Gibberellin Homeostasis Perturbation Alters Sugar Metabolism and Developmental Traits in Agapanthus praecox subsp. orientalis
Gibberellins (GAs) are essential hormones that regulate plant growth and development, yet the downstream metabolic pathways through which they modulate phenotypic plasticity remain poorly understood. Here, we investigated the GA-mediated regulatory network in Agapanthus praecox subsp. orientalis by integrating phenotypic, transcriptomic, and targeted metabolomic analyses across three complementary perturbation strategies: gradient paclobutrazol (PAC) treatments, GA20ox RNA interference (RNAi) lines, and exogenous GA4 rescue. PAC suppressed vegetative growth dose-dependently and completely arrested floral development at 200 mg·L−1, while increasing soluble sugar and starch contents; plants treated with it in the first year displayed enhanced vegetative growth in the following season, suggesting a possible carbon legacy effect. GA20ox silencing caused dwarfism and flowering failure, which were largely rescued by GA4. Exogenous GA4 restored bioactive GA pools to above wild-type levels without recovering endogenous synthesis, indicating functional compensation. Transcriptomic and qRT-PCR analyses revealed that sugar metabolism-related genes and metabolites underwent the most pronounced changes among all tested categories; these changes were partially reversed by GA4, though certain catabolic genes remained suppressed, revealing hierarchical regulatory logic. Collectively, these findings indicate that GA is closely associated with growth and carbohydrate allocation, and that the GA–sugar metabolic axis represents a major downstream component in developmental plasticity. This study provides species-specific insights into GA-mediated growth regulation and offers implications for ornamental crop management.