Meiotic chromosomal recombination defect in sake yeasts

Area of Science:

• Microbiology
• Yeast Genetics

Background:

• Sake yeast strains belong to Saccharomyces cerevisiae and possess a heterothallic life cycle, enabling cross-hybridization for breeding superior strains.
• Cross-hybridization in sake yeast is challenging due to low spore development and germination rates, suggesting underlying genetic issues.

Purpose of the Study:

• To investigate the hypothesis that defects in meiotic recombination machinery cause chromosome loss and poor spore viability in sake yeast.
• To analyze the meiotic recombination process in sake yeast strains, specifically Kyokai no. 7 (K7).

Main Methods:

• Analysis of segregation patterns in heterozygous sites within chromosomes of haploid K7 strains.
• Whole-genome sequencing of haploid K7 strains to compare bases derived from heterozygosities.
• Construction and analysis of double heterozygous disruptants (CAN1 and URA3) in K7 after sporulation.

Main Results:

• No recombinant segregants were detected in K7 using any of the three experimental methods, indicating a meiotic recombination defect.
• Similar meiotic recombination defects were observed in other sake yeast strains (K6, K9, K10).
• Rapamycin treatment improved sporulation efficiency but not meiotic recombination in K7; spo13 disruptants produced non-recombinant asci.

Conclusions:

• Sake yeast strains, including K7, K6, K9, and K10, exhibit significant defects in their meiotic recombination machinery.
• These recombination defects likely contribute to the challenges in breeding new sake yeast strains through cross-hybridization.