Dynamic Nutrient Signaling Networks in Plants.

Nutrients are vital to life through intertwined sensing, signaling, and metabolic processes. Emerging research focuses on how distinct nutrient signaling networks integrate and coordinate gene expression, metabolism, growth, and survival. We review the multifaceted roles of sugars, nitrate, and phosphate as essential plant nutrients in controlling complex molecular and cellular mechanisms of dynamic signaling networks. Key advances in central sugar and energy signaling mechanisms mediated by the evolutionarily conserved master regulators HEXOKINASE1 (HXK1), TARGET OF RAPAMYCIN (TOR), and SNF1-RELATED PROTEIN KINASE1 (SNRK1) are discussed. Significant progress in primary nitrate sensing, calcium signaling, transcriptome analysis, and root-shoot communication to shape plant biomass and architecture are elaborated. Discoveries on intracellular and extracellular phosphate signaling and the intimate connections with nitrate and sugar signaling are examined. This review highlights the dynamic nutrient, energy, growth, and stress signaling networks that orchestrate systemwide transcriptional, translational, and metabolic reprogramming, modulate growth and developmental programs, and respond to environmental cues.

The yeast AMP-activated protein kinase Snf1 phosphorylates the inositol polyphosphate kinase Kcs1.

The yeast Snf1/AMP-activated kinase (AMPK) maintains energy homeostasis, controlling metabolic processes and glucose derepression in response to nutrient levels and environmental cues. Under conditions of nitrogen or glucose limitation, Snf1 regulates pseudohyphal growth, a morphological transition characterized by the formation of extended multicellular filaments. During pseudohyphal growth, Snf1 is required for wild-type levels of inositol polyphosphate (InsP), soluble phosphorylated species of the six-carbon cyclitol inositol that function as conserved metabolic second messengers. InsP levels are established through the activity of a family of inositol kinases, including the yeast inositol polyphosphate kinase Kcs1, which principally generates pyrophosphorylated InsP7. Here, we report that Snf1 regulates Kcs1, affecting Kcs1 phosphorylation and inositol kinase activity. A snf1 kinase-defective mutant exhibits decreased Kcs1 phosphorylation, and Kcs1 is phosphorylated in vivo at Ser residues 537 and 646 during pseudohyphal growth. By in vitro analysis, Snf1 directly phosphorylates Kcs1, predominantly at amino acids 537 and 646. A yeast strain carrying kcs1 encoding Ser-to-Ala point mutations at these residues (kcs1-S537A,S646A) shows elevated levels of pyrophosphorylated InsP7, comparable to InsP7 levels observed upon deletion of SNF1. The kcs1-S537A,S646A mutant exhibits decreased pseudohyphal growth, invasive growth, and cell elongation. Transcriptional profiling indicates extensive perturbation of metabolic pathways in kcs1-S537A,S646A. Growth of kcs1-S537A,S646A is affected on medium containing sucrose and antimycin A, consistent with decreased Snf1p signaling. This work identifies Snf1 phosphorylation of Kcs1, collectively highlighting the interconnectedness of AMPK activity and InsP signaling in coordinating nutrient availability, energy homoeostasis, and cell growth.

Tudor staphylococcal nuclease is a docking platform for stress granule components and is essential for SnRK1 activation in Arabidopsis.

Tudor staphylococcal nuclease (TSN; also known as Tudor-SN, p100, or SND1) is a multifunctional, evolutionarily conserved regulator of gene expression, exhibiting cytoprotective activity in animals and plants and oncogenic activity in mammals. During stress, TSN stably associates with stress granules (SGs), in a poorly understood process. Here, we show that in the model plant Arabidopsis thaliana, TSN is an intrinsically disordered protein (IDP) acting as a scaffold for a large pool of other IDPs, enriched for conserved stress granule components as well as novel or plant-specific SG-localized proteins. While approximately 30% of TSN interactors are recruited to stress granules de novo upon stress perception, 70% form a protein-protein interaction network present before the onset of stress. Finally, we demonstrate that TSN and stress granule formation promote heat-induced activation of the evolutionarily conserved energy-sensing SNF1-related protein kinase 1 (SnRK1), the plant orthologue of mammalian AMP-activated protein kinase (AMPK). Our results establish TSN as a docking platform for stress granule proteins, with an important role in stress signalling.

The serine-threonine protein kinase Snf1 orchestrates the expression of plant cell wall-degrading enzymes and is required for full virulence of the maize pathogen Colletotrichum graminicola.

