Cytokinins (CKs) and their metabolites and derivatives are essential for cell division, plant growth regulation and development. They are typically found at minute concentrations in plant tissues containing very complicated biological matrices. Therefore, defined standards labelled with stable isotopes are required for precise metabolic profiling and quantification of CKs, as well as in vivo elucidation of CK biosynthesis in various plant species. In this work, 11 [15N]-labelled C6-purine derivatives were prepared, among them 5 aromatic (4, 5, 6, 7, 8) and 3 isoprenoid (9, 10, 11) CKs. Compared to current methods, optimized syntheses of 6-amino-9H-[15N5]-purine (adenine) and 6-chloro-9H-[15N4]-purine (6-chloropurine) were performed to achieve more effective, selective and generally easier approaches. The chemical identity and purity of prepared compounds were confirmed by physico-chemical analyses (TLC; HRMS; HPLC-MS; 1H, 13C, 15N NMR). The presented approach is applicable for the synthesis of any other desired [15N4]-labelled C6-substituted purine derivatives.

• Klíčová slova
• 15N-labelled, cytokinin, purine, synthesis,
• Publikační typ
• časopisecké články MeSH

Almost 25 years ago, an enzyme named zeatin cis-trans isomerase from common bean has been described by Bassil et al. (1993). The partially purified enzyme required an external addition of FAD and dithiothreitol for the conversion of cis-zeatin to its trans- isomer that occurred only under light. Although an existence of this important enzyme involved in the metabolism of plant hormones cytokinins was generally accepted by plant biologists, the corresponding protein and encoding gene have not been identified to date. Based on the original paper, we purified and identified an enzyme from maize, which shows the described zeatin cis-trans isomerase activity. The enzyme belongs to nucleotide pyrophosphatase/phosphodiesterase family, which is well characterized in mammals, but less known in plants. Further experiments with the recombinant maize enzyme obtained from yeast expression system showed that rather than the catalytic activity of the enzyme itself, a non-enzymatic flavin induced photoisomerization is responsible for the observed zeatin cis-trans interconversion in vitro. An overexpression of the maize nucleotide pyrophosphatase/phosphodiesterase gene led to decreased FAD and increased FMN and riboflavin contents in transgenic Arabidopsis plants. However, neither contents nor the ratio of zeatin isomers was altered suggesting that the enzyme is unlikely to catalyze the interconversion of zeatin isomers in vivo. Using enhanced expression of a homologous gene, functional nucleotide pyrophosphatase/phosphodiesterase was also identified in rice.

• Klíčová slova
• flavins, isomerization, maize, nucleotide pyrophosphatase/phosphodiesterase, zeatin,
• Publikační typ
• časopisecké články MeSH

Among phytohormones, cytokinins (CKs) play an important role in controlling crucial aspects of plant development. Not only plants but also diverse microorganisms are able to produce phytohormones, including CKs, though knowledge concerning their biosynthesis and metabolism is still limited. In this work we demonstrate that the fungus Leptosphaeria maculans, a hemi-biotrophic pathogen of oilseed rape (Brassica napus), causing one of the most damaging diseases of this crop, is able to modify the CK profile in infected B. napus tissues, as well as produce a wide range of CKs in vitro, with the cis-zeatin derivatives predominating. The endogenous CK spectrum of L. maculans in vitro consists mainly of free CK bases, as opposed to plants, where other CK forms are mostly more abundant. Using functional genomics, enzymatic and feeding assays with CK bases supplied to culture media, we show that L. maculans contains a functional: (i) isopentenyltransferase (IPT) involved in cZ production; (ii) adenosine kinase (AK) involved in phosphorylation of CK ribosides to nucleotides; and (iii) CK-degradation enzyme cytokinin oxidase/dehydrogenase (CKX). Our data further indicate the presence of cis-trans isomerase, zeatin O-glucosyltransferase(s) and N6-(Δ2-isopentenyl)adenine hydroxylating enzyme. Besides, we report on a crucial role of LmAK for L. maculans fitness and virulence. Altogether, in this study we characterize in detail the CK metabolism of the filamentous fungi L. maculans and report its two novel components, the CKX and CK-related AK activities, according to our knowledge for the first time in the fungal kingdom. Based on these findings, we propose a model illustrating CK metabolism pathways in L. maculans.

