Auxin and cytokinins have been identified as key regulators of plant development. Recently, these phytohormones have been shown to interact during important developmental processes, including positioning, identity acquisition and maintenance of meristem organizing centres, regulation of balance between cell division and differentiation, and postembryonic de novo organogenesis. Here, we discuss recent advances in our understanding of the underlying molecular mechanisms at the levels of regulating metabolism, signalling, gene expression and protein stability.

• MeSH
• Arabidopsis genetika   růst a vývoj   metabolismus   MeSH
• biologický transport genetika   MeSH
• cytokininy metabolismus   MeSH
• kyseliny indoloctové metabolismus   MeSH
• meristém růst a vývoj   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin metabolismus   MeSH
• rostliny genetika   metabolismus   MeSH
• signální transdukce MeSH
• vývoj rostlin MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH

• MeSH
• cytokininy metabolismus   MeSH
• flavoproteiny antagonisté a inhibitory   metabolismus   MeSH
• jedlá semena enzymologie   MeSH
• oxidoreduktasy metabolismus   MeSH
• rostlinné geny MeSH
• sekvence aminokyselin MeSH
• transport elektronů MeSH

The formation of glycoconjugates depends on nucleotide sugars, which serve as donor substrates for glycosyltransferases in the lumen of Golgi vesicles and the endoplasmic reticulum (ER). Import of nucleotide sugars from the cytosol is an important prerequisite for these reactions and is mediated by nucleotide sugar transporters. Here, we report the identification of REPRESSOR OF CYTOKININ DEFICIENCY 1 (ROCK1, At5g65000) as an ER-localized facilitator of UDP-N-acetylglucosamine (UDP-GlcNAc) and UDP-N-acetylgalactosamine (UDP-GalNAc) transport in Arabidopsis thaliana. Mutant alleles of ROCK1 suppress phenotypes inferred by a reduced concentration of the plant hormone cytokinin. This suppression is caused by the loss of activity of cytokinin-degrading enzymes, cytokinin oxidases/dehydrogenases (CKXs). Cytokinin plays an essential role in regulating shoot apical meristem (SAM) activity and shoot architecture. We show that rock1 enhances SAM activity and organ formation rate, demonstrating an important role of ROCK1 in regulating the cytokinin signal in the meristematic cells through modulating activity of CKX proteins. Intriguingly, genetic and molecular analysis indicated that N-glycosylation of CKX1 was not affected by the lack of ROCK1-mediated supply of UDP-GlcNAc. In contrast, we show that CKX1 stability is regulated in a proteasome-dependent manner and that ROCK1 regulates the CKX1 level. The increased unfolded protein response in rock1 plants and suppression of phenotypes caused by the defective brassinosteroid receptor bri1-9 strongly suggest that the ROCK1 activity is an important part of the ER quality control system, which determines the fate of aberrant proteins in the secretory pathway.

• MeSH
• Arabidopsis metabolismus   ultrastruktura   MeSH
• biologický transport MeSH
• cytokininy metabolismus   MeSH
• endoplazmatické retikulum metabolismus   MeSH
• fenotyp MeSH
• meristém metabolismus   ultrastruktura   MeSH
• proteiny huseníčku metabolismus   MeSH
• transportní proteiny metabolismus   MeSH
• uridindifosfát-N-acetylgalaktosamin metabolismus   MeSH
• uridindifosfát-N-acetylglukosamin metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Identification of mutants with impairments in auxin biosynthesis and dynamics by forward genetic screening is hindered by the complexity, redundancy and necessity of the pathways involved. Furthermore, although a few auxin-deficient mutants have been recently identified by screening for altered responses to shade, ethylene, N-1-naphthylphthalamic acid (NPA) or cytokinin (CK), there is still a lack of robust markers for systematically isolating such mutants. We hypothesized that a potentially suitable phenotypic marker is root curling induced by CK, as observed in the auxin biosynthesis mutant CK-induced root curling 1 / tryptophan aminotransferase of Arabidopsis 1 (ckrc1/taa1). Phenotypic observations, genetic analyses and biochemical complementation tests of Arabidopsis seedlings displaying the trait in large-scale genetic screens showed that it can facilitate isolation of mutants with perturbations in auxin biosynthesis, transport and signaling. However, unlike transport/signaling mutants, the curled (or wavy) root phenotypes of auxin-deficient mutants were significantly induced by CKs and could be rescued by exogenous auxins. Mutants allelic to several known auxin biosynthesis mutants were re-isolated, but several new classes of auxin-deficient mutants were also isolated. The findings show that CK-induced root curling provides an effective marker for discovering genes involved in auxin biosynthesis or homeostasis.

