AaABF3, an Abscisic Acid-Responsive Transcription Factor, Positively Regulates Artemisinin Biosynthesis in Artemisia annua.

Yijun Zhong,Yanan Ma,Xueqing Fu,Xiaolong Hao,Kexuan Tang,Ling Li,Qifang Pan,Sadaf Kayani,Lihui Xie,Xiaofen Sun,Qian Shen

doi:10.3389/fpls.2018.01777

Abstract

Artemisinin is well known for its irreplaceable curative effect on the devastating parasitic disease, Malaria. This sesquiterpenoid is specifically produced in Chinese traditional herbal plant Artemisia annua. Earlier studies have shown that phytohormone abscisic acid (ABA) plays an important role in increasing the artemisinin content, but how ABA regulates artemisinin biosynthesis is still poorly understood. In this study, we identified that AaABF3 encoded an ABRE (ABA-responsive elements) binding factor. qRT-PCR analysis showed that AaABF3 was induced by ABA and expressed much higher in trichomes where artemisinin is synthesized and accumulated. To further investigate the mechanism of AaABF3 regulating the artemisinin biosynthesis, we carried out dual-luciferase analysis, yeast one-hybrid assay and electrophoretic mobility shift assay. The results revealed that AaABF3 could directly bind to the promoter of ALDH1 gene, which is a key gene in artemisinin biosynthesis, and activate the expression of ALDH1. Functional analysis revealed that overexpression of AaABF3 in A. annua enhanced the production of artemisinin, while RNA interference of AaABF3 resulted in decreased artemisinin content. Taken together, our results demonstrated that AaABF3 played an important role in ABA-regulated artemisinin biosynthesis through direct regulation of artemisinin biosynthesis gene, ALDH1.

Highlights

Malaria is considered to be a great threat to public health in the world
ABF3 is an ABA–responsive elements (ABREs)-binding protein, which is induced by environmental stress and requires abscisic acid (ABA) for its full activity (Choi et al, 2000; Uno et al, 2000)
AaABF3 can only activate the promoter of ALDH1, the expression of ADS, CYP71AV1, and DBR2 are altered by the over-expression or down regulation of AaABF3

Summary

Introduction

Malaria is considered to be a great threat to public health in the world. According to World Health Organization (WHO), Malaria has caused 445000 deaths globally in 2016 (World Health Organization [WHO], 2017). The carbocation formation and cyclization of amorpha-4, 11-diene from farnesyl pyrophosphate (FPP), a linear isoprene precursor, initiate the whole biosynthesis process (Bouwmeester et al, 1999; Wen and Yu, 2011). This initial step is catalyzed by amorpha-4, 11-diene synthase (ADS). CYP71AV1 and ALDH1 convert artemisinic aldehyde to artemisinic acid (Ro et al, 2006; Teoh, 2009). ADS, CYP71AV1, DBR2, and ALDH1 are considered to be key enzymes in artemisinin biosynthesis (Ikram and Simonsen, 2017)

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Results

Conclusion