Abstract
SULTR1;1 and SULTR1;2 encode high-affinity sulfate transporters co-localizing at epidermis and cortex of Arabidopsis roots during sulfur-starvation (-S). The double mutant, sultr1;1 sultr1;2, was impaired of high-affinity sulfate uptake activity, causing severe growth defects.The wild-type plants showed significantly higher level of sulfate uptake as compared with the sum of uptake rates independently measured for sultr1;1 and sultr1;2 single mutants, suggesting that co-expression of SULTR1;1 and SULTR1;2 on -S may synergistically facilitate the acquisition of sulfate. Co-expression of SULTR1;1 and SULTR1;2 also resulted in synergistically increasing sulfate transport activities in yeast; however this positive regulatory effect was repressed by the supply of organic sulfur. Physical interaction between SULTR1;1 and SULTR1;2 was demonstrated by co-purification of their complex. SULTR1;1-SULTR1;2 complex was stably formed both under +S and -S conditions and functioned as a regulatory unit of sulfate transport, optimizing sulfate uptake capacity in response to the change in sulfur conditions.
