Alfalfa (Medicago sativa L) is one of the leguminous forage crops which is grown most extensive and had high economic benefit around the world. However, many abiotic stresses such as high salinity, drought and low temperature severely reduce the growth and yield of alfalfa, and result in further degradation of vegetation and ecosystems. Therefore, better understanding the adaptation mechanism of alfalfa to various abiotic stresses and improving stress-tolerance by genetic engineering technology have an impo...