AtPAP1 Interacts With and Activates SmbHLH51, a Positive Regulator to Phenolic Acids Biosynthesis in Salvia miltiorrhiza.

Yucui Wu,Bin Wang,Xiaoyan Cao,Lin Li,Yuan Zhang,Zhezhi Wang,Xiaorong Guo

doi:10.3389/fpls.2018.01687

Abstract

Phenolic acids from Salvia miltiorrhiza have drawn considerable attention in recent years because of their remarkable pharmacological activities. We previously reported that Arabidopsis thaliana transcription factor production of anthocyanin pigment 1 (AtPAP1) has strong capability to promote the production of phenolic acids in S. miltiorrhiza. However, the responsible molecular mechanism is unclear. Here, we analyzed the transcriptome of transgenic S. miltiorrhiza that over-expressed AtPAP1. Transcriptome analysis revealed 4,152 genes that were differentially expressed due to ectopic AtPAP1 overexpression. SmbHLH51, a novel bHLH gene significantly up-regulated by constitutive expression of AtPAP1, was isolated from S. miltiorrhiza for detailed functional characterization. SmbHLH51 localizes in the nuclei and interacts with AtPAP1, indicating that they probably comprise a regulatory transcription complex. Enhanced or reduced expression of SmbHLH51 was achieved in S. miltiorrhiza by gain- or loss-of-function assays, respectively, revealing that SmbHLH51 is a positive transcriptional regulator of the pathway for phenolic acid biosynthesis. We propose that applying this functional genomics approach through the transcriptomic analyses is an efficient means for identifying novel genes involved in plant secondary metabolism.

Highlights

Salvia miltiorrhiza Bunge, a well-known member of the Labiatae family, is emerging as a model plant system for research in regulation of secondary metabolites because of its significant medicinal values, high transformation efficiency and published genome data (Shao and Lu, 2013; Xu et al, 2015b)
We isolated the promoter of SmbHLH51 and used it to examine whether AtPAP1 could directly activate the expression of SmbHLH51 by Agrobacterium-mediated transient expression in tobacco (Nicotiana benthamiana)
We propose that bHLHs, which is activated by AtPAP1 and can interact with AtPAP1 in S. miltiorrhiza, is potentially involved in the regulation of phenolic acids biosynthesis

Summary

Introduction

Salvia miltiorrhiza Bunge, a well-known member of the Labiatae family, is emerging as a model plant system for research in regulation of secondary metabolites because of its significant medicinal values, high transformation efficiency and published genome data (Shao and Lu, 2013; Xu et al, 2015b). The bioactive components of S. miltiorrhiza are divided into two groups: lipidsoluble tanshinones and water-soluble phenolic acids. The latter group includes rosmarinic acid (RA) and salvianolic acid B (Sal B), which are attracting increased attention because of their marked pharmacological activities coupled with their traditional use as herbs steeped in boiling water in China (Petersen and Simmonds, 2003; Wu et al, 2012b). The phenolic acids distribute in different parts of Salvia miltiorrhiza and the content of total phenolic acids from leaves was significantly higher than those in roots and stems (Li et al, 2011)

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