AUTHOR=Bizzarri Melissa , Cassanelli Stefano , Bartolini Laura , Pryszcz Leszek P. , Dušková Michala , Sychrová Hana , Solieri Lisa 

TITLE=Interplay of Chimeric Mating-Type Loci Impairs Fertility Rescue and Accounts for Intra-Strain Variability in Zygosaccharomyces rouxii Interspecies Hybrid ATCC42981

JOURNAL=Frontiers in Genetics

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2019.00137

DOI=10.3389/fgene.2019.00137

ISSN=1664-8021

ABSTRACT=<p>The pre-whole genome duplication (WGD) <italic>Zygosaccharomyces</italic> clade comprises several allodiploid strain/species with industrially interesting traits. The salt-tolerant yeast ATCC42981 is a sterile and allodiploid strain which contains two subgenomes, one of them resembling the haploid parental species <italic>Z. rouxii</italic>. Recently, different mating-type-like (<italic>MTL</italic>) loci repertoires were reported for ATCC42981 and the Japanese strain JCM22060, which are considered two stocks of the same strain. <italic>MTL</italic> reconstruction by direct sequencing approach is challenging due to gene redundancy, structure complexities, and allodiploid nature of ATCC42981. Here, DBG2OLC and MaSuRCA hybrid <italic>de novo</italic> assemblies of ONT and Illumina reads were combined with <italic>in vitro</italic> long PCR to definitively solve these incongruences. ATCC42981 exhibits several chimeric <italic>MTL</italic> loci resulting from reciprocal translocation between parental haplotypes and retains two <italic>MAT</italic>a/<italic>MAT</italic>α expression loci, in contrast to <italic>MAT</italic>α in JCM22060. Consistently to these reconstructions, JCM22060, but not ATCC42981, undergoes mating and meiosis. To ascertain whether the damage of one allele at the <italic>MAT</italic> locus regains the complete sexual cycle in ATCC42981, we removed the <italic>MAT</italic>α expressed locus by gene deletion. The resulting <italic>MAT</italic>a/- hemizygous mutants did not show any evidence of sporulation, as well as of self- and out-crossing fertility, probably because incomplete silencing at the chimeric <italic>HML</italic>α cassette masks the loss of heterozygosity at the <italic>MAT</italic> locus. We also found that <italic>MAT</italic>α deletion switched off a2 transcription, an activator of a-specific genes in pre-WGD species. These findings suggest that regulatory scheme of cell identity needs to be further investigated in <italic>Z. rouxii</italic> protoploid yeast.</p>