In its 2018-19 fiscal year, the Oregon Wine Board of Directors granted $437,500 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 is an associate professor in grapevine genetics and genomics in the Department of Horticulture at Oregon State University and a core faculty member of the Oregon Wine Research Institute (OWRI). His current research focuses on the characterization of genes related to performance traits in grapevines such as fruit composition, tolerance to drought and disease resistance. The current project described below has received funding from OWB, OWRI and the Erath Family Foundation.

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

Project objectives:
The overall objective of the project is to understand the role of an auxin-related protein, ARF4, on the control of the timing of ripening initiation. Specific project objectives are to:

  1. Validate the influence of Auxin Response Factor 4 (ARF4) on the timing of ripening initiation in grape berries using genetically engineered microvines.
  2. Identify the ripening-related genes regulated by ARF4 with a focus on abscisic acid synthesis (a ripening promoter) and sugar metabolism.
  3. Determine the changes in fruit composition in grape berries with delayed or advanced ripening due to altered expression of ARF4 in genetically engineered microvines.

Importance to the Oregon wine community:
Rapidly evolving climate conditions (extended or shortened growing seasons), greater frequency of heatwaves, and optimized strategies for harvest logistics have prompted the scientific community to provide the wine industry with more genetic bases for important traits related to yield and fruit quality. In this regard, there is a need to identify the genes that control the ripening initiation, referred to by viticulturists as véraison. This basic information can be useful in developing new innovative practices in the field aimed at manipulating the timing of ripening initiation for the benefit of Oregon grape growers.

Progress so far:
We have established a streamlined methodology for genetic engineering of microvines at OSU. We have generated at least 20 independent transgenic plants that either induce or turn off the activity of ARF4 in the microvines. All of the plants were transferred in the greenhouse and we expect to characterize these plants within the next six months.

The use of a chemically induced system gives us the flexibility to decide when and where the transgene will be expressed in the microvine. This will prevent any significant side effects of the transformation. The induction was tested in tissue culture and in the greenhouse on different parts of the microvine, specifically leaves and shoots.

In addition, we have conducted a protein-protein assay that confirms that ARF4 interacts in vivo with other important proteins that are related to the ripening initiation in grape berries.

Next steps
Once we have berries on the transgenic plants, we will induce the transgenes to turn on or turn off the activity of ARF4 in the berries. We will then conduct several experiments on the “induced” grape berries, including metabolite and gene expression analyses to determine the influence of ARF4 on the timing of the ripening initiation and the ripening process itself towards harvest. Overall, we will evaluate the real contribution of ARF4 to the timing of ripening initiation.