Abstract
We demonstrate that SULTR2;1/SULTR3;5 and SULTR4;1/SULTR4;2 are essential components that regulate the root-to-shoot transport of sulfate. SULTR2;1 and SULTR3;5 were both expressed in xylem parenchyma and pericycle cells in roots. In a yeast expressing system, SULTR3;5 accelerated sulfate uptake when co-expressed with SULTR2;1. In planta, the root-to-shoot transport of sulfate was restricted in the knockouts suggesting that SULTR2;1/SULTR3;5 provide maximum capacity of sulfate uptake. SULTR4 facilitates efflux of sulfate from the vacuoles and regulates internal distribution of sulfate. GFP fusion protein of SULTR4 was accumulated in the tonoplast and was localized in the pericycle and xylem parenchyma cells of roots and hypocotyls. Vacuoles isolated from the sultr4;1 sultr4;2 mutant showed excess accumulation of sulfate, which was substantially decreased by overexpression of SULTR4;1-GFP. In seedlings, supplied sulfate was retained in the root of the sultr4;1 sultr4;2 mutant, whereas decreased accumulation of sulfate was found in the root of SULTR4;1-GFP overexpressing plants.
