Constitutive Expression of a High-Affinity Sulfate Transporter in Indian Mustard Affects Metal Tolerance and Accumulation
Stormy Dawn Lindblom, Salah Abdel-Ghany, Brady R. Hanson, Seongbin Hwang, Norman Terry, and Elizabeth A. H. Pilon-Smits* Reproduced from Journal of Environmental Quality. Published by ASA, CSSA, and SSSA. All copyrights reserved. ABSTRACTThe 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-richcompounds. 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 lesstolerant than wild-type plants to Cd and Cr. SHST1 plants accumulated significantly more Cd, Cr, and W in their roots than wildtype 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 ofSHST1 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 theexpression of a gene that confers enhanced metal translocation or tolerance.
and metalloids are increasingly released into the environment by human activities such as industry, mining operations, use of ammunition, traffic, and agriculture, resulting in contamination that threatens natural ecosystems and human well-being (Lantzy and Mackenzie, 1979; Nriagu, 1979; Ross, 1994). A relatively newtechnology for environmental cleanup is phytoremediation, which uses plants and their associated microbes to extract, degrade, or stabilize pollutants. Metal extraction into harvestable plant tissues may be further enhanced by genetic engineering. Already, transgenic plants with enhanced metal tolerance and accumulation have been created via (over)expression of metal transporter proteins(Samuelsen et al., 1998; Arazi et al., 1999; Van
S.D. Lindblom, S. Abdel-Ghany, B.R. Hanson, E.A.H. Pilon-Smits, Biology Department, Colorado State University, Anatomy/Zoology Building, Fort Collins, CO 80523. S. Hwang, Department of Molecular Biology, Sejong University, Kwangjin-Gu Kunja-Dong 98, Seoul 143747, Korea. N. Terry, Department of Plant and Microbial Biology, University ofCalifornia at Berkeley, 111 Koshland Hall, Berkeley, CA 94720. Received 7 Apr. 2005. *Corresponding author (epsmits@lamar. colostate.edu). Published in J. Environ. Qual. 35:726–733 (2006). Technical Reports: Bioremediation and Biodegradation doi:10.2134/jeq2005.0119 ª ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA
der Zaal et al., 1999; Curie et al., 2000; Hirschi et al., 2000). The purposeof this study was to test the role of the sulfate transporter in tolerance to and accumulation of various metal(loid)s. Sulfur is an essential element for plant primary metabolism as a structural component of proteins and lipids, antioxidants, regulatory molecules, metal-binding molecules, and cofactors and coenzymes. Plants take up sulfur primarily in the form of sulfate. After uptake most...