MsPIP2;2, a novel aquaporin gene from Medicago sativa, confers salt tolerance in transgenic Arabidopsis

Aquaporins (AQPs) are channel proteins that facilitate water transport across cell membranes and play important roles in many biological processes. However, most AQP functions are still poorly understood in the plant kingdom. Here, MsPIP2;2 was isolated and identified from alfalfa (Medicago sativa). MsPIP2;2 was localized to the plasma membrane, and its expression was induced by salt and abscisic acid (ABA) treatment. Overexpression of MsPIP2;2 in Arabidopsis increased the seed germination rate, seedling root length, survival rate, proline content and antioxidant defence activity and decreased cell membrane damage and reactive oxygen species (ROS) accumulation compared to those in WT under salt stress. The salt tolerance of MsPIP2;2 was affected by Ca2+ and pH in transgenic Arabidopsis plants. MsP/P2;2-overexpressing plants maintained a better K+/Na+ ratio and higher Ca2+ content under salt stress. The higher K+/Na+ maintenance in transgenic plants was mainly achieved by increasing Na efflux and K retention in roots via regulating the expression of the related ion channel genes. Stress-responsive genes, including P5CS1, RD29A, DREB2 and KIN2, were upregulated in transgenic plants under salt stress. These results suggest that MsPIP2;2 confers salt tolerance by regulating antioxidant defence system-mediated ROS scavenging, K/Na ion homeostasis and stress-responsive gene expression in plants.