A Novel Bifunctional Wax Ester Synthase Involved in Early Triacylglycerol Accumulation in Unicellular Green Microalga Haematococcus pluvialis Under High Light Stress.

Haiyan Ma,Qiang Hu,Danxiang Han,Song Zou,Jie Zheng,Yanhua Li,Liang Zhao

doi:10.3389/fbioe.2021.794714

Abstract

The bulk of neutral lipids, including astaxanthin esters and triacylglycerols (TAGs), are accumulated in the green microalga Haematococcus pluvialis under high light (HL) stress. In this study, a novel bifunctional wax ester synthase (WS) gene was cloned from H. pluvialis upon HL stress. The overexpression of HpWS restored the biosynthesis of wax esters and TAGs in neutral lipid-deficient yeast mutant Saccharomyces cerevisiae H1246 fed with C18 alcohol and C18:1/C18:3 fatty acids, respectively. Under HL stress, HpWS was substantially upregulated at the transcript level, prior to that of the type I diacylglycerol:acyl-CoA acyltransferase encoding gene (HpDGAT1). HpDGAT1 is the major TAG synthase in H. pluvialis. In addition, the application of xanthohumol (a DGAT1/2 inhibitor) in the H. pluvialis cells did not completely eliminate the TAG biosynthesis under HL stress at 24 h. These results indicated that HpWS may contribute to the accumulation of TAGs in H. pluvialis at the early stage under HL stress. In addition, the overexpression of HpWS in Chlamydomonas reinhardtii bkt5, which is engineered to produce free astaxanthin, enhanced the production of TAGs and astaxanthin. Our findings broaden the understanding of TAG biosynthesis in microalgae and provide a new molecular target for genetic manipulation in biotechnological applications.

Highlights

Photosynthetic microalgae accumulate neutral lipids mainly in the form of triacylglycerols (TAGs) under unfavorable conditions, such as nutrient limitation, high temperature, and high light (HL) intensities (Chisti, 2007; Hu et al, 2008; Georgianna and Mayfield, 2012)
The phylogenetic analysis indicated that HpWS belongs to the membrane-bound O-acyltransferase (MBOAT) superfamily, clustered with acyl CoA:sterol acyltransferase (ASAT) or acylCoA wax alcohol acyltransferase (AWAT) from the plant and algae
It is closer to the DGAT1 family than the DGAT2 family (Figure 1A)

Summary

Introduction

Photosynthetic microalgae accumulate neutral lipids mainly in the form of triacylglycerols (TAGs) under unfavorable conditions, such as nutrient limitation, high temperature, and high light (HL) intensities (Chisti, 2007; Hu et al, 2008; Georgianna and Mayfield, 2012). Diacylglycerol (DAG) is converted to TAGs by an acyl-CoA:DAG acyltransferase (DGAT), which is the committed step of TAG biosynthesis (Yen et al, 2008). TAGs can be synthesized by phospholipid:DAG acyltransferase (PDAT) in the acyl-CoA independent pathway. It has been reported that multifunctional acyltransferases can synthesize TAGs in some plant and algae species. In Arabidopsis thaliana, two phytyl ester synthases (PESs), PES1 and PES2, can employ acyl-CoAs and galactolipids as acyl donors to synthesize phytyl ester and TAGs (Lippold et al, 2012). In diatom Phaeodactylum tricornutum, a dual-function PtWS/DGAT was identified to synthesize wax ester (WEs) and TAGs. The dual-function PtWS/DGAT was considered to be a promising target for genetic engineering in the microalgal-based lipid industry (Cui et al, 2018). MOBAT with wax synthase (WS) and DGAT activity was characterized in Chromochloris zofingiensis (Xu et al, 2021)

Methods

Results

Conclusion