Histone acetylation by SAGA Complex but not by NuA4 Complex is Required for filamentation programme in Candida albicans

Candida albicans, a major human fungal pathogen undergoes filamentation from yeast to hyphal state under filamentation-inducing conditions. Gcn5 and Esa1 are key histone H3 and H4 acetyltransferases, respectively, encoded by the budding yeast and other eukaryotes. While Gcn5, a subunit of the SAGA complex, and Esa1, a subunit of the NuA4 complex are critical for C. albicans virulence and hyphal induction, how the relative HAT activities impinge on hyphal gene expression during filamentation is less understood. We found that hyphal gene promoters are hyperacetylated at H3K9 and H4 upon filamentation. By creating point mutations in the HAT domain of Gcn5 and Esa1, we investigated the relative requirement of the SAGA and NuA4 HAT activities for filamentation response. We show that Gcn5 HAT activity is essential for hyperacetylation of H3K9 and H4 at promoters and across hyphal gene ORFs. Surprisingly, the Esa1 HAT domain mutation did not impair H4 acetylation at hyphal genes suggesting that Gcn5 HAT activity is sufficient for H4 (and H3K9) acetylation. Paradoxically, the Esa1 HAT mutant formed filaments constitutively and showed elevated H3K9ac and H4ac at promoters under inducing conditions. Furthermore, we show that the basic helix-loop-helix transcriptional regulator Efg1 is essential for Gcn5-mediated hyperacetylation and RNA pol II recruitment to promoters. Thus, our results indicate that the SAGA-mediated H3K9 and H4 acetylation is sufficient and essential for induction of C. albicans filamentation.