Abstract

R2R3-MYB transcription factors play important roles in the regulation of plant flavonoid metabolites. In the current study,NtMYB3, a novel R2R3-MYB transcriptional factor isolated from Chinese narcissus (Narcissus tazettaL. var.chinensis), was functionally characterized. Phylogenetic analysis indicated that NtMYB3 belongs to the AtMYB4-like clade, which includes repressor MYBs involved in the regulation of flavonoid biosynthesis. Transient assays showed thatNtMYB3significantly reduced red pigmentation induced by the potato anthocyanin activatorStMYB-AN1in agro-infiltrated leaves of tobacco. Over-expression ofNtMYB3decreased the red color of transgenic tobacco flowers, with qRT-PCR analysis showing thatNtMYB3repressed the expression levels of genes involved in anthocyanin and flavonol biosynthesis. However, the proanthocyanin content in flowers of transgenic tobacco increased as compared to wild type.NtMYB3showed expression in all examined narcissus tissues; the expression level in basal plates of the bulb was highest. A 968 bp promoter fragment of narcissusFLS(NtFLS) was cloned, and transient expression and dual luciferase assays showedNtMYB3repressed the promoter activity. These results reveal thatNtMYB3is involved in the regulation of flavonoid biosynthesis in narcissus by repressing the biosynthesis of flavonols, and this leads to proanthocyanin accumulation in the basal plate of narcissus.Keywords:Chinese narcissus;flavonol;R2R3-MYB;flavonoid repressor;anthocyanin