MAL62 overexpression enhances uridine diphosphoglucose-dependent trehalose synthesis and glycerol metabolism for cryoprotection of baker’s yeast in lean dough

Abstract

Background: In Saccharomyces cerevisiae, the alpha-glucosidase (maltase) is a key enzyme in maltose metabolism. 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.Results: RNA sequencing (RNA-seq) revealed that MAL62 overexpression increased transcription of 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, cell viability in the late phase of prefermentation freezing coupled with MAL62 overexpression was slightly reduced, which can be explained by the increase in intracellular glycerol concentration which was consistent with the elevated transcription of glycerol synthesis pathways. Conclusions: The increased freezing tolerance by MAL62 overexpression is mainly achieved by the increased trehalose content via the UDPG-dependent pathway, and glycerol plays a secondary role. These findings shed new light to the mechanism of yeast response to freezing in lean bread dough and can help the improvement of industrial yeast strains.