Arabidopsis Acyl-Coenzyme-A-Binding Protein ACBP1 interacts with AREB1 and mediates salt and osmotic signaling in seed germination and seedling growth

Arabidopsis ACYL-COENZYME-A-BINDING PROTEIN1 (ACBP1) plays a positive role in abscisic acid (ABA) signaling during seed dormancy and germination. As a putative component of the ABA signaling pathway, its potential role in salt and osmotic signaling was tested using ACBP1pro::GUS transgenic lines, ACBP1-overexpressors (ACBP1-OXs), the acbp1 mutant and ACBP1-complemented lines (acbp1-COM). ACBP1-OXs were more sensitive than the wild type to NaCl and mannitol during seed germination and seedling establishment, while the acbp1 mutant was less sensitive during seed germination. Germination assays were conducted using the ABA biosynthesis inhibitor, fluridone, to determine whether the ACBP1 response was ABA-related. The germination potential of Col-0, acbp1, ACBP1-OXs, and acbp1-COM recovered to a level similar to the water control when fluridone was applied to NaCl- and mannitol-treated seeds, indicating that phenotypic variation amongst these lines was related to de novo ABA biosynthesis. Furthermore, yeast two-hybrid, bimolecular complementation assays and pull-down assays showed that ACBP1 interacted with ABA-RESPONSIVE ELEMENT BINDING PROTEIN1 (AREB1) via its ankyrin repeats. The target genes of AREB1 were up-regulated in ACBP1-OXs but down-regulated in acbp1; and the localization of DsRed-AREB1 was affected in ACBP1-OX. These results indicate that ACBP1 promotes ABA signaling under salt and osmotic stress during seed to seedling transition.