Characterization of the Bubblegum acyl-CoA synthetase of Microchloropsis gaditana

International audienceThe metabolic pathways of glycerolipids are well described in cells containing chloroplasts limited by a two-membrane en-velope but not in cells containing plastids limited by four membranes, including heterokonts. Fatty acids (FAs) producedin the plastid, palmitic and palmitoleic acids (16:0 and 16:1), are used in the cytosol for the synthesis of glycerolipids viavarious routes, requiring multiple acyl-Coenzyme A (CoA) synthetases (ACS). Here, we characterized an ACS of theBubblegum subfamily in the photosynthetic eukaryote Microchloropsis gaditana, an oleaginous heterokont used for theproduction of lipids for multiple applications. Genome engineering with TALE-N allowed the generation of MgACSBGpoint mutations, but no knockout was obtained. Point mutations triggered an overall decrease of 16:1 in lipids, a specificincrease of unsaturated 18-carbon acyls in phosphatidylcholine and decrease of 20-carbon acyls in the betaine lipid diacyl-glyceryl–trimethyl–homoserine. The profile of acyl-CoAs highlighted a decrease in 16:1-CoA and 18:3-CoA. Structuralmodeling supported that mutations affect accessibility of FA to the MgACSBG reaction site. Expression in yeast defectivein acyl-CoA biosynthesis further confirmed that point mutations affect ACSBG activity. Altogether, this study supports acritical role of heterokont MgACSBG in the production of 16:1-CoA and 18:3-CoA. In M. gaditana mutants, the excess satu-rated and monounsaturated FAs were diverted to triacylglycerol, thus suggesting strategies to improve the oil content inthis microalg