• Klíčová slova
• Leptosphaeria maculans, adenosine kinase, cytokinin, cytokinin oxidase/dehydrogenase, isopentenyltransferase, zeatin cis/trans isomerase,
• Publikační typ
• časopisecké články MeSH

While the molecular basis for cytokinin action is quite well understood in flowering plants, little is known about the cytokinin signal transduction in early diverging land plants. The genome of the bryophyte Physcomitrella patens (Hedw.) B.S. encodes three classical cytokinin receptors, the CHASE domain-containing histidine kinases, CHK1, CHK2, and CHK3. In a complementation assay with protoplasts of receptor-deficient Arabidopsis thaliana as well as in cytokinin binding assays, we found evidence that CHK1 and CHK2 receptors can function in cytokinin perception. Using gene targeting, we generated a collection of CHK knockout mutants comprising single (Δchk1, Δchk2, Δchk3), double (Δchk1,2, Δchk1,3, Δchk2,3), and triple (Δchk1,2,3) mutants. Mutants were characterized for their cytokinin response and differentiation capacities. While the wild type did not grow on high doses of cytokinin (1 µM benzyladenine), the Δchk1,2,3 mutant exhibited normal protonema growth. Bud induction assays showed that all three cytokinin receptors contribute to the triggering of budding, albeit to different extents. Furthermore, while the triple mutant showed no response in this bioassay, the remaining mutants displayed budding responses in a diverse manner to different types and concentrations of cytokinins. Determination of cytokinin levels in mutants showed no drastic changes for any of the cytokinins; thus, in contrast to Arabidopsis, revealing only small impacts of cytokinin signaling on homeostasis. In summary, our study provides a first insight into the molecular action of cytokinin in an early diverging land plant and demonstrates that CHK receptors play an essential role in bud induction and gametophore development.

• Klíčová slova
• Bryophyte, Physcomitrella patens, cytokinin, cytokinin receptor, evolution, moss, phytohormone, plant growth regulator, signaling, two-component system.,
• MeSH
• biotest MeSH
• butadieny farmakologie   MeSH
• cytokininy farmakologie   MeSH
• fenotyp MeSH
• fyziologická adaptace MeSH
• genový knockout MeSH
• hemiterpeny farmakologie   MeSH
• mechy účinky léků   genetika   metabolismus   MeSH
• mutace genetika   MeSH
• pentany farmakologie   MeSH
• receptory buněčného povrchu chemie   metabolismus   MeSH
• regulace genové exprese u rostlin MeSH
• rostlinné proteiny chemie   metabolismus   MeSH
• terciární struktura proteinů MeSH
• vztahy mezi strukturou a aktivitou MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• butadieny MeSH
• cytokininy MeSH
• hemiterpeny MeSH
• isoprene MeSH Prohlížeč
• pentany MeSH
• receptory buněčného povrchu MeSH
• rostlinné proteiny MeSH

