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MetaCyc Pathway: cis-zeatin biosynthesis
Inferred from experiment

Pathway diagram: cis-zeatin biosynthesis

This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Synonyms: cis-cytokinins biosynthesis, tRNA-dependent cytokinin biosynthesis

Superclasses: BiosynthesisHormones BiosynthesisPlant Hormones BiosynthesisCytokinins Biosynthesis

Some taxa known to possess this pathway include : Arabidopsis thaliana col

Expected Taxonomic Range: Embryophyta

General Background

Cytokinins have profound physiological roles in plants, e.g. promotion of cell division, release of lateral buds from apical dominance, and delay of senescence. The biological activity of cytokinins have long been studied. However, the uncertainty persists as to how different classes of cytokinins play different roles in plant development. The main form of cytokinin in plant cytoplasmic prenylated-tRNAs is cis-zeatin [Taller]. Although cis-zeatins can sometimes be found in plants in the tRNA-free form [Nicander95], and even be the predominant form of cytokinins in the species Cicer arietinum [Emery98], the physiological relevance of cis-hydroxylated cytokinins remains unclear. Indeed, in plants, it has been shown that cis-cytokinins have only low activity. The most biologically-relevant cytokinins have a trans-hydroxylated N6 side-chain.

With the uncovered existence of a zeatin cis-trans isomerase [Bassil93] came the postulate that cis-type cytokinins could contribute to the synthesis of trans-type cytokinins. This possibility is however thought to be improbable [Kasahara04]. In Arabidopsis thaliana the trans-type cytokinins are synthesized in plastids from DMAPP precursors originating from the plastidic methylerythritol phosphate pathway I. The cis-type cytokinins, on the other hand, are synthesized through prenylation of tRNA molecules in the cytosol using DMAPP precursors originating from the cytosolic mevalonate pathway.

About This Pathway

So far only one enzyme has been characterized for the tRNA-dependent cytokinin biosynthesis in Arabidopsis. The tRNA isopentenyltransferase activity of the enzyme encoded by IPT2 was demonstrated by heterologous expression of the gene in yeast [Golovko02]. To date no enzyme able to catalyze the stereo-specific hydroxylation of the isoprene side chain has been found and it is not known whether this hydroxylation step occurs after pentenylation of the tRNA adenine using DMAPP as a substrate or whether an hydroxylated analogue of DMAPP could give cis-zeatin-tRNA directly [Golovko02].

Unification Links: AraCyc:PWY-2781


Bassil93: Bassil NV, Mok D, Mok MC (1993). "Partial Purification of a cis-trans-Isomerase of Zeatin from Immature Seed of Phaseolus vulgaris L." Plant Physiol 102(3);867-872. PMID: 12231873

Emery98: Emery RJ, Leport L, Barton JE, Turner NC, Atkins CA (1998). "cis-isomers of cytokinins predominate in chickpea seeds throughout their development." Plant Physiol 117(4);1515-23. PMID: 9701607

Golovko02: Golovko A, Sitbon F, Tillberg E, Nicander B (2002). "Identification of a tRNA isopentenyltransferase gene from Arabidopsis thaliana." Plant Mol Biol 49(2);161-9. PMID: 11999372

Kasahara04: Kasahara H, Takei K, Ueda N, Hishiyama S, Yamaya T, Kamiya Y, Yamaguchi S, Sakakibara H (2004). "Distinct isoprenoid origins of cis- and trans-zeatin biosyntheses in Arabidopsis." J Biol Chem 279(14);14049-54. PMID: 14726522

Nicander95: Nicander B, Bjorkman PO, Tillberg E (1995). "Identification of an N-Glucoside of cis-Zeatin from Potato Tuber Sprouts." Plant Physiol 109(2);513-516. PMID: 12228609

Taller: Taller B.J.. "Distribution, biosynthesis, and function of cytokinins in tRNA." Cytokinins: Chemistry, Activity and Function, CRC Press, Boca Raton, FL, pp101-112.

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

BRENDA14: BRENDA team (2014). Imported from BRENDA version existing on Aug 2014.

Caillet88: Caillet J, Droogmans L (1988). "Molecular cloning of the Escherichia coli miaA gene involved in the formation of delta 2-isopentenyl adenosine in tRNA." J Bacteriol 170(9);4147-52. PMID: 3045085

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Leung97: Leung HC, Chen Y, Winkler ME (1997). "Regulation of substrate recognition by the MiaA tRNA prenyltransferase modification enzyme of Escherichia coli K-12." J Biol Chem 272(20);13073-83. PMID: 9148919

Moore00: Moore JA, Mathis JR, Poulter CD (2000). "Escherichia coli dimethylallyl diphosphate:tRNA dimethylallyltransferase: pre-steady-state kinetic studies." Biochim Biophys Acta 1479(1-2);166-74. PMID: 11004538

Moore97: Moore JA, Poulter CD (1997). "Escherichia coli dimethylallyl diphosphate:tRNA dimethylallyltransferase: a binding mechanism for recombinant enzyme." Biochemistry 36(3);604-14. PMID: 9012675

Rosenbaum72: Rosenbaum N, Gefter ML (1972). "Delta 2 -isopentenylpyrophosphate: transfer ribonucleic acid 2 -isopentenyltransferase from Escherichia coli. Purification and properties of the enzyme." J Biol Chem 247(18);5675-80. PMID: 4341485

Soderberg01: Soderberg T, Poulter CD (2001). "Escherichia coli dimethylallyl diphosphate:tRNA dimethylallyltransferase: site-directed mutagenesis of highly conserved residues." Biochemistry 40(6);1734-40. PMID: 11327834

Takei01: Takei K, Sakakibara H, Sugiyama T (2001). "Identification of genes encoding adenylate isopentenyltransferase, a cytokinin biosynthesis enzyme, in Arabidopsis thaliana." J Biol Chem 276(28);26405-10. PMID: 11313355

Takei04: Takei K, Yamaya T, Sakakibara H (2004). "Arabidopsis CYP735A1 and CYP735A2 encode cytokinin hydroxylases that catalyze the biosynthesis of trans-Zeatin." J Biol Chem 279(40);41866-72. PMID: 15280363

Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by Pathway Tools version 19.5 (software by SRI International) on Sat Apr 30, 2016, biocyc11.