DOCSLIB.ORG

The Elusive Cytokinin Biosynthetic Pathway

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Elusive Cytokinin Biosynthetic Pathway View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector South African Journal of Botany 2003, 69(3): 269–281 Copyright © NISC Pty Ltd Printed in South Africa — All rights reserved SOUTH AFRICAN JOURNAL OF BOTANY ISSN 0254–6299 Opinion Paper The elusive cytokinin biosynthetic pathway NJ Taylor, WA Stirk and J van Staden* Research Centre for Plant Growth and Development, School of Botany and Zoology, University of Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa * Corresponding author, e-mail: [email protected] Received 26 March 2003, accepted in revised form 14 April 2003 Although 40 years have passed since the first discovery exist in plants. CK biosynthetic mutants, which over- of a naturally occurring cytokinin (CK) in plants, the produce CKs as a result of IPT overexpression, are also biosynthetic pathway still remains unresolved. starting to be identified and this should help overcome Numerous factors have contributed to the lack of suc- the past difficulties experienced in determining the cess in this area, but most alarming has been the site(s) of CK biosynthesis in plants. On the other hand, reliance upon unproven hypotheses and preconceived aromatic CK biosynthesis has seen no progress in the ideas. The greatest obstacle has been the identification last few years and remains strictly speculative. This and isolation of CK biosynthetic enzymes in plants, review aims to evaluate the current status of knowledge which have only recently been isolated and charac- with respect to CK biosynthesis, to identify gaps in the terised in Arabidopsis. This has led to the classical iso- knowledge and to suggest ways by which to move for- prenoid CK biosynthetic pathway being partly chal- ward. lenged and the suggestion that multiple pathways might Abbreviations: ABA = abscisic acid, Ade = adenine, ADP = adenosine-5’-diphosphate, AMP = adenosine-5’-monophosphate, ATP = adenosine-5’-triphosphate, BA = benzyladenine, BA9G = benzyladenine-9-glucoside, BAR = benzyladenine riboside, CK = cytokinin, DHZ = dihydrozeatin, DHZMP = dihydrozeatin riboside-5’-monophosphate, DHZN9G = dihydrozeatin-N9-glu- coside, DHZR = dihydrozeatin riboside, DMAPP = dimethylallyl pyrophosphate, DOXP = 1-deoxy-D-xylulose-5-phosphate, DXR = 1-deoxy-D-xylulose-5-phosphate reductoisomerase, GA = gibberellin, GA-3-P = gylceraldehyde-3-phosphate, HMG- CoA = 3-hydroxy-methylglutaryl coenzyme A, HMGR = 3-hydroxy-methylglutaryl coenzyme A reductase, hoc = high shoot- organogenic capacity, iP = isopentenyladenine, iPA = isopentenyladenosine, iPDP = isopentenyladenosine-5’-diphosphate, iPMP = isopentenyladenosine-5’-monophosphate, iPNG = isopentenyladenine-N-glucoside, IPP = isopentenyl pyrophos- phate, ipt = isopentenyl transferase, iPTP = isopentenyladenosine-5’-triphosphate, MEP = methylerythritol 4-phosphate, 2MeS-oTOG = 2-methylthiopurine-ortho-topolin-O-glucoside, mT= meta-topolin, mTOG = meta-topolin-O-glucoside, mTROG = meta-topolin riboside-O-glucoside, MVA = mevalonic acid, oT= ortho-topolin, oTOG = ortho-topolin-O-glucoside, oTR = ortho-topolin riboside, pga = plant growth activator, PPFM = pink pigmented facultative methyltrophs, pTOG = para-topolin-O- glucoside, SHO = shooting, Z = zeatin, ZDP = trans-zeatin-riboside diphosphate, ZMP = trans-zeatin-riboside monophos- phate, ZN7G = zeatin-N7-glucoside, ZN9G = zeatin-N9-glucoside, ZR = zeatin riboside, ZTP = trans-zeatin-riboside triphos- phate Introduction Hormone biosynthesis in general remains a stumbling block mays endosperm tissue in the 1960s (Miller 1961, Letham for plant scientists, with very few hormone biosynthetic path- 1963). Numerous complicating factors have prohibited rapid ways having being elucidated fully. Cytokinin (CK) biosyn- advance in this area, which include the extremely low levels thesis remains firmly entrenched as a grey area, with little of endogenous CKs, the central role of the likely precursors headway having been made with respect to the biosynthetic (adenine and its nucleoside and nucleotide) in cellular pathway in ‘normal’ (i.e. non-transformed) higher plants, metabolism, the existence of numerous (currently more than since the first discovery of a naturally occurring CK in Zea 40) native substances with more or less pronounced CK 270 Taylor, Stirk and Van Staden