Sedentary plant-parasitic cyst nematodes are biotrophs that cause significant losses in agriculture. Parasitism is based on modifications of host root cells that lead to the formation of a hypermetabolic feeding site (a syncytium) from which nematodes withdraw nutrients. The host cell cycle is activated in an initial cell selected by the nematode for feeding, followed by activation of neighboring cells and subsequent expansion of feeding site through fusion of hundreds of cells. It is generally assumed that nematodes manipulate production and signaling of the plant hormone cytokinin to activate cell division. In fact, nematodes have been shown to produce cytokinin in vitro; however, whether the hormone is secreted into host plants and plays a role in parasitism remained unknown. Here, we analyzed the spatiotemporal activation of cytokinin signaling during interaction between the cyst nematode, Heterodera schachtii, and Arabidopsis using cytokinin-responsive promoter:reporter lines. Our results showed that cytokinin signaling is activated not only in the syncytium but also in neighboring cells to be incorporated into syncytium. An analysis of nematode infection on mutants that are deficient in cytokinin or cytokinin signaling revealed a significant decrease in susceptibility of these plants to nematodes. Further, we identified a cytokinin-synthesizing isopentenyltransferase gene in H. schachtii and show that silencing of this gene in nematodes leads to a significant decrease in virulence due to a reduced expansion of feeding sites. Our findings demonstrate the ability of a plant-parasitic nematode to synthesize a functional plant hormone to manipulate the host system and establish a long-term parasitic interaction.

• Klíčová slova
• Arabidopsis thaliana, IPT, cell cycle, cyst nematode, cytokinin,
• MeSH
• Arabidopsis * genetika   metabolismus   parazitologie   MeSH
• cytokininy genetika   metabolismus   MeSH
• hlístice fyziologie   MeSH
• interakce hostitele a parazita fyziologie   MeSH
• molekulární sekvence - údaje MeSH
• nemoci rostlin parazitologie   MeSH
• sekvence nukleotidů MeSH
• signální transdukce * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• cytokininy MeSH

Cytokinins, a class of phytohormones, are adenine derivatives common to many different organisms. In plants, these play a crucial role as regulators of plant development and the reaction to abiotic and biotic stress. Key enzymes in the cytokinin synthesis and degradation in modern land plants are the isopentyl transferases and the cytokinin dehydrogenases, respectively. Their encoding genes have been probably introduced into the plant lineage during the primary endosymbiosis. To shed light on the evolution of these proteins, the genes homologous to plant adenylate isopentenyl transferase and cytokinin dehydrogenase were amplified from the genomic DNA of cyanobacterium Nostoc sp. PCC 7120 and expressed in Escherichia coli. The putative isopentenyl transferase was shown to be functional in a biochemical assay. In contrast, no enzymatic activity was detected for the putative cytokinin dehydrogenase, even though the principal domains necessary for its function are present. Several mutant variants, in which conserved amino acids in land plant cytokinin dehydrogenases had been restored, were inactive. A combination of experimental data with phylogenetic analysis indicates that adenylate-type isopentenyl transferases might have evolved several times independently. While the Nostoc genome contains a gene coding for protein with characteristics of cytokinin dehydrogenase, the organism is not able to break down cytokinins in the way shown for land plants.

• MeSH
• biologická evoluce MeSH
• cytokininy metabolismus   MeSH
• Escherichia coli enzymologie   růst a vývoj   MeSH
• fylogeneze MeSH
• geneticky modifikované rostliny genetika   růst a vývoj   metabolismus   MeSH
• molekulární sekvence - údaje MeSH
• mutace genetika   MeSH
• mutageneze cílená MeSH
• Nostoc enzymologie   genetika   MeSH
• oxidoreduktasy genetika   metabolismus   MeSH
• prenyltransferáza genetika   metabolismus   MeSH
• regulace genové exprese enzymů MeSH
• rekombinantní proteiny metabolismus   MeSH
• sekvence aminokyselin MeSH
• sekvenční homologie aminokyselin MeSH
• tabák enzymologie   růst a vývoj   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• cytokinin oxidase MeSH Prohlížeč
• cytokininy MeSH
• oxidoreduktasy MeSH
• prenyltransferáza MeSH
• rekombinantní proteiny MeSH

