Production of Se-methylselenocysteine in transgenic plants expressing selenocysteine methyltransferase.
BACKGROUND
It has become increasingly evident that dietary Se plays a significant role in reducing the incidence of lung, colorectal and prostate cancer in humans. Different forms of Se vary in their chemopreventative efficacy, with Se-methylselenocysteine being one of the most potent. Interestingly, the Se accumulating plant Astragalus bisulcatus (Two-grooved poison vetch) contains up to 0.6% of its shoot dry weight as Se-methylselenocysteine. The ability of this Se accumulator to biosynthesize Se-methylselenocysteine provides a critical metabolic shunt that prevents selenocysteine and selenomethionine from entering the protein biosynthetic machinery. Such a metabolic shunt has been proposed to be vital for Se tolerance in A. bisulcatus. Utilization of this mechanism in other plants may provide a possible avenue for the genetic engineering of Se tolerance in plants ideally suited for the phytoremediation of Se contaminated land. Here, we describe the overexpression of a selenocysteine methyltransferase from A. bisulcatus to engineer Se-methylselenocysteine metabolism in the Se non-accumulator Arabidopsis thaliana (Thale cress).


RESULTS
By over producing the A. bisulcatus enzyme selenocysteine methyltransferase in A. thaliana, we have introduced a novel biosynthetic ability that allows the non-accumulator to accumulate Se-methylselenocysteine and gamma-glutamylmethylselenocysteine in shoots. The biosynthesis of Se-methylselenocysteine in A. thaliana also confers significantly increased selenite tolerance and foliar Se accumulation.


CONCLUSIONS
These results demonstrate the feasibility of developing transgenic plant-based production of Se-methylselenocysteine, as well as bioengineering selenite resistance in plants. Selenite resistance is the first step in engineering plants that are resistant to selenate, the predominant form of Se in the environment.
Ellis
Danielle R
DR
Center for Plant Environmental Stress Physiology, 1165 Horticulture Building, Purdue University, West Lafayette, IN 47907, USA. ellisd@purdue.edu
Sors
Thomas G
TG
Brunk
Dennis G
DG
Albrecht
Carrie
C
Orser
Cindy
C
Lahner
Brett
B
Wood
Karl V
KV
Harris
Hugh H
HH
Pickering
Ingrid J
IJ
Salt
David E
DE
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D027883:Astragalus Plant / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000031:analogs & derivatives* / Q000096:biosynthesis*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D013058:Mass Spectrometry / Q000379:methods; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism; D016566:Organoselenium Compounds; D018520:Plant Shoots / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D012643:Selenium / Q000032:analysis / Q000494:pharmacology; D017279:Selenocysteine / Q000031:analogs & derivatives; D018038:Sodium Selenite / Q000494:pharmacology
D016566:Organoselenium Compounds; D017279:Selenocysteine; D008780:Methyltransferases; C100751:selenocysteine methyltransferase; D012643:Selenium; D018038:Sodium Selenite; D003545:Cysteine; C002979:selenomethylselenocysteine