Acyl-CoA-binding proteins mediate stress tolerance in plants

Abstract

Acyl-CoA-binding proteins (ACBPs) from the model plant Arabidopsis have been recently reported to mediate stress tolerance. The AtACBP protein family, which shows conservation at the acyl-CoAbinding domain, is encoded by six genes (AtACBP1 to AtACBP6) distributed across four classes in Arabidopsis thaliana. In the monocot, rice, six genes also encode ACBPs; however, their distribution across the four classes differs from Arabidopsis. Class I ACBPs consist of small (*10 kDa) proteins, Class II ACBPs comprise of proteins with ankyrin repeats, Class III ACBPs are large proteins[70 kDa and Class IV ACBPs contain kelch motifs. The ankyrin repeats of Class II ACBPs and the kelch motifs of Class IV ACBPs can potentially facilitate protein–protein interactions. Experiments using acbp mutants and transgenic Arabidopsis overexpressing AtACBPs have shown that these proteins can mediate various forms of stress tolerance. Sometimes AtACBPs work together with their protein partners which have also been identified as stress-related proteins. It has been demonstrated that AtACBP1- and AtACBP2-overexpressors can better withstand heavy metal/oxidative stress, AtACBP2-overexpressors tolerate drought stress, AtACBP3-overexpressors are protected against biotic stress and AtACBP6-overexpressors are freezing tolerant. The ability of the acyl-CoA-binding domain of recombinant AtACBPs in binding acyl-CoA esters has been tested using Lipidex assays as well as in isothermal titration calorimetry. The lipid-binding properties of AtACBPs provide explanation, to a certain extent, on their ability to better withstand stress treatments as lipids form important components of cellular membranes. Given that transgenic Arabidopsis overexpressing AtACBPs from the 35SCaMV promoter are conferred enhanced tolerance to various stresses, these proteins show promise for applications in agriculture and phytoremediation.