Plant Physiology Preview
Published on April 19, 2002; 10.1104/pp.001776
Received December 19, 2001
Returned for revision January 29, 2002
Accepted January 31, 2002
Molecular and Biochemical Characterization of a
Cold-Regulated Phosphoethanolamine
N-Methyltransferase from Wheat
Jean-Benoit Frenette Charron , Ghislain Breton , Jean Danyluk , Ingrid Muzac , Ragai K. Ibrahim , and Fathey Sarhan *
Département des Sciences Biologiques, Université du Québec à Montréal, Case Postale 8888, Succursale "Centre-Ville," Montreal, Québec, Canada H3C 3P8 (J.B.F.C., G.B., J.D., F.S.); and Plant Biochemistry Laboratory, Department of Biology, Concordia University, 1455 De Maisonneuve Boulevard West, Montréal, Québec, Canada H3G 1M8 (I.M., R.K.I.)
* Corresponding author; email: sarhan.fathey{at}uqam.ca.
A cDNA that encodes a methyltransferase (MT) was cloned from a cold-acclimated wheat (Triticum aestivum) cDNA library. Molecular analysis indicated that the enzyme WPEAMT (wheat phosphoethanolamine [P-EA] MT) is a bipartite protein with two separate sets of S-adenosyl-L-Met-binding domains, one close to the N-terminal end and the second close to the C-terminal end. The recombinant protein was found to catalyze the three sequential methylations of P-EA to form phosphocholine, a key precursor for the synthesis of phosphatidylcholine and glycine betaine in plants. Deletion and mutation analyses of the two S-adenosyl-L-Met-binding domains indicated that the N-terminal domain could perform the three N-methylation steps transforming P-EA to phosphocholine. This is in contrast to the MT from spinach (Spinacia oleracea), suggesting a different functional evolution for the monocot enzyme. The truncated C-terminal and the N-terminal mutated enzyme were only able to methylate phosphomonomethylethanolamine and phosphodimethylethanolamine, but not P-EA. This may suggest that the C-terminal part is involved in regulating the rate and the equilibrium of the three methylation steps. Northern and western analyses demonstrated that both Wpeamt transcript and the corresponding protein are up-regulated during cold acclimation. This accumulation was associated with an increase in enzyme activity, suggesting that the higher activity is due to de novo protein synthesis. The role of this enzyme during cold acclimation and the development of freezing tolerance are discussed.
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