Cytokinin (CK) N-glucosides are the most abundant group of CK metabolites in many species; however, their physiological role in planta was for a long time perceived as irreversible storage CK forms only. Recently, a comprehensive screen showed that only vascular plants form CK N-glucosides in contrast to mosses, algae, and fungi. The formation of CK N-glucosides as biologically inactive CK conjugates thus represents an evolutionarily young mechanism for deactivation of CK bases. Even though CK N-glucosides are not biologically active themselves due to their inability to activate the CK perception system, new data on CK N-glucoside metabolism show that trans-zeatin (tZ) N7- and N9-glucosides are metabolized in vivo, efficiently releasing free CK bases that are most probably responsible for the biological activities observed in a number of bioassays. Moreover, CK N-glucosides' subcellular localization as well as their abundance in xylem both point to their possible plasma membrane transport and indicate a role also as CK transport forms. Identification of the enzyme(s) responsible for the hydrolysis of tZ N7- and N9-glucosides, as well as the discovery of putative CK N-glucoside plasma membrane transporter, would unveil important parts of the overall picture of CK metabolic interconversions and their physiological importance.

Institute of Experimental Botany of the Czech Academy of Sciences Prague Czechia

Zobrazit více v PubMed

Benková E., Witters E., Van Dongen W., Kolár J., Motyka V., Brzobohatý B., et al. (1999). Cytokinins in tobacco and wheat chloroplasts. Occurrence and changes due to light/dark treatment. Plant Physiol. 121 245–252. 10.1104/pp.121.1.245 PubMed DOI PMC

Blagoeva E., Dobrev P., I, Malbeck J., Motyka V., Strnad M., Hanus̆ J., et al. (2004). Cytokinin N-glucosylation inhibitors suppress deactivation of exogenous cytokinins in radish, but their effect on active endogenous cytokinins is counteracted by other regulatory mechanisms. Physiol. Plantarum 121 215–222. 10.1111/j.1399-3054.2004.00320.x PubMed DOI

Bowles D., Lim E., Poppenberger B., Vaistij E. (2006). Glycosyltransferases of lipophilic small molecules. Annu. Rev. Plant Biol. 57 567–597. 10.1146/annurev.arplant.57.032905.105429 PubMed DOI

Brzobohatý B., Moore I., Kristoffersen P., Bako L., Campos N., Schell J., et al. (1993). Release of active cytokinin by a beta-glucosidase localized to the maize root meristem. Science 262 1051–1054. 10.1126/SCIENCE.8235622 PubMed DOI

Drábková L. Z., Dobrev P. I., Motyka V. (2015). Phytohormone profiling across the bryophytes. PLoS One 10:e0125411. 10.1371/journal.pone.0125411 PubMed DOI PMC

Entsch B., Letham D. S. (1979). Enzymic glucosylation of the cytokinin, 6-benzylaminopurine. Plant Sci. Lett. 14 205–212. 10.1016/0304-4211(79)90061-0 DOI

Entsch B., Parker C. W., Letham D. S., Summons R. E. (1979). Preparation and characterization, using high-performance liquid chromatography, of an enzyme forming glucosides of cytokinins. Biochim. Biophys. Acta Enzymol. 570 124–139. 10.1016/0005-2744(79)90207-9 PubMed DOI

Filipi T., Mazura P., Janda L., Kiran N. S., Brzobohatý B. (2012). Engineering the cytokinin-glucoside specificity of the maize β-d-glucosidase Zm-p60.1 using site-directed random mutagenesis. Phytochemistry 74 40–48. 10.1016/j.phytochem.2011.10.008 PubMed DOI

Fox J., Cornette J., Deleuze G., Dyson W., Giersak C., Niu P., et al. (1973). The formation, isolation, and biological activity of a cytokinin 7-glucoside. Plant Physiol. 52 627–632. 10.1104/pp.52.6.627 PubMed DOI PMC

Gajdošová S., Spíchal L., Kamínek M., Hoyerová K., Novák O., Dobrev P. I., et al. (2011). Distribution, biological activities, metabolism, and the conceivable function of cis-zeatin-type cytokinins in plants. J. Exp. Bot. 62 2827–2840. 10.1093/jxb/erq457 PubMed DOI

