CAREER: Genetic Engineering Approaches for the in Vivo Study of Plant Metabolism of Selenium and Other Oxyanions

Colorado State University, Fort Collins CO

Investigators

Abstract

Selenium (Se) and sulfur metabolism in plants are thought to make use of the same enzymes. Previous studies by this investigator have shown that overexpression of ATP sulfurylase (involved in sulfate reduction) promotes selenate reduction and leads to accumulation of organic selenium. The goals of this project are to pinpoint more enzymes that are rate-controlling for Se fluxes in plants, and to clarify any involvement of the sulfate assimilation enzymes in uptake and reduction of the related elements tellurium, molybdenum, and tungsten. Selenocysteine appears to be a control point for Se allocation into proteins (toxic), into volatile forms, or into various accumulated forms. By overexpression of two enzymes, two different Se "sinks" will be created: one as low-toxic, insoluble elemental Se, the other as low-toxic volatile Se. The effects of these new Se sinks on the Se fluxes in the plant will be tested by measuring the forms of Se accumulated by the transgenic plants, and by measuring their Se tolerance, accumulation and volatilization. To study the effect of simultaneous overexpression of two enzymes in the pathway, different transgenics will be crossed and the Se fluxes in the double-transgenics studied. The other objective of this project is to test the hypothesis that the sulfate assimilation pathway is also involved in uptake and reduction of tellurate, molybdate, and tungstate. To this end, available transgenic Indian mustard plants (Brassica juncea) that overexpress enzymes involved in uptake and reduction of sulfate/selenate will be analyzed for tolerance and accumulation of tellurium, molybdenum and tungsten, and for the accumulated forms of these elements. The new information generated by these studies may be employed for the genetic manipulation of plants with altered metabolic properties, e.g. with enhanced or reduced trace element accumulation. This is of significance since these elements are of environmental and/or medical importance, as pollutants, micronutrients, etc. An essential part of this CAREER project will be the development of a graduate course on environmental cleanup using plants (phytoremediation) and a senior-level plant physiology course. These courses will be designed to make optimal use of multimedia and on-line resources.