Abscisic Acid Metabolism in Leaves and Roots of Four Vitis Species in Response to Water Deficit

Abstract Background: Abscisic acid is a phytohormone involved in water deficit response. Abscisic acid metabolism is regulated by biosynthesis, conjugation, and catabolism. NCED3 is the rate limiting step of abscisic acid biosynthesis and is a key contributor to plant water deficit responses. In this study NCED3 transcript accumulation and abscisic acid metabolism were further characterized as key water deficit responses in four Vitis species (Vitis vinifera (Cabernet Sauvignon), Vitis champinii (Ramsey), Vitis riparia (Riparia Gloire), and Vitis vinifera x Vitis girdiana (SC2)) under three levels of water deficit in leaves and roots. Results: The concentrations of abscisic acid and derivative metabolites increased with water deficit and was dependent upon the species. RNA-Seq and RT-qPCR data were consistent with the changes in abscisic acid metabolite concentrations; the corresponding transcript abundances substantiate NCED3 as a key gene in the water deficit response; however, NCED3 protein concentrations assayed in Western Blots were not affected. Major differences in abscisic acid metabolism at the gene, protein, and metabolite levels were detected between leaves and roots in these four species. NCED3 transcript abundance and abscisic acid concentration in drought-tolerant Ramsey increased earlier and more significantly than the other species during long-term, moderate to severe water deficits but were not stimulated as much by short-term, rapid dehydration. In drought-sensitive Riparia, NCED3 transcript abundance and abscisic acid metabolite concentrations increased to a lower extent than in Ramsey during moderate to severe water deficits, but short-term rapid dehydration induced a significantly higher abscisic acid concentration in Riparia than Ramsey. Conclusions: Grapevine species have distinct abscisic acid metabolism that depends highly on the severity and duration of stress and organ (leaves or roots). This study confirms that abscisic acid metabolism and NCED3 are part of a core water deficit response in Vitis species. Relative quantities of transcripts, proteins, abscisic acid and derivative metabolites were determined, but many aspects of abscisic acid metabolism and water deficit responses warrant additional investigation. This study provides a better understanding of how Vitis is adapted to dry environments, which may be exploited for future breeding programs.