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What are the implications of variation in root hair length on tolerance to phosphorus deficiency in combination with water stress in barley (Hordeum vulgare)?

What are the implications of variation in root hair length on tolerance to phosphorus deficiency in combination with water stress in barley (Hordeum vulgare)? | plant developments | Scoop.it

The results confirmed the robustness of the root hair phenotypes in soils and their relationship to rhizosheath production. The data demonstrated that root hair length is important for shoot P accumulation and biomass, while only the presence of root hairs is critical for yield. Root hair presence was also critical for tolerance to extreme combined P deficit and drought stress, with genotypes with no root hairs suffering extreme growth retardation in comparison with those with root hairs.

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Root growth is modulated by differential hormonal sensitivity in neighboring cells

Root growth is modulated by differential hormonal sensitivity in neighboring cells | plant developments | Scoop.it
A biweekly scientific journal publishing high-quality research in molecular biology and genetics, cancer biology, biochemistry, and related fields
PMG's insight:

coordination between two types of epidermal root cells, hair and nonhair cells, establishes root sensitivity to the plant hormones brassinosteroids (BRs). While expression of the BR receptor BRASSINOSTEROID-INSENSITIVE1 (BRI1) in hair cells promotes cell elongation in all tissues, its high relative expression in nonhair cells is inhibitory. Elevated ethylene and deposition of crystalline cellulose underlie the inhibitory effect of BRI1. We propose that the relative spatial distribution of BRI1, and not its absolute level, fine-tunes growth.

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The AHP6 cytokinin signaling inhibitor mediates an auxin-cytokinin crosstalk that regulates the timing of organ initiation at the shoot apical meristem

The AHP6 cytokinin signaling inhibitor mediates an auxin-cytokinin crosstalk that regulates the timing of organ initiation at the shoot apical meristem | plant developments | Scoop.it
Phyllotaxis, the spatio-temporal pattern of organogenesis at the shoot apical meristem, emerges in large part from inhibitory fields consisting in auxin-depleted areas centered on organs. We recently demonstrated the existence of an additional hormone-based inhibitory field generated by Arabidopsis Histidine Phosphotransfer Protein 6 (AHP6), an inhibitor of cytokinin signaling. We have shown that the spatio-temporal distribution of AHP6 in the meristem is essential for optimizing the rhythmicity of organ initiation. Here, we further analyzed AHP6 expression using fluorescent whole mount mRNA in situ hybridization and demonstrate a precise control of AHP6 level and expression domain over time. While we previously showed a regulation of AHP6 directly downstream of auxin, we show here that AHP6 transcription is unlikely influenced by cytokinin distribution in the meristem. Finally, we provide evidence that cytokinins and auxin might act synergistically during organ initiation, providing a plausible explanation for how AHP6 regulates phyllotaxis.
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Cell surface ABP1-TMK auxin-sensing complex activate... [Science. 2014] - PubMed - NCBI

Cell surface ABP1-TMK auxin-sensing complex activate... [Science. 2014] - PubMed - NCBI | plant developments | Scoop.it
PubMed comprises more than 23 million citations for biomedical literature from MEDLINE, life science journals, and online books. Citations may include links to full-text content from PubMed Central and publisher web sites.
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TMK) receptor-like kinases interact with ABP1 and transduce auxin signal to activate plasma membrane-associated ROPs [Rho-like guanosine triphosphatases (GTPase) from plants], leading to changes in the cytoskeleton and the shape of leaf pavement cells in Arabidopsis. The interaction between ABP1 and TMK at the cell surface is induced by auxin and requires ABP1 sensing of auxin. 

