Effect of overexpression of SNF1 on the transcriptional and metabolic landscape of baker's yeast under freezing stress.

BACKGROUND: Freezing stress is the key factor that affecting the cell activity and fermentation performance of baker's yeast in frozen dough production. Generally, cells protect themselves from injury and maintain metabolism by regulating gene expression and modulating metabolic patterns in stresses. The Snf1 protein kinase is an important regulator of yeast in response to stresses. In this study, we aim to study the role of the catalytic subunit of Snf1 protein kinase in the cell tolerance and dough leavening ability of baker's yeast during freezing. Furthermore, the effects of SNF1 overexpression on the global gene expression and metabolite profile of baker's yeast before and after freezing were analysed using RNA-sequencing and untargeted UPLC - QTOF-MS/MS, respectively. RESULTS: The results suggest that overexpression of SNF1 was effective in enhancing the cell tolerance and fermentation capacity of baker's yeast in freezing, which may be related to the upregulated proteasome, altered metabolism of carbon sources and protectant molecules, and changed cell membrane components. SNF1 overexpression altered the level of leucin, proline, serine, isoleucine, arginine, homocitrulline, glycerol, palmitic acid, lysophosphatidylcholine (LysoPC), and lysophosphatidylethanolamine (LysoPE) before freezing, conferring cells resistance in freezing. After freezing, relative high level of proline, lysine, and glycerol maintained by SNF1 overexpression with increased content of LysoPC and LysoPE. CONCLUSIONS: This study will increase the knowledge of the cellular response of baker's yeast cells to freezing and provide new opportunities for the breeding of low-temperature resistant strains.

Enhanced multi-stress tolerance and glucose utilization of Saccharomyces cerevisiae by overexpression of the SNF1 gene and varied beta isoform of Snf1 dominates in stresses.

BACKGROUND: The Saccharomyces cerevisiae Snf1 complex is a member of the AMP-activated protein kinase family and plays an important role in response to environmental stress. The α catalytic subunit Snf1 regulates the activity of the protein kinase, while the ß regulatory subunits Sip1/Sip2/Gal83 specify substrate preferences and stress response capacities of Snf1. In this study, we aim to investigate the effects of SNF1 overexpression on the cell tolerance and glucose consumption of S. cerevisiae in high glucose, ethanol, and heat stresses and to explore the valid Snf1 form in the light of ß subunits in these stresses. RESULTS: The results suggest that overexpression of SNF1 is effective to improve cell resistance and glucose consumption of S. cerevisiae in high glucose, ethanol, and heat stresses, which might be related to the changed accumulation of fatty acids and amino acids and altered expression levels of genes involved in glucose transport and glycolysis. However, different form of ß regulatory subunits dominated in stresses with regard to cell tolerance and glucose utilization. The Sip1 isoform was more necessary to the growth and glucose consumption in ethanol stress. The glucose uptake largely depended on the Sip2 isoform in high sugar and ethanol stresses. The Gal83 isoform only contributed inferior effect on the growth in ethanol stress. Therefore, redundancy and synergistic effect of ß subunits might occur in high glucose, ethanol, and heat stresses, but each subunit showed specificity under various stresses. CONCLUSIONS: This study enriches the understanding of the function of Snf1 protein kinase and provides an insight to breed multi-stress tolerant yeast strains.

Komagataeibacter cocois sp. nov., a novel cellulose-producing strain isolated from coconut milk.

Phylogenetic analysis was performed on a cellulose-producing strain, designated WE7T, isolated from contaminated coconut milk. The analysis utilized nearly complete 16S rRNA gene sequences, as well as concatenated partial sequences of the housekeeping genes dnaK, groEL and rpoB, and allowed identification of the strain as belonging to the genus Komagataeibacter. DNA-DNA correlation or average nucleotide identity analysis was performed between WE7T and its closest phylogenetic neighbours, and the resulting values were below the species level (<70 % and <95 %), suggesting that the strain represents a novel species in genus Komagataeibacter. Strain WE7T was coupled with Komagataeibacter species more tightly than with Gluconacetobacter species in a 16S rRNA gene sequence phylogenetic tree. Strain WE7T can be differentiated from closely related Komagataeibacter and Gluconacetobacter entanii species by the ability to grow on the carbon sources d-mannitol, sodium d-gluconate and glycerol, the ability to form acid by d-fructose, sucrose, d-mannitol, d-galactose and ethanol, and the ability to grow without acetic acid. The major fatty acid of WE7T is C18 : 1ω9c (52.3 %). The DNA G+C content of WE7T is 63.2 mol%. The name Komagataeibacter cocois sp. nov. is proposed, with the type strain WE7T (=CGMCC 1.15338T=JCM 31140T).

Embryo and anther regulation of the mabinlin II sweet protein gene in Capparis masaikai Lévl.

Mabinlin II is one of the major sweet proteins stored in the seeds of Capparis masaikai Lévl. Its promoter region (779 bp) located 5' upstream of the mabinlin II gene has been isolated and named as MBL-779 (GenBank accession number, EU014073). This promoter contains two typical TATA box regions and a series of motifs related to seed-specific promoters, such as ACGT motifs, RY motif, napin motif, and G box. The MBL-779 promoter drove GUS gene to transiently express in the embryos of bean, maize, and rice seeds or to constantly express in the embryos and anthers of the transgenic Arabidopsis. The MBL-779 promoter regulated gene expression from approximately the 12th day and peaked on approximately the 16th day after flowering in Arabidopsis. The -300-bp promoter region is a minimal sequence required to functionally regulate gene expression. The CAATs at -325 to -322 bp and -419 to -416 bp and the region at -485 to -770 bp play a role in the quantitative regulation of gene expression. The RY motif, CATGAC, at -117 to -112 bp and the ACGT within the G box (CACGTG) at -126 to -123 bp positively regulate gene expression.