2019-20 OWB Funded Research | Determining the role of the protein ARF4 in the timing of grape ripening

In its 2019-20 fiscal year, the Oregon Wine Board of Directors granted $417,000 to researchers for nine projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is part of a series to let you know about the status of these projects.

Dr. Laurent Deluc, associate professor of grape genomics at Oregon State University and the Oregon Wine Research Institute, has prepared the update below. This project receives major financial support from the Oregon Wine Board as part of its viticulture research grant program, as well as from the Erath Family Foundation and the State Fermentation Initiative.

Determining the role of Auxin-Response Factor 4 in the timing of ripening initiation in Vitis vinifera

Project Objectives:
In 2016, we initiated a research project aiming to understand the role of an Auxin-related protein (ARF4) on the timing of ripening initiation in grape berries. We outlined three objectives:

1. Validate the influence of ARF4 on the timing of ripening initiation in grape berries using genetically engineered grapevines (microvine model).
2. Evaluate the impact of ARF4 on genes involved in the activity of sugar and abscisic acid (ABA) metabolisms, two major promoters of ripening.
3. Assess the changes on fruit composition at maturity when the activity of ARF4 is altered.

Importance to the Oregon Wine Community:
Rapidly evolving climate conditions and future market demands may require the possibility for growers to manipulate key transitional phases of grape berry development like véraison. Therefore, having a better understanding of the main regulators responsible for ripening is necessary to devise new field strategies for proactively controlling the ripening process and achieving optimal ripeness at maturity.

Currently, there is a critical gap in the knowledge as to what controls the timing of ripening initiation. We identified a regulatory protein, ARF4, that we believe is a major regulator that decides when grape berries enter the ripening phase. Through this project, we will provide the Oregon wine community with the foundational knowledge for the possible development of translational tools in the fields aiming to delay or advance the timing of ripening initiation.

Progress so far:
The project is currently in its last phase. We have identified the potential “partners” of ARF4, some of them known to play a critical role in the induction of the ripening process in fleshy fruits. This seems to reinforce the importance of our candidate ARF4. We have propagated all the Genetically Engineered (GE) microvines needed to evaluate the role of ARF4 in delaying the timing of ripening initiation. Best candidate GE microvines have been transferred to the greenhouse facility where they are growing in a temperature and light controlled environment to optimize their growing conditions.

Next Steps:
The next steps for us are to:

1. characterize the GE microvines to understand the role of ARF4 on the regulation of the other actors of the ripening process, i.e. ABA and sugar; and
2. evaluate the impact of altered activity of ARF4 on the fruit composition of GE microvines at maturity stage.

This will be achieved during the next three-to-six months once we have microvines bearing enough fruit per plant.