Arabidopsis acyl-CoA-binding protein ACBP6 can potentially bind lipids in the phloem

Abstract

In higher plants, the phloem translocates macromolecules such as assimilates, hormones, ribonucleic acids and proteins. Although lipids are also present in the phloem sap, their movement in an aqueous environment is not understood. Earlier proteomic analysis of phloem sap proteins revealed some lipidbinding proteins, of which acyl-CoA-binding proteins (ACBPs) have been widely identified in various species including cucumber, pumpkin and rice. Given the high affinities of plant ACBPs to acyl-CoA esters and some phospholipids, Arabidopsis thaliana was used as a model plant to study if any ACBP member plays a role in long-distance lipid trafficking via the phloem. Histochemical screening of the six members showed that AtACBP6 is a promising candidate due to its high promoter activity in vasculature. While AtACBP6 protein was immunolocalized in the wild-type phloem, the acbp6 knockout mutant (SALK_104339) was devoid of AtACBP6. When phloem lipids were collected from cut petioles of the wild type and acbp6 for analysis by gas chromatography-mass spectrometry, their differential lipid composition implicates a potential role of AtACBP6 in regulating phloem-associated lipid signals.