activity (Letham and Palni 1983, Zañímalová et al. 1999) and side chain methyl groups can be further modified by hydrox- most alarmingly, the reliance on incorrect or only partially ylation to yield the cis-isomer of Z, which is the major com- correct assumptions concerning CK biosynthesis. Advances ponent of plant tRNA (Prinsen et al. 1997). The IPP for the in modern techniques and instrumentation (such as LC-MS biosynthesis of tRNA CKs is most probably derived from and GC-MS) have allowed the purification and identification mevalonic acid (MVA), as Murai et al. (1975) demonstrated of minute quantities of compounds and thus the difficulties the incorporation of label from MVA into cis-zeatin riboside experienced in the past have largely been resolved. With the (cis-ZR) in tobacco callus tRNA. advances in molecular biology and the completion of plant Although it has been suggested that CKs derived from genomic sequences, the day should be rapidly approaching tRNA could comprise up to 50% of the free CK pool in plants when we know the pathway(s) for CK biosynthesis in plants. (Barnes et al. 1980, Maaβ and Klämbt 1981), it is unlikely Aspects yet to be proven remain points of intense debate that tRNA mediated CK biosynthesis is of great biological and scrutiny. significance. Evidence to support the predominance of a Naturally occurring CKs are adenine derivatives with at direct route for CK biosynthesis is as follows: least one substituent at the N6-position and they are defined 1) tRNA in CK-dependent tissues contain CKs, yet an by their ability to promote cell division in cultured tissues in exogenous supply is still necessary for the growth of the presence of auxin (Miller et al. 1955, Skoog et al. 1965). these tissues (Chen and Hall 1969, Burrows 1976). According to the substituent at this position, CKs can be 2) The levels of free CKs in pea root tips exceed the divided into three groups: (1) isoprenoid (zeatin (Z), N6-Δ2- amount present in tRNA by 27-fold (Short and Torrey isopentenyladenine and its derivatives); (2) isoprenoid- 1972). It should be noted that the method these authors derived (dihydrozeatin (DHZ) and its derivatives); and (3) employed involved acid hydrolysis of tRNA, which aromatic CKs (Zañímalová et al. 1999). This review will destroys isopentenyladenosine (iPA) and thus the CK attempt to evaluate the current situation with regard to CK content in tRNA may have been underestimated (Letham biosynthesis, to identify shortcomings in currently accepted and Palni 1983). theories and finally to suggest possible ways in which knowl- 3) The low rates of tRNA turnover in plant tissues do not edge in this field can be furthered. In view of the differences support the view that tRNA degradation contributes sig- between the isoprenoid and aromatic N6 side chains, it is nificantly to the pool of free CKs (Trewavas 1970, Hall unlikely that they have the same biosynthetic origin (Van 1973). Staden and Crouch 1996, Prinsen et al. 1997, Mok and Mok 4) Certain free CKs in higher plants are not found in tRNA 2001) and they will therefore be considered separately. (e.g. aromatic CKs) and vice versa. cis-Z is the predom- inant CK in tRNA, but this CK exhibits little biological Biosynthesis of isoprenoid cytokinins activity in the soybean callus bioassay (Van Staden and Drewes 1991) and the trans-isomer is the major free CK Three different pathways for the biosynthesis of isoprenoid in higher plants (Mok and Mok 2001 and references CKs in plants are currently proposed. Initially it was believed therein). However, the existence of cis-trans-isomerase that tRNA was the main source of free CKs in plants (Mok and Martin 1994) may support a function for tRNA (Swaminathan and Bock 1977). Subsequently, it was as a supplementary source of free CKs in plants. This demonstrated that there was a direct route for CK biosyn- enzyme has been partially purified from Phaseolus vul- thesis that did not involve tRNA degradation (Taya et al. garis (Mok et al. 1992, Bassil et al. 1993). 