• MeSH
• Arabidopsis enzymologie   genetika   MeSH
• biologický transport účinky léků   MeSH
• cytokininy metabolismus   MeSH
• fenotyp MeSH
• kořeny rostlin enzymologie   genetika   růst a vývoj   MeSH
• kyseliny indoloctové metabolismus   farmakologie   MeSH
• mutace MeSH
• proteiny huseníčku genetika   metabolismus   MeSH
• regulátory růstu rostlin biosyntéza   MeSH
• semenáček účinky léků   růst a vývoj   metabolismus   MeSH
• signální transdukce účinky léků   MeSH
• tryptofantransaminasa genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Auxin and cytokinin are key endogenous regulators of plant development. Although cytokinin-mediated modulation of auxin distribution is a developmentally crucial hormonal interaction, its molecular basis is largely unknown. Here we show a direct regulatory link between cytokinin signalling and the auxin transport machinery uncovering a mechanistic framework for cytokinin-auxin cross-talk. We show that the CYTOKININ RESPONSE FACTORS (CRFs), transcription factors downstream of cytokinin perception, transcriptionally control genes encoding PIN-FORMED (PIN) auxin transporters at a specific PIN CYTOKININ RESPONSE ELEMENT (PCRE) domain. Removal of this cis-regulatory element effectively uncouples PIN transcription from the CRF-mediated cytokinin regulation and attenuates plant cytokinin sensitivity. We propose that CRFs represent a missing cross-talk component that fine-tunes auxin transport capacity downstream of cytokinin signalling to control plant development.

• MeSH
• Arabidopsis MeSH
• chromatinová imunoprecipitace MeSH
• cytokininy metabolismus   MeSH
• geneticky modifikované rostliny MeSH
• konfokální mikroskopie MeSH
• kořeny rostlin metabolismus   MeSH
• kvantitativní polymerázová řetězová reakce MeSH
• kyseliny indoloctové metabolismus   MeSH
• membránové transportní proteiny genetika   metabolismus   MeSH
• proteiny huseníčku genetika   metabolismus   MeSH
• regulace genové exprese u rostlin MeSH
• responzivní elementy MeSH
• signální transdukce MeSH
• transkripční faktory genetika   metabolismus   MeSH
• zelené fluorescenční proteiny MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Cytokinins are plant hormones, derivatives of adenine with a side chain at the N6-position. They are involved in many physiological processes. While the metabolism of trans-zeatin and isopentenyladenine, which are considered to be highly active cytokinins, has been extensively studied, there are others with less obvious functions, such as cis-zeatin, dihydrozeatin, and aromatic cytokinins, which have been comparatively neglected. To help explain this duality, we present a novel hypothesis metaphorically comparing various cytokinin forms, enzymes of CK metabolism, and their signalling and transporter functions to the comics superheroes Hulk and Deadpool. Hulk is a powerful but short-lived creation, whilst Deadpool presents a more subtle and enduring force. With this dual framework in mind, this review compares different cytokinin metabolites, and their biosynthesis, translocation, and sensing to illustrate the different mechanisms behind the two CK strategies. This is put together and applied to a plant developmental scale and, beyond plants, to interactions with organisms of other kingdoms, to highlight where future study can benefit the understanding of plant fitness and productivity.