Colletotrichum graminicola, the causal agent of maize leaf anthracnose and stalk rot, differentiates a pressurized infection cell called an appressorium in order to invade the epidermal cell, and subsequently forms biotrophic and necrotrophic hyphae to colonize the host tissue. While the role of force in appressorial penetration is established (Bechinger et al., 1999), the involvement of cell wall-degrading enzymes (CWDEs) in this process and in tissue colonization is poorly understood, due to the enormous number and functional redundancy of these enzymes. The serine/threonine protein kinase gene SNF1 identified in Sucrose Non-Fermenting yeast mutants mediates de-repression of catabolite-repressed genes, including many genes encoding CWDEs. In this study, we identified and functionally characterized the SNF1 homolog of C. graminicola. Δsnf1 mutants showed reduced vegetative growth and asexual sporulation rates on media containing polymeric carbon sources. Microscopy revealed reduced efficacies in appressorial penetration of cuticle and epidermal cell wall, and formation of unusual medusa-like biotrophic hyphae by Δsnf1 mutants. Severe and moderate virulence reductions were observed on intact and wounded leaves, respectively. Employing RNA-sequencing we show for the first time that more than 2,500 genes are directly or indirectly controlled by Snf1 in necrotrophic hyphae of a plant pathogenic fungus, many of which encode xylan- and cellulose-degrading enzymes. The data presented show that Snf1 is a global regulator of gene expression and is required for full virulence.

Sugar sensing in C4 source leaves: a gap that needs to be filled.

Plant growth depends on sugar production and export by photosynthesizing source leaves and sugar allocation and import by sink tissues (grains, roots, stems, and young leaves). Photosynthesis and sink demand are tightly coordinated through metabolic (substrate, allosteric) feedback and signalling (sugar, hormones) mechanisms. Sugar signalling integrates sugar production with plant development and environmental cues. In C3 plants (e.g. wheat and rice), it is well documented that sugar accumulation in source leaves, due to source-sink imbalance, negatively feeds back on photosynthesis and plant productivity. However, we have a limited understanding about the molecular mechanisms underlying those feedback regulations, especially in C4 plants (e.g. maize, sorghum, and sugarcane). Recent work with the C4 model plant Setaria viridis suggested that C4 leaves have different sugar sensing thresholds and behaviours relative to C3 counterparts. Addressing this research priority is critical because improving crop yield requires a better understanding of how plants coordinate source activity with sink demand. Here we review the literature, present a model of action for sugar sensing in C4 source leaves, and suggest ways forward.

N-acetylglucosamine transporter, Ngt1, undergoes sugar-responsive endosomal trafficking in Candida albicans.

N-acetylglucosamine (GlcNAc), an important amino sugar at the infection sites of the fungal pathogen Candida albicans, triggers multiple cellular processes. GlcNAc import at the cell surface is mediated by GlcNAc transporter, Ngt1 which seems to play a critical role during GlcNAc signaling. We have investigated the Ngt1 dynamics that provide a platform for further studies aimed at understanding the mechanistic insights of regulating process(es) in C. albicans. The expression of this transporter is prolific and highly sensitive to even very low levels (˂2 µM) of GlcNAc. Under these conditions, Ngt1 undergoes phosphorylation-associated ubiquitylation as a code for internalization. This ubiquitylation process involves the triggering proteins like protein kinase Snf1, arrestin-related trafficking adaptors (ART) protein Rod1, and yeast ubiquitin ligase Rsp5. Interestingly, analysis of ∆snf1 and ∆rsp5 mutants revealed that while Rsp5 is promoting the endosomal trafficking of Ngt1-GFPɤ, Snf1 hinders the process. Furthermore, colocalization experiments of Ngt1 with Vps17 (an endosomal marker), Sec7 (a trans-Golgi marker), and a vacuolar marker revealed the fate of Ngt1 during sugar-responsive endosomal trafficking. ∆ras1 and ∆ubi4 mutants showed decreased ubiquitylation and delayed endocytosis of Ngt1. According to our knowledge, this is the first report which illustrates the mechanistic insights that are responsible for endosomal trafficking of a GlcNAc transporter in an eukaryotic organism.

Mitochondrial phosphatidylethanolamine synthesis affects mitochondrial energy metabolism and quiescence entry through attenuation of Snf1/AMPK signaling in yeast.

