Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2009
Publication Date: 7/22/2009
Citation: Li, L., Zhou, X., Yang, Y., Thannhauser, T.W., Kochian, L.V. 2009. A broccoli COQ5 methyltransferase involved in ubiquinone biosynthesis mediates selenium volatilization. Meeting Abstract.
Technical Abstract: Biological selenium volatilization, which converts selenium into volatile compounds, provides an important means for the cleanup of selenium polluted environments. To identify novel genes whose products are involved in plant selenium volatilization, a broccoli cDNA encoding COQ5 methyltransferase (BoCOQ5-2) in ubiquinone biosynthetic pathway was isolated. Its function was authenticated by complementing a yeast coq5 mutant and by detecting increased cellular ubiquinone levels in BoCOQ5-2 transformed bacteria. Proteomic analysis of differentially expressed proteins between bacteria expressing BoCOQ5-2 and those containing the empty vector further supported its functional role in ubiquinone biosynthesis. BoCOQ5-2 was found to specifically promote selenium volatilization but not sulfur emission in both bacteria and transgenic Arabidopsis plants. Bacteria expressing BoCOQ5-2 produced an over 160-fold increase in volatile selenium compounds when they were exposed to selenate. Consequently, the BoCOQ5-2 transformed bacteria had dramatically enhanced tolerance to selenate and selenite, and contained reduced levels of total selenium in the cells. Transgenic Arabidopsis expressing BoCOQ5-2 volatilized three times more Se than the vector only control plants when treated with selenite and exhibited significant tolerance to selenium. BoCOQ5-2 represents the first plant enzyme that is not known to be directly involved in sulfur/selenium metabolism, yet mediates selenium volatilization. This discovery opens up new prospective regarding our understanding of the complete metabolism of selenium and could lead to ways to modify selenium accumulator plants with increased efficiency in the phytoremediation of selenium contaminated environments.