Arabidopsis membrane-associated acyl-CoA-binding protein ACBP1 is involved in stem cuticle formation

The membrane-anchored Arabidopsis thaliana ACYL-COA-BINDING PROTEIN1 (AtACBP1) plays important roles in embryogenesis and abiotic stress responses, and interacts with long-chain (LC) acyl-CoA esters. Here, AtACBP1 function in stem cuticle formation was investigated. Transgenic Arabidopsis transformed with an AtACBP1pro::GUS construct revealed beta-glucuronidase (GUS) expression on the stem (but not leaf) surface, suggesting a specific role in stem cuticle formation. Isothermal titration calorimetry results revealed that (His)(6)-tagged recombinant AtACBP1 interacts with LC acyl-CoA esters (18:1-, 18:2-, and 18:3-CoAs) and very-long-chain (VLC) acyl-CoA esters (24:0-, 25: 0-, and 26:0-CoAs). VLC fatty acids have been previously demonstrated to act as precursors in wax biosynthesis. Gas chromatography (GC)-flame ionization detector (FID) and GC-mass spectrometry (MS) analyses revealed that an acbp1 mutant showed a reduction in stem and leaf cuticular wax and stem cutin monomer composition in comparison with the wild type (Col-0). Consequently, the acbp1 mutant showed fewer wax crystals on the stem surface in scanning electron microscopy and an irregular stem cuticle layer in transmission electron microscopy in comparison with the wild type. Also, the mutant stems consistently showed a decline in expression of cuticular wax and cutin biosynthetic genes in comparison with the wild type, and the mutant leaves were more susceptible to infection by the necrotrophic pathogen Botrytis cinerea. Taken together, these findings suggest that AtACBP1 participates in Arabidopsis stem cuticle formation by trafficking VLC acyl-CoAs.