The Ups2-Mdm35 complex mediates intramitochondrial phosphatidylserine (PS) transport to facilitate mitochondrial phosphatidylethanolamine (PE) synthesis. In the present study, we found that ups2∆ yeast showed increased mitochondrial ATP production and enhanced quiescence (G0) entry in the post-diauxic shift phase. Transcriptomic and biochemical analyses revealed that the depletion of Ups2 leads to overactivation of the yeast AMPK homolog Snf1. Inactivation of Snf1 by depletion of an Snf1-activating kinase, Sak1 canceled the changes in mitochondrial ATP production and quiescence entry observed in ups2∆ cells. Furthermore, among the factors regulated by Snf1, upregulation of pyruvate carboxylase, Pyc1 and downregulation of acetyl-CoA carboxylase, Acc1, respectively, were sufficient to increase mitochondrial ATP production and quiescence entry. These results suggested that a normal PE synthesis mediated by Ups2-Mdm35 complex attenuates Snf1/AMPK activity, and that Snf1-mediated regulation of carbon metabolisms has great impacts on mitochondrial energy metabolism and quiescence entry. We also found that depletion of Ups2 together with the cell-cycle regulators Whi5 and Whi7, functional orthologs of the Rb1 tumor suppressor, caused a synthetic growth defect in yeast. Similarly, knockdown of PRELID3b, the human homolog of Ups2, decreased the viability of Rb1-deficient breast cancer cells, suggesting that PRELID3b is a potential target for cancer therapy.

Zuo1, a ribosome-associated J protein, is involved in glucose repression in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, the J-protein Zuo1 and the nonconventional Hsp70 homologue Ssz1 stimulate the ATPase activity of the chaperone proteins Ssb1 and Ssb2 (Ssb1/2), which are associated with the ribosomes. The dephosphorylation of sucrose nonfermenting 1 (Snf1) on Thr210 is required for glucose repression. The Ssb1/2 and 14-3-3 proteins Bmh1 and Bmh2 appear to be responsible for the dephosphorylation of Snf1 on Thr210 and glucose repression. Here, we investigated the role of Zuo1 in glucose repression. The zuo1∆ strain as well as the ssb1∆ssb2∆ strain exhibited a glucose-specific growth defect during logarithmic growth on glucose. Many of the respiratory chain genes examined were statistically significantly upregulated, but less than 2-fold, in the zuo1∆ strain as well as in the ssb1∆ssb2∆ strain on glucose. In addition, excessive phosphorylation of Snf1 on Thr210 was observed in the zuo1∆ strain as well as in the ssb1∆ssb2∆ strain in the presence of glucose. The mRNA levels of SSB1/2 and BMH1 were statistically significantly reduced by approximately 0.5- to 0.8-fold relative to the wild-type level in the zuo1∆ strain on glucose. These results suggest that Zuo1 is responsible for glucose repression, possibly by increasing the mRNA levels of SSB1/2 and BMH1 during growth on glucose.

Spatial expression patterns of genes encoding sugar sensors in leaves of C4 and C3 grasses.

BACKGROUND AND AIMS: The mechanisms of sugar sensing in grasses remain elusive, especially those using C4 photosynthesis even though a large proportion of the world's agricultural crops utilize this pathway. We addressed this gap by comparing the expression of genes encoding components of sugar sensors in C3 and C4 grasses, with a focus on source tissues of C4 grasses. Given C4 plants evolved into a two-cell carbon fixation system, it was hypothesized this may have also changed how sugars were sensed. METHODS: For six C3 and eight C4 grasses, putative sugar sensor genes were identified for target of rapamycin (TOR), SNF1-related kinase 1 (SnRK1), hexokinase (HXK) and those involved in the metabolism of the sugar sensing metabolite trehalose-6-phosphate (T6P) using publicly available RNA deep sequencing data. For several of these grasses, expression was compared in three ways: source (leaf) versus sink (seed), along the gradient of the leaf, and bundle sheath versus mesophyll cells. KEY RESULTS: No positive selection of codons associated with the evolution of C4 photosynthesis was identified in sugar sensor proteins here. Expressions of genes encoding sugar sensors were relatively ubiquitous between source and sink tissues as well as along the leaf gradient of both C4 and C3 grasses. Across C4 grasses, SnRK1ß1 and TPS1 were preferentially expressed in the mesophyll and bundle sheath cells, respectively. Species-specific differences of gene expression between the two cell types were also apparent. CONCLUSIONS: This comprehensive transcriptomic study provides an initial foundation for elucidating sugar-sensing genes within major C4 and C3 crops. This study provides some evidence that C4 and C3 grasses do not differ in how sugars are sensed. While sugar sensor gene expression has a degree of stability along the leaf, there are some contrasts between the mesophyll and bundle sheath cells.

