Endoplasmic reticulum acyltransferase with prokaryotic substrate preference contributes to triacylglycerol assembly in Chlamydomonas

Understanding the unique features of triacylglycerol (TAG) metabolism in microalgae may be necessary to realize the full potential of these organisms for biofuel and biomaterial production. In the unicellular green alga Chlamydomonas reinhardtii a chloroplastic (prokaryotic) pathway has been proposed to play a major role in TAG precursor biosynthesis. However, as reported here, C. reinhardtii contains a chlorophyte-specific lysophosphatidic acid acyltransferase, CrLPAAT2, that localizes to endoplasmic reticulum (ER) membranes. Unlike canonical, ER-located LPAATs, CrLPAAT2 prefers palmitoyl-CoA over oleoyl-CoA as the acyl donor substrate. RNA-mediated suppression of CrLPAAT2 indicated that the enzyme is required for TAG accumulation under nitrogen deprivation. Our findings suggest that Chlamydomonas has a distinct glycerolipid assembly pathway that relies on CrLPAAT2 to generate prokaryotic-like TAG precursors in the ER.