Mss11, a transcriptional activator, is required for hyphal development in Candida albicans

Candida albicans undergoes a morphological transition from yeast to hyphae in response to a variety of stimuli and growth conditions. We previously isolated a LisH domain containing transcription factor Flo8, which is essential for hyphal development in C. albicans. To search the putative binding partner of Flo8 in C. albicans, we identified C. albicans Mss11, a functional homolog of Saccharomyces cerevisiae Mss11, which also contains a LisH motif at its N terminus. C. albicans Mss11 can interact with Flo8 via the LisH motif by in vivo coimmunoprecipitation. The results of a chromatin immunoprecipitation (ChIP) assay showed that more Mss11 and Flo8 proteins bound to the upstream activating sequence region of HWP1 promoter in hyphal cells than in yeast cells, and the increased binding of each of these two proteins responding to hyphal induction was dependent on the other. Overexpression of MSS11 enhanced filamentous growth. Deletion of MSS11 caused a profound defect in hyphal development and the induction of hypha-specific genes. Our data suggest that Mss11 functions as an activator in hyphal development of C. albicans. Furthermore, overexpression of FLO8 can bypass the requirement of Mss11 in filamentous formation, whereas overexpression of MSS11 failed to promote hyphae growth in flo8 mutants. In summary, we show that the expression level of MSS11 increases during hyphal induction, and the enhanced expression of MSS11 may contribute to cooperative binding of Mss11 and Flo8 to the HWP1 promoter.