A GA2-oxidase gene introgressed from Cucurbita pepo drives developmental reversal of dominance and semi-dwarfism in Cucurbita moschata

Plant architecture is a key determinant of crop productivity and agronomic efficiency. Here, we report a semi-dwarf Cucurbita moschata line, Sd1 , exhibiting developmental reversal of dominance (DRoD), characterized by early-stage dwarfism followed by partial recovery of stem elongation. Genetic analysis revealed that this phenotype is governed by a dominant dwarf gene, Sd-1 , and a temporally acting elongation QTL, Vlp-1 . Fine mapping identified Sd-1 as a gibberellin 2-oxidase (GA2ox) gene with a protein sequence identical to the CpDw allele from C. pepo , suggesting interspecific introgression. Promoter variation drives elevated Sd-1 expression, resulting in depletion of bioactive gibberellin (GA₄) and early growth repression. Despite GA deficiency, transcriptomic and hormone profiling revealed early divergence between dwarf and semi-dwarf lines. The semi-dwarf line exhibits increased auxin and salicylic acid levels, which facilitate partial recovery of stem elongation through GA-independent mechanisms. Together, these findings establish a temporal genetic framework for DRoD and highlight the potential of regulatory variation and hormone rebalancing for optimizing plant architecture in cucurbit breeding. These findings reveal a temporally coordinated genetic module linking GA deficiency to hormone-mediated compensatory growth, providing a framework for optimizing plant architecture.