Betaine Lipid in euKaryotes – BLinK

To answer these questions, we will rely on complementary approaches: i) molecular biology and phylogeny to identify the gene of DGTA synthase and analyse the appearance and disappearance of betaine lipid synthase and PC synthase throughout the algae evolution. Because DGCC is not commercially available and microalgae species producing DGCC are not easy to cultivate in laboratory, we will focus our work on DGTS and DGTA; ii) biophysical and physicochemical tools such as neutron diffraction and computer simulations to determine to what extent betaine lipids are suited to substitute PC lipids; and iii) biochemistry, physiology and electron microscopy to study the biological impact of PC lipid replacement by betaine lipids on membrane architecture.

Our expected results will be the integration of the information generated by phylogeny, biophysic and in vivo study in a scheme picturing the interplay between betaine lipids and PC lipids and addressing the puzzling question of betaine lipids’ absence in higher plants. Moreover, the project will provide missing data on the evolution of lipid metabolism that may help comprehend the control of phospholipid versus non-phosphorus lipid balance during phosphate starvation and, on longer term, enhance omega-3 FA production and TAG accumulation for industrial applications. Additional deliverables include the identification of new enzymes involved in betaine lipid synthesis and the phylogenetic reconstruction of betaine lipid synthases and enzymes involved in PC synthesis.

Output of this project includes scientific communications and publications, based on the project results and might highlight new targets for improving triacylglycerol and/or essential omega-3 fatty acids productivity in microalgae.

1 article in preparation

Microalgae are today considered a new feedstock to produce a variety of biomolecules, most prominently triacylglycerol (TAG, containing three fatty acids) and essential ?3 fatty acids (FAs). The purposeful exertion of stress conditions, like phosphate starvation, is a common route to accumulate TAG in microalgae. A better understanding of why and how microalgae induce the biosynthesis of FAs and TAG under such stress conditions would help advancing the development of genetically engineered strains to produce biofuels or high-value products.
Under phosphate starvation, phospholipids in extraplastidial membranes are replaced by betaine lipids in microalgae. Betaine lipids, which are glycerolipids with two FAs, are hypothesized to be analogues of the main eukaryote phosphoglycerolipid phosphatidylcholine (PC) and they often contain a high proportion of ?3 fatty acids. In higher plants, the synthesis of betaine lipid is lost, driving plants to other strategies to cope with phosphate starvation: they replace their phospholipids by glycolipids and do not accumulate TAG as much as microalgae.
The objective of the BLinK project is to evaluate to what extent betaine lipids and PC lipids share physicochemical properties and could substitute each other in vivo, and how the presence of betaine lipid affects the lipid remodelling response to phosphate starvation. The project is organized in three axes:
1.) the comparison of betaine and PC lipids’ biosynthetic pathways throughout algae evolution,
2.) the analysis of betaine lipids’ physicochemical properties in terms of membrane fluidity, bending rigidity, as well as membrane-membrane interactions, for comparison with those of PC lipids, and
3.) the in vivo investigation in two microalgae species, Phaeodactylum tricornutum (a diatom) and Nannochloropsis gaditana (an eustigmatophyte), genetically engineered to lack either PC or betaine lipids.
The results obtained in these axes will be integrated in a scheme picturing the interplay between betaine lipids and PC lipids and addressing the puzzling question of betaine lipids’ absence in higher plants. Moreover, the project will provide missing data on the evolution of lipid metabolism that may help comprehend the control of phospholipid versus non-phosphorus lipid balance and, on longer term, enhance ?3 FA production and TAG accumulation for industrial applications. Additional deliverables include the identification of new enzymes involved in betaine lipid synthesis and the phylogenetic reconstruction of betaine lipid synthases and enzymes involved in PC synthesis.