Timing and Order of the Molecular Events Marking the Onset of Berry Ripening in Grapevine.

Grapevine (Vitis vinifera) is a model for the investigation of physiological and biochemical changes during the formation and ripening of nonclimacteric fleshy fruits. However, the order and complexity of the molecular events during fruit development remain poorly understood. To identify the key molecular events controlling berry formation and ripening, we created a highly detailed transcriptomic and metabolomic map of berry development, based on samples collected every week from fruit set to maturity in two grapevine genotypes for three consecutive years, resulting in 219 samples. Major transcriptomic changes were represented by coordinated waves of gene expression associated with early development, veraison (onset of ripening)/midripening, and late-ripening and were consistent across vintages. The two genotypes were clearly distinguished by metabolite profiles and transcriptional changes occurring primarily at the veraison/midripening phase. Coexpression analysis identified a core network of transcripts as well as variations in the within-module connections representing varietal differences. By focusing on transcriptome rearrangements close to veraison, we identified two rapid and successive shared transitions involving genes whose expression profiles precisely locate the timing of the molecular reprogramming of berry development. Functional analyses of two transcription factors, markers of the first transition, suggested that they participate in a hierarchical cascade of gene activation at the onset of ripening. This study defined the initial transcriptional events that mark and trigger the onset of ripening and the molecular network that characterizes the whole process of berry development, providing a framework to model fruit development and maturation in grapevine.

Comparative metabolic footprinting of a large number of commercial wine yeast strains in Chardonnay fermentations.

Wine has been made for thousands of years. In modern times, as the importance of yeast as an ingredient in winemaking became better appreciated, companies worldwide have collected and marketed specific yeast strains for enhancing positive and minimizing negative attributes in wine. It is generally believed that each yeast strain contributes uniquely to fermentation performance and wine style because of its genetic background; however, the impact of metabolic diversity among wine yeasts on aroma compound production has not been extensively studied. We characterized the metabolic footprints of 69 different commercial wine yeast strains in triplicate fermentations of identical Chardonnay juice, by measuring 29 primary and secondary metabolites; we additionally measured seven attributes of fermentation performance of these strains. We identified up to 1000-fold differences between strains for some of the metabolites and observed large differences in fermentation performance, suggesting significant metabolic diversity. These differences represent potential selective markers for the strains that may be important to the wine industry. Analysis of these metabolic traits further builds on the known genomic diversity of these strains and provides new insights into their genetic and metabolic relatedness.