1978). Finally, a second side chain precursor, other than CK moieties in tRNA are always located at the strategic 37 isopentenyl pyrophosphate (IPP), was suggested such that position adjacent to the 3’-end anticodon (Sprinzl et al. 1989, trans-zeatin-riboside monophosphate (ZMP) synthesis can 1991). This very specific location of CKs in tRNA, together occur independently of isopentenyladenosine-5’-monophos- with the distribution of tRNA species, indicates a specific role phate (iPMP) (Åstot et al. 2000). of CK moieties in tRNA function, which could possibly be proteosynthetic in nature, involving the enhancement of Cytokinins in tRNA tRNA translational efficiency (Laten et al. 1978, Landick et al. 1990). In fact, Kamínek (1992) argued that plants have The first discovery of an N6-Δ2-isopentenyladenine (iP) evolved efficient mechanisms to prevent tRNA-derived CKs residue in tRNA in the 1960s (Hall et al. 1966, Zachau et al. from interfering with hormonal regulation. The reduced num- 1966) prompted the theory that CKs were derived from the ber of tRNA species containing CKs in higher plants and the degradation of tRNA. Modified bases, including isopenteny- predominance
Load more

Recommended publications
  • Auxins and Cytokinins in Plant Development 2018
    International Journal of Molecular Sciences Meeting Report Auxins and Cytokinins in Plant Development 2018 Jan Petrasek 1, Klara Hoyerova 1, Vaclav Motyka 1 , Jan Hejatko 2 , Petre Dobrev 1, Miroslav Kaminek 1 and Radomira Vankova 1,* 1 Laboratory of Hormonal Regulations in Plants, Institute of Experimental Botany, The Czech Academy of Sciences, Rozvojova 263, 16502 Prague 6, Czech Republic; [email protected] (J.P.); [email protected] (K.H.); [email protected] (V.M.); [email protected] (P.D.); [email protected] (M.K.) 2 CEITEC–Central European Institute of Technology and Functional Genomics and Proteomics, NCBR, Faculty of Science, Masaryk University, 62500 Brno, Czech Republic; [email protected] * Correspondence: [email protected]; Tel.: +420-225-106-427 Received: 15 February 2019; Accepted: 18 February 2019; Published: 20 February 2019 Abstract: The international symposium “Auxins and Cytokinins in Plant Development” (ACPD), which is held every 4–5 years in Prague, Czech Republic, is a meeting of scientists interested in the elucidation of the action of two important plant hormones—auxins and cytokinins. It is organized by a group of researchers from the Laboratory of Hormonal Regulations in Plants at the Institute of Experimental Botany, the Czech Academy of Sciences. The symposia already have a long tradition, having started in 1972. Thanks to the central role of auxins and cytokinins in plant development, the ACPD 2018 symposium was again attended by numerous experts who presented their results in the opening, two plenary lectures, and six regular sessions, including two poster sessions. Due to the open character of the research community, which is traditionally very well displayed during the meeting, a lot of unpublished data were presented and discussed.
    [Show full text]
  • Endogenous Levels of Cytokinins, Indole-3-Acetic Acid And
    www.nature.com/scientificreports OPEN Endogenous levels of cytokinins, indole-3-acetic acid and abscisic acid in in vitro grown potato: A contribution to potato hormonomics Martin Raspor 1,6*, Václav Motyka 2,6, Slavica Ninković 1, Petre I. Dobrev 2, Jiří Malbeck 3, Tatjana Ćosić 1, Aleksandar Cingel 1, Jelena Savić 1, Vojin Tadić 4 & Ivana Č. Dragićević 5 A number of scientifc reports published to date contain data on endogenous levels of various phytohormones in potato (Solanum tuberosum L.) but a complete cytokinin profle of potato tissues, that would include data on all particular molecular forms of cytokinin, has still been missing. In this work, endogenous levels of all analytically detectable isoprenoid cytokinins, as well as the auxin indole- 3-acetic acid (IAA), and abscisic acid (ABA) have been determined in shoots and roots of 30 day old in vitro grown potato (cv. Désirée). The results presented here are generally similar to other data reported for in vitro grown potato plants, whereas greenhouse-grown plants typically contain lower levels of ABA, possibly indicating that in vitro grown potato is exposed to chronic stress. Cytokinin N-glucosides, particularly N7-glucosides, are the dominant cytokinin forms in both shoots and roots of potato, whereas nucleobases, as the bioactive forms of cytokinins, comprise a low proportion of cytokinin levels in tissues of potato. Diferences in phytohormone composition between shoots and roots of potato suggest specifc patterns of transport and/or diferences in tissue-specifc metabolism of plant hormones. These results represent a contribution to understanding the hormonomics of potato, a crop species of extraordinary economic importance.