Sucrose-nonfermenting 1 kinase activates histone acetylase GCN5 to promote cellulase production in Trichoderma.

Trichoderma serves as the primary producer of cellulases and hemicellulases in industrial settings as it readily secretes a variety of cellulolytic enzymes. The protein kinase SNF1 (sucrose-nonfermenting 1) can enable cells to adapt to changes in carbon metabolism by phosphorylating key rate-limiting enzymes involved in the maintenance of energy homeostasis and carbon metabolism within cells. Histone acetylation is an important epigenetic regulatory mechanism that influences physiological and biochemical processes. GCN5 is a representative histone acetylase involved in promoter chromatin remodeling and associated transcriptional activation. Here, the TvSNF1 and TvGCN5 genes were identified in Trichoderma viride Tv-1511, which exhibits promising activity with respect to its ability to produce cellulolytic enzymes for biological transformation. The SNF1-mediated activation of the histone acetyltransferase GCN5 was herein found to promote cellulase production in T. viride Tv-1511 via facilitating changes in histone acetylation. These results demonstrated that cellulolytic enzyme activity and the expression of genes encoding cellulases and transcriptional activators were clearly enhanced in T. viride Tv-1511 mutants in which TvSNF1 and TvGCN5 were overexpressed, with concomitant changes in histone H3 acetylation levels associated with these genes. GCN5 was also found to be directly recruited to promoter regions to alter histone acetylation, while SNF1 functioned upstream as a transcriptional activator that promotes GCN5 upregulation at the mRNA and protein levels in the context of cellulase induction in T. viride Tv-1511. These findings underscore the important role that this SNF1-GCN5 cascade plays in regulating cellulase production in T. viride Tv-1511 by promoting altered histone acetylation, offering a theoretical basis for the optimization of T. viride in the context of industrial cellulolytic enzyme production. KEY POINTS: • SNF1 kinase and GCN5 acetylase promoted cellulase production in Trichoderma by increasing the expression of genes encoding cellulases and transcriptional activators • SNF1 and GCN5 promoted cellulase production by driving H3ac modifications, and GCN5 directly band to the promoter regions to catalyze distinct H3ac modifications • SNF1 acts upstream of GCN5 as a transcriptional activator in the cellulase production of Trichoderma.

Lipid accumulation and SNF1 transcriptional analysis of Mucor circinelloides on xylose under nitrogen limitation.

Sucrose non-fermenting 1 (SNF1) plays a crucial role in utilizing non-glucose carbon sources and regulating lipid metabolism. However, the mechanism by which SNF1 regulates lipid accumulation in oleaginous filamentous fungi in response to nutrient signals remains unclear. In the present study, by analysing the growth and lipid accumulation of M. circinelloides on xylose under nitrogen limitation, combined with the transcriptional changes of each subunit of SNF1, the regulation of SNF1 between nutrient signal and lipid accumulation was explored. The results showed that with the increase of carbon/nitrogen (C/N) ratio, the xylose consumption and cell growth of M. circinelloides decreased, and the lipid accumulation increased gradually. The optimal C/N ratio was 160:1, and the maximum lipid yield was 4.1 g/L. Two subunits of SNF1, Snf-α1 and Snf-ß, are related to the regulation of lipid metabolism in response to nutrient signals from different external nitrogen sources. This is the first report on the transcriptional analysis of SNF1 subunits on xylose metabolism under nitrogen limitation. This study provides a basis for further understanding of lipid synthesis mechanism on xylose in oleaginous fungi, and it also lays a foundation for the genetic engineering of high-lipid strain.

The polyHIS Tract of Yeast AMPK Coordinates Carbon Metabolism with Iron Availability.

Energy status in all eukaryotic cells is sensed by AMP-kinases. We have previously found that the poly-histidine tract at the N-terminus of S. cerevisiae AMPK (Snf1) inhibits its function in the presence of glucose via a pH-regulated mechanism. We show here that in the absence of glucose, the poly-histidine tract has a second function, linking together carbon and iron metabolism. Under conditions of iron deprivation, when different iron-intense cellular systems compete for this scarce resource, Snf1 is inhibited. The inhibition is via an interaction of the poly-histidine tract with the low-iron transcription factor Aft1. Aft1 inhibition of Snf1 occurs in the nucleus at the nuclear membrane, and only inhibits nuclear Snf1, without affecting cytosolic Snf1 activities. Thus, the temporal and spatial regulation of Snf1 activity enables a differential response to iron depending upon the type of carbon source. The linkage of nuclear Snf1 activity to iron sufficiency ensures that sufficient clusters are available to support respiratory enzymatic activity and tests mitochondrial competency prior to activation of nuclear Snf1.

