Suchergebnisse

Many factors, such as must composition, juice clarification, fermentation temperature, or inoculated yeast strain, strongly affect the alcoholic fermentation and aromatic profile of wine. As fermentation temperature is effectively controlled by the wine industry, low-temperature fermentation (10–15°C) is becoming more prevalent in order to produce white and "rosé" wines with more pronounced aromatic profiles. Elucidating the response to cold in Saccharomyces cerevisiae is of paramount importance for the selection or genetic improvement of wine strains. Previous research has shown the strong implication of oxidative stress response in adaptation to low temperature during the fermentation process. Here we aimed first to quantify the correlation between recovery after shock with different oxidants and cold, and then to detect the key genes involved in cold adaptation that belong to sulfur assimilation, peroxiredoxins, glutathione-glutaredoxins, and thioredoxins pathways. To do so, we analyzed the growth of knockouts from the EUROSCARF collection S. cerevisiae BY4743 strain at low and optimal temperatures. The growth rate of these knockouts, compared with the control, enabled us to identify the genes involved, which were also deleted and validated as key genes in the background of two commercial wine strains with a divergent phenotype in their low-temperature growth. We identified three genes, AHP1, MUP1, and URM1, whose deletion strongly impaired low-temperature growth. ; This work has been financially supported from the Spanish Government through MINECO and FEDER funds (AGL2013-47300-C3-3-R and PCIN-2015-143 grants) and from Generalitat Valenciana through PROMETEOII/2014/042 grant, awarded to JG. This study has been carried out in the context of the European Project ERA-IB "YeastTempTation" EG also thanks the Spanish government for an FPI grant BES-2011-044498. ; Peer reviewed

Iron is an essential element for all eukaryotic organisms because it participates as a redox active cofactor in a wide range of biological processes, including protein synthesis. Translation is probably the most energy consuming process in cells. Therefore, one of the initial responses of eukaryotic cells to stress or nutrient limitation is the arrest of mRNA translation. In first instance, the budding yeast Saccharomyces cerevisiae responds to iron deficiency by activating iron acquisition and remodeling cellular metabolism in order to prioritize essential over non-essential iron-dependent processes. We have determined that, despite a global decrease in transcription, mRNA translation is actively maintained during a short-term exposure to iron scarcity. However, a more severe iron deficiency condition induces a global repression of translation. Our results indicate that the Gcn2-eIF2α pathway limits general translation at its initiation step during iron deficiency. This bulk translational inhibition depends on the uncharged tRNA sensing Gcn1-Gcn20 complex. The involvement of the Gcn2-eIF2α pathway in the response to iron deficiency highlights its central role in the eukaryotic response to stress or nutritional deprivation, which is conserved from yeast to mammals. ; This work was supported by predoctoral contracts from the Spanish Ministry of Science, Innovation and Universities (MICINN) to AMR and LRA, and European Union Funds (FEDER) and MICINN grants BIO2017-87828-C2-1-P to SP and BFU2016-77728-C3-3-P to PA. ; Peer reviewed

Fermentation at low temperatures is one of the most popular current winemaking practices because of its reported positive impact on the aromatic profile of wines. However, low temperature is an additional hurdle to develop Saccharomyces cerevisiae wine yeasts, which are already stressed by high osmotic pressure, low pH and poor availability of nitrogen sources in grape must. Understanding the mechanisms of adaptation of S. cerevisiae to fermentation at low temperature would help to design strategies for process management, and to select and improve wine yeast strains specifically adapted to this winemaking practice. The problem has been addressed by several approaches in recent years, including transcriptomic and other high-throughput strategies. In this work we used a genome-wide screening of S. cerevisiae diploid mutant strain collections to identify genes that potentially contribute to adaptation to low temperature fermentation conditions. Candidate genes, impaired for growth at low temperatures (12 °C and 18 °C), but not at a permissive temperature (28 °C), were deleted in an industrial homozygous genetic background, wine yeast strain FX10, in both heterozygosis and homozygosis. Some candidate genes were required for growth at low temperatures only in the laboratory yeast genetic background, but not in FX10 (namely the genes involved in aromatic amino acid biosynthesis). Other genes related to ribosome biosynthesis (SNU66 and PAP2) were required for low-temperature fermentation of synthetic must (SM) in the industrial genetic background. This result coincides with our previous findings about translation efficiency with the fitness of different wine yeast strains at low temperature. ; Funding from the Spanish Government trough MINECO and FEDER funds: MINECO AGL2012-32064 and AGL2015-63629-R grants, INIA RM2012-00007-00-00 grant, MINECO RTC-2014-2186-2 and MINECO PCIN-2015-143 grants is acknowledged. ; Peer reviewed

Iron is an essential micronutrient that participates as a cofactor in a broad range of metabolic processes including mitochondrial respiration, DNA replication, protein translation and lipid biosynthesis. Adaptation to iron deficiency requires the global reorganization of cellular metabolism directed to optimize iron utilization. The budding yeast Saccharomyces cerevisiae has been widely used to characterize the responses of eukaryotic microorganisms to iron depletion. In this report, we used a genomic approach to investigate the contribution of transcription rates to the modulation of mRNA levels during adaptation of yeast cells to iron starvation. We reveal that a decrease in the activity of all RNA polymerases contributes to the down-regulation of many mRNAs, tRNAs and rRNAs. Opposite to the general expression pattern, many genes including components of the iron deficiency response, the mitochondrial retrograde pathway and the general stress response display a remarkable increase in both transcription rates and mRNA levels upon iron limitation, whereas genes encoding ribosomal proteins or implicated in ribosome biogenesis exhibit a pronounced fall. This expression profile is consistent with an activation of the environmental stress response. The phosphorylation stage of multiple regulatory factors strongly suggests that the conserved nutrient signaling pathway TORC1 is inhibited during the progress of iron deficiency. These results suggest an intricate crosstalk between iron metabolism and the TORC1 pathway that should be considered in many disorders. ; This work was supported by predoctoral contracts from the Spanish Ministry of Science, Innovation and Universities (MICINN) to AMR and LRA; a fellowship from the "Generalitat de Catalunya" (Spain) to SMM; European Union Funds (FEDER) and MICINN grants BIO2017-87828-C2-1-P to SP, BIO2017-87828-C2-2-P to MATR, BFU2016-77728-C3-3-P to JEPO, and BFU2015-71978-REDT to SP and JEPO; and Regional Government of Valencia PROMETEOII 2015/006 grant to JEPO.