Abstract
Saccharomyces cerevisiae and its closely related yeasts undergo mating type switching by replacing DNA sequences at the active mating type locus (MAT) with one of two silent mating type cassettes. Recently, a novel mode of mating type switching was reported in methylotrophic yeast, including Ogataea polymorpha, which utilizes chromosomal recombination between inverted-repeat sequences flanking two MAT loci. The inversion is highly regulated and occurs only when two requirements are met: haploidy and nutritional starvation. However, links between this information and the mechanism associated with mating type switching are not understood. Here we investigated the roles of transcription factors involved in yeast sexual development, such as mating type genes and the conserved zinc finger protein Rme1. We found that co-presence of mating type a1 and α2 genes was sufficient to prevent mating type switching, suggesting that ploidy information resides solely in the mating type locus. Additionally, RME1 deletion resulted in a reduced rate of switching, and ectopic expression of O. polymorpha RME1 overrode the requirement for starvation to induce MAT inversion. These results suggested that mating type switching in O. polymorpha is likely regulated by two distinct transcriptional programs that are linked to the ploidy and transmission of the starvation signal.
Highlights
Similar to many other organisms, yeast senses and engages appropriate response programs following changes in their environment, including invasive growth, dimorphic transitions, and sexual differentiation
Because ste2∆ cells cannot respond to α-factor, homothallic ste2∆ cells are able to mate with cells expressing a identity
K. lactis employs essentially the same 3-mating type locus (MAT) system as S. cerevisiae for mating type switching, the molecular mechanisms and their regulation differ in order to allow adaption to species-specific life cycles[3,6,10]
Summary
Similar to many other organisms, yeast senses and engages appropriate response programs following changes in their environment, including invasive growth, dimorphic transitions, and sexual differentiation. S. cerevisiae and the fission yeast Schizosaccharomyces pombe, pheromones and pheromone receptor genes are targets of transcriptional regulation by pheromone signalling, which is transmitted through a heterotrimeric G protein and the downstream MAP kinase pathway to ensures the robustness of the signalling and the engagement of cells to the mating process[13,14,15] Many of these genes are transcriptionally induced by starvation in yeast species, such as S. pombe, K. lactis, and Candida lusitaniae, where sexual development is restricted under starvation conditions[16,17,18,19]
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