Skoog, strong and miller proposed the definition of cytokinin. Cytokinin biosynthesis and regulation sciencedirect. Transzeatin biosynthesis oryza sativa wikipathways. Environmental inputs into cytokinin synthesis and signalling. Modulation of auxin and cytokinin responses by early steps of. Cytokinin biosynthesis is a multistep process requiring the activity of several different genes. It may use atp, adp, or amp as substrates and may use dimethylallyl pyrophosphate dmapp or hydroxymethylbutenyl pyrophosphate hmbpp as prenyl donors.
Findings tell us that ck biosynthesis pathways in plants and bacteria evolved independently in. 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. An antagonistic interaction between auxin and cytokinin biosynthesis has also been suggested in both developing roots and shoots. Thus, the biosynthetic pathway of zeatin is the fundamental research cis question to be elucidated in rice, maize, legume and other crop plants. Elements of the auxin and cytokinin pathways involved in biosynthesis, degradation, transport, and signaling are. Auxincytokinin interaction regulates meristem development. Adenosine phosphateisopentenyltransferase ipt catalyses the first reaction in the biosynthesis of isoprene cytokinins. 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. Description this record contains general information about the cytokinin signaling pathway collected across. Pdf the elusive cytokinin biosynthetic pathway wendy. Cytokinins are essential plant hormones that control cell division, shoot meristem initiation, leaf and root differentiation, chloroplast biogenesis, stress tolerance, and senescence 18. Cytokinin concentrations are high in the meristematic regions and in areas of continuous growth, such as the root subapical zone, young leaves, and. Cytokinin levels in plants are regulated by biosynthesis and inactivation pathways. 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.
Cytokinin signaling in plant development the company of biologists. The progress was achieved by identifying a series of key genes encoding enzymes and proteins controlling critical steps in biosynthesis, translocation, and signaling. Two biosynthetic pathways have been proposed for cytokinin biosynthesis. This record contains general information about the cytokinin signaling pathway collected across species. Plant isopentenyltransferases that catalyze the first and ratelimiting steps of cytokinin biosynthesis have recently been identified. Unlike bacterial enzymes, which catalyze the transfer of the isopentenyl moiety from dimethylallyldiphosphate dmapp to the n 6 position of. In plants, the cytokinin ck phytohormones regulate numerous biological processes, including responses to environmental stresses, via a complex network of ck signaling. The phytohormones auxin and cytokinin interact to regulate many plant growth and developmental processes. The indirect pathway of cytokinin biosynthesis involves turnover of trna containing ciszeatin. Recently, an alternative pathway for cytokinin biosynthesis has been proposed by astot et al. This was demonstrated through kinematic analysis of ga biosynthesis 101 mutants in maize nelissen et al. Evolution of cytokinin biosynthesis and degradation, journal of. Cytokinins are adenine derivatives with an isoprenoid side chain and play an essential role in plant development.
In vitro studies showed that ckxs have different affinities for each of their substrates. A stot c, dolez al k, nordstro m a, wang q, kunkel t, moritz t, chua nh. Adenine is the parent compound of naturally occurring cytokinins, though it does not activate cytokinin responses. Cytokinin signaling arabidopsis thaliana wikipathways. Modulation of auxin and cytokinin responses by early steps of the phenylpropanoid pathway jasmina kurepa, timothy e.
In plants, the cytokinin metabolic processes, including cytokinin biosynthesis, interconversion, inactivation and degradation, play critical roles in the regulation of cytokinin homeostasis and. 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. Cytokinin homeostasis is spatially and temporally regulated by a fine balance between synthesis and catabolism. This enzyme shows a stronger affinity for isopentenyltype cytokinins than the zeatin type, and it is induced by cytokinin overproduction 19, 20.
Auxin cytokinin interaction regulates meristem development. Cytokinin oxidase activity in the cellular slime mold dictyostelium discoideum. 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. 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. Proceedings of the national academy of sciences, usa 97, 1477814783. Glucosyl conjugates are inactive in bioassays, and these conjugated figure 1. Dec 19, 2000 the ipmpdependent cytokinin biosynthesis pathway fig. Although 40 years have passed since the first discovery of a naturally occurring cytokinin ck in plants, the biosynthetic pathway still remains unresolved. Cytokinins are perceived by membranelocalized histidinekinase receptors and are transduced. The naturally occurring cytokinins transzeatin tz, n 6.
