In arabidopsis thaliana, the model species for plant research, cytokinin biosynthesis is controlled by the atpadp isopentenyltransferase ipt genes, which encode ratelimiting enzymes in cytokinin biosynthesis. In addition to exogenous cytokinin treatment, we elevated in vivo cytokinin levels in flowers by expressing the arabidopsis adenosine phosphateisopentenyltransferase 8 ipt8, which encodes a ratelimiting enzyme in cytokinin biosynthesis 27, from the ap1 promoter. Jul 01, 2016 adenosine phosphateisopentenyltransferase ipt catalyses the first reaction in the biosynthesis of isoprene cytokinins. A recent study has shown that ectopic cytokinin results in a rapid increase in auxin biosynthesis in young roots and shoots jones et al. Skoog, strong and miller proposed the definition of cytokinin. Cytokinin oxidase activity in the cellular slime mold dictyostelium discoideum. Apr 29, 2003 cytokinins are adenine derivatives with an isoprenoid side chain and play an essential role in plant development. Cytokinin signaling pathway starts from receiving of the ligand cytokinin by the cytokinin receptors a dimer, followed by a phosphate relay by acceptor and donor domains of the receptors and then the histidine phosphotransmitters hps. An antagonistic interaction between auxin and cytokinin biosynthesis has also been suggested in both developing roots and shoots.
In this study, we analyzed timecourse expression levels of four biosynthesis pathway genes hemd, heme2, pora, and chlg and two degradation pathway genes clh2 and rccr during. The elusive cytokinin biosynthetic pathway sciencedirect. Cytokinin biosynthesis promotes cortical cell responses. Cytokinin biosynthesis and perception wiley online library. The main step of the cytokinin biosynthesis pathway is the transfer of the isopentenyl group from dimethylallyl diphosphate dmapp to atp, adp, or amp catalyzed by isopentenyltransferases ipts. A stot c, dolez al k, nordstro m a, wang q, kunkel t, moritz t, chua nh. Regulation of cytokinin biosynthesis, compartmentalization. Cytokinins in arabidopsis, tools, pathways and interaction with auxin. Two biosynthetic pathways have been proposed for cytokinin biosynthesis. However, the regulatory mechanisms linking atipt activity and cytokinin biosynthesis with cytokinin homeostasis and isoprenoid synthesis are not well understood. Plant growth hormone cytokinins control the crop seed. Cytokinin homeostasis is spatially and temporally regulated by a fine balance between synthesis and catabolism. Pdf the elusive cytokinin biosynthetic pathway wendy. Cytokinin signaling arabidopsis thaliana wikipathways.
Arabidopsis cytokinin signaling pathway science signaling. The key biosynthetic and metabolic pathways of cytokinins. Cytokinin biosynthesis promotes cortical cell responses during nodule development1open dugald reid,a marcin nadzieja,a ondrej novak,b anne b. Cytokinin biosynthesis and metabolism springerlink. Elements involved in the biosynthesis, inactivation, transport, perception, and signaling of these hormones have been elucidated, revealing the variety of mechanisms by which signal output from these pathways can be regulated. Findings tell us that ck biosynthesis pathways in plants and bacteria evolved independently in. The naturally occurring cytokinins transzeatin tz, n6. Cytokinins are perceived by membranelocalized histidine kinase receptors. Cytokinin concentrations are high in the meristematic regions and in areas of continuous growth, such as the root subapical zone, young leaves, and. The first is the direct pathway, involving formation of n6isopentenyladenosine monophosphate i6amp from amp and dimethylallyl pyrophosphate dmapp. We found that ub3 could bind and regulate the promoters of lonely guy1 log1 and type.
This was demonstrated through kinematic analysis of ga biosynthesis 101 mutants in maize nelissen et al. The biosynthesis of isoprenoid cytokinins starts with transfer of the isoprenoid moiety to adenine either in its nucleotide forms or bound to rna. Astot c, dolezal k, nordstrom a, wang q, kunkel t, moritz t, chua nh, sandberg g. Thanks to the accomplishment of the arabidopsis thaliana genome project arabidopsis genome initiative, 2000 and the development of sensitive technologies for plant hormone analysis, several breakthroughs in ck biosynthesis, metabolism, and signal transduction were achieved during the last decade. Cytokinins are key regulators of a large number of processes in plant development, which is highly plastic and adaptive, and remarkably resilient and selfperpetuating. Cytokinins are adenine derivatives with an isoprenoid side chain and play an essential role in plant development. Cytokinins in arabidopsis, tools, pathways and interaction. Biologically active cytokinins are highlighted in yellow, with the free base cytokinin. Evolution of cytokinin biosynthesis and degradation, journal of. Furthermore, genetic and molecular lines of evidence indicate that increased cytokinin biosynthesis and reception enhanced the fm determinacy defect of ag10, whereas attenuated cytokinin biosynthesis and reception rescued the fm indeterminacy of ag10 arf329 figures 3 to 5. An alternative cytokinin biosynthesis pathway pnas. The cytokinin signaling pathway can be modulated by nutrients, stress, and other hormones, and is integrated into a signaling network in both shoots and roots. Oct, 2018 topic cytokinin biosynthesis and functions phytohormone part11 csir netplant biology about this channel this channel will have the syllabus wise lectures video for csirnetlifescience.
