In Saccharomyces cerevisiae, alpha-glucosidase (maltase) is a key enzyme in maltose metabolism. In addition, the overexpression of the alpha-glucosidase-encoding gene MAL62 has been shown to increase the freezing tolerance of yeast in lean dough. However, its cryoprotection mechanism is still not clear. RNA sequencing (RNA-seq) revealed that MAL62 overexpression increased uridine diphosphoglucose (UDPG)-dependent trehalose synthesis. The changes in transcript abundance were confirmed by quantitative reverse transcription–polymerase chain reaction (qRT-PCR) and enzyme activity assays. When the UDPG-dependent trehalose synthase activity was abolished, MAL62 overexpression failed to promote the synthesis of intracellular trehalose. Moreover, in strains lacking trehalose synthesis, the cell viability in the late phase of prefermentation freezing coupled with MAL62 overexpression was slightly reduced, which can be explained by the increase in the intracellular glycerol concentration. This result was consistent with the elevated transcription of glycerol synthesis pathway members. The increased freezing tolerance by MAL62 overexpression is mainly achieved by the increased trehalose content via the UDPG-dependent pathway, and glycerol also plays an important role. These findings shed new light on the mechanism of yeast response to freezing in lean bread dough and can help to improve industrial yeast strains.

中文翻译：

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MAL62的过表达增强了尿苷二磷酸葡萄糖依赖性海藻糖的合成和甘油的代谢，从而为瘦面团中的面包酵母进行冷冻保护

在酿酒酵母中，α-葡萄糖苷酶（麦芽糖酶）是麦芽糖代谢中的关键酶。另外，已经表明α-葡糖苷酶编码基因MAL62的过表达增加了瘦面团中酵母的冷冻耐受性。但是，其冷冻保护机制仍不清楚。RNA测序（RNA-seq）显示MAL62过表达增加了尿苷二磷酸葡萄糖（UDPG）依赖性海藻糖的合成。转录丰度的变化已通过定量逆转录聚合酶链反应（qRT-PCR）和酶活性测定得到了证实。当取消了UDPG依赖性海藻糖合酶活性时，MAL62过表达不能促进细胞内海藻糖的合成。此外，在缺乏海藻糖合成的菌株中，在优选冷冻的后期，加上MAL62过表达，细胞活力略有降低，这可以用细胞内甘油浓度的增加来解释。该结果与甘油合成途径成员的转录升高一致。MAL62过表达增加的抗冻性主要是通过经由UDPG依赖性途径增加海藻糖含量来实现的，甘油也起着重要的作用。这些发现为酵母对稀面包面团中冷冻反应的反应机理提供了新的启示，并有助于改善工业酵母菌株。该结果与甘油合成途径成员的转录升高一致。MAL62过表达增加的抗冻性主要是通过经由UDPG依赖性途径增加海藻糖含量来实现的，甘油也起着重要的作用。这些发现为酵母对稀面包面团中冷冻反应的反应机理提供了新的启示，并有助于改善工业酵母菌株。该结果与甘油合成途径成员的转录升高一致。MAL62过表达增加的抗冻性主要是通过经由UDPG依赖性途径增加海藻糖含量来实现的，甘油也起着重要的作用。这些发现为酵母对稀面包面团中冷冻反应的反应机理提供了新的启示，并有助于改善工业酵母菌株。