Betaine lipids: Biosynthesis, functional diversity and evolutionary perspectives

Betaine lipids (BL) are relatively understudied non‑phosphorus glycerolipids. They are predominantly found in algae but have also been detected in other unicellular eukaryotes, fungi, bacteria, and some bryophytes and pteridophytes. These extraplastidial lipids are considered as substitute for phospholipids in organisms, particularly under phosphate (Pi) deficiency. This review provides a broader perspective on the roles and functions of BL, revealing their functional diversity across species and environments. It also discuss the biosynthetic pathways of BL. Indeed, the pathway for DGTS (1(3),2-diacylglyceryl-3(1)-O-4'-(N,N,N-trimethyl)-homoserine), the most widespread and studied BL form, is completely known, whereas the pathway for DGTA (1(3),2-diacylglyceryl-3(1)-O-2'-(N,N,N-trimethyl)-β-alanine) is only partially understood. In this review, the role of the BTA1 gene, responsible for the synthesis of DGTS, is discussed. It is revealed to be essential in DGTA synthesis as it enables the production of its intermediate, DGTS. A phylogenetic analysis, conducted on BTA1 gene, does not seem to link the phylogenetic position of BTA1 with the BL species produced but confirms the distribution trends, with a BL diversification in marine environments and the gradual disappearance of DGTS in the evolution of the green lineage. Further research is needed to elucidate the specific roles and biosynthetic pathways of BL across different species.