Cytokinins are essential plant hormones that control cell division, shoot meristem initiation, leaf and root differentiation, chloroplast biogenesis, stress tolerance, and senescence 18. Regulation of cytokinin biosynthesis, compartmentalization and translocation. The naturally occurring cytokinins transzeatin tz, n 6. Recent findings demonstrate that cytokinin biosynthesis pathways in plants and bacteria utilize distinct substrate, that cytokinin biosynthesis and homeostasis are finely controlled by other phytohormones and inorganic nitrogen sources, and that. The proposed biosynthesis of zeatin tridiphosphate in arabidopsis is shown on the left side of the figure. It is a compound which besides other activities induces cytokinesis, i. The key step of the ip biosynthesis is commonly assumed to be isopentenyl. These results demonstrate that cytokinin functions in fm determinacy. Numerous factors have contributed to the lack of success in this area, but most alarming has.
The elusive cytokinin biosynthetic pathway article pdf available in south african journal of botany 693. This record contains information specific to the arabidopsis cytokinin signaling pathway in arabidopsis thaliana, cytokinin signaling has been implicated in control of the stem cell pool in the shoot meristem, leaf and root differentiation, vasculature patterning, chloroplast biogenesis, photomorphogenesis, apical dominance, gravitropism, fertility, seed development. The phytohormone cytokinin plays diverse roles in plant development, influencing many agriculturally important processes, including growth, nutrient responses and the response to biotic and abiotic stresses. This enzyme shows a stronger affinity for isopentenyltype cytokinins than the zeatin type, and it is induced by cytokinin overproduction 19, 20.
The enzymes are localized in plastids or the cytoplasm where they utilize the intermediate dimethylallyldiphosphate from the methylerythritolphosphate or mevalonic acid pathways. Furthermore, we performed transcriptome sequencing and protein. A response regulators arrs, which participate in cytokinin biosynthesis and. Cytokinin oxidasedehydrogenases ckx catalyze the degradation step armstrong 1994, galuszka 2001, schmulling 2003. We have tested the proposed biosynthesis route by using an inducible cytokinin production system, to limit the possibility of. Cytokinin signaling in plant development the company of biologists. Opinion paper the elusive cytokinin biosynthetic pathway n. Heckmann,a,2 niels sandal,a and jens stougaarda,3 acentre for carbohydrate recognition and signaling, department of molecular biology and genetics, aarhus university, aarhus c 8000, denmark blaboratory of growth regulators, faculty of science. Dec 19, 2000 the ipmpdependent cytokinin biosynthesis pathway fig. Sep 30, 2010 biosynthesis cytokinins biosynthesis started by the ipt isopentenyl tranferase enzyme major pathway figure 21.
Heckmann,a,2 niels sandal,a and jens stougaarda,3 acentre for carbohydrate recognition and signaling, department of molecular biology and genetics, aarhus university, aarhus c 8000, denmark. Auxin and cytokinin play fairly important roles in many aspects of plant growth and development. Thus, the biosynthetic pathway of zeatin is the fundamental research cis question to be elucidated in rice, maize, legume and other crop plants. This record contains general information about the cytokinin signaling pathway collected across species. In vitro studies showed that ckxs have different affinities for each of their substrates. Cytokinin levels in plants are regulated by biosynthesis and inactivation pathways. Farnesylation directs atipt3 subcellular localization and. An alternative cytokinin biosynthesis pathway crister astot, karel dolezal, anders nordstro. In most instances, cytokinin function is modulated, supported, or antagonized by other hormones andor environmental stimuli. Like auxin, cytokinin is also a key regulator for various aspects of plant growth and development. Evolution of cytokinin biosynthesis and degradation pdf. Transzeatin biosynthesis oryza sativa wikipathways.
