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. 

Timing of the ripening phase is a major trait for grapevine production. Understanding the genetics behind this trait could lead to the development of innovative practices in the field aimed to “manipulate” the ripening phase. In our lab, we believe we identified a protein that decides when a grape berry enters the ripening phase at véraison. This protein should be seen as a “go-between” of the signaling of auxin, a major plant growth regulator in plants. We believe this messenger protein, named Auxin-Response Factor 4 [ARF4], is essential to deciding when a grape berry enters the ripening phase.

To prove our concept, we developed a series of three objectives to determine 1) the function of ARF4 during the ripening initiation by altering its expression in grapevines; 2) the likely partners of ARF4 involved in its activity during ripening; and 3) the contribution of ARF4 on fruit composition at maturity.

For the first objective, we successfully conducted a first series of genetic transformations on a new model of grapevine (microvine) more amenable to conducting functional genetic analysis. This material was imported from Australia in collaboration with Dr. Mark Thomas from the CSIRO (Australia). We are currently in the second phase of the work, which requires in-vitro selection of the embryogenic cells of microvines for which our protein of interest is modified. Once selected, the cells will be propagated and “redirected” to generate in vitro plants before being transferred in greenhouse conditions to analyze them.

For the second objective, we identified about 173 proteins that could interact with ARF4. We consider these results very interesting because some identified interactors are part of major plant signalings known to induce the ripening not only in grapes (sugar, ABA, brassinosteroids), but also in other fruit models (ethylene). This strongly reinforces the idea that ARF4 might play a key role during the timing of ripening initiation in cooperation with other major plant growth regulators.

Finally, for the third objective, we successfully developed a new method for quantification of major metabolites belonging to the primary and secondary metabolisms in grape berries. This work was performed in collaboration with the Mass Spectrometry center at OSU. To date, we are able to accurately quantify approximately 50 metabolites from berry samples at different phases of ripening ranging from véraison to harvest. We are able to cover several families of polar compounds that include major sugars, organic acids, amino acids and polyphenolic compounds (monomer and dimers of tannins, anthocyanin and flavonols).

This year, we made substantial progress in reaching our objective. We established the microvine genetic platform at OSU. We initiated our first series of genetic transformation. We identified new relevant protein partners to ARF4, our protein of interest. Finally, we developed a new analytical method combining GC and LC/MS/MS technologies to quantify major compounds that usually serve as “metrics” to assess berry ripeness (malate, tartrate, glucose, fructose, etc.). Such analytical methods will be important to validate the impact of ARF4 on the final fruit composition at maturity of our microvines.

See the previous update for this project, published June 2017.