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. 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. The first enzyme identified in the arabidopsis cytokinin biosynthetic pathway is adenosine phosphateisopentenyltransferases ipts. Cytokinin biosynthesis promotes cortical cell responses. 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. Astot c, dolezal k, nordstrom a, wang q, kunkel t, moritz t, chua nh, sandberg g. Cytokinin synthesis, signaling, and functionadvances and. 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. Recent findings demonstrate that cytokinin biosynthesis pathways in plants and. Cytokinin biosynthesis promotes cortical cell responses during nodule development1open dugald reid,a marcin nadzieja,a ondrej novak,b anne b. Plant growth hormone cytokinins control the crop seed. 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.
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. Cytokinins are key regulators of a large number of processes in plant development, which is highly plastic and adaptive, and remarkably resilient and selfperpetuating. The key biosynthetic and metabolic pathways of cytokinins are summarized in fig. For the biosynthetic pathway, reactions in which the genes encoding the enzymes have been identi. 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. Evolution of cytokinin biosynthesis and degradation journal.
In contrast, the reduced cytokinin level represses auxin biosynthesis. The proposed biosynthesis of zeatin tridiphosphate in arabidopsis is shown on the left side of the figure. 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. The biosynthesis of isoprenoid cks, in particular ip, is most studied, while the biosynthesis pathway of aromatic cks is practically unknown 5,8. Cytokinin biosynthesis two biosynthetic pathways have been proposed for cytokinin biosynthesis. 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. In most instances, cytokinin function is modulated, supported, or antagonized by other hormones andor environmental stimuli. Biologically active cytokinins are highlighted in yellow, with the free base cytokinin. An alternative cytokinin biosynthesis pathway request pdf. Cytokinin biosynthesis and metabolism springerlink.
The ipmpdependent cytokinin biosynthesis pathway fig. The first is the direct pathway, involving formation of. This reaction is the ratelimiting step in cytokinin biosynthesis. Proposed biosynthetic and metabolic pathway for cytokinins.
Cytokinin pathway mediates apetala1 function in the in. We have tested the proposed biosynthesis route by using an inducible cytokinin production system, to limit the possibility of. Cytokinin signaling in plant development development. 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. It is a compound which besides other activities induces cytokinesis, i. A recent study has shown that ectopic cytokinin results in a rapid increase in auxin biosynthesis in young roots and shoots jones et al. Numerous factors have contributed to the lack of success in this area, but most alarming has. 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. 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. Evolution of cytokinin biosynthesis and degradation pdf. The level of active cytokinin can be decreased through conjugation to glucose bajguz and piotrowska, 2009. Cytokinin signaling fernando j ferreira and joseph j kieber cytokinins in. Hirose n1, takei k, kuroha t, kamadanobusada t, hayashi h, sakakibara h. Cytokinin biosynthesis and perception wiley online library.
Regulation of cytokinin biosynthesis, compartmentalization and. Cytokinin signaling fernando j ferreira and joseph j kieber. It specifically reacts with the cytokinin 5monophosphates, but not with di or triphosphate, amp or any cytokinin ribosides or bases. An alternative cytokinin biosynthesis pathway pnas. However, elevated epidermal cytokinin biosynthesis or response during this 144 early stage was not detected. The elusive cytokinin biosynthetic pathway article pdf available in south african journal of botany 693. The schematic represents the cytokinin biosynthesis pathway from iprmp and tzrmp to the active cytokinin forms isopentenyladenine ip and trans. Biosynthesis cytokinins trna breakdown not the major pathway for cytokinin synthesis 9. 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.
It also became clear that interfering with any of these steps greatly impacts all on stages of growth and development. Ipt3 expression is also induced by increasing external sulphate and phosphate concentrations hirose et al. To date, the ck biosynthesis pathways are not completely deciphered. 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. 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. Arabidopsis cytokinin signaling pathway science signaling. Pdf evolution of cytokinin biosynthesis and degradation.
