The arabidopsis acyl-CoA-binding proteins ACBP1 and ACBP2 are essential for early embryo development

Abstract

In Arabidopsis thaliana, a family of six genes (ACbp1 to ACbp6) encodes acyl-CoA-binding proteins (ACBPs) which show conservation at the acyl-CoA-binding domain. n-terminal transmembrane domains and C-terminal ankyrin repeats are also present in ACBP1 and ACBP2. ACBP1 has been observed to accumulate in embryos of developing seeds and has been proposed to function in lipid transfer. Using ACBP2-specific antibodies in immunolocalization, we showed that ACBP2 is similarly expressed in Arabidopsis embryos during seed development. Since ACBP1 and ACBP2 are highly conserved (82% identity) and are both expressed in embryos, we investigated if they function redundantly in lipid metabolism during seed development. Our findings revealed that the acbp1 and acbp2 single mutants are similar to wild type in growth and development, but the acbp1acbp2 double mutant is embryo lethal and embryos aborted at early embryogenesis. Lethality in the double mutant was overcome by introduction of an ACbp1 cDNA. Lipid and acyl-CoA analyses indicated that siliques (but not leaves) of the acbp1 mutant accumulate galactolipid monogalactosyldiacylglycerol and 18:0-CoA. In contrast, the levels of most polyunsaturated species of phospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylserine had declined. Further observations demonstrated that recombinant ACBP1 and ACBP2 bind unsaturated phosphatidylcholine and acyl-CoA esters in vitro. Taken together, our results suggest that ACBP1 and ACBP2 are essential in lipid transfer during early embryogenesis in Arabidopsis.