Constitutive expression of a high-affinity sulfate transporter in Indian mustard affects metal tolerance and accumulation

The Stylosanthes hamata SHST1 gene encodes a high-affinity sulfate transporter located in the plasma membrane. In this study the S. hamata SHST1 gene was constitutively expressed in Indian mustard Brassica juncea (L.) Czern.] to investigate its importance for tolerance and accumulation of various oxyanions that may be transported by SHST1 and for cadmium, which is detoxified by sulfur-rich compounds. The transgenic SHST1 lines SHST1-12C and SHST1-4C were compared with wild-type Indian mustard for tolerance and accumulation of arsenate, chromate, tungstate, vanadate, and cadmium. As seedlings the SHST1 plants accumulated significantly more Cd and W, and somewhat more Cr and V. The SHST1 seedlings were less tolerant to Cd, Mo, and V compared to wild-type plants. Mature SHST1 plants were less tolerant than wild-type plants to Cd and Cr. SHST1 plants accumulated significantly more Cd, Cr, and W in their roots than wild-type plants. In their shoots they accumulated significantly more Cr and somewhat more V and W. Shoot Cd accumulation was significantly lower than in wild-type, and As levels were somewhat reduced. Compared to wild-type plants, sulfur accumulation was enhanced in roots of SHST1 plants but not in shoots. Together these results suggest that SHST1 can facilitate uptake of other oxyanions in addition to sulfate and that SHST1 mediates uptake in roots rather than root-to-shoot translocation. Since SHST1 overexpression led to enhanced accumulation of Cr, Cd, V, and W, this approach shows some potential for phytoremediation, especially if it could be combined with the expression of a gene that confers enhanced metal translocation or tolerance.