Over-expression of Medicago Acyl-CoA-binding 2 genes enhance salt and drought tolerance in Arabidopsis

Acyl-CoA-binding proteins (ACBPs) are mainly involved in acyl-CoA ester binding and trafficking in eukaryotic cells, and they function in lipid metabolism, membrane biosynthesis, cellular signaling, stress response, disease resistance, and other biological activities in plants. However, the roles of ACBP family members in Medicago remain unclear. In this study, a total of eight ACBP genes were identified in the genome of Medicago truncatula and Medicago sativa, and they were clustered into four sub-families (Class I-IV). Many cis-acting elements related to abiotic response were identified in the promoter region of these ACBP genes, in particular light-responsive elements. These ACBP genes exhibited distinct expression pattern in various tissues, and the expression level of MtACBP1/MsACBP1 and MtACBP2/MsACBP2 gene pairs were significantly increased under NaCl treatment. Subcellular localization analysis showed that MtACBP1/MsACBP1 and MtACBP2/MsACBP2 were localized in the endoplasmic reticulum of tobacco epidermal cells. Arabidopsis seedlings over-expressing MtACBP2/MsACBP2 displayed increased root length than the wild type under short light, Cu²⁺, ABA, PEG, and NaCl treatments. Over-expression of MtACBP2/MsACBP2 also significantly enhanced Arabidopsis tolerance under NaCl and PEG treatments in mature plants. Collectively, our study identified salt and drought responsive ACBP genes in Medicago and verified their functions in increasing resistance against salt and drought stresses.