The comparison of the cytokinin biosynthesis pathway in rice nontransgenic plants ub3. Auxin response factor3 regulates floral meristem determinacy. Cytokinin oxidasedehydrogenases ckx catalyze the degradation step armstrong 1994, galuszka 2001, schmulling 2003. The current model for cytokinin signaling is a multistep phosphorelay similar to the prokaryotic twocomponent systems that are used in responses to environmental stimuli. 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. 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. 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. Auxin and cytokinin play fairly important roles in many aspects of plant growth and development. When the possible donor compounds become available. Modulation of auxin and cytokinin responses by early steps. Dna binding assay to elucidate the regulatory pathway of ub3.
Cytokinins in arabidopsis, tools, pathways and interaction with auxin. An alternative cytokinin biosynthesis pathway crister astot, karel dolezal, anders nordstro. Overexpression of several cytokinin biosynthesis pathway genes leads to. Biosynthesis cytokinins biosynthesis started by the ipt isopentenyl tranferase enzyme major pathway figure 21. Recent findings demonstrated that the ck biosynthesis pathway in agrobacterium in fected plants is distinct from that in higher plants in terms of. The phenylpropanoid pathway is responsible for the synthesis of numerous compounds important for plant growth and responses to the environment. Isopentenyl transferasesthe first step in cytokinin biosynthesis.
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. These results demonstrate that cytokinin functions in fm determinacy. The enzymes are localized in plastids or the cytoplasm where they utilize the intermediate dimethylallyldiphosphate from the methylerythritolphosphate or mevalonic acid pathways. The key step of the ip biosynthesis is commonly assumed to be isopentenyl. Cytokinins are perceived by membranelocalized histidine kinase receptors. Cytokinins can also be produced by recycled trnas in plants and bacteria. Pdf cytokinin is one of the socalled classic plant growth phytohormones and functions to promote cell division and cell differentiation.
Dmadp and hmbdp used in cytokinin biosynthesis are produced by the methylerythritol phosphate pathway mep. Phosphorelay systems also called twocomponent signaling systems are prevalent in. Crosstalk occurs at many levels ranging from cytokinin biosynthesis, modification, transport, and degradation, to perception and intracellular signaling. Cytokinins in arabidopsis, tools, pathways and interaction. A response regulators arrs, which participate in cytokinin biosynthesis and. Opinion paper the elusive cytokinin biosynthetic pathway n. Arabidopsis knoxi proteins activate 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. Farnesylation directs atipt3 subcellular localization and. Apr 29, 2003 cytokinins are adenine derivatives with an isoprenoid side chain and play an essential role in plant development. Sep 30, 2010 biosynthesis cytokinins biosynthesis started by the ipt isopentenyl tranferase enzyme major pathway figure 21. Jul 01, 2016 adenosine phosphateisopentenyltransferase ipt catalyses the first reaction in the biosynthesis of isoprene cytokinins. Regulation of cytokinin biosynthesis, compartmentalization and translocation.
The biosynthesis of isoprenoid cytokinins starts with transfer of the isoprenoid moiety to adenine either in its nucleotide forms or bound to rna. Furthermore, we performed transcriptome sequencing and protein. We found that ub3 could bind and regulate the promoters of lonely guy1 log1 and type. Evolution of cytokinin biosynthesis and degradation. Dolez al k, nordstro m a, wang q, kunkel t, moritz t, chua nh. Like auxin, cytokinin is also a key regulator for various aspects of plant growth and development. The key biosynthetic and metabolic pathways of cytokinins. Biosynthesis of cytokinin request pdf researchgate. Regulation of cytokinin biosynthesis, compartmentalization. The first is the direct pathway, involving formation of n6isopentenyladenosine monophosphate i6amp from amp and dimethylallyl pyrophosphate dmapp. 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. The elusive cytokinin biosynthetic pathway sciencedirect. 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 naturally occurring cytokinins transzeatin tz, n6. However, the regulatory mechanisms linking atipt activity and cytokinin biosynthesis with cytokinin homeostasis and isoprenoid synthesis are not well understood. Unbranched3 regulates branching by modulating cytokinin. These results suggest that the cytokinin biosynthesis gene atipt7 is a major target of knoxi proteins.