Long-term effects of abscisic acid (ABA) on the grape berry phenylpropanoid pathway: Gene expression and metabolite content

Abstract

ABA has been proposed as the main signal triggering the onset of the ripening process in grapes, and modulating the secondary metabolism in grape berry skins. To determine the effect of ABA on secondary metabolism in berries, clusters of Carmenere were sprayed with 0 mu LL-1 ABA; 50 mu LL-1 ABA and 100 mu LL-1 ABA during pre-veraison, and the gene expression of the transcription factors and enzymes of the phenylpropanoid pathway were assessed from veraison to 70 days after veraison (DAV). Additionally, flavonols, tannins and anthocyanins were assessed from veraison until harvest (110 DAV). ABA accelerated sugar and anthocyanin accumulation at veraison. The grape transcript abundance of VvDFR, VvANS, VvUFGT and VvMybA1, all peaking around veraison mimicked the concentration of ABA throughout the season. The highest anthocyanin concentration occurred 35 DAV for all treatments, but higher pigment concentrations were observed in ABA-treated berries at veraison and from 60 to 70 DAV to harvest. VvPAL was also increased by treatment at the higher concentration of ABA from veraison to 40 DAV. Regarding flavanol synthesis, VvLAR2 and VvMyb4A decreased from veraison until 40 DAV and then increased again until 70 DAV. Compared to the control, both ABA treatments resulted in a less-than-proportional reduction of the expression of both genes compared to the control and, after 40 DAV, in a more-than proportional increase compared to the control, suggesting a long-term effect of the pre-veraison ABA spray on the berries. A concomitant increase in flavanols was observed in berries after 40 DAV, and this occurred at a higher extent in berries treated with the highest ABA concentration.