmr and GlnA) when AreA was knockdown. Yeast one-hybrid and electrophoretic mobility shift assay results showed that AreA could directly bind to the promoter of fps (encoding farnesyl-diphosphate synthase) to activate its expression. However, GA biosynthesis was increased (27% in the ammonia source and 77% in the nitrate source) in AreAi mutant strains versus that in control strains. These results showed that another important factor must participate in regulating GA biosynthesis other than the direct activation of AreA. Furthermore, we found that the content of nitric oxide (NO) was increased approximately 2.7-folds in the nitrate source compared with that in the ammonia. By adding the NO donor (SNP) or scavenger (cPTIO) and using NR-silenced or NR-overexpressed strains, we found that there was a negative correlation between the NO contents and GA biosynthesis. NO generated by nitrate reductase (NR) during the nitrogen utilization burst and could negatively influence GA biosynthesis. As a global transcription factor, AreA could also regulate the expression of NR. Our studies provide novel insight into the dual functions of AreA in GA biosynthesis during nitrogen assimilation.