    [Show full text]
  • Auxins Cytokinins and Gibberellins TD-I Date: 3/4/2019 Cell Enlargement in Young Leaves, Tissue Differentiation, Flowering, Fruiting, and Delay of Aging in Leaves
    Informational TD-I Revision 2.0 Creation Date: 7/3/2014 Revision Date: 3/4/2019 Auxins, Cytokinins and Gibberellins Isolation of the first Cytokinin Growing cells in a tissue culture medium composed in part of coconut milk led to the realization that some substance in coconut milk promotes cell division. The “milk’ of the coconut is actually a liquid endosperm containing large numbers of nuclei. It was from kernels of corn, however, that the substance was first isolated in 1964, twenty years after its presence in coconut milk was known. The substance obtained from corn is called zeatin, and it is one of many cytokinins. What is a Growth Regulator? Plant Cell Growth regulators (e.g. Auxins, Cytokinins and Gibberellins) - Plant hormones play an important role in growth and differentiation of cultured cells and tissues. There are many classes of plant growth regulators used in culture media involves namely: Auxins, Cytokinins, Gibberellins, Abscisic acid, Ethylene, 6 BAP (6 Benzyladenine), IAA (Indole Acetic Acid), IBA (Indole-3-Butyric Acid), Zeatin and trans Zeatin Riboside. The Auxins facilitate cell division and root differentiation. Auxins induce cell division, cell elongation, and formation of callus in cultures. For example, 2,4-dichlorophenoxy acetic acid is one of the most commonly added auxins in plant cell cultures. The Cytokinins induce cell division and differentiation. Cytokinins promote RNA synthesis and stimulate protein and enzyme activities in tissues. Kinetin and benzyl-aminopurine are the most frequently used cytokinins in plant cell cultures. The Gibberellins is mainly used to induce plantlet formation from adventive embryos formed in culture.
    [Show full text]
  • A Genetic Framework for Regulation and Seasonal Adaptation of Shoot Architecture in Hybrid Aspen
    A genetic framework for regulation and seasonal adaptation of shoot architecture in hybrid aspen Jay P. Mauryaa,b, Pal C. Miskolczia, Sanatkumar Mishraa, Rajesh Kumar Singha, and Rishikesh P. Bhaleraoa,1 aUmeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 87 Umeå, Sweden; and bDepartment of Botany, Institute of Science, Banaras Hindu University, Varanasi 221005, Uttar Pradesh, India Edited by Ronald R. Sederoff, North Carolina State University, Raleigh, NC, and approved April 14, 2020 (received for review March 14, 2020) Shoot architecture is critical for optimizing plant adaptation and time–related transcription factor RAV1 has been validated in productivity. In contrast with annuals, branching in perennials branching in trees (17–19). However, information on branching native to temperate and boreal regions must be coordinated with control in perennials is fragmented, and there is a significant gap seasonal growth cycles. How branching is coordinated with in our knowledge of how branching is controlled and integrated seasonal growth is poorly understood. We identified key compo- with seasonal growth cycles in perennial trees (20). Therefore, nents of the genetic network that controls branching and its using functional genetic approaches, we elucidated the genetic regulation by seasonal cues in the model tree hybrid aspen. network that mediates control of branching and its regulation by Our results demonstrate that branching and its control by sea- seasonal cues in the model tree hybrid aspen. These studies re- sonal cues is mediated by mutually antagonistic action of aspen veal the key role played by the mutually antagonistic action of orthologs of the flowering regulators TERMINAL FLOWER 1 LAP1 and TFL1 in mediating control of branching and its re- (TFL1)andAPETALA1 (LIKE APETALA 1/LAP1).
