Calmodulin-like gene MtCML40 is involved in salt tolerance by regulating MtHKTs transporters in Medicago truncatula

•A gene encoding a calmodulin-like proteins from legume model plant Medicago truncatula was isolated and functionally characterized.•Expression of MtCML40 was up-regulated by salt, cold and osmotic stress as well as ABA treatment, suggesting a role of MtCML40 in abiotic stress.•Overexpression of MtCML40 led to greater accumulation of Na+ in shoots, thus rendering the transgenic M. truncatula seedlings more sensitive to salt stress.•Overexpression of MtCML40 down-regulated MtHKT1;1 and MtHKT1;2 that encoded proteins associated with removal of Na+ from shoots.