Flocculation and transcriptional adaptation to fermentation conditions in a recombinant wine yeast strain defective for KNR4/SMI1

Abstract

KNR4 defective recombinant wine yeast strains were previously shown to oversecrete mannoproteins during alcoholic fermentation and, depending on the genetic background, to contribute to protein stability of white wines. We have tried to get a deeper insight into the consequences of KNR4 deletion in a wine yeast strain, from both a biological and an enological standpoint, and to understand the mechanisms leading to improved mannoprotein release. In fermentation experiments, followed by aging on lees, and compared to the parent strain, the recombinant strain shows increased release of mannoproteins during the fermentation but little increase during aging. Mannoprotein release by the recombinant strain takes place mainly during the fermentation step. In contrast, autolysis of the recombinant strain keeps going after aging for 78 days. In addition, the recombinant strain is moderately flocculent, which would be interesting for the production of sparkling wines. This might be related to changes in the expression of Flo1p-regulated genes. The new biological processes affected by KNR4 deletion in wine yeasts, as revealed by this transcriptomic study are flocculation, adaptation to anaerobiosis, oxidative stress response, and ethanol tolerance, as well as FKS1 overexpression; but no overexpression was detected for genes coding for major structural mannoproteins of the cell wall.

Knr4: a disordered hub protein at the heart of fungal cell wall signalling

“…Indeed, mannoproteins released by yeast cells are key determinants of the stability of wine against haze and positively impact several other quality properties of wine including their aroma, colour, astringency, mouthfeel, malolactic fermentation and the formation of foam by sparkling wines (Gonzalez‐Ramos and Gonzalez, ). Homozygous deletions of the KNR4 gene have been conducted in industrial (wine) yeast strains and shown to ensure improved oenological parameters (Gonzalez‐Ramos et al ., , ; Penacho et al ., ). In addition, the surface properties of KNR4 deletion strains affect their sorption capacities, which are also relevant to oenology because yeast cell walls are well known and widely used to reduce the concentration of undesirable molecules in wine, such as fatty acids and volatile phenols (Pradelles et al ., ).…”

“…cerevisiae upon overexpression (Martin et al ., ). Global transcriptomic profiles of knr4 Δ mutant and overexpression mutant further revealed a wide range of genes whose expression is directly or indirectly affected by its absence or its gene dosage (Martin‐Yken et al ., ; Lagorce et al ., ; Penacho et al ., ), most of which have functions in cell cycle, cell wall synthesis and morphogenesis. In addition to the transcriptional control of G1/S transition mentioned earlier, Knr4 also participates in the transcriptional response to heat and cell wall stress.…”

Reprogramming of the Ethanol Stress Response in Saccharomyces cerevisiae by the Transcription Factor Znf1 and Its Effect on the Biosynthesis of Glycerol and Ethanol

“…Cell wall biosynthesis is also associated with the cell wall integrity signaling HOG pathway ( 9 , 40 ). In fact, SMI1 deletion not only results in defective cell wall structure but also increases autolysis during fermentation and decreases cell proliferation ( 41 ). Additionally, LHS1 expression is upregulated under ethanol stress in the tolerant yeast strain CECT10094 ( 15 ).…”

Involvement of Smi1 in cell wall integrity and glucan synthase Bgs4 localization during fission yeast cytokinesis

“…It will be interesting to investigate whether Smi1 regulates septum integrity through these pathways in the future. Smi1 also regulates transcription of genes involved in cell cycle, cell wall synthesis, morphogenesis, and heat and cell wall stress in a variety of fungi (Martin-Yken et al, 2002;Lagorce et al, 2003;Penacho et al, 2012). It will be interesting to determine whether Smi1 has these functions in fission yeast besides its role in cytokinesis, especially whether Smi1 also regulates Bgs4 transcription.…”

“…The roles of Smi1 as a hub are also supported by its numerous interaction partners, including many synthetic lethal interactions (Goehring et al, 2003;Costanzo et al, 2010). Smi1 also regulates transcription of genes involved in cell cycle, cell wall synthesis, morphogenesis, and transcriptional responses to heat and cell wall stress in different fungi (Martin-Yken et al, 2002;Lagorce et al, 2003;Penacho et al, 2012). In the smi1 mutant, the SBF transcription factor is constitutively hyper-activated instead of peaking at the G1/S transition (Kim et al, 2010), and at least two cell cycle checkpoints are impaired: the morphogenesis checkpoint, which coordinates cell division with bud growth (Harrison et al, 2001;Mizunuma et al, 2001;Miyakawa and Mizunuma, 2007) and the mechanism controlling the daughter cell size (Dagkessamanskaia et al, 2010a;Dagkessamanskaia et al, 2010b).…”