Galichet A., Hoyerová K., Kamínek M., Gruissem W. (2008). Farnesylation directs AtIPT3 subcellular localization and modulates cytokinin biosynthesis in Arabidopsis. Plant Physiol. 146 1155–1164. 10.1104/pp.107.107425 PubMed DOI PMC

Galuszka P., Frébort I., Šebela M., Sauer P., Jacobsen S., Peč P. (2001). Cytokinin oxidase or dehydrogenase? Eur. J. Biochem. 268 450–461. PubMed

Galuszka P., Popelková H., Werner T., Frébortová J., Pospíšilová H., Mik V., et al. (2007). Biochemical characterization of cytokinin oxidases/dehydrogenases from Arabidopsis thaliana expressed in Nicotiana tabacum L. J. Plant Growth Regul. 26 255–267. 10.1007/s00344-007-9008-5 DOI

Hluska T., Dobrev P. I., Tarkowská D., Frébortová J., Zalabák D., Kopečný D., et al. (2016). Cytokinin metabolism in maize: novel evidence of cytokinin abundance, interconversions and formation of a new trans-zeatin metabolic product with a weak anticytokinin activity. Plant Sci. 247 127–137. 10.1016/j.plantsci.2016.03.014 PubMed DOI

Hošek P., Hoyerová K., Kiran N. S., Dobrev P. I., Zahajská L., Filepová R., et al. (2020). Distinct metabolism of N-glucosides of isopentenyladenine and trans-zeatin determines cytokinin metabolic spectrum in Arabidopsis. New Phytol. 225 2423–2438. 10.1111/nph.16310 PubMed DOI

Hothorn M., Dabi T., Chory J., Jolla L., Jolla L. (2011). Structural basis for cytokinin recognition by Arabidopsis thaliana histidine kinase 4. Nat. Chem. Biol. 7 766–768. 10.1038/nchembio.667.Structural PubMed DOI PMC

Hou B., Lim E. K., Higgins G. S., Bowles D. J. (2004). N-glucosylation of cytokinins by glycosyltransferases of Arabidopsis thaliana. J. Biol. Chem. 279 47822–47832. 10.1074/jbc.M409569200 PubMed DOI

Jiskrová E., Novák O., Pospíšilová H., Holubová K., Karády M., Galuszka P., et al. (2016). Extra- and intracellular distribution of cytokinins in the leaves of monocots and dicots. N. Biotechnol. 33 735–742. 10.1016/j.nbt.2015.12.010 PubMed DOI

Kasahara H., Takei K., Ueda N., Hishiyama S., Yamaya T., Kamiya Y., et al. (2004). Distinct isoprenoid origins of cis- and trans-zeatin biosyntheses in Arabidopsis. J. Biol. Chem. 279 14049–14054. 10.1074/jbc.M314195200 PubMed DOI

Kieber J. J., Schaller G. E. (2018). Cytokinin signaling in plant development. Development 145:dev149344. 10.1242/dev.149344 PubMed DOI

Kowalska M., Galuszka P., Frébortová J., Šebela M., Béres T., Hluska T., et al. (2010). Vacuolar and cytosolic cytokinin dehydrogenases of Arabidopsis thaliana: heterologous expression, purification and properties. Phytochemistry 71 1970–1978. 10.1016/j.phytochem.2010.08.013 PubMed DOI

Kuroha T., Tokunaga H., Kojima M., Ueda N., Ishida T., Nagawa S., et al. (2009). Functional analyses of LONELY GUY cytokinin-activating enzymes reveal the importance of the direct activation pathway in Arabidopsis. Plant Cell 21 3152–3169. 10.1105/tpc.109.068676 PubMed DOI PMC

Laloue M., Terrine C., Guern J., Laloue M., Terrine C., Guern J. (1977). Cytokinins: metabolism and biological activity of N6- (A12- Isopentenyl) adenosine and N6- (42-Isopentenyl) adenine in tobacco cells and callus1. Plant Physiol. 59 478–483. 10.1104/pp.59.3.478 PubMed DOI PMC

Lizák B., Csala M., Benedetti A., Bánhegyi G. (2008). The translocon and the non-specific transport of small molecules in the endoplasmic reticulum (Review). Mol. Membr. Biol. 25 95–101. 10.1080/09687680701670481 PubMed DOI

