Abstract
Phenolic acids and tanshinones are two major bioactive components in Salvia miltiorrhiza Bunge. A novel endogenous R2R3-MYB transcription factor, SmMYB36, was identified in this research. This transcript factor can simultaneously influence the content of two types of components in SmMYB36 overexpression hairy roots. SmMYB36 was mainly localized in the nucleus of onion epidermis and it has transactivation activity. The overexpression of SmMYB36 promoted tanshinone accumulation but inhibited phenolic acid and flavonoid biosynthesis in Salvia miltiorrhiza hairy roots. The altered metabolite content was due to changed metabolic flow which was regulated by transcript expression of metabolic pathway genes. The gene transcription levels of the phenylpropanoid general pathway, tyrosine derived pathway, methylerythritol phosphate pathway and downstream tanshinone biosynthetic pathway changed significantly due to the overexpression of SmMYB36. The wide distribution of MYB binding elements (MBS, MRE, MBSI and MBSII) and electrophoretic mobility shift assay results indicated that SmMYB36 may be an effective tool to regulate metabolic flux shifts.
Highlights
MYB transcription factors are widespread throughout the plant world, regulating development, primary and secondary metabolism and abiotic and biotic stress[25, 26]
Sequence analysis indicated that SmMYB36 contained a complete open reading frame (ORF) and encoded a putative protein of 160 amino acid residues with predicted molecular weight of 18 kDa
Motif analysis indicates that SmMYB36 contains a DNEI motif that is widely present in subgroup 4 and 555, 66
Summary
MYB transcription factors are widespread throughout the plant world, regulating development, primary and secondary metabolism and abiotic and biotic stress[25, 26]. Li et al found that some R2R3-MYBs in the same subgroup showed similar functions to metabolic pathways, while others were species-specialized transcription factors[30]. The overexpression of PtMYB14 and VvMYB5b influenced the accumulation of terpenoids and phenylpropanoids[31, 32], which indicated that members of two above subgroups may regulate both terpenoid and phenylpropanoid biosynthetic pathways. The heterologous expression of AtMYB75 (AtPAP1) and snapdragon Rosea[1] in S. miltiorrhiza leads to the up-regulation of the expression level of core phenylpropanoid pathway genes and enhanced content of rosmarinic acid and salvianolic acid B58, 59. The overexpression of SmPAP1 promotes the accumulation of rosmarinic acid, salvianolic acid B, total phenolics and total flavonoids in transgenic S. miltiorrhiza Bge.f.alba roots[60]. Heterogeneous and the endogenous transcription factors might exhibit different functions due to different genetic backgrounds or induction effects[32]
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