When the possible donor compounds become available. Dmadp and hmbdp used in cytokinin biosynthesis are produced by the methylerythritol phosphate pathway mep. To date, the ck biosynthesis pathways are not completely deciphered. Recently, an alternative pathway for cytokinin biosynthesis has been proposed by astot et al. The first is the direct pathway, involving formation of. In plants, the cytokinin metabolic processes, including cytokinin biosynthesis, interconversion, inactivation and degradation, play critical roles in the regulation of cytokinin homeostasis and. Cytokinins can also be produced by recycled trnas in plants and bacteria. Although 40 years have passed since the first discovery of a naturally occurring cytokinin ck in plants, the biosynthetic pathway still remains unresolved. Adenosine phosphateisopentenyltransferase ipt catalyses the first reaction in the biosynthesis of isoprene cytokinins. Evolution of cytokinin biosynthesis and degradation. Proposed biosynthetic and metabolic pathway for cytokinins. Cytokinin synthesis, signaling, and functionadvances and.
For the biosynthetic pathway, reactions in which the genes encoding the enzymes have been identi. Biosynthesis of cytokinin request pdf researchgate. An alternative cytokinin biosynthesis pathway request pdf. Environmental inputs into cytokinin synthesis and signalling. However, elevated epidermal cytokinin biosynthesis or response during this 144 early stage was not detected. Auxin cytokinin interaction regulates meristem development. Biosynthesis cytokinins biosynthesis started by the ipt isopentenyl tranferase enzyme major pathway figure 21. It also became clear that interfering with any of these steps greatly impacts all on stages of growth and development. In plants, the cytokinin ck phytohormones regulate numerous biological processes, including responses to environmental stresses, via a complex network of ck signaling. Dna binding assay to elucidate the regulatory pathway of ub3. Evolution of cytokinin biosynthesis and degradation journal.
Glucosyl conjugates are inactive in bioassays, and these conjugated figure 1. Arabidopsis knoxi proteins activate cytokinin biosynthesis. Cytokinin signaling in plant development development. Cytokinin biosynthesis is a multistep process requiring the activity of several different genes. The cytokinin biosynthesis gene ipt3 is upregulated by nitrate, and there is a great reduction in cytokinin accumulation in response to nitrate in an ipt3 mutant background takei et al. Since the discovery of cytokinins in the 1950s, it has been clearly established that they play an important role in various processes in the growth and development of plants, including the promotion of cell division, the counteraction of senescence, the regulation of apical dominance and the transmission of nutritional signals. Modulation of auxin and cytokinin responses by early steps. Recent findings demonstrated that the ck biosynthesis pathway in agrobacterium in fected plants is distinct from that in higher plants in terms of. Proceedings of the national academy of sciences, usa 97, 1477814783. These results suggest that the cytokinin biosynthesis gene atipt7 is a major target of knoxi proteins. Overexpression of several cytokinin biosynthesis pathway genes leads to.
Unlike bacterial enzymes, which catalyze the transfer of the isopentenyl moiety from dimethylallyldiphosphate dmapp to the n 6 position of. Biosynthesis cytokinins trna breakdown not the major pathway for cytokinin synthesis 9. Cytokinins are perceived by membranelocalized histidinekinase receptors and are transduced. This reaction is the ratelimiting step in cytokinin biosynthesis. Cytokinin signaling fernando j ferreira and joseph j kieber. They provided evidence that ipt could use an unknown compound of terpenoid origin as a side chain donor instead of dmapp, and the initial product of the pathway istranszeatin 5. The current model for cytokinin signaling is a multistep phosphorelay similar to the prokaryotic twocomponent systems that are used in responses to environmental stimuli. Regulation of cytokinin biosynthesis, compartmentalization and. Modulation of auxin and cytokinin responses by early steps of. The level of active cytokinin can be decreased through conjugation to glucose bajguz and piotrowska, 2009. It specifically reacts with the cytokinin 5monophosphates, but not with di or triphosphate, amp or any cytokinin ribosides or bases.
Auxincytokinin interaction regulates meristem development. As reported for the first time in rice pubkurakawa07 the enzyme cytokinin nucleoside 5monophosphate phosphoribohydrolase converts cytokinin nucleotide such as transzeatin riboside monophosphate tzprmp into isopentenyladenine a free base form and ribose 5monophosphate. The first enzyme identified in the arabidopsis cytokinin biosynthetic pathway is adenosine phosphateisopentenyltransferases ipts. The key biosynthetic and metabolic pathways of cytokinins are summarized in fig. Activation of only a subset of cytokinin biosynthesis genes by knoxi proteins suggests that cytokinin biosynthesis is controlled by both knoxidependent and knoxiindependent pathways, indicating the existence. The progress was achieved by identifying a series of key genes encoding enzymes and proteins controlling critical steps in biosynthesis, translocation, and signaling. Crosstalk occurs at many levels ranging from cytokinin biosynthesis, modification, transport, and degradation, to perception and intracellular signaling. The phytohormones auxin and cytokinin interact to regulate many plant growth and developmental processes.
