The biosynthesis of anthocyanins involves the synergistic interaction between transcription factors and cis-regulatory elements in the promoter regions of structural genes, such as
CHI,
CHS,
ANS,
UFGT,
DFR, and
F3H (Tanaka et al.
2008, Li et al.
2016, Chaves-Silva et al.
2018, Ma, Constabel
2019). The transcription factors that regulate anthocyanin biosynthesis primarily include MYB, bHLH and WD40 (Gonzalez et al.
2008). Furthermore, increasing evidence indicates that the expression of the members of the MBW complex, specifically MYBs and bHLHs, is modulated by environmental temperatures and other stimuli, suggesting a novel role for the MBW regulatory complex in response to environmental effects on anthocyanin synthesis in plants (Ban et al.
2007, Rowan et al.
2009, Lin-Wang et al.
2011). However, the molecular mechanism by which MBW components regulate anthocyanin biosynthesis and organ coloration in response to environmental stimuli is largely unknown. MYB, especially the R2R3-MYB transcription factor, Specific binding to target gene DNA is a major determinant of the spatial and temporal accumulation characteristics of anthocyanin glycosides (Albert et al.
2010; Yan et al.
2021), such as MdMYB10 in apple, DcMYB7 in
Daucus carota, and LrMYB15 in
Lilium regale (Espley et al.
2007; Xu et al.
2019; Yin et al.
2021). Therefore, identifying the R2R3-MYB gene, which regulates anthocyanin biosynthesis in ornamental plants, is particularly important for unraveling the transcriptional regulatory mechanism of color formation in them. bHLH, as the second-largest transcription factor family in plants, was also involved in regulating anthocyanin synthesis and stress responses (Feller et al.
2011). For example, the bHLH transcription factor BrTT8 promotes anthocyanin synthesis in turnip under abiotic stress (Zhang et al.
2020a), and MdbHLH3 in apple enhanced anthocyanin accumulation in fruits under low-temperature stress (Xie et al.
2012). It has been shown that the regulation of phycocyanin by bHLH is mainly accomplished by means of interactions with other transcription factors. Furthermore, more studies have shown that bHLH can influence anthocyanin accumulation by interacting with MYB transcription factors (Zhao et al.
2019). In
Dendrobium sp., the transcription factors DhMYB2 and DhbHLH1 are co-expressed with anthocyanin biosynthesis genes DhDFR and DhANS in petals to regulate anthocyanin synthesis (Li et al.
2017). In red pear (
Pyrus), PyWRKY26 could interact with PybHLH3 and could bind to the PyMYB114 promoter and activate the transcription of PyMYB114, which results in anthocyanin accumulation in red-skinned pear (Chuang L et al.
2020). Currently, the regulatory role of bHLH in anthocyanin has yielded results in fruit trees, but studies in ornamental flowers have been less involved.