Cytokinins (CKs) are well-established as important phytohormonal regulators of plant growth and development. An increasing number of studies have also revealed the function of these hormones in plant responses to biotic and abiotic stresses. While the function of certain CK classes, including trans-zeatin and isopentenyladenine-type CKs, have been studied in detail, the role of cis-zeatin-type CKs (cZs) in plant development and in mediating environmental interactions is less well defined. Here we provide a comprehensive summary of the current knowledge about abundance, metabolism and activities of cZs in plants. We outline the history of their analysis and the metabolic routes comprising cZ biosynthesis and degradation. Further we provide an overview of changes in the pools of cZs during plant development and environmental interactions. We summarize studies that investigate the role of cZs in regulating plant development and defence responses to pathogen and herbivore attack and highlight their potential role as 'novel' stress-response markers. Since the functional roles of cZs remain largely based on correlative data and genetic manipulations of their biosynthesis, inactivation and degradation are few, we suggest experimental approaches using transgenic plants altered in cZ levels to further uncover their roles in plant growth and environmental interactions and their potential for crop improvement.

• Klíčová slova
• Abiotic stress, c-io6A37-tRNA, cis-zeatin, herbivory, pathogen, plant growth, prenylated tRNA.,
• MeSH
• býložravci MeSH
• fyziologie rostlin * MeSH
• potravní řetězec * MeSH
• regulace genové exprese u rostlin * MeSH
• regulátory růstu rostlin metabolismus   MeSH
• vývoj rostlin MeSH
• zeatin metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• regulátory růstu rostlin MeSH
• zeatin MeSH

BACKGROUND: Bryophytes represent a very diverse group of non-vascular plants such as mosses, liverworts and hornworts and the oldest extant lineage of land plants. Determination of endogenous phytohormone profiles in bryophytes can provide substantial information about early land plant evolution. In this study, we screened thirty bryophyte species including six liverworts and twenty-four mosses for their phytohormone profiles in order to relate the hormonome with phylogeny in the plant kingdom. METHODOLOGY: Samples belonging to nine orders (Pelliales, Jungermanniales, Porellales, Sphagnales, Tetraphidales, Polytrichales, Dicranales, Bryales, Hypnales) were collected in Central and Northern Bohemia. The phytohormone content was analysed with a high performance liquid chromatography electrospray tandem-mass spectrometry (HPLC-ESI-MS/MS). PRINCIPAL FINDINGS: As revealed for growth hormones, some common traits such as weak conjugation of both cytokinins and auxins, intensive production of cisZ-type cytokinins and strong oxidative degradation of auxins with abundance of a major primary catabolite 2-oxindole-3-acetic acid were pronounced in all bryophytes. Whereas apparent dissimilarities in growth hormones profiles between liverworts and mosses were evident, no obvious trends in stress hormone levels (abscisic acid, jasmonic acid, salicylic acid) were found with respect to the phylogeny. CONCLUSION: The apparent differences in conjugation and/or degradation strategies of growth hormones between liverworts and mosses might potentially show a hidden link between vascular plants and liverworts. On the other hand, the complement of stress hormones in bryophytes probably correlate rather with prevailing environmental conditions and plant survival strategy than with plant evolution.

• MeSH
• Bryophyta klasifikace   metabolismus   MeSH
• cyklopentany analýza   metabolismus   MeSH
• cytokininy analýza   metabolismus   MeSH
• fylogeneze MeSH
• hmotnostní spektrometrie s elektrosprejovou ionizací MeSH
• kyselina abscisová analýza   metabolismus   MeSH
• kyselina salicylová analýza   metabolismus   MeSH
• kyseliny indoloctové analýza   metabolismus   MeSH
• oxindoly MeSH
• oxylipiny analýza   metabolismus   MeSH
• regulátory růstu rostlin analýza   metabolismus   MeSH
• vysokoúčinná kapalinová chromatografie MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• 2-oxindole-3-acetic acid MeSH Prohlížeč
• cyklopentany MeSH
• cytokininy MeSH
• jasmonic acid MeSH Prohlížeč
• kyselina abscisová MeSH
• kyselina salicylová MeSH
• kyseliny indoloctové MeSH
• oxindoly MeSH
• oxylipiny MeSH
• regulátory růstu rostlin MeSH