SoNAC72-SoMYB44/SobHLH130 module contributes to flower color fading via regulating anthocyanin biosynthesis by directly binding to the <i>SoUFGT1</i> promoter in lilac (<i>Syringa oblata</i>)

The fading of flower color is caused by changes in anthocyanin content during flower development in many plants, including lilac (<i>Syringa oblata</i>). However, the molecular regulatory mechanism of this phenomenon is still poorly understood. UDP-glucose: flavonoid 3-<i>O</i>-glucosyltransferase (UFGT) has a pivotal role in the formation of stable anthocyanins. Here, <i>SoUFGT1</i> and three transcription factors, SoMYB44, SobHLH130, and SoNAC72, were identified and verified to participate in anthocyanin production in lilac. Overexpressing <i>SoMYB44</i> promoted <i>SoUFGT1</i> expression in lilac petals. The yeast one-hybrid (Y1H) and dual-luciferase (Dual-LUC) assays demonstrated that SoMYB44 activated <i>SoUFGT1</i>, thereby bolstering anthocyanin accumulation. The overexpression and silencing of <i>SoNAC72</i> in petals revealed that it facilitated anthocyanin accumulation. The Y1H and Dual-LUC assays verified that SoNAC72 was capable of directly binding to the <i>SoMYB44</i> promoter to activate the latter's expression. In addition, SobHLH130 was also displayed to mediate anthocyanin accumulation in petals. By using yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays, the interaction between SoMYB44 and SobHLH130 was confirmed. These results corroborated that SoNAC72 regulates <i>SoMYB44</i> expression, and SoMYB44 interacts with SobHLH130 to trigger <i>SoUFGT1</i> expression in lilac, which then contributes to their anthocyanin accumulation. In sum, along with lilac flower development, the lower expression of <i>SoNAC72</i> and <i>SobHLH130</i> reduces <i>SoMYB44</i> transcripts and depresses transcriptional regulation of <i>SoUFGT1</i>, thus diminishing anthocyanin biosynthesis, leading to the fading of petal color. These study's findings provide valuable new insight for understanding the formation and regulatory mechanisms of flower color in lilac.