Characterization of the promoter, downstream target genes and recognition DNA sequence of Mhy1, a key filamentation-promoting transcription factor in the dimorphic yeast Yarrowia lipolytica.

Msn2/Msn4-family zinc finger transcription factors play important roles in stress response in yeast. However, some members of this family show significant functional divergence in different species. Here, we report that in the dimorphic yeast Yarrowia lipolytica, the Msn2/Msn4-like protein Mhy1 is a key regulator of yeast-to-hypha dimorphic transition but not stress response. Both MHY1 deletion and overexpression affect filamentation. In contrast, YlMsn4, the other Msn2/Msn4-like protein, regulates tolerance to acid-induced stress. We show that MHY1 has an unusually long (about 3800 bp) promoter featuring an upstream located enhancer and a double stress response element (STRE) motif, the latter of which mediates Mhy1's regulation on its own transcription. Transcriptome profiling conducted in wild-type strain, mhy1Δ mutant and MHY1-overexpressing mutant revealed about 100 genes that are highly differentially expressed (≥ 5-fold) in each of the 2 mutants compared to the wild-type strain. The largest group of genes downregulated in mhy1Δ mutant encodes cell wall proteins or enzymes involved in cell wall organization, suggesting that Mhy1 may regulate dimorphic transition by controlling these cell wall genes. We confirmed that the genes YALI0C23452, YALI0C15268 and YALI0B09955 are directly regulated by Mhy1. We also characterized the Mhy1 consensus binding site as 5'-WNAGGGG-3' (W = A or T; N = A, T, G or C). These results provide new insight in the functions of Msn2/Msn4-family transcription factors in fungi and the mechanism by which Mhy1 regulates dimorphic transition.