• MeSH
• Arabidopsis metabolismus   MeSH
• biologické modely MeSH
• biologický transport MeSH
• biotest MeSH
• cytokininy metabolismus   MeSH
• fyziologie rostlin * MeSH
• glykosylace MeSH
• hydrolýza MeSH
• kinetika MeSH
• kinetin metabolismus   MeSH
• oxidoreduktasy metabolismus   MeSH
• regulátory růstu rostlin metabolismus   MeSH
• rostliny metabolismus   MeSH
• signální transdukce * MeSH
• vazba proteinů MeSH
• zeatin analogy a deriváty   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH

Cytokinins are a class of phytohormones, signalling molecules specific to plants. They act as regulators of diverse physiological processes in complex signalling pathways. It is necessary for plants to continuously regulate cytokinin distribution among different organs, tissues, cells, and compartments. Such regulatory mechanisms include cytokinin biosynthesis, metabolic conversions and degradation, as well as cytokinin membrane transport. In our review, we aim to provide a thorough picture of the latter. We begin by summarizing cytokinin structures and physicochemical properties. Then, we revise the elementary thermodynamic and kinetic aspects of cytokinin membrane transport. Next, we review which membrane-bound carrier proteins and protein families recognize cytokinins as their substrates. Namely, we discuss the families of "equilibrative nucleoside transporters" and "purine permeases", which translocate diverse purine-related compounds, and proteins AtPUP14, AtABCG14, AtAZG1, and AtAZG2, which are specific to cytokinins. We also address long-distance cytokinin transport. Putting all these pieces together, we finally discuss cytokinin distribution as a net result of these processes, diverse in their physicochemical nature but acting together to promote plant fitness.

• MeSH
• Arabidopsis metabolismus   MeSH
• biologický transport MeSH
• buněčná membrána metabolismus   MeSH
• cytokininy metabolismus   MeSH
• homeostáza MeSH
• hydrofobní a hydrofilní interakce MeSH
• kinetika MeSH
• kořeny rostlin metabolismus   MeSH
• membránové transportní proteiny metabolismus   MeSH
• proteiny huseníčku genetika   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin metabolismus   MeSH
• signální transdukce fyziologie   MeSH
• termodynamika MeSH
• výhonky rostlin metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Plant growth and development are critically influenced by unpredictable abiotic factors. To survive fluctuating changes in their environments, plants have had to develop robust adaptive mechanisms. The dynamic and complementary actions of the auxin and cytokinin pathways regulate a plethora of developmental processes, and their ability to crosstalk makes them ideal candidates for mediating stress-adaptation responses. Other crucial signaling molecules responsible for the tremendous plasticity observed in plant morphology and in response to abiotic stress are reactive oxygen species (ROS). Proper temporal and spatial distribution of ROS and hormone gradients is crucial for plant survival in response to unfavorable environments. In this regard, the convergence of ROS with phytohormone pathways acts as an integrator of external and developmental signals into systemic responses organized to adapt plants to their environments. Auxin and cytokinin signaling pathways have been studied extensively. Nevertheless, we do not yet understand the impact on plant stress tolerance of the sophisticated crosstalk between the two hormones. Here, we review current knowledge on the function of auxin and cytokinin in redirecting growth induced by abiotic stress in order to deduce their potential points of crosstalk.

