MAL62 overexpression enhances uridine diphosphoglucose-dependent trehalose synthesis and glycerol metabolism for cryopro
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Microbial Cell Factories Open Access
RESEARCH
MAL62 overexpression enhances uridine diphosphoglucose‑dependent trehalose synthesis and glycerol metabolism for cryoprotection of baker’s yeast in lean dough Xi Sun1,2* , Jun Zhang1,2, Zhi‑Hua Fan1,2, Ping Xiao1,2, Feng Li3,4, Hai‑Qing Liu1,2 and Wen‑Bi Zhu5
Abstract Background: 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. Results: 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 treha‑ lose 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. Conclusions: The increased freezing tolerance by MAL62 overexpression is mainly achieved by the increased treha‑ lose 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. Keywords: Saccharomyces cerevisiae, Trehalose synthesis pathway, Alpha-glucosidase, Maltose, Glycerol, Freezing tolerant, RNA-seq, Lean dough Background The use of frozen dough is now gradually emerging in a multitude of bakery and food chains due to its less time-consuming production after freezing and cheaper bake-off stations [1, 2]. However, freezing often causes *Correspondence: [email protected] 1 College of Biological Engineering, Tianjin Agricultural University, Tianjin 300384, People’s Republic of China Full list of author information is available at the end of the article
oxidative stress and cell death to baker’s yeast [3], which reduces the yeast growth and gas production capacity [4, 5]. A number of protective molecules have been identified in yeast stress tolerance [6–8]. Among them, the disaccharide trehalose, which protects the cell membrane and stabilizes the protein structure, has captured wide attention [9]. Yeast trehalose is regulated by two major biosynthetic systems, system I and II. System I is uridine-5ʹ-diphosphoglucose (UDPG) dependent and contains several protein complexes, including
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