Tomato Silicon Influx Transporter SlLsi1 Participates in Selenite Uptake and Selenomethionine Transport and Improves Fruit Quality

The molecular mechanism of plant selenium (Se) uptake is poorly understood. Here, we demonstrated that the silicon (Si) influx transporter Lsi1 mediates selenite uptake and selenomethionine transport in tomato. SlLsi1 overexpression increased the selenite uptake rate and Se concentrations in both shoots and xylem sap, while it decreased the symplastic Se concentration and the concentrations of different Se species in roots. SlLsi1 overexpression increased the Se concentrations in the xylem sap and shoots when plants were supplied with selenomethionine. SlLsi1 demonstrated selenite influx transport activity and selenomethionine efflux transport activity when expressed in yeast. Si did not affect selenite uptake in tomato or yeast cells, but solution pH affected the uptake, with uptake being higher at a lower pH. SlLsi1 overexpression promoted Se accumulation in tomato fruits with added selenite and improved yield and nutritional quality. These results suggest that SlLsi1 participates in selenite uptake and selenomethionine transport in tomatoes.