Solieri Lisa, Dakal Tikam Chand, Giudici Paolo, Cassanelli Stefano
Department of Life Sciences, University of Modena and Reggio Emilia, 42122, Reggio Emilia, Italy
Department of Life Sciences, University of Modena and Reggio Emilia, 42122, Reggio Emilia, Italy.
G3 (Bethesda). 2014 Jun 17;4(6):1011-25. doi: 10.1534/g3.114.010405.
Sexual reproduction and breeding systems are driving forces for genetic diversity. The mating-type (MAT) locus represents a mutation and chromosome rearrangement hotspot in yeasts. Zygosaccharomyces rouxii complex yeasts are naturally faced with hostile low water activity (aw) environments and are characterized by gene copy number variation, genome instability, and aneuploidy/allodiploidy. Here, we investigated sex-determination system in Zygosaccharomyces sapae diploid strain ABT301(T), a member of the Z. rouxii complex. We cloned three divergent mating type-like (MTL) α-idiomorph sequences and designated them as ZsMTLα copies 1, 2, and 3. They encode homologs of Z. rouxii CBS 732(T) MATα2 (amino acid sequence identities spanning from 67.0 to 99.5%) and MATα1 (identity range 81.5-99.5%). ABT301(T) possesses two divergent HO genes encoding distinct endonucleases 100% and 92.3% identical to Z. rouxii HO. Cloning of MATA: -idiomorph resulted in a single ZsMTLA: locus encoding two Z. rouxii-like proteins MATA: 1 and MATA: 2. To assign the cloned ZsMTLα and ZsMTLA: idiomorphs as MAT, HML, and HMR cassettes, we analyzed their flanking regions. Three ZsMTLα loci exhibited the DIC1-MAT-SLA2 gene order canonical for MAT expression loci. Furthermore, four putative HML cassettes were identified, two containing the ZsMTLα copy 1 and the remaining harboring ZsMTLα copies 2 and 3. Finally, the ZsMTLA: locus was 3'-flanked by SLA2, suggesting the status of MAT expression locus. In conclusion, Z. sapae ABT301(T) displays an aααα genotype missing of the HMR silent cassette. Our results demonstrated that mating-type switching is a hypermutagenic process in Z. rouxii complex that generates genetic diversity de novo. This error-prone mechanism could be suitable to generate progenies more rapidly adaptable to hostile environments.
有性生殖和繁殖系统是遗传多样性的驱动力。交配型（MAT）位点是酵母中的一个突变和染色体重排热点。鲁氏接合酵母复合种酵母自然面临恶劣的低水分活度（aw）环境，其特征是基因拷贝数变异、基因组不稳定和非整倍体/异源二倍体。在此，我们研究了鲁氏接合酵母复合种成员嗜杀接合酵母二倍体菌株ABT301(T)中的性别决定系统。我们克隆了三个不同的交配型样（MTL）α-特异型序列，并将它们命名为ZsMTLα拷贝1、2和3。它们编码与鲁氏接合酵母CBS 732(T) MATα2（氨基酸序列同一性范围为67.0%至99.5%）和MATα1（同一性范围为81.5 - 99.5%）同源的蛋白。ABT301(T)拥有两个不同的HO基因，编码与鲁氏接合酵母HO分别有100%和92.3%同一性的不同内切核酸酶。克隆MATA: -特异型导致单个ZsMTLA:位点，其编码两个鲁氏接合酵母样蛋白MATA: 1和MATA: 2。为了将克隆的ZsMTLα和ZsMTLA:特异型指定为MAT、HML和HMR盒，我们分析了它们的侧翼区域。三个ZsMTLα位点表现出对于MAT表达位点典型的DIC1 - MAT - SLA2基因顺序。此外，鉴定出四个推定的HML盒，两个包含ZsMTLα拷贝1，其余的含有ZsMTLα拷贝2和3。最后，ZsMTLA:位点的3'侧翼是SLA2，表明其MAT表达位点的状态。总之，嗜杀接合酵母ABT301(T)表现出缺少HMR沉默盒的aααα基因型。我们的结果表明，交配型转换是鲁氏接合酵母复合种中的一个高突变过程，它从头产生遗传多样性。这种易出错的机制可能适合更快地产生更能适应恶劣环境的后代。
