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Transgenic tobacco plants expressing a rice cysteine synthase gene are tolerant to toxic levels of cadmium
Authors:Emiko Harada   Yong-Eui Choi   Atsunari Tsuchisaka   Hitoshi Obata  Hiroshi Sano  
Affiliation:aResearch and Education Center for Genetic Information, Nara Institute of Science and Technology, Ikoma, Nara 630-0101, Japan;bFaculty of Bioresources, Mie University, Tsu, Mie 514-8507, Japan;cPresent address: Korea Ginseng Institute, Chung-Ang University, Ansung, Kyunggi 456-756, Korea;dPresent address: Plant Gene Expression Center, University of California, Berkeley, Albany, CA 94710, USA
Abstract:Plants tolerate heavy metals through sequestration with cysteine-rich peptides, phytochelatins. In this reaction, the rate limiting step is considered to be the supply of cysteine, which is synthesized by cysteine synthase (CS, EC 4.2.99.8) from hydrogen sulfide andO-acetylserine. In this study, we transformed tobacco (Nicotiana tabacum) plants withRCS1, a cytosolic cysteine synthase gene of rice (Oryza sativa), and examined their sensitivity to cadmium. The transgenic plants had up to 3-fold higher activity of cysteine synthase than wild-type plants. Upon exposure to cadmium, they exhibited obvious tolerance with much greater growth than wild-type plants. The level of phytochelatins in shoots was higher in transgenic than in wild-type plants after cadmium treatment, suggesting that cadmium was actively trapped by phytochelatins. However, the cadmium concentration per g fresh weight of whole transgenic plants was 20 percnt; lower than that of wild-type plants, suggesting cadmium to be either actively excreted or diluted by fast growth. Genetic analysis of progenies clearly showed segregation of cadmium tolerance, indicating that the trait resulted from the introduced gene. These results suggest that introduction of a cysteine synthase gene into tobacco plants resulted not only in high level production of sulfur-containing compounds that detoxify cadmium, but also in active elimination of cadmium toxicity from plant bodies.
Keywords:cadmium tolerance   cysteine synthase   Nicotiana tabacum   sulfur   thiol
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