Multiple transcription factors and genes jointly regulate the light-dependent flavonoid biosynthesis mechanism of stem color in Hydrangea macrophylla

The coloration of hydrangea stems significantly enhances their ornamental value and resilience, yet its molecular mechanisms remain poorly understood. The formation of colored stems is regulated by biological macromolecular such as transcription factors and structural genes. This study investigated the biochemical and molecular mechanisms underlying dark purplish-red stem formation in the self-crossbred hydrangea variety "Taube," with a particular focus on light-dependent regulation. Biochemical assays revealed light-regulated flavonoid biosynthesis, pivotal for aesthetic and functional traits. Network analysis identified key genes and transcription factors linked to pigmentation. Integration of metabolomic data with transcription factor analysis identified four key regulatory elements—MYC1, MYC2-like, MYB12, and MYB1R1—as significantly associated with stem pigmentation. These findings elucidate the complex interplay of physiological and biochemical processes governing stem color formation in hydrangeas, involving the coordinated regulation of flavonoid biosynthesis, accumulation, and distribution by multiple transcription factors and genes. This study lays the groundwork for breeding hydrangeas with enhanced stem coloration.