Sunflower acyl-CoA:Lyso-phosphatidic acid acyltransferases and their contribution to the distribution of fatty acids in sunflower seed storage triacylglycerols

Triacylglycerols (TAG) are storage lipids that are accumulated in oilseeds to feed the embryo during germination. TAGs are synthesized by sequential acylation of the glycerol-3P molecule through the action of acyltransferase enzymes located in the endoplasmic reticulum. Among these enzymes lysophosphatidyl-acyl-CoA acyltransferase (LPAAT) is responsible for the acylation of the sn-2 position of TAG, thus partially determining the distribution of fatty acids within them. In the present study, eight genes encoding LPAATs were identified in the sunflower genome. Two of them, HaLPAAT2A and HaLPAAT2C, were significantly expressed in the developing seeds during the TAG accumulation phase. The localization and structure of these LPAATs were studied, and they were expressed in yeast to analyse the impact of their expression in the host lipids and acyl-CoA pool. These genes were able to partially complement the phenotype of the Arabidopsis lpaat2-3 insertional mutant. The HaLPAATs were assayed and characterized in membrane fractions prepared from the transformed yeasts lines, showing high specificity towards polyunsaturated linoleoyl- and linolenoyl-CoA derivatives. Finally, the structure of these enzymes was modelled and the substrate specificity was discussed in terms of the interactions of the acyl-CoA substrates with the active center of the enzyme.