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Abstract
Arsenic is a metalloid that occurs naturally at parts per million (ppm) levels in the earth's crust. Natural and human activities have contributed to arsenic mobilization and increased concentration in the environment, such that World Health Organization guidelines for arsenic levels in drinking water are exceeded at many locations, worldwide. This translates into an increased risk of arsenic-related illnesses for millions of people. Recent studies demonstrate that increasing thiol-sinks in transgenic plants by overexpressing the bacterial gamma-glutamylcysteine synthetase (ECS) gene results in a higher tolerance and accumulation of metals and metalloids such as cadmium, mercury, and arsenic. We used Agrobacterium-mediated transformation to genetically engineer eastern cottonwood with a bacterial ECS gene. Eastern cottonwood plants expressing ECS had elevated thiol group levels, consistent with increased ECS activity. In addition, these ECS-expressing plants had enhanced growth on levels of arsenate toxic to control plants in vitro. Furthermore, roots of ECS-expressing plants accumulated significantly more arsenic than control roots (approximately twice as much), while shoots accumulated significantly less arsenic than control shoots (approximately two-thirds as much). We discuss potential mechanisms for shifting the balance of plant arsenic distribution from root accumulation to shoot accumulation, as it pertains to arsenic phytoremediation.
ACKNOWLEDGMENTS
We thank Xiuqin Xia, Taryn Kormanik, Andrew Heaton, Yujing Li, Aaron Smith, and Rebecca Auxier for technical assistance. This research was supported by funds allocated to the Warnell School of Forestry and Natural Resources by the University of Georgia Foundation, by U.S. Department of Energy Environmental Management Sciences grant DEG0796ER20257 (to R.B.M.), and by National Research Service Award 1F32ES015414-01 (to M.S.L.).