The GID1-DELLA2 Signaling Module Mediates Gibberellin-Induced Seed Germination in Sainfoin ( Onobrychis viciifolia )

Sainfoin (Onobrychis viciifolia) is an important perennial forage legume, but poor seed germination severely limits its establishment and utilization. Gibberellin (GA) signaling plays a central role in germination; however, the molecular mechanisms underlying GA-mediated germination regulation in sainfoin remain largely unknown. In this study, 11 DELLA family genes were identified, and OvDELLA2 was characterized as a key regulator of seed germination. OvDELLA2 encodes a nucleus-localized protein and is highly induced during germination. Agrobacterium-mediated seed-imbibition transient transformation system was established to facilitate functional analysis in sainfoin. Functional analyses demonstrated that OvDELLA2 overexpression significantly inhibited germination, radicle elongation, and storage reserve mobilization, whereas OvGID1 overexpression enhanced GA responsiveness and promoted germination. Protein interaction assays revealed a GA3-dependent interaction between OvDELLA2 and OvGID1, indicating conservation of the canonical GA-GID1-DELLA signaling module. This study provides insights into GA-regulated seed and offers a platform for functional genomics and molecular breeding in sainfoin.