Overexpression of Arabidopsis acyl-CoA-binding protein ACBP2 enhances drought tolerance

Arabidopsis thaliana acyl-CoA-binding protein 2 (ACBP2) is a stress-responsive protein that is also important in embryogenesis. Here, we assign a role for ACBP2 in abscisic acid (ABA) signalling during seed germination, seedling development and the drought response. ACBP2 was induced by ABA and drought, and transgenic Arabidopsis overexpressing ACBP2 (ACBP2-OXs) showed increased sensitivity to ABA treatment during germination and seedling development. ACBP2-OXs also displayed improved drought tolerance and ABA-mediated reactive oxygen species (ROS) production in guard cells, thereby promoting stomatal closure, reducing water loss and enhancing drought tolerance. In contrast, acbp2 mutant plants showed decreased sensitivity to ABA in root development and were more sensitive to drought stress. RNA analyses revealed that ACBP2 overexpression up-regulated the expression of Respiratory Burst Oxidase Homolog D (AtrbohD) and AtrbohF, two NAD(P)H oxidases essential for ABA-mediated ROS production, whereas the expression of Hypersensitive to ABA1 (HAB1), an important negative regulator in ABA signalling, was down-regulated. In addition, transgenic plants expressing ACBP2pro:GUS showed beta-glucuronidase (GUS) staining in guard cells, confirming a role for ACBP2 at the stomata. These observations support a positive role for ACBP2 in promoting ABA signalling in germination, seedling development and the drought response.