A U-box E3 ubiquitin ligase CmPUB15 targets CmMYB73 to regulate anthocyanin biosynthesis in response to low temperatures in chrysanthemum.

During annual chrysanthemum production, low temperatures (10°C, the same below) can promote anthocyanin accumulation in petals. However, the specific mechanism behind this phenomenon remains unclear. In this study, we identified CmMYB73, an SG22 R2R3-MYB transcription factor, as a negative regulator of anthocyanin biosynthesis in chrysanthemum. CmMYB73 responds to low temperatures in opposite ways at the transcriptional and protein levels. Further investigations revealed that CmPUB15, a U-box E3 ubiquitin ligase, interacts with CmMYB73 and is significantly upregulated by low temperatures at the transcriptional level. CmMYB73 is ubiquitinated by CmPUB15 and subsequently degraded via the 26S proteasome pathway, leading to the accumulation of anthocyanin in chrysanthemum petals. Our findings outline a novel pathway for anthocyanin biosynthesis under low temperatures and provide insights for molecular breeding efforts to enhance chrysanthemum flower color.