Abstract
An essential life process for plants is the assimilation of sulfur, which is available to plant roots as sulfate that is taken up into cells where it is reduced and assimilated. Plants can sense the availability of sulfur, but the sensor has not been identified. Two Arabidopsis thaliana mutants were isolated (termed sel1-15 and sel1-16), that show increased expression of a sulfur-deficiency-activated gene beta glucosidase 28 (BGLU28) when grown on medium with high sulfate content (Zhang et al. 2014). The mutants are missense alleles of SULTR1;2 encoding a high affinity sulfate transporter. Although the mutants are defective in sulfate transport they show higher expression of BGLU28 and other sulfur-deficiency-activated genes even when they are treated with a very high dose of sulfate such that the intracellular concentration of sulfate and its metabolite glutathione (GSH) are identical to wild type. The reduced sensitivity to inhibition of gene expression is also observed in sel1 mutants fed with the sulfur assimilation products cysteine and GSH. The results suggest that SULTR1; 2 may have a second role in addition to its known function as a high affinity sulfate transporter. It may also have a regulatory role in response to sulfur nutrient status.