Characterization of the traditional sake yeast Hiroshima no. 6 and its application to sake yeast cross-breeding.

概要

Sake yeast strains possess many features (high ethanol production, fermentation at
low temperature, non-requirement of biotin for cell growth, and more) (Shimoi et al.,
2002; Wu et al., 2005) that differ from those of the laboratory yeast strains. The genome
sequence analysis of the representative sake yeast Kyokai no.7 (K7) in 2011 enabled
comparative genomics between K7 and the laboratory strain S288c (Akao et al., 2011).
The sake yeasts that are most commonly used today are mainly members of the K7 group
including K6, K7, K9, and K10 strains, which are genetically closely related (Azumi et
al., 2011). Characteristics of the K7 group strains include a high ability to produce both
alcohol and an aroma component ester at low temperature, and low sporulation ability,
i.e., forming only a few spores under sporulation-inducing conditions (Nakazawa et al.,
1992).
It was recently reported that the loss-of-function of the MSN4 and RIM15 genes
involved in the stress response of yeast cause high ethanol fermentation (Watanabe et al.,
2011; Watanabe et al., 2012). In budding yeast, the transcription factors Msn2p and
Msn4p (hereafter, 'Msn2p/4p') play an important role in the response and adaptation to
various stressors such as heat shock and ethanol through the transcriptional activation of
target genes, and a genetic analysis indicated that the Rim15p protein kinase is an
upstream activator of Msn2p/4p (Cameroni et al., 2004). A genome sequence analysis of
K7 revealed that K7 has single-nucleotide polymorphisms (SNPs) causing reduced
functions of MSN4 and RIM15 genes (Watanabe et al., 2011). The MSN4 gene of K7 has
loss-of-function due to two mutations; one is the single nucleotide substitution at the start
codon (from aTg to aCg) and the other is the nonsense mutation at the 1,540th cytosine
(codon conversion from Caa to Taa) in the middle of the reading frame. As a result, the
expression of the target genes of Msn2p/4p is reduced, and the response to heat and acute
ethanol stress is reduced (Watanabe et al., 2011). ...

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