• MeSH
• biologický transport MeSH
• cytokininy metabolismus   MeSH
• fyziologická adaptace MeSH
• fyziologický stres * MeSH
• fyziologie rostlin * MeSH
• genové regulační sítě MeSH
• kyseliny indoloctové metabolismus   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin metabolismus   MeSH
• rostliny genetika   metabolismus   MeSH
• signální transdukce MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

The Arabidopsis (Arabidopsis thaliana) gynoecium consists of two congenitally fused carpels made up of two lateral valve domains and two medial domains, which retain meristematic properties and later fuse to produce the female reproductive structures vital for fertilization. Polar auxin transport (PAT) is important for setting up distinct apical auxin signaling domains in the early floral meristem remnants allowing for lateral domain identity and outgrowth. Crosstalk between auxin and cytokinin plays an important role in the development of other meristematic tissues, but hormone interaction studies to date have focused on more accessible later-stage gynoecia and the spatiotemporal interactions pivotal for patterning of early gynoecium primordia remain unknown. Focusing on the earliest stages, we propose a cytokinin-auxin feedback model during early gynoecium patterning and hormone homeostasis. Our results suggest that cytokinin positively regulates auxin signaling in the incipient gynoecial primordium and strengthen the concept that cytokinin regulates auxin homeostasis during gynoecium development. Specifically, medial cytokinin promotes auxin biosynthesis components [YUCCA1/4 (YUC1/4)] in, and PINFORMED7 (PIN7)-mediated auxin efflux from, the medial domain. The resulting laterally focused auxin signaling triggers ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN6 (AHP6), which then represses cytokinin signaling in a PAT-dependent feedback. Cytokinin also down-regulates PIN3, promoting auxin accumulation in the apex. The yuc1, yuc4, and ahp6 mutants are hypersensitive to exogenous cytokinin and 1-napthylphthalamic acid (NPA), highlighting their role in mediolateral gynoecium patterning. In summary, these mechanisms self-regulate cytokinin and auxin signaling domains, ensuring correct domain specification and gynoecium development.

• MeSH
• Arabidopsis embryologie   genetika   metabolismus   MeSH
• biologické modely MeSH
• biologický transport MeSH
• cytokininy metabolismus   MeSH
• homeostáza MeSH
• květy embryologie   MeSH
• kyseliny indoloctové metabolismus   MeSH
• proteiny huseníčku genetika   metabolismus   MeSH
• regulace genové exprese u rostlin MeSH
• regulátory růstu rostlin metabolismus   MeSH
• rostlinné geny MeSH
• rozvržení tělního plánu * MeSH
• signální transdukce * MeSH
• upregulace MeSH
• Publikační typ
• časopisecké články MeSH

Cytokinins comprise a group of phytohormones with an organ-specific mode of action. Although the mechanisms controlling the complex networks of cytokinin metabolism are partially known, the role of individual cytokinin types in the maintenance of cytokinin homeostasis remains unclear. Utilizing the overproduction of single-chain Fv antibodies selected for their ability to bind trans-zeatin riboside and targeted to the endoplasmic reticulum, we post-synthetically modulated cytokinin ribosides, the proposed transport forms of cytokinins. We observed asymmetric activity of cytokinin biosynthetic genes and cytokinin distribution in wild-type tobacco seedlings with higher cytokinin abundance in the root than in the shoot. Antibody-mediated modulation of cytokinin ribosides further enhanced the relative cytokinin abundance in the roots and induced cytokinin-related phenotypes in an organ-specific manner. The activity of cytokinin oxidase/dehydrogenase in the roots was strongly up-regulated in response to antibody-mediated formation of the cytokinin pool in the endoplasmic reticulum. However, we only detected a slight decrease in the root cytokinin levels. In contrast, a significant decrease of cytokinins occurred in the shoot. We suggest the roots as the main site of cytokinin biosynthesis in tobacco seedlings. Conversely, cytokinin levels in the shoot seem to depend largely on long-range transport of cytokinin ribosides from the root and their subsequent metabolic activation.

• MeSH
• cytokininy fyziologie   MeSH
• fenotyp * MeSH
• homeostáza * MeSH
• isopentenyladenosin analogy a deriváty   metabolismus   MeSH
• protilátky produkované rostlinami fyziologie   MeSH
• regulátory růstu rostlin fyziologie   MeSH
• semenáček fyziologie   MeSH
• tabák fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH