Arabidopsis acyl-CoA-binding proteins ACBP1 and ACBP2 show different roles in freezing stress.

In our recent paper in Plant Physiology, we have reported that recombinant Arabidopsis thaliana acyl-CoA-binding protein ACBP1 binds phosphatidic acid (PA) in vitro and acbp1 mutant plants are conferred freezing tolerance. ACBP1-overexpressors were freezing sensitive and accumulated more PA, in contrast to acbp1 mutants which had reduced PA and elevated PC levels. Such changes in PC and PA were consistent with the expression of the mRNA encoding phospholipase Dα1 (PLDα1), a major enzyme that promotes the hydrolysis of PC to PA. In contrast, the expression of phospholipase Dδ (PLDδ), which plays a positive role in freezing tolerance, was up-regulated in acbp1 mutants and down-regulated in ACBP1-overexpressors. Reduced PLDα1 expression and decreased hydrolysis of PC to PA may have enhanced membrane stability in the acbp1 mutants. Given the PA- and acyl-CoA-binding abilities of ACBP1, the expression of PLDα1 and PLDδ could be subject to regulation by PA or acyl-CoA esters maintained by ACBP1, if ACBP1 were to resemble the yeast 10-kD ACBP in modulating gene expression during stress responses. Interestingly, another membrane-associated ACBP, ACBP2, which shows high (76.9%) conservation in amino acid homology to ACBP1, did not appear to be involved in the freezing response.