Comparison between two isoforms of glycerol-3-phosphate acyltransferase in microalga Myrmecia incisa: Subcellular localization and role in triacylglycerol synthesis

Abstract

Microalgae represent a rich and naturally occurring source of triacylglycerol (TAG), and the microalgae-derived TAG has enormous potential in bioenergy, bio-based materials and other agricultural innovations. Glycerol-3-phosphate acyltransferase (GPAT) is a key enzyme that catalyzes the biosynthesis of TAG. Previously our lab has reported the first GPAT in the oleaginous alga Myrmecia incisa, and in the present study, a new GPAT was further identified from the same alga, which was designated as MiGPAT2. A full-length cDNA of MiGPAT2 consisting of a 1374-bp ORF, a 153-bp 5′-UTR and a 271-bp 3′-UTR was cloned. The putative protein composed of 457 amino acids, possessing the HX4D motif that acts as the activity center of GPAT catalysis. Emphasis was put on the comparison between two MiGPATs regarding subcellular localization and TAG synthesis function. A polyclonal and monoclonal antibody were separately prepared for MiGPAT1 and MiGPAT2, and the following immunogold labeling showed they were localized on chloroplast and endoplasmic reticulum (ER), respectively. This was further confirmed by the GFP fusion studies. Both MiGPATs were expressed heterologously in a GPAT-deficient yeast mutant, and it was found that MiGPAT2 played key roles in the de novo TAG biosynthesis, whereas MiGPAT1 was more involved in the phospholipid formation, contributing to TAG production via an indirect way. Findings of the present study expanded our knowledge on functional and evolutionary relationships of GPAT members in M. incisa, suggesting the possibility of genetic manipulation of GPAT in this alga for enhanced TAG production.