ARS | Publication request: SELENOCYSTEINE SE-METHYLTRANSFERASE AND SE-METHYLSELENOCYSTEINE SYNTHESIS IN BROCCOLI

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 16, 2005
Publication Date: July 16, 2005
Citation: Li, L., Lyi, S.M., Heller, L.I., Rutzke, M., Welch, R.M., Kochian, L.V. 2005. Selenocysteine se-methyltransferase and se-methylselenocysteine synthesis in broccoli. American Society of Plant Biologists Annual Meeting. P. 554.

Technical Abstract: Selenium is an essential micronutrient that has important health benefits beyond its essentiality for animals and humans. Se is considered to be an anti-cancer agent with Se-methylselenocysteine as one of the most effective chemopreventative compounds. Broccoli has the ability to accumulate high levels of selenium with majority of selenoamino acids as Se-methylselenocysteine. Thus it provides a good model to study the regulation of Se-methylselenocysteine accumulation in plants. We have cloned a cDNA encoding selenocysteine Se-methyltransferase, the key enzyme responsible for Se-methylselenocysteine formation from broccoli. This clone, designated as BoSMT, was functionally expressed in E. coli and its identity was confirmed by its substrate specificity in the methylation of selenocysteine. Studies of BoSMT gene expression and Se-methylselenocysteine accumulation in response to selenate, selenite, and sulfate treatments showed that the BoSMT transcript and Se-methylselenocysteine synthesis were significantly up-regulated in plants exposed to selenate but were low in plants supplied with selenite. Simultaneous treatment of selenate with selenite significantly reduced Se-methylselenocysteine production. In addition, high levels of sulfate reduced selenate uptake and resulted in a significant reduction of BoSMT mRNA level and Se-methylselenocysteine production. Our results indicate that Se-methylselenocysteine accumulation closely correlated with the BoSMT gene expression and the total Se status in tissues and provide information for maximizing the Se-methylselenocysteine production in broccoli. Overexpression and knock out of this gene in broccoli are being carried out to investigate the effect of alteration of SeMSC formation on the overall Se metabolism in the plant.