Pdf cytokinin is one of the socalled classic plant growth phytohormones and functions to promote cell division and cell differentiation. Unbranched3 regulates branching by modulating cytokinin. Because the pp biosynthesis and cytokinin response pathways are not directly linked, we attempted to distinguish between the growth inhibition resulting from reduced pp levels and growth inhibition induced by reduced cytokinin signaling by feeding severely dwarfed kmd1kfb20 oe lines with. Cytokinin signaling fernando j ferreira and joseph j kieber cytokinins in. In contrast, the reduced cytokinin level represses auxin biosynthesis. Cytokinin biosynthesis two biosynthetic pathways have been proposed for cytokinin biosynthesis. Dolez al k, nordstro m a, wang q, kunkel t, moritz t, chua nh. Auxin response factor3 regulates floral meristem determinacy. Elements of the auxin and cytokinin pathways involved in biosynthesis, degradation, transport, and signaling are. The phenylpropanoid pathway is responsible for the synthesis of numerous compounds important for plant growth and responses to the environment.
Cytokinins cks play a crucial role in various phases of plant growth and development, but the basic molecular mechanisms of their biosynthesis and signal transduction only recently became clear. Phosphorelay systems also called twocomponent signaling systems are prevalent in. By an unknown mechanism, stress signals are perceived and transmitted through the hisasp phosphorelay, an important component of the ck signal transduction pathway, triggering ckresponsive genes. Description this record contains general information about the cytokinin signaling pathway collected across. Hirose n1, takei k, kuroha t, kamadanobusada t, hayashi h, sakakibara h. Issn 14016230, isbn 9157667012 cytokinins are plant hormones, and their relative abundance in proportion to auxin determines whether shoots or roots are formed in callus tissue. The biosynthesis of isoprenoid cks, in particular ip, is most studied, while the biosynthesis pathway of aromatic cks is practically unknown 5,8. Isopentenyl transferasesthe first step in cytokinin biosynthesis. Plant isopentenyltransferases that catalyze the first and ratelimiting steps of cytokinin biosynthesis have recently been identified. Mar 30, 2006 recent findings demonstrate that cytokinin biosynthesis pathways in plants and bacteria utilize distinct substrate, that cytokinin biosynthesis and homeostasis are finely controlled by other phytohormones and inorganic nitrogen sources, and that cytokinin receptors have overlapping but specific functions.
Adenine is the parent compound of naturally occurring cytokinins, though it does not activate cytokinin responses. The comparison of the cytokinin biosynthesis pathway in rice nontransgenic plants ub3. The schematic represents the cytokinin biosynthesis pathway from iprmp and tzrmp to the active cytokinin forms isopentenyladenine ip and trans. Pdf evolution of cytokinin biosynthesis and degradation. Ipt3 expression is also induced by increasing external sulphate and phosphate concentrations hirose et al. Modulation of auxin and cytokinin responses by early steps of the phenylpropanoid pathway jasmina kurepa, timothy e. Recent findings demonstrate that cytokinin biosynthesis pathways in plants and. The interaction between auxin and cytokinin is particularly important to control a few developmental processes, such as the formation and maintenance of meristems that are essential to establish the whole plant body. Cytokinin perception and signal transduction the cytokinin signal transduction pathway involves a hisasp phosphorelay similar to that found in bacterial twocomponent signaling systems, which are the major routes by which bacteria. The indirect pathway of cytokinin biosynthesis involves turnover of trna containing ciszeatin. It may use atp, adp, or amp as substrates and may use dimethylallyl pyrophosphate dmapp or hydroxymethylbutenyl pyrophosphate hmbpp as prenyl donors. Cytokinin biosynthesis and regulation sciencedirect. The ipmpdependent cytokinin biosynthesis pathway fig. Recent findings demonstrate that cytokinin biosynthesis pathways in plants and bacteria utilize distinct substrate, that cytokinin biosynthesis and homeostasis are finely controlled by other phytohormones and inorganic nitrogen sources, and that cytokinin receptors have overlapping but specific functions.
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