TcMYC2a, a Basic Helix-Loop-Helix Transcription Factor, Transduces JA-Signals and Regulates Taxol Biosynthesis in Taxus chinensis.

Meng Zhang,Shengying Zhao,Longjiang Yu,Mi Wei,Xiaofei Jin,Ying Chen,Weifang Liao,Chunhua Fu

doi:10.3389/fpls.2018.00863

Meng Zhang, Shengying Zhao + Show 6 more

Open Access

https://doi.org/10.3389/fpls.2018.00863

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Abstract

The multitherapeutic taxol, which can be obtained from Taxus spp., is the most widely used anticancer drug. Taxol biosynthesis is significantly regulated by jasmonate acid (JA), one of the most important endogenous hormones in land plants. Nevertheless, the JA-inducing mechanism remains poorly understood. MYC2 is one of the key regulators of JA signal transfer and the biosynthesis of various secondary metabolites. Here, TcMYC2a was identified to contain a basic helix–loop–helix (bHLH)-leucine zipper domain, a bHLH-MYC_N domain, and a BIF/ACT-like domain. TcMYC2a was also found to bind with TcJAZ3 in yeast, which was a homolog of Arabidopsis JASMONATE ZIM-domain JAZ proteins, indicating that TcMYC2a had a similar function to AtMYC2 of JA signal transduction. TcMYC2a was able to affect the expression of GUS reporter gene by binding with the T/G-box, G-box, and E-box, which were the key cis-elements of TASY and TcERF12/15 promoter. TcMYC2a overexpression also led to significantly increased expression of TASY, tat, dbtnbt, t13h, and t5h genes. Additionally, TcERF15, which played the positive role to regulate tasy gene, was up-regulated by TcMYC2a. All these results revealed that TcMYC2a can regulate taxol biosynthesis either directly or via ERF regulators depending on JA signaling transduction.

Highlights

Taxol is widely used as an essential anticancer medicine for the effective clinical treatment of ovarian cancer, breast cancer, lung cancer, Kaposi sarcoma, cervical cancer, and pancreatic cancer, among others (Schiff et al, 1979)
Jasmonate acid signaling pathway is proved to be one of the most important regulating systems in land plants; it is involved in growth, development, (a)biotic defense, and secondary metabolism (Roberts, 2001)
The mechanism by which taxol biosynthesis regulate Jasmonate acid (JA) signals can promote our understanding on the significance of the JA signaling pathway in both gymnosperm and angiosperm

Summary

INTRODUCTION

Taxol is widely used as an essential anticancer medicine for the effective clinical treatment of ovarian cancer, breast cancer, lung cancer, Kaposi sarcoma, cervical cancer, and pancreatic cancer, among others (Schiff et al, 1979). The physically interactions of JASMONATE ZIM-domain (JAZ) with several downstream transcription factors reportedly control the JA signal-transduction system, called the JA signaling pathway (Deshaies, 1999; Thines et al, 2007; De Geyter et al, 2012). JA-inducible OsMYC2 drastically enhances the activity of naringenin 7-O-methyltransferase (OsNOMT) promoter and is essential for JA-inducible sakuranetin production (Ogawa et al, 2017b) All these studies indicate that MYC2 is a vital regulator of secondary-metabolite biosynthesis and that the JAZ–MYC2 complex is critical to the JA signaling pathway. TcERF12 and TcERF15 are JA-responsive ERF factors that negatively and positively regulate TASY gene expression by binding with the GCC-box (Zhang et al, 2015b). A series of experiments would be performed to determine the function of TcMYC2a in taxol biosynthesis and explain the regulation system

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