    [Show full text]
  • The Interaction of Cytokinin and Strigolactone in Controlling Shoot Branching in Arabidopsis Thaliana
    The Interaction of Cytokinin and Strigolactone in controlling Shoot Branching in Arabidopsis thaliana By Neelam Chaudhary Imperial College London Department of Life Sciences November 2013 A thesis submitted for the degree of Doctor of Philosophy and the Diploma of Imperial College London 1 For my Father (Late) and Mother They struggled hard to strengthen my faith in Almighty Allah and supported me to fulfil my dreams and to achieve my goals through their constant unconditional love, encouragement and prayers. For Scientists especially Life Scientists They spare time learning new ways to understand and solve problems in hopes of paving a better future for newer generations. They are more dedicated to making solid achievements than in running after swift but synthetic happiness. 2 ABSTRACT Shoot branching is regulated by auxin, cytokinin (CK) and strigolactone (SL). Cytokinin, being the only promoter of shoot branching, is antagonistic in function to auxin and strigolactone, which inhibit shoot branching. There is a close relationship between auxin and strigolactone, mediating each other to suppress shoot branching. Strigolactone reduces auxin transport from the buds, thus arresting bud outgrowth. On the other hand, auxin increases strigolactone production to control apical dominance. Antagonistic interaction between auxin and cytokinin has been reported as auxin inhibits lateral bud outgrowth by limiting CK supply to axillary buds. Previously, it has been found that levels of tZ-type CKs are extremely low in xylem sap of strigolactone mutants of Arabidopsis and pea.The current research aimed to explore the interaction between cytokinin and strigolactone, especially the regulatory mechanisms behind these low cytokinin levels.
    [Show full text]
  • Florigen Governs Shoot Regeneration
    Florigen Governs Shoot Regeneration Yaarit Kutsher Agricultural Research Organization Michal Fisler Agricultural Research Organization Adi DORON-FAIGENBOIM Agricultural Research Organization Moshe Reuveni ( [email protected] ) Agricultural Research Organization Research Article Keywords: reproductive stage (owering), protocols of shoot regeneration in plants, tobacco origen mRNA Posted Date: April 30th, 2021 DOI: https://doi.org/10.21203/rs.3.rs-450479/v1 License: This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License Page 1/16 Abstract It is widely known that during the reproductive stage (owering), plants do not root well. Most protocols of shoot regeneration in plants utilize juvenile tissue. Adding these two realities together encouraged us to study the role of origen in shoot regeneration. Mature tobacco tissue that expresses the endogenous tobacco origen mRNA regenerates poorly, while juvenile tissue that does not express the origen regenerates shoots well. Inhibition of Nitric Oxide (NO) synthesis reduced shoot regeneration as well as promoted owering and increased tobacco origen level. In contrast, the addition of NO (by way of NO donor) to the tissue increased regeneration, delayed owering, reduced tobacco origen mRNA. Ectopic expression of origen genes in tobacco or tomato decreased regeneration capacity signicantly. Overexpression pear PcFT2 gene increased regeneration capacity. During regeneration, origen mRNA was not changed. We conclude that origen presence in mature tobacco leaves reduces roots and shoots regeneration and is the possible reason for the age-related decrease in regeneration capacity. Introduction Plant regeneration by rebuilding new organs (organogenesis) results from new organ formation through dedifferentiation of differentiated plant cells and reorganization of cell division to create new organ meristems and new vascular connection between the explant and the newly regenerating organ 1,2.
    [Show full text]
  • Florigen Governs Shoot Regeneration
    bioRxiv preprint doi: https://doi.org/10.1101/2021.03.16.435564; this version posted March 17, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Florigen governs shoot regeneration. From Plant Science Institute ARO Volcani Center, PO Box 6, Bet Dagan 50250, Israel Yaarit Kutsher - [email protected] Michal Fisler - [email protected] Adi Faigenboim - [email protected] Moshe Reuveni – [email protected] - Corresponding author Plant Science Institute, ARO, Volcani Center, 68 Hamakabim Rd, PO Box 15159 Rishon LeZion 7528809, Israel, Tel. 972-3-968-3830 Abstract It is widely known that during the reproductive stage (flowering), plants do not root well. Most protocols of shoot regeneration in plants utilize juvenile tissue. Adding these two realities together encouraged us to studied the role of florigen in shoot regeneration. Mature tobacco tissue that expresses the endogenous tobacco florigen mRNA regenerates poorly, while juvenile tissue that does not express the florigen regenerates shoots well. Inhibition of Nitric Oxide (NO) synthesis reduced shoot regeneration as well as promoted flowering and increased tobacco florigen level. In contrast, the addition of NO (by way of NO donor) to the tissue increased regeneration, delayed flowering, reduced tobacco florigen mRNA. Ectopic expression of florigen genes in tobacco or tomato decreased regeneration capacity significantly. Overexpression pear PcFT2 gene increased regeneration capacity. During regeneration, florigen mRNA was not changed.
