Abstract
Yam (Dioscorea opposita) 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 DELLA-GAI2 acting as a negative regulator of GA signaling. Overexpression of DoDELLA-GAI2 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 DoDELLA-GAI2 gene expression. The yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays confirmed a direct interaction between DoDELLA-GAI2 and DoMTCPB, an upstream gene-encoding key enzyme in ETH biosynthesis. DoDELLA-GAI2 acts as a negative regulator of ETH synthesis by interacting with DoMTCPB. GA-induced degradation of DoDELLA-GAI2 relieves this inhibition, promoting ETH production and contributing to tuber growth. Taken together, our findings reveal a novel mechanism based on DoDELLA-GAI2 integrating the GA and ETH signaling processes to regulate tuber development in D. opposita, offering a potential target for improving yam crop productivity.