Abstract
SULTR1;1 and SULTR1;2 are high-affinity sulfate transporters localizing at the epidermis and cortex of Arabidopsis roots. The double knockout mutant, sultr1;1 sultr1;2, was unable to grow on a low-sulfate medium containing 15 μM sulfate; however the growth was partially rescued by the addition of 1.5 mM sulfate to the medium, suggesting that the sultr1;1 sultr1;2 mutant may utilize a low-affinity transport system for sulfate uptake. The cell type-specificities of all sulfate transporters were analyzed by expressing the reporter fusion gene constructs in Arabidopsis. Among them, SULTR3;4 was suggested to localize at the endodermis and phloem of roots. In yeast, SULTR3;4 mediated sulfate import, but showed a linear increase of sulfate uptake activity when the extracellular concentration of sulfate was elevated up to 1 mM. In addition, SULTR3;4 mRNA was accumulated significantly in the roots of sultr1;1 sultr1;2 mutant, suggesting its contribution in compensating the high-affinity uptake of sulfate in Arabidopsis.