    [Show full text]
  • Integration of Cytokinin and Gibberellin Signalling by Arabidopsis
    RESEARCH ARTICLE 2073 Development 134, 2073-2081 (2007) doi:10.1242/dev.005017 Integration of cytokinin and gibberellin signalling by Arabidopsis transcription factors GIS, ZFP8 and GIS2 in the regulation of epidermal cell fate Yinbo Gan1, Chang Liu2, Hao Yu2 and Pierre Broun1,* The effective integration of hormone signals is essential to normal plant growth and development. Gibberellins (GA) and cytokinins act antagonistically in leaf formation and meristem maintenance and GA counteract some of the effects of cytokinins on epidermal differentiation. However, both can stimulate the initiation of defensive epidermal structures called trichomes. To understand how their relative influence on epidermal cell fate is modulated, we investigated the molecular mechanisms through which they regulate trichome initiation in Arabidopsis. The control by cytokinins of trichome production requires two genes expressed in late inflorescence organs, ZFP8 and GIS2, which encode C2H2 transcription factors related to GLABROUS INFLORESCENCE STEMS (GIS). Cytokinin-inducible GIS2 plays a prominent role in the cytokinin response, in which it acts downstream of SPINDLY and upstream of GLABROUS1. In addition, GIS2 and ZFP8 mediate, like GIS, the regulation of trichome initiation by gibberellins. By contrast, GIS does not play a significant role in the cytokinin response. Collectively, GIS, ZFP8 and GIS2, which encode proteins that are largely equivalent in function, play partially redundant and essential roles in inflorescence trichome initiation and in its regulation by GA and cytokinins. These roles are consistent with their pattern of expression and with the regional influence of GA and cytokinins on epidermal differentiation. Our findings show that functional specialization within a transcription factor gene family can facilitate the integration of different developmental cues in the regulation of plant cell differentiation.
    [Show full text]
  • HALLMARK DISSERTATION Fi
    The Roles of Cytokinins and Cytokinin-N-Glucosides in Development and Gene Expression of Arabidopsis thaliana by Howard Tucker Hallmark A dissertation submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Auburn, Alabama August 08, 2020 Keywords: Arabidopsis, cytokinin, trans-Zeatin, isopentenyladenine, glucosides, senescence Copyright 2020 by Howard Tucker Hallmark Approved by Aaron M. Rashotte, Chair, Professor of Biological Sciences Leslie R. Goertzen, Associate Professor of Biological Sciences Sang-Wook Park, Assistant Professor of Plant Pathology Haruka Wada, Assistant Professor of Biological Sciences Abstract The phytohormone cytokinin (CK) was first discovered over sixty years ago, and the decades following have produced an enormous amount of data about the various roles CK plays in intracellular signaling, gene expression, and plant development. An often-overlooked characteristic of this phytohormone is that it is not one single molecule; “cytokinin” is a generalized term for dozens of molecules which occur naturally in plants. Much of CK research has used synthetic CKs or only a single form of CK because it has long been believed that only a small subset of CKs display biological activity. Much of this dissertation focuses on CK-N- glucosides (CKNGs), long believed to be inactive forms of CK. Chapter 1 provides a broad overview of CK biology and their functions in plants, with particular focus on the model plant species Arabidopsis thaliana, which the rest of this dissertation work is completed in. Chapter 2 reviews recent advances in understanding of Cytokinin Response Factors, a family of transcription factors involved in response to a variety of environmental signals.
    [Show full text]
  • Cytokinin but Not Gibberellin Application Had Major Impact on the Phenylpropanoid Pathway in Grape
    UC Davis UC Davis Previously Published Works Title Cytokinin but not gibberellin application had major impact on the phenylpropanoid pathway in grape. Permalink https://escholarship.org/uc/item/2nk0s2bx Journal Horticulture research, 8(1) ISSN 2662-6810 Authors Tyagi, Kamal Maoz, Itay Kochanek, Bettina et al. Publication Date 2021-03-01 DOI 10.1038/s41438-021-00488-0 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Tyagi et al. Horticulture Research (2021) 8:51 Horticulture Research https://doi.org/10.1038/s41438-021-00488-0 www.nature.com/hortres ARTICLE Open Access Cytokinin but not gibberellin application had major impact on the phenylpropanoid pathway in grape Kamal Tyagi 1,2,ItayMaoz 1, Bettina Kochanek1,NoaSela3, Larry Lerno2,4, Susan E. Ebeler 2 and Amnon Lichter 1 Abstract Cytokinin and gibberellic acid (GA) are growth regulators used to increase berry size in seedless grapes and it is of interest to understand their effects on the phenylpropanoid pathway and on ripening processes. GA3 and synthetic cytokinin forchlorfenuron (N-(2-chloro-4-pyridyl)-N′-phenylurea, CPPU) and their combination were applied to 6 mm diameter fruitlets of ‘Sable Seedless’, and berries were sampled 51 and 70 days (d) following application. All treatments increased berry size and delayed sugar accumulation and acid degradation with a stronger effect of CPPU. CPPU, but not GA, reduced berry color and the levels of anthocyanins. While CPPU reduced the levels of anthocyanins by more than 50%, the combined treatment of GA+CPPU reduced the levels by about 25% at 51 d. CPPU treatment had minor effects on flavonols content but increased the levels of monomeric flavan-3-ols by more than two-fold.
