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 tazetta L. 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 that NtMYB3 significantly reduced red pigmentation induced by the potato anthocyanin activator StMYB-AN1 in agro-infiltrated leaves of tobacco. Over-expression of NtMYB3 decreased the red color of transgenic tobacco flowers, with qRT-PCR analysis showing that NtMYB3 repressed 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. NtMYB3 showed expression in all examined narcissus tissues; the expression level in basal plates of the bulb was highest. A 968 bp promoter fragment of narcissus FLS (NtFLS) was cloned, and transient expression and dual luciferase assays showed NtMYB3 repressed the promoter activity. These results reveal that NtMYB3 is 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.
Highlights
Chinese narcissus (Narcissus tazetta L. var. chinensis Roem) belongs to the Amaryllidaceae family and is a perennial bulbous plant widely cultivated in East Asia and China
Flavonoids belong to a class of secondary metabolites, which are mainly classified into main subgroups, including isoflavones, flavones, flavonols, flavan-diols, chalcones, anthocyanins, and proanthocyanidins [3]
NtMYB3 is related to the AtMYB4-like clade, which includes NtMYB2 [19]
Summary
Chinese narcissus (Narcissus tazetta L. var. chinensis Roem) belongs to the Amaryllidaceae family and is a perennial bulbous plant widely cultivated in East Asia and China. Most R2R3-MYB genes reported in flavonoid biosynthetic pathway regulate anthocyanin pigmentation, such as ZmC1 and ZmPl in maize, OgMYB1 in orchid, and LhMYB6/LhMYB12 in Asiatic Hybrid Lily [14,15]. NtMYB2, a R2R3-MYB in Chinese narcissus, was found to repress anthocyanin biosynthesis [19]. A high expression level of the genes that encode the FLS or DFR steps play a key role in regulating flux through the different branches of the flavonoid biosynthetic pathway [21]. The anthocyanin content of flowers carrying NtMYB3 gene was significantly decreased compared to those of wild type (Figure 5). These results suggested that NtMYB3 may play a role in the flavonoid biosynthesis of basal plates. The error bars stand for the SE of three biological replicates
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