UCSF

Fungi have evolved diverse morphological strategies to adapt and thrive in harsh environmental conditions. Although the transcriptional circuits that underlie these cellular changes have been studied in many systems, it is not known how they evolve to regulate specialized morphologies in distant fungal species. I approached this question beginning with the characterization of Saccharomyces cerevisiae Mor1, a conserved transcriptional regulator of fungal morphology. I demonstrated that Mor1 is required for haploid invasive growth and diploid pseudohyphal development, and that this is due to the direct regulation of gene expression through a specific and conserved DNA sequence motif. Whole genome ChIP-Chip further identified Mor1 as a novel core component of the filamentous growth regulatory circuit in S, cerevisiae. Mor1 is an ortholog of Candida albicans Wor1, the master regulator of the white to opaque phenotypic switch. This switch is essential for mating, alters morphology, and contributes to biofilm formation of C. albicans. By comparing Mor1 target genes to those of Wor1, I observed that while there is in general a widespread divergence of downstream targets, there is a striking overlap of a subset of targets encompassing many transcriptional regulators involved in morphogenesis. In addition, Mor1, Wor1, and the Histoplasma capsulatum ortholog Ryp1, all can function at the same discrete DNA motif within the Flo11 promoter when expressed in S. cerevisiae. These results suggest that despite dramatically diverged morphological phenotypes, a conserved regulator governs a conserved set of transcription factors required for basic morphological processes throughout the fungi.