    [Show full text]
  • Crosstalk Between Hydrogen Sulfide and Other Signal Molecules
    International Journal of Molecular Sciences Review Crosstalk between Hydrogen Sulfide and Other Signal Molecules Regulates Plant Growth and Development Lijuan Xuan y, Jian Li y, Xinyu Wang and Chongying Wang * Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China; [email protected] (L.X.); [email protected] (J.L.); [email protected] (X.W.) * Correspondence: [email protected]; Tel./Fax: +86-093-1891-4155 These authors contributed equally to this work. y Received: 31 May 2020; Accepted: 24 June 2020; Published: 28 June 2020 Abstract: Hydrogen sulfide (H2S), once recognized only as a poisonous gas, is now considered the third endogenous gaseous transmitter, along with nitric oxide (NO) and carbon monoxide (CO). Multiple lines of emerging evidence suggest that H2S plays positive roles in plant growth and development when at appropriate concentrations, including seed germination, root development, photosynthesis, stomatal movement, and organ abscission under both normal and stress conditions. H2S influences these processes by altering gene expression and enzyme activities, as well as regulating the contents of some secondary metabolites. In its regulatory roles, H2S always interacts with either plant hormones, other gasotransmitters, or ionic signals, such as abscisic acid (ABA), ethylene, auxin, 2+ CO, NO, and Ca . Remarkably, H2S also contributes to the post-translational modification of proteins to affect protein activities, structures, and sub-cellular localization. Here, we review the functions of H2S at different stages of plant development, focusing on the S-sulfhydration of proteins mediated by H2S and the crosstalk between H2S and other signaling molecules.
    [Show full text]
  • NIH Public Access Author Manuscript Plant J
    NIH Public Access Author Manuscript Plant J. Author manuscript; available in PMC 2010 January 15. NIH-PA Author ManuscriptPublished NIH-PA Author Manuscript in final edited NIH-PA Author Manuscript form as: Plant J. 2009 February ; 57(4): 606±614. doi:10.1111/j.1365-313X.2008.03711.x. Regulation of ACS protein stability by cytokinin and brassinosteroid Maureen Hansen, Hyun Sook Chae†, and Joseph J. Kieber* Department of Biology, University of North Carolina, Chapel Hill, NC 27599−3280, USA Summary A major question in plant biology is how phytohormone pathways interact. Here, we explore the mechanism by which cytokinins and brassinosteroids affect ethylene biosynthesis. Ethylene biosynthesis is regulated in response to a wide variety of endogenous and exogenous signals, including the levels of other phytohormones. Cytokinins act by increasing the stability of a subset of ACC synthases, which catalyze the generally rate-limiting step in ethylene biosynthesis. The induction of ethylene by cytokinin requires the canonical cytokinin two-component response pathway, including histidine kinases, histidine phosphotransfer proteins and response regulators. The cytokinin-induced myc–ACS5 stabilization occurs rapidly (<60 min), consistent with a primary output of this two-component signaling pathway. We examined the mechanism by which another phytohormone, brassinosteroid, elevates ethylene biosynthesis in etiolated seedlings. Similar to cytokinin, brassinosteroid acts post-transcriptionally by increasing the stability of ACS5 protein, and its effects on ACS5 were additive with those of cytokinin. These data suggest that ACS is regulated by phytohormones through regulatory inputs that probably act together to continuously adjust ethylene biosynthesis in various tissues and in response to various environmental conditions.
    [Show full text]