Integrative transcriptome and metabolome analyses reveal the molecular mechanism of re-flowering induction in Hydrangea macrophylla

Flowering duration is pivotal for ornamental appeal, with re-flowering being essential for prolonging the decorative period and enhancing the aesthetics of flowers. We conducted transcriptome and metabolome sequencing analyses on the primary and secondary flower buds of H. macrophylla cv 'White Angel', aiming to reveal the molecular regulatory mechanism of secondary flowering. Results showed that the key MADS-box transcription factor family genes closely related to flowering regulation such as AGL42, AGL24, and SVP demonstrated a substantial increase in expression levels within the secondary flower buds. The up-regulation of these genes may promote the transition from vegetative growth to reproductive growth by regulating the expression of downstream target genes, thus triggering secondary flowering. In addition, genes related to starch and sucrose metabolism (such as TPS and TPP) were significantly overexpressed in secondary flower buds, promoting the accumulation of energy metabolites such as Trehalose-6p, Trehalose and D-Glucose, which may create conditions for secondary flowering by providing necessary energy support. At the same time, terpenoid biosynthesis-related genes (such as KO, KAO, GA2ox and GA3ox) were highly expressed in secondary flower buds, significantly increasing the contents of GA4 and GA7, while decreasing the level of GA3. These dynamic changes of gibberellins (GAs) may regulate the expression of flowering related genes. Further promote the occurrence of secondary flowering. In summary, this study revealed the synergistic effect of genes and metabolites in the regulation of secondary flowering of Hydrangea macrophylla 'White Angel', and the MADS-box transcription factor directly promoted the transformation of reproductive growth through up-regulated expression. The accumulation of starch, sucrose and its derivatives and gibberellin metabolites may trigger the secondary flowering process of plants through energy supply and hormone signal regulation. These findings provide a new perspective for in-depth analysis of the flowering regulation mechanism of Hydrangea macrophylla, and lay a theoretical foundation for further cultivation of horticultural varieties with excellent ornamental characteristics.