The effects of down-regulating expression of Arabidopsis thaliana membrane-associated acyl-CoA binding protein 2 on acyl-lipid composition

Multiple classes of acyl-CoA binding proteins are encoded by plant genomes, including a plant-unique class of predicted integral membrane-proteins. Transcript analysis revealed that both of the integral membrane-acyl-CoA binding proteins of Arabidopsis thaliana, ACBP1 and ACBP2, are expressed in all organs. Expression of ACBP2 was highest in developing roots and flowers, and was four-fold greater than expression of ACBP1. Polyclonal antibodies against recombinant ACBP2 specifically recognized a Mr 47k protein that accumulated to similar levels in A. thaliana leaves, flowers, and siliques (0.05–0.07% total protein), but was two-fold more abundant in roots. To study the potential role(s) of ACBP2 in acyl-CoA metabolism, expression was down-regulated using hairpin RNA interference (RNAi). Three RNAi lines with at least 70% reduced levels of the ACBP2 protein were analyzed, but displayed no gross alterations in growth or developmental phenotype. A systematic analysis of lipids from developing leaves by electrospray tandem-mass spectrometry revealed little change in the levels of the eight major lipid classes but significant changes in fatty acid composition were observed, particularly for the phospholipids. These data suggest a specialized rather than general role for ACBP2 in plant acyl-lipid metabolism.