Abstract
The unicellular green alga Haematococcus pluvialis has been recognized as an industry strain to produce simultaneously esterified astaxanthin (EAST) and triacylglycerol (TAG) under stress induction. It is necessary to identify the key enzymes involving in synergistic accumulation of EAST and TAG in H. pluvialis. In this study, a novel diacylglycerol acyltransferase 1 was systematically characterized by in vivo and in silico assays. The upregulated expression of HpDGAT1 gene was positively associated with the significant increase of TAG and EAST contents under stress conditions. Functional complementation by overexpressing HpDGAT1 in a TAG-deficient yeast strain H1246 revealed that HpDGAT1 could restore TAG biosynthesis and exhibited a high substrate preference for monounsaturated fatty acyl-CoAs (MUFAs) and polyunsaturated fatty acyl-CoAs (PUFAs). Notably, heterogeneous expression of HpDGAT1 in Chlamydomonas reinhardtii and Arabidopsis thaliana resulted in a significant enhancement of total oils and concurrently a high accumulation of MUFAs- and PUFAs-rich TAGs. Furthermore, molecular docking analysis indicated that HpDGAT1 contained AST-binding sites. These findings evidence a possible dual-function role for HpDGAT1 involving in TAG and EAST synthesis, demonstrating that it is a potential target gene to enrich AST accumulation in this alga and to design oil production in both commercial algae and oil crops.
Highlights
Microalgae have been recognized as the promising biological resource for commercial production of oil, healthy food, aquacultural feed, pharmaceuticals, biofuels, and bio-based chemicals (Durrett et al, 2008; Hu et al, 2008; Xin et al, 2019)
The 1,811 bp HpDGAT1 in length contained a 1,560 bp open reading frame (ORF) encoding 519 amino acids with MW of 58.7 kDa and pI of 9.8 (Supplementary Figure S2A). This protein was detected to have several conserved domains, such as chloroplast transduction peptide (CTP, 56 aa), TM helices (9 TMs), and phosphorylation sites (18) (Supplementary Figures S2B,E). All these analyses suggested that HpDGAT1 might be a membranebound DGAT1 enzyme localized in the chloroplast
The unicellular green alga H. pluvialis is well characterized for its ability to produce high levels of natural esterified astaxanthin (EAST) and TAGs in a tightly associated model under stress conditions, representing an ideal industrial producer of both oils and ASTs (Lorenz and Cysewski, 2000; Chen et al, 2015; Bilbao et al, 2020) despite the detail mechanism underlying TAG and AST biosynthesis remains unclear in this alga
Summary
Microalgae have been recognized as the promising biological resource for commercial production of oil, healthy food, aquacultural feed, pharmaceuticals, biofuels, and bio-based chemicals (Durrett et al, 2008; Hu et al, 2008; Xin et al, 2019). HpDGAT1’s Function in TAG Production the molecular mechanism underlying lipid biosynthesis and oil accumulation in these microalgae is not elucidated in detail yet (Durrett et al, 2008; Hu et al, 2008). The known studies demonstrate that triacylglycerols (TAGs) are the predominant forms of storage lipid in various organisms including higher plants and microalgae. In the acyl-CoA-dependent pathway, diacylglycerol acyltransferase (DGAT) catalyzing the committed step of TAG assembly has been used as the core target for manipulating TAG production in a number of organisms (Lung and Weselake, 2006; Liu et al, 2012; Jin and Jiang, 2015; Xu et al, 2018). Four types of DGATs have been identified, including the membrane-bound DGAT1 and DGAT2 with low sequence similarity between them, the cytosol-soluble DGAT3, and the dual-function of WS/DGAT having both wax ester and TAG biosynthesis activities (Xu et al, 2018)
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