Unmethylated Cyc1 downregulates hyphal specific genes and upregulates hyphal suppressors in Candida albicans
Our genetic screen reveals that deletion of CTM1, which abolishes the lysine trimethylation of cytochrome c (Cyc1), results in inhibition of hyphal morphogenesis in Candida albicans. Similar results are observed in the unmethylatable Cyc1 mutant (cyc1K79A). To elucidate how unmethylated Cyc1 inhibits hyphal growth, we performed RNA-Seq analysis by comparing WT (BWP17), ctm1?/?, and cyc1K79A cells grown in yeast and hyphal condition. Consistent with previous published data, many hyphal specific genes (HSGs), such as ALS3, ECE1, HWP1, and UME6, are upregulated while three major hyphal suppressor genes, TUP1, NRG1, and RFG1, are downregulated when WT cells switch from yeast to hyphal growth. Similar changes are observed in ctm1?/? and cyc1K79A cells upon hyphal induction, even though most mutant cells maintain yeast morphology throughout the induction. Further comparisons reveal that the basal transcriptional levels of HSGs are much lower in ctm1?/? and cyc1K79A cells than those in WT cells. Upon hyphal induction, the levels of HSGs in ctm1?/? and cyc1K79A cells increase but still remain lower than their basal levels in WT cells. In contrast, the hyphal suppressor genes (especially NRG1) exhibit much higher basal transcriptional levels in ctm1?/? and cyc1K79A cells than in WT cells. Their transcriptional levels reduce upon hyphal induction but still remain higher than the basal levels in WT cells. Together, these data suggest that unmethylated Cyc1 inhibits hyphal morphogenesis via transcriptional regulation of HSGs and hyphal suppressor genes. Overall design: Three C. albicans strains, including WT (BWP17), ctm1?/?, and cyc1K79A, were grown in YPD at 30°C overnight and subjected to hyphal induction with 10% fetal bovine serine (FBS) and incubation at 37°C for 1-2 h. Three types of samples (overnight yeast cultures, 1 h and 2 h hyphal induction cultures) from each strains were taken for RNA-Seq. We then performed gene expression profiling analysis using data obtained from RNA-Seq of there different strains at three timeppoints.