Characterization of VvmiR166s-Target Modules and Their Interaction Pathways in Modulation of Gibberellic-Acid-Induced Grape Seedless Berries.

Exogenous GA is widely used to efficiently induce grape seedless berry development for significantly improving berry quality. Recently, we found that VvmiR166s are important regulators of response to GA in grapes, but its roles in GA-induced seedless grape berry development remain elusive. Here, the precise sequences of VvmiR166s and their targets , and were determined in grape cv. '', and the cleavage interactions of VvmiR166s- modules and the variations in their cleavage roles were confirmed in grape berries. Exogenous GA treatment significantly induced a change in their expression correlations from positive to negative between VvmiR166s and their target genes at the seeds during the stone-hardening stages (32 DAF-46 DAF) in grape berries, indicating exogenous GA change action modes of VvmiR166s on their targets in this process, in which exogenous GA mainly enhanced the negative regulatory roles of VvmiR166s on among all three VvmiR166s-target pairs. The transient OE-VvmiR166a-h/OE-VvHB15 in tobacco confirmed that out of the VvmiR166 family, VvmiR166h/a/b might be the main factors in modulating lignin synthesis through inhibiting , of which VvmiR166h-- and VvmiR166a/b-- are the potential key regulatory modules in lignin synthesis. Together with the GA-induced expression modes of VvmiR166s- and genes related to lignin synthesis in grape berries, we revealed that GA might repress lignin synthesis mainly by repressing levels via mediating VvmiR166s- modules in GA-induced grape seedless berries. Our findings present a novel insight into the roles of VvmiR66s that are responsive to GA in repressing the lignin synthesis of grape seedless berries, with different lignin-synthesis-enzyme-dependent action pathways in diverse plants, which have important implications for the molecular breeding of high-quality seedless grape berries.