Dr. Laurent Deluc, associate professor of grape genomics at OSU and OWRI, has prepared the update below. This project receives funding from the Oregon Wine Board as part of its viticulture and enology research grant program, as well as from the Erath Family Foundation and the Fermentation Initiative. 

Understanding the factors that control grape berry ripening is one of the major goals in grapevine research. Both genetic and environmental factors are assumed to work in concert to control the ripening process in order to shape the biochemical composition of the fruits around maturity and thereby the organoleptic characteristics of the wine. During berry development, plant hormones and other signal molecules, like sugar, orchestrate the physiological changes leading to the development of mature fruits towards harvest. Environmental changes are also “integrated” by the fruits through plant growth regulators as part of their development in order for the fruits to respond to environmental and nutrient changes.

The identification of these major “signal molecules” and how they change the fruit composition towards maturity is of major interest for devising field strategies aimed at improving fruit quality and promoting an improved selection of existing and/or new cultivars more amenable to coping with evolving environmental conditions. This is an important aspect to consider in light of climate changes that may put at risk premium wine grapes known to grow within narrow climate ranges.

For the past four years, our research efforts have focused on the role of one plant growth regulator, auxin, in deciding the timing of the ripening initiation, or véraison, in grape berries. This research has been conducted at both the genetic and physiological levels. We identified one important regulatory protein (Auxin-Response Factor 4 [ARF4]) that may be a major contributing factor to the ripening initiation process in grape berries. The overarching goal of the current project is to validate the function of that protein using a genetic engineering approach.

As part of a collaboration with Dr. Mark Thomas from the CSIRO (Australia), we are using a new grapevine system, the “microvine,” recently acquired at OSU for genetic transformation. After a preliminary series of conclusive assays using strawberry fruits, we are finalizing the benchwork to conduct the genetic transformation on the microvines. The microvines will then be tested and we will determine the influence of the protein ARF4 not only on the timing of ripening initiation, but also on the fruit composition at harvest.

Another part of the research project is to determine whether the protein ARF4 works alone or if it needs partner(s) to decide when the fruits enter the ripening phase. We are currently in the process of identifying these potential partners of ARF4. Such information will be essential in the long term to devise a targeted field strategy aimed at “manipulating” the timing of véraison. This project involves one collaborator at the OSU Department of Horticulture, Dr. Hiro Nonogaki, who is involved in the design of the genetic system used for the microvines, and collaboration with the OSU Mass Spectrometry Center as part of the development of a new analytical method aimed at measuring primary and secondary metabolites in grape berries.