title: Daphnetin methylation stabilizes the activity of phosphoribulokinase in wheat during cold acclimation.
abstract: The methylation of daphnetin (7,8-dihydroxycoumarin) to its 8-methyl derivative is catalyzed by a wheat (Triticum aestivum L.) O-methyltransferase (TaOMT1). This enzyme is regulated by cold and photosystem II excitation pressure (plastid redox state). Here, we investigated the biological significance of this methylation and its potential role in modulating the activity of kinases in wheat. To identify the potential kinases that may interact with daphnetin in wheat, the soluble protein extract from aerial parts of cold-acclimated wheat was purified by DEAE-cellulose separation and affinity chromatography on a daphnetin derivative (7,8-dihydroxy-4-coumarin acetic acid)-EAH sepharose column. Mass spectrometric analysis indicated that wheat phosphoribulokinase (TaPRK) is the major kinase that binds to daphnetin. This TaPRK plays an important role in regulating the flow of carbon through the Calvin cycle, by catalyzing the final step in the regeneration of ribulose 1,5-bisphosphate from ribulose-5-phosphate (Ru5P) and ATP. The activities of TaPRK, endogenous or recombinant, are inhibited by daphnetin in a specific and dose-dependent manner, but not by its monomethyl derivative (7-methyl, 8-hydroxycoumarin). Furthermore, HPLC-MS analysis of wheat extracts reveals that 7,8-dimethoxycoumarin is more abundant than its monomethyl derivative. The results also show that cold acclimation does not alter the level of TaPRK mRNA or its enzyme activity, and thus ensures the stable generation of ribulose 1,5-biphosphate.
authors: Département des Sciences biologiques, Université du Québec à Montréal, C.P 8888, Succ. Centre-Ville, Montréal, QC H2X 3X8, Canada.
authors: Khalil
authors: K
authors: Kane
authors: Amira
authors: A
authors: Moheb
authors: Yukihara
authors: Y
authors: Fukushi
authors: René
authors: R
authors: Roy
authors: Norman P A
authors: NP
authors: Hüner
authors: Ragai K
authors: RK
authors: Ibrahim
authors: Fathey
authors: F
authors: Sarhan
mesh_terms: D000064:Acclimatization; D003080:Cold Temperature; D003374:Coumarins / Q000378:metabolism / Q000494:pharmacology; D013058:Mass Spectrometry; D008745:Methylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012274:Ribulosephosphates / Q000235:genetics / Q000378:metabolism; D014908:Triticum / Q000201:enzymology* / Q000378:metabolism; D014468:Umbelliferones / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D003374:Coumarins; D012333:RNA, Messenger; D012274:Ribulosephosphates; D014468:Umbelliferones; C001933:ribulose-1,5 diphosphate; C049536:8-hydroxycoumarin; D017853:Phosphotransferases (Alcohol Group Acceptor); C022390:phosphoribulokinase; C039952:daphnetin