Regulation of blue infertile flower pigmentation by WD40 transcription factor HmWDR68 in Hydrangea macrophylla 'forever summer'.

BACKGROUND: WD40 transcription factors are crucial in plant growth and developmental, significantly impacting plant growth regulation. This study investigates the WD40 transcription factor HmWDR68's role in developing the distinctive blue infertile flower colors in Hydrangea macrophylla 'Forever Summer'.

METHODS AND RESULTS: The HmWDR68 gene was isolated by PCR, revealing an open reading frame of 1026 base pairs, which encodes 341 amino acids. Characterized by four WD40 motifs, HmWDR68 is a member of the WD40 family. Phylogenetic analysis indicates that HmWDR68 shares high homology with PsWD40 in Camellia sinensis and CsWD40 in Paeonia suffruticosa, both of which are integral in anthocyanin synthesis regulation. Quantitative real-time PCR (qRT-PCR) analysis demonstrated that HmWDR68 expression in the blue infertile flowers of 'Forever Summer' hydrangea was significantly higher compared to other tissues and organs. Additionally, in various hydrangea varieties with differently colored infertile flowers, HmWDR68 expression was markedly elevated in comparison to other hydrangea varieties, correlating with the development of blue infertile flowers. Pearson correlation analysis revealed a significant association between HmWDR68 expression and the concentration of delphinidin 3-O-glucoside, as well as key genes involved in anthocyanin biosynthesis (HmF3H, HmC3'5'H, HmDFR, and HmANS) in the blue infertile flowers of 'Forever Summer' hydrangea (P < 0.01).

CONCLUSION: These findings suggest HmWDR68 may specifically regulate blue infertile flower formation in hydrangea by enhancing delphinidin-3-O-glucoside synthesis, modulating expression of HmF3H, HmC3'5'H, HmDFR and HmANS. This study provides insights into HmWDR68's role in hydrangea's blue flowers development, offering a foundation for further research in this field.