Location: Crop Improvement and Genetics Research
Project Number: 2030-21220-003-012-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 20, 2022
End Date: Sep 19, 2024
Objective:
Smoke exposure during grape ripening can affect the chemical composition of the fruit, resulting in wines with undesirable smoky aromas referred as smoke taint (Summerson et al., 2021). Smoky characteristics are derived from volatile phenols present in the smoke, including guaiacol, 4-methylguaiacol, syringols, and cresols. The smoke-derived volatile phenols accumulate as non-volatile glycoconjugates in grapes, suggesting that they are metabolized into stable glycosidic forms through the action of one or several glycosyltransferases (GTs) in the berry.
Approach:
1. Evaluation of the GT gene variability among grapevine cultivars
Concentration of glycoconjugates of smoke-derived phenolics after controlled smoke exposure was showed to vary between grape cultivars (van der Hulst, 2011), suggesting that the response to smoke exposure might depend on the genetic background of the cultivar. To answer this hypothesis, GT genes will be annotated in the genome assemblies of several grape cultivars based on their protein domain composition (PFAM and Carbohydrate-Active Enzyme (CAZy)). Genomes will include the red cultivars: Cabernet Franc, Cabernet Sauvignon, Merlot, Pinot Noir, Zinfandel, and the white cultivars: Chardonnay, Riesling, Semillon. These cultivars represent almost all of the grape cultivars grown in North American for wine production and their chromosome genome scale assemblies produced by the laboratory of the Cantu Lab are available for the study. GTs identified in the different cultivars will be then compared to assess the variability of GT gene content between cultivars. In addition, protein sequences of the predicted GTs will be compared at sequence level to identify amino acid changes between cultivars and their putative effect on protein conformation and enzyme activity.
2. Identification of highly expressed GT gene(s) during ripening
Varietal difference in glycosylation of smoke-derived phenolics could also be due to a difference of available GTs in the berry tissue at the time of smoke exposure. To identify GT genes with an expression level suggesting a potential role in the glycosylation of smoke-derived phenolics, expression of the GT genes will be profiled in diverse grape cultivars during berry development, and specifically from post véraison to harvest when the sensitivity to smoke exposure is the highest (Summerson et al., 2021). RNA-seq data from several published works on grape berry development from different cultivars will be used, such as the highly detailed transcriptomic study on Pinot noir and Cabernet Sauvignon (Fasoli et al., 2018) and the comparative transcriptomics study of five red and five white cultivars (Massonnet et al., 2017).
3. Identification of the GT gene(s) induced by smoke exposure
Effect of smoke exposure on the expression of GT genes in the berry pericarp of several grape cultivars will be assessed using RNA-seq data produced by collaborators and by generating RNA-seq data. We will ask growers the permission to sample fruits that have been naturally exposed to smoke. We also propose to perform experiments in control environment in the field. Plants from two grapevine cultivars, Cabernet Sauvignon and Chardonnay, will be exposed to straw-derived smoke at mid-ripening using a purpose-built smoke tent (van der Hulst, 2011). Fruit from smoke-exposed and control plants will be sampled just after each treatment and at commercial maturity in triplicate. An RNA-seq assay will be performed on berry skin and berry pulp separately.
