Transcriptome-Wide Identification of WRKY Transcription Factor and Functional Characterization of RgWRKY37 Involved in Acteoside Biosynthesis in Rehmannia glutinosa.

Fengqing Wang,Xin Zuo,Xu Yang,Jingyu Zhi,Mingming Li,Xiangyang Liu,Caixia Xie,Yajing Li,Xinrong Li,Chunyan Miao

doi:10.3389/fpls.2021.739853

Abstract

WRKYs play important roles in plant metabolism, but their regulation mechanism in Rehmannia glutinosa remains elusive. In this study, 37 putative WRKY transcription factors (TFs) with complete WRKY domain from R. glutinosa transcriptome sequence data were identified. Based on their conserved domains and zinc finger motif, the R. glutinosa WRKY TFs were divided into five groups. Structural feature analysis shows that the 37 RgWRKY proteins contain WRKYGQK/GKK domains and a C2H2/C2HC-type zinc finger structure. To identify the function of RgWRKY members involved in acteoside biosynthesis, transcriptional profiles of 37 RgWRKYs in hairy roots under salicylic acid (SA), methyl jasmonate (MeJA), and hydrogen peroxide (H2O2) treatments were systematically established using RNA-seq analysis. Based on the correlationship between the expression levels of RgWRKY genes and acteoside content, RgWRKY7, RgWRKY23, RgWRKY34, RgWRKY35, and RgWRKY37 were suggested to be involved in acteoside biosynthesis in R. glutinosa, and RgWRKY37 was selected for gene functional research. Overexpression of RgWRKY37 increased the content of acteoside and total phenylethanoid glycosides (PhGs) in hairy roots and enhanced the transcript abundance of seven enzyme genes involved in the acteoside biosynthesis pathway. These results strongly suggest the involvement of the WRKY transcription factor in the regulation of acteoside biosynthesis.

Highlights

Rehmannia glutinosa L. is a perennial herb of Scrophulariaceae and is widely distributed in Northern China, including Henan and Shanxi provinces
A total of 115 unigenes were retrieved in the R. glutinosa transcriptome database by BLASTn
The results showed that 44 cDNA sequences had complete open reading frames (ORFs), and 37 WRKY gene cDNA sequences were eventually obtained after removing four redundant sequences (Table 1)

Summary

Introduction

Rehmannia glutinosa L. is a perennial herb of Scrophulariaceae and is widely distributed in Northern China, including Henan and Shanxi provinces. Many tissues and organs of R. glutinosa plants, especially tuberous roots and leaves, are rich in many active components, such as iridoid glycosides (IGs), phenylethanoid glycosides (PhGs), flavonoids, polysaccharides, and amino acids (Zhang et al, 2008a; Liu et al, 2014). The tuberous root of R. glutinosa is a WRKY Involved in R. glutinosa Acteoside Biosynthesis traditional Chinese herb, recorded in the Chinese medical classics as “Shennong’s Herbal.”. It is considered a “top-grade” herb in China (Zhi et al, 2018). Many studies have revealed that the tuberous root of R. glutinosa is rich in a variety of active ingredients with pharmacological activity in the human immune, the blood system, and the endocrine, cardiovascular, and nervous system (Zhang et al, 2008b). Rehmannia glutinosa has become an effective traditional Chinese medicine (TCM) for decreasing blood glucose (Qin et al, 2018), and it has been noted for its antioxidant (Li et al, 2020a), antiinflammatory (Liu et al, 2012), anti-depressant (Wang et al, 2018), and anti-aging (Bai et al, 2018) properties

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