Overexpression of LjPLT3 Enhances Salt Tolerance in Lotus japonicus .

Intracellular polyols are used as osmoprotectants by many plants under environmental stress. However, few studies have shown the role of polyol transporters in the tolerance of plants to abiotic stresses. Here, we describe the expression characteristics and potential functions of polyol transporter LjPLT3 under salt stress. Using promoter-reporter gene plants showed that was expressed in the vascular tissue of leaf, stem, root, and nodule. The expression was also induced by NaCl treatment. Overexpression of in modified the growth rate and saline tolerance of the transgenic plants. The seedlings displayed reduced plant height under both nitrogen-sufficient and symbiotic nitrogen fixation conditions when 4 weeks old. The nodule number of plants was reduced by 6.7-27.4% when 4 weeks old. After exposure to a NaCl treatment in Petri dishes for 10 days, seedlings had a higher chlorophyll concentration, fresh weight, and survival rate than those in the wild type. For symbiotic nitrogen fixation conditions, the decrease in nitrogenase activity of plants was slower than that of the wild type after salt treatment. Compared to the wild type, both the accumulation of small organic molecules and the activity of antioxidant enzymes were higher under salt stress. Considering the concentration of lower reactive oxygen species (ROS) in transgenic lines, we speculate that overexpression of in might improve the ROS scavenging system to alleviate the oxidative damage caused by salt stress, thereby increasing plant salinity tolerance. Our results will direct the breeding of forage legumes in saline land and also provide an opportunity for the improvement of poor and saline soils.