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CurrOpinPlantBiol: DNA assembly for plant biology: techniques and tools

CurrOpinPlantBiol: DNA assembly for plant biology: techniques and tools | plant developments | Scoop.it

Via Mary Williams
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A Highly Selective Biosensor with Nanomolar Sensitivity Based on Cytokinin Dehydrogenase

A Highly Selective Biosensor with Nanomolar Sensitivity Based on Cytokinin Dehydrogenase | plant developments | Scoop.it
PLOS ONE: an inclusive, peer-reviewed, open-access resource from the PUBLIC LIBRARY OF SCIENCE. Reports of well-performed scientific studies from all disciplines freely available to the whole world.
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Lotus japonicus Cytokinin Receptors Work Partially Redundantly to Mediate Nodule Formation

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 L. japonicus contains a small family of four cytokinin receptor genes, which all respond to M. lotiinfection. We show that within the root cortex, LHK1 performs an essential role but also works partially redundantly with LHK1A and LHK3 to mediate cell divisions for nodule primordium formation. The LHK1 receptor is also presumed to partake in mediating a feedback mechanism that negatively regulates bacterial infections at the root epidermis. Interestingly, the Arabidopsis thaliana AHK4receptor gene can functionally replace Lhk1 in mediating nodule organogenesis, indicating that the ability to perform this developmental process is not determined by unique, legume-specific properties of LHK1.

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Boron deficiency results in early repression of a cytokinin receptor gene and abnormal cell differentiation in the apical root meristem of Arabidopsis thaliana

Boron deficiency results in early repression of a cytokinin receptor gene and abnormal cell differentiation in the apical root meristem of Arabidopsis thaliana | plant developments | Scoop.it
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Detection of cycline B1 by GUS staining of a promoter-reporter construct revealed that low B led to a reduced zone of cell division. The expression of CRE1/WOL/AHK4, encoding an integral membrane protein with histidine kinase domain that mediates cytokinin signaling and root xylem differentiation, was inhibited under B deficiency resulting in arrested xylem development at the protoxylem stage. Because the transition from cell division to cell differentiation in apical root meristems is controlled by cytokinins, this result support the hypothesis that signaling mechanisms during cell differentiation and organogenesis are highly sensitive to B deficiency, and together with previous reports that link the micronutrient with auxin or ethylene control of root architecture, suggests that B could play a role in regulation of hormone mediated early plant development signaling.

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Cytokinin signaling stabilizes the response activator ARR1 - Kurepa - The Plant Journal - Wiley Online Library

Cytokinin signaling stabilizes the response activator ARR1 - Kurepa - The Plant Journal - Wiley Online Library | plant developments | Scoop.it
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ytokinin signaling increases the abundance of ARR1, a ubiquitously expressed RRB, by preventing its degradation by the 26S proteasome. We also show that the RRAs act to suppress ARR1 accumulation, thus providing an explanation for their inhibitory action in cytokinin signaling. Collectively, our results reveal an additional regulatory mechanism in the cytokinin response pathway that involves the cytokinin–dependent stability control of a major RRB response activator.

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The ERECTA receptor kinase regulates Arabidopsis shoot apical meristem size, phyllotaxy and floral meristem identity

The ERECTA receptor kinase regulates Arabidopsis shoot apical meristem size, phyllotaxy and floral meristem identity | plant developments | Scoop.it
PMG's insight:

ERECTA (ER) pathway as a second receptor kinase signaling pathway that regulates WUS expression, and therefore shoot apical and floral meristem size, independently of the CLV pathway. We demonstrate that reduction in class III HD-ZIP and ER function together leads to a significant increase in WUS expression, resulting in extremely enlarged shoot meristems and a switch from spiral to whorled vegetative phyllotaxy. We further show that strong upregulation of WUS in the inflorescence meristem leads to ectopic expression of the AGAMOUS homeotic gene to a level that switches cell fate from floral meristem founder cell to carpel founder cell, suggesting an indirect role for ER in regulating floral meristem identity. This work illustrates the delicate balance between stem cell specification and differentiation in the meristem and shows that a shift in this balance leads to abnormal phyllotaxy and to altered reproductive cell fate.

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Developmental Cell - Auxin-Callose-Mediated Plasmodesmal Gating Is Essential for Tropic Auxin Gradient Formation and Signaling

Developmental Cell - Auxin-Callose-Mediated Plasmodesmal Gating Is Essential for Tropic Auxin Gradient Formation and Signaling | plant developments | Scoop.it
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 operation of an auxin-GSL8 feedback circuit that regulates the level of plasmodesmal-localized callose in order to locally downregulate symplasmic permeability during hypocotyl tropic response. This system likely involves a plasmodesmal switch that would prevent the dissipation of a forming gradient by auxin diffusion through the symplasm. This regulatory system may represent a mechanism by which auxin could also regulate symplasmic delivery of a wide range of signaling agents.

