Gibberellin Mediates VvmiR397a-VvLAC4 via VvSLR1-VvWRKY26 Cascade Signal to Repress the Seed-Stone Development During GA-Induced Grape Parthenocarpy.

Exogenous gibberellin (GA) effectively inhibits the development of lignified seed-stone in grapes by inducing parthenocarpic seedless berries and significantly improving berry quality. However, the molecular mechanisms underlying this process remain elusive. Here, we uncovered the roles of miR397a in GA signalling-mediated grape seed-stone development through VvSLR1-VvWRKY26 cascade modulation in grapes, indicating 'VvSLR1-VvWRKY26-VvmiR397a-VvLAC4' is the key signalling regulatory module in lignin synthesis of seed-stone in GA-induced grape parthenocarpic berries. VvSLR1 inhibits VvmiR397a expression through interaction with VvWRKY26 and promotes the laccase-mediated lignin synthesis, while GA depresses lignin synthesis by overcoming VvSLR1-mediated multi-level cascade signals. We identified GA responsive cis-element of VvMIR397a promoter bound by VvWRKY26, which activated VvmiR397a expression, whereby inhibiting VvLAC4 level. The expression patterns and cleavage roles' variation of VvmiR397a-VvLAC4 during the seed stones of grape stone-hardening stage indicated that this pair is the one main regulatory module from VvLACs family in this process. Overexpression of VvMIR397a in tobacco and short tandem target mimic (STTM) assays of VvmiR397a/FvmiR397 in grape/strawberry highlighted the function of miR397a-LACs module during modulation of lignin synthesis. Our findings shed novel insights into the GA-responsive roles of VvmiR397a through multi-level cascade signals during modulation of grape seed-stone development, which has important implications for the molecular breeding of high-quality seedless grape berries.