Abstract
In haploid cells of Ogataea (Hansenula) polymorpha an environmental signal, nitrogen starvation, induces a reversible change in the structure of a chromosome. This process, mating-type switching, inverts a 19-kb DNA region to place either MATa or MATα genes under centromeric repression of transcription, depending on the orientation of the region. Here, we investigated the genetic pathway that controls switching. We characterized the transcriptomes of haploid and diploid O. polymorpha by RNAseq in rich and nitrogen-deficient media, and found that there are no constitutively a-specific or α-specific genes other than the MAT genes themselves. We mapped a switching defect in a sibling species (O. parapolymorpha strain DL-1) by interspecies bulk segregant analysis to a frameshift in the transcription factor EFG1, which in Candida albicans regulates filamentous growth and white-opaque switching. Gene knockout, overexpression and ChIPseq experiments show that EFG1 regulates RME1, which in turn regulates STE12, to achieve mating-type switching. All three genes are necessary both for switching and for mating. Overexpression of RME1 or STE12 is sufficient to induce switching without a nitrogen depletion signal. The homologous recombination genes RAD51 and RAD17 are also necessary for switching. The pathway controlling switching in O. polymorpha shares no components with the regulation of HO in S. cerevisiae, which does not involve any environmental signal, but it shares some components with mating-type switching in Kluyveromyces lactis and with white-opaque phenotypic switching in C. albicans.
Highlights
In yeast species that can reproduce sexually, the ability of a cell to mate with other cells is governed by which mating-type genes it expresses [1, 2]
We previously found that in the yeast Ogataea polymorpha, homothallism is achieved by a novel mating-type switching mechanism that exchanges the locations of MATa and MATα genes between expression and repression contexts
Our initial approach to search for genes involved in mating-type switching in O. polymorpha was to look for differences between the transcriptomes of cells that are switching and cells that are not switching
Summary
In yeast species (unicellular fungi) that can reproduce sexually, the ability of a cell to mate with other cells is governed by which mating-type genes it expresses [1, 2]. In ascomycete yeasts, these genes are located at a single genomic site called the mating-type (MAT) locus. In some ascomycete yeasts such as Saccharomyces cerevisiae, haploid cells are able to change their MAT genotypes by a process called matingtype switching [3, 4] During this process, DNA at the MAT locus is physically replaced, exchanging a MATa allele for a MATα allele or vice versa. Mating-type switching is a form of secondary homothallism [5] because it enables a yeast strain to mate with any other strain of the same species, regardless of their initial mating types, by means of fusion between a-cells and α-cells [6, 7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
