DoDELLA-GAI2 Integrates Gibberellin and Ethylene Signaling to Regulate Chinese Yam (Dioscorea opposita) Tuber Development

Yam (<i>Dioscorea opposita</i>) tuber development is a complex process regulated by various phytohormones, with gibberellin (GA) playing a crucial role. However, the underlying mechanisms and interaction of GA with other phytohormone pathways on yam tuber development remain incompletely understood. This study investigated the regulatory role of GA and its crosstalk with other phytohormones during yam tuber growth through phenotypic, cytological, physiological, and transcriptomic as well as targeted phytohormone metabolomics analyses. The results reveal that exogenous GA promoted tuber enlargement increases vascular bundle and the number and diameter of sieve tubes, and alters the expression of GA anabolism genes and GA signal transduction pathways. Integrated transcriptome and targeted metabolomics analyses revealed coordinated changes in GA and ethylene (ETH) biosynthesis and signaling pathways during tuber development, particularly <i>DELLA-GAI2</i> acting as a negative regulator of GA signaling. Overexpression of <i>DoDELLA-GAI2</i> in transgenic tobacco significantly reduced GA level, starch, cytokinin (CTK), and ETH content, as well as aerenchyma tissue growth and parenchyma cell size. Exogenous GA and ethephon treatments increased GA, starch, CTK, and ETH content, and downregulated <i>DoDELLA-GAI2</i> gene expression. The yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays confirmed a direct interaction between <i>DoDELLA-GAI2</i> and <i>DoMTCPB</i>, an upstream gene-encoding key enzyme in ETH biosynthesis. <i>DoDELLA-GAI2</i> acts as a negative regulator of ETH synthesis by interacting with <i>DoMTCPB</i>. GA-induced degradation of <i>DoDELLA</i>-<i>GAI2</i> relieves this inhibition, promoting ETH production and contributing to tuber growth. Taken together, our findings reveal a novel mechanism based on <i>DoDELLA-GAI2</i> integrating the GA and ETH signaling processes to regulate tuber development in <i>D. opposita</i>, offering a potential target for improving yam crop productivity.