Lomin S. N., Krivosheev D. M., Steklov M. Y., Arkhipov D. V., Osolodkin D. I., Schmülling T., et al. (2015). Plant membrane assays with cytokinin receptors underpin the unique role of free cytokinin bases as biologically active ligands. J. Exp. Bot. 66 1851–1863. 10.1093/jxb/eru522 PubMed DOI PMC

Mameaux S., Cockram J., Thiel T., Steuernagel B., Stein N., Taudien S., et al. (2012). Molecular, phylogenetic and comparative genomic analysis of the cytokinin oxidase/dehydrogenase gene family in the Poaceae. Plant Biotechnol. J. 10 67–82. 10.1111/j.1467-7652.2011.00645.x PubMed DOI

Moffatt B. A., Wang L., Allen M. S., Stevens Y. Y., Qin W., Snider J., et al. (2000). Adenosine kinase of Arabidopsis. Kinetic properties and gene expression. Plant Physiol. 124 1775–1785. 10.1104/pp.124.4.1775 PubMed DOI PMC

Morrison E. N., Knowles S., Hayward A., Thorn R. G., Saville B. J., Emery R. J. N. (2015). Detection of phytohormones in temperate forest fungi predicts consistent abscisic acid production and a common pathway for cytokinin biosynthesis. Mycologia 107 245–257. 10.3852/14-157 PubMed DOI

Paces V., Werstiuk E. V. A., Hall R. H. (1971). Conversion of N6-(Δ2-Isopentenyl)adenosine to adenosine by enzyme activity in tobacco tissue. Plant Physiol. 48 775–778. 10.1104/pp.48.6.775 PubMed DOI PMC

Parker C., Letham D. S., Cowley D. E., MacLeod J. K. (1972). Raphanatin, an unusual purine derivative and a metabolite of zeatin. Biochem. Biophys. Res. Commun. 49 460–466. 10.1016/0006-291X(72)90433-0 PubMed DOI

Podlešáková K., Zalabák D., Èudejková M., Plíhal O., Szüèová L., Doležal K., et al. (2012). Novel cytokinin derivatives do not show negative effects on root growth and proliferation in submicromolar range. PLoS One 7:e39293. 10.1371/journal.pone.0039293 PubMed DOI PMC

Romanov G. A., Lomin S. N., Schmülling T. (2018). Cytokinin signaling: from the ER or from the PM? That is the question! New Phytol. 18 41–53. 10.1111/nph.14991 PubMed DOI

Šimura J., Antoniadi I., Široká J., Tarkowská D., Strnad M., Ljung K., et al. (2018). Plant hormonomics: multiple phytohormone profiling by targeted metabolomics. Plant Physiol. 177 476–489. 10.1104/pp.18.00293 PubMed DOI PMC

Šmehilová M., Dobrůšková J., Novák O., Takáč T., Galuszka P. (2016). Cytokinin-specific Glycosyltransferases possess different roles in cytokinin homeostasis maintenance. Front. Plant Sci. 7:1264. 10.3389/fpls.2016.01264 PubMed DOI PMC

Spíchal L., Rakova N. Y., Riefler M., Mizuno T., Romanov G. A., Strnad M., et al. (2004). Two cytokinin receptors of Arabidopsis thaliana, CRE1/AHK4 and AHK3, Differ in their ligand specificity in a bacterial assay. Plant Cell Physiol. 45 1299–1305. 10.1093/pcp/pch132 PubMed DOI

Stirk W. A., Ördög V., Novák O., Rolčík J., Strnad M., Bálint P., et al. (2013). Auxin and cytokinin relationships in 24 microalgal strains. J. Phycol. 49 459–467. 10.1111/jpy.12061 PubMed DOI

Takei K., Ueda N., Aoki K., Kuromori T., Hirayama T., Shinozaki K., et al. (2004). AtIPT3 is a key determinant of nitrate-dependent cytokinin biosynthesis in Arabidopsis. Plant Cell Physiol. 45 1053–1062. 10.1093/pcp/pch119 PubMed DOI

Trdá L., Barešová M., Šašek V., Nováková M., Zahajská L., Dobrev P. I., et al. (2017). Cytokinin metabolism of pathogenic fungus Leptosphaeria maculans involves isopentenyltransferase, adenosine kinase and cytokinin oxidase/dehydrogenase. Front. Microbiol. 8:e01374. 10.3389/fmicb.2017.01374 PubMed DOI PMC

