DgMYB4 orchestrates anthocyanin modification and acyl-glucose donor biosynthesis in Delphinium grandiflorum

To elucidate the seasonal variation in flower coloration of Delphinium grandiflorum cv. F₁ Super Platinum Blue, we performed transcriptome analysis and heterologous expression in Nicotiana tabacum, and molecular interaction assays. Flowers in early summer (PB1) displayed deeper blue coloration and more than 8-fold higher total anthocyanin content than those in early spring (PB2). In PB1, cyanodelphin was the major anthocyanin, whereas both cyanodelphin and violdelphin accumulated in PB2. Transcriptome data revealed that DgMYB4, an R2R3-MYB, was significantly upregulated in PB1. Ectopic expression of DgMYB4 in tobacco promoted anthocyanin accumulation and induced multiple anthocyanin-related genes. Mechanistically, yeast one-hybrid assays showed that DgMYB4 could bind the tested tobacco promoter fragments of NtANS, NtF3GT, NtF3GRhaT, and NtpHBAGT2, whereas dual-luciferase assays demonstrated DgMYB4-dependent promoter activation that was markedly enhanced by DgbHLH, particularly for NtF3GRhaT and NtpHBAGT2. Thus, our results support a model in which DgMYB4 contributes to coordinated regulation of core anthocyanin biosynthesis, downstream modification, and acyl-glucose donor-related processes. Greenhouse temperature monitoring and transcriptomic analyses revealed an association between contrasting seasonal cultivation conditions and differential DgMYB4 expression. These findings identify DgMYB4 as an important candidate regulator linking anthocyanin accumulation with downstream structural modification in Delphinium.