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Yucasin is a potent inhibitor of YUCCA, a key enzyme in auxin biosynthesis - Nishimura - 2014 - The Plant Journal - Wiley Online Library

Yucasin is a potent inhibitor of YUCCA, a key enzyme in auxin biosynthesis - Nishimura - 2014 - The Plant Journal - Wiley Online Library | plant developments | Scoop.it
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5–(4–chlorophenyl)-4H-1,2,4–triazole-3–thiol (yucasin) as a potent inhibitor of IAA biosynthesis inYUC-expressing coleoptile tips. Enzymatic analysis of recombinant AtYUC1-His suggested that yucasin strongly inhibited YUC1-His activity against the substrate IPyA in a competitive manner. Phenotypic analysis of Arabidopsis YUC1 over-expression lines (35S::YUC1) demonstrated that yucasin acts in IAA biosynthesis catalyzed by YUC. In addition, 35S::YUC1 seedlings showed resistance to yucasin in terms of root growth. A loss-of-function mutant of TAA1, sav3–2, was hypersensitive to yucasin in terms of root growth and hypocotyl elongation of etiolated seedlings. Yucasin combined with the TAA1 inhibitor l–kynurenine acted additively in Arabidopsis seedlings, producing a phenotype similar to yucasin-treated sav3–2 seedlings, indicating the importance of IAA biosynthesis via the IPyA pathway in root growth and leaf vascular development. 

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Cytokinin as a mediator for regulating root system architecture in response to environmental cues

Root system architecture (RSA) is developmentally controlled by genetic pathways and their interaction with various environmental cues, in particular soil conditions.
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the transcript levels of cytokinin genes in the root responds to changes in nutrient availability in distinct ways. IPT3,IPT5, CYP735A2, LOG5 and CKX4 are particularly responsive cytokinin metabolism genes, genes encoding different type-A response regulators and the transcriptions factor genes ARR10 and CRF6 are among the most responsive signalling genes. This finding supports the hypothesis that environmental cues operate through fine-tuned transcriptional regulation of cytokinin genes to modulate root development.

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Cytokinin antagonizes abscisic acid-mediated inhibition of cotyledon greening by promoting the degradation of ABI5 protein in Arabidopsis

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cytokinin specifically antagonizes ABA-mediated inhibition on cotyledon greening with minimal effects on seed germination in Arabidopsis (Arabidopsis thaliana). We found that the cytokinin-antagonized ABA effect is dependent on a functional cytokinin signaling pathway, mainly involved in the cytokinin receptor gene CRE1/AHK4, downstream AHP2, 3, 5 genes, and a type-B response regulator gene ARR12, which genetically acts upstream of ABI5 to regulate cotyledon greening. Cytokinin has no apparent effect on the transcription of ABI5. However, cytokinin efficiently promotes the proteasomal degradation of ABI5 protein in a cytokinin signaling-dependent manner. These results define a genetic pathway, through which cytokinin specifically induces the degradation of ABI5 protein, thereby antagonizing ABA-mediated inhibition on postgerminative growth.

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Genetic Control of Plant Development by Overriding a Geometric Division Rule: Developmental Cell

Genetic Control of Plant Development by Overriding a Geometric Division Rule: Developmental Cell | plant developments | Scoop.it
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a complete 4D map of early Arabidopsis embryogenesis and used computational analysis to demonstrate that several divisions follow a rule that uses the smallest wall area going through the center of the cell. In other cases, however, cell division clearly deviates from this rule, which invariably leads to asymmetric cell division. By analyzing mutant embryos and through targeted genetic perturbation, we show that response to the hormone auxin triggers a deviation from the “shortest wall” rule. Our work demonstrates that a simple default rule couples division orientation to cell geometry in the embryo and that genetic regulation can create patterns by overriding the default rule.