Trifunović-Momčilov M., Motyka V., Dragićević I., Petrić M., Jevremović S., Malbeck J., et al. (2016). Endogenous phytohormones in spontaneously regenerated centaurium erythraea rafn. plants grown in vitro. J. Plant Growth Regul. 35 543–552. 10.1007/s00344-015-9558-x DOI

Van Staden J., Drewes F. E. (1991). The biological activity of cytokinin derivatives in the soybean callus bioassay. Plant Growth Regul. 10 109–115. 10.1007/BF00024957 DOI

Vyroubalová S., Vaclavikova K., Tureckova V., Novak O., Smehilova M., Hluska T., et al. (2009). Characterization of new maize genes putatively involved in cytokinin metabolism and their expression during osmotic stress in relation to cytokinin levels. Plant Physiol. 151 433–447. 10.1104/pp.109.142489 PubMed DOI PMC

Wang J., Ma X. M., Kojima M., Sakakibara H., Hou B. K. (2011). N-glucosyltransferase UGT76C2 is involved in cytokinin homeostasis and cytokinin response in Arabidopsis thaliana. Plant Cell Physiol. 52 2200–2213. 10.1093/pcp/pcr152 PubMed DOI

Werner T., Motyka V., Laucou V., Smets R., Van Onckelen H., Schmuelling T. (2003). Cytokinin-deficient transgenic Arabidopsis plants show functions of cytokinins in the regulation of shoot and root meristem activity. Plant Cell 15 2532–2550. 10.1105/tpc.014928.) PubMed DOI PMC

Yang M., Fehl C., Lees K. V., Lim E. K., Offen W. A., Davies G. J., et al. (2018). Functional and informatics analysis enables glycosyltransferase activity prediction. Nat. Chem. Biol. 14 1109–1117. 10.1038/s41589-018-0154-9 PubMed DOI

Zalabák D., Galuszka P., Mrízová K., Podlešáková K., Gu R., Frébortová J. (2014). Biochemical characterization of the maize cytokinin dehydrogenase family and cytokinin profiling in developing maize plantlets in relation to the expression of cytokinin dehydrogenase genes. Plant Physiol. Biochem. 74 283–293. 10.1016/j.plaphy.2013.11.020 PubMed DOI

Zhang K., Novak O., Wei Z., Gou M., Zhang X., Yu Y., et al. (2014). Arabidopsis ABCG14 protein controls the acropetal translocation of root-synthesized cytokinins. Nat Commun. 5:3274. 10.1038/ncomms4274 PubMed DOI

Zhang X., Chen Y., Lin X., Hong X., Zhu Y., Li W., et al. (2013). Adenine phosphoribosyl transferase 1 is a key enzyme catalyzing cytokinin conversion from nucleobases to nucleotides in Arabidopsis. Mol. Plant 6 1661–1672. 10.1093/mp/sst071 PubMed DOI

Žižková E., Dobrev P. I., Muhovski Y., Hošek P., Hoyerová K., Haisel D., et al. (2015). Tomato (Solanum lycopersicum L.) SlIPT3 and SlIPT4 isopentenyltransferases mediate salt stress response in tomato. BMC Plant Biol. 15:85. 10.1186/s12870-015-0415-7 PubMed DOI PMC

Žižková E., Kubeš M., Dobrev P. I., Přibyl P., Šimura J., Zahajská L., et al. (2017). Control of cytokinin and auxin homeostasis in cyanobacteria and algae. Ann. Bot. 119 151–166. 10.1093/aob/mcw194 PubMed DOI PMC

Dynamic changes of endogenous phytohormones and carbohydrates during spontaneous morphogenesis of Centaurium erythraea Rafn

Integrating the Roles for Cytokinin and Auxin in De Novo Shoot Organogenesis: From Hormone Uptake to Signaling Outputs

Dynamics of Auxin and Cytokinin Metabolism during Early Root and Hypocotyl Growth in Theobroma cacao

Hormopriming to Mitigate Abiotic Stress Effects: A Case Study of N 9-Substituted Cytokinin Derivatives With a Fluorinated Carbohydrate Moiety