Effect of Different Carbons on Lipid Production and SNF1 Transcription in Mucor Circinelloides.

Sucrose non-fermenting 1 (SNF1) protein kinase plays an important role in the utilization of selective carbon sources and regulation of lipid metabolism. In order to further explore the function of SNF1 in regulating lipid accumulation by responding nutritional signals from non-glucose carbon sources, in the present study, the lipid production and SNF1 transcriptional levels of Mucor circinelloides were analyzed and compared on different carbon sources. The results indicated that M. circinelloides could effectively utilize some secondary metabolic carbon sources of monosaccharides and disaccharides for growth and lipids production, such as fructose, maltose and galactose. Snf-ß subunit was associated with the regulation of lipid metabolism in response to nutritional signals from different carbon sources. This is the first report on the transcriptional analysis of SNF1 subunits on different carbons metabolism in oleaginous filamentous fungi. This research has suggested that genetic engineering of SNF1 subunits will alter the lipid production of M. circinelloides from alternative carbon sources. Supplementary Information: The online version contains supplementary material available at 10.1007/s12088-023-01070-z.

Valproate activates the Snf1 kinase in Saccharomyces cerevisiae by decreasing the cytosolic pH.

Valproate (VPA) is a widely used mood stabilizer, but its therapeutic mechanism of action is not understood. This knowledge gap hinders the development of more effective drugs with fewer side effects. Using the yeast model to elucidate the effects of VPA on cellular metabolism, we determined that the drug upregulated expression of genes normally repressed during logarithmic growth on glucose medium and increased levels of activated (phosphorylated) Snf1 kinase, the major metabolic regulator of these genes. VPA also decreased the cytosolic pH (pHc) and reduced glycolytic production of 2/3-phosphoglycerate. ATP levels and mitochondrial membrane potential were increased, and glucose-mediated extracellular acidification decreased in the presence of the drug, as indicated by a smaller glucose-induced shift in pH, suggesting that the major P-type proton pump Pma1 was inhibited. Interestingly, decreasing the pHc by omeprazole-mediated inhibition of Pma1 led to Snf1 activation. We propose a model whereby VPA lowers the pHc causing a decrease in glycolytic flux. In response, Pma1 is inhibited and Snf1 is activated, resulting in increased expression of normally repressed metabolic genes. These findings suggest a central role for pHc in regulating the metabolic program of yeast cells.

The multiple effects of REG1 deletion and SNF1 overexpression improved the production of S-adenosyl-L-methionine in Saccharomyces cerevisiae.

BACKGROUND: Saccharomyces cerevisiae is often used as a cell factory for the production of S-adenosyl-L-methionine (SAM) for diverse pharmaceutical applications. However, SAM production by S. cerevisiae is negatively influenced by glucose repression, which is regulated by a serine/threonine kinase SNF1 complex. Here, a strategy of alleviating glucose repression by deleting REG1 (encodes the regulatory subunit of protein phosphatase 1) and overexpressing SNF1 (encodes the catalytic subunit of the SNF1 complex) was applied to improve SAM production in S. cerevisiae. SAM production, growth conditions, glucose consumption, ethanol accumulation, lifespan, glycolysis and amino acid metabolism were analyzed in the mutant strains. RESULTS: The results showed that the multiple effects of REG1 deletion and/or SNF1 overexpression exhibited a great potential for improving the SAM production in yeast. Enhanced the expression levels of genes involved in glucose transport and glycolysis, which improved the glucose utilization and then elevated the levels of glycolytic intermediates. The expression levels of ACS1 (encoding acetyl-CoA synthase I) and ALD6 (encoding aldehyde dehydrogenase), and the activity of alcohol dehydrogenase II (ADH2) were enhanced especially in the presence of excessive glucose levels, which probably promoted the conversion of ethanol in fermentation broth into acetyl-CoA. The gene expressions involved in sulfur-containing amino acids were also enhanced for the precursor amino acid biosynthesis. In addition, the lifespan of yeast was extended by REG1 deletion and/or SNF1 overexpression. As expected, the final SAM yield of the mutant YREG1ΔPSNF1 reached 8.28 g/L in a 10-L fermenter, which was 51.6% higher than the yield of the parent strain S. cerevisiae CGMCC 2842. CONCLUSION: This study showed that the multiple effects of REG1 deletion and SNF1 overexpression improved SAM production in S. cerevisiae, providing new insight into the application of the SNF1 complex to abolish glucose repression and redirect carbon flux to nonethanol products in S. cerevisiae.

Bulk autophagy induction and life extension is achieved when iron is the only limited nutrient in Saccharomyces cerevisiae.

We have investigated the effects that iron limitation provokes in Saccharomyces cerevisiae exponential cultures. We have demonstrated that one primary response is the induction of bulk autophagy mediated by TORC1. Coherently, Atg13 became dephosphorylated whereas Atg1 appeared phosphorylated. The signal of iron deprivation requires Tor2/Ypk1 activity and the inactivation of Tor1 leading to Atg13 dephosphorylation, thus triggering the autophagy process. Iron replenishment in its turn, reduces autophagy flux through the AMPK Snf1 and the subsequent activity of the iron-responsive transcription factor, Aft1. This signalling converges in Atg13 phosphorylation mediated by Tor1. Iron limitation promotes accumulation of trehalose and the increase in stress resistance leading to a quiescent state in cells. All these effects contribute to the extension of the chronological life, in a manner totally dependent on autophagy activation.

Identification of novel compounds that inhibit SnRK2 kinase activity by high-throughput screening.

Abscisic acid (ABA) is a major phytohormone that regulates abiotic stress responses and development. SNF1-rerated protein kinase 2 (SnRK2) is a key regulator of ABA signaling. To isolate compounds which directly affect SnRK2 activity, we optimized a fluorescence-based system for high-throughput screening (HTS) of SnRK2 kinase regulators. Using this system, we screened a chemical library consisting of 16,000 compounds and identified ten compounds (INH1-10) as potential SnRK2 inhibitors. Further characterization of these compounds by in vitro phosphorylation assays confirmed that three of the ten compounds were SnRK2-specific kinase inhibitors. In contrast, seven of ten compounds inhibited ABA-responsive gene expression in Arabidopsis cells. From these results, INH1 was identified as a SnRK2-specific inhibitor in vitro and in vivo. We propose that INH1 could be a lead compound of chemical tools for studying ABA responses in various plant species.

The regulation of Saccharomyces cerevisiae Snf1 protein kinase on glucose utilization is in a glucose-dependent manner.

Protein phosphorylation catalyzed by protein kinases is the major regulatory mechanism that controls many cellular processes. The regulatory mechanism of one protein kinase in different signals is distinguished, probably inducing multiple phenotypes. The Saccharomyces cerevisiae Snf1 protein kinase, a member of the AMP­activated protein kinase family, plays important roles in the response to nutrition and environmental stresses. Glucose is an important nutrient for life activities of cells, but glucose repression and osmotic pressure could be produced at certain concentrations. To deeply understand the role of Snf1 in the regulation of nutrient metabolism and stress response of S. cerevisiae cells, the role and the regulatory mechanism of Snf1 in glucose metabolism are discussed in different level of glucose: below 1% (glucose derepression status), in 2% (glucose repression status), and in 30% glucose (1.66 M, an osmotic equivalent to 0.83 M NaCl). In summary, Snf1 regulates glucose metabolism in a glucose-dependent manner, which is associated with the different regulation on activation, localization, and signal pathways of Snf1 by varied glucose. Exploring the regulatory mechanism of Snf1 in glucose metabolism in different concentrations of glucose can provide insights into the study of the global regulatory mechanism of Snf1 in yeast and can help to better understand the complexity of physiological response of cells to stresses.

'Sugarcoating' 2-deoxyglucose: mechanisms that suppress its toxic effects.

Yeast and cancer cells are metabolically similar as they use fermentation of glucose as a primary means of generating energy. Reliance on glucose fermentation makes both of these cell types highly sensitive to the toxic glucose analog, 2-deoxyglucose. Here we review the cellular and metabolic pathways that play a role in 2-deoxyglucose sensitivity and discuss how the modifications to these pathways result in acquisition of 2-deoxyglucose resistance. Insights gained from genetic and proteomic studies in yeast provide new ideas for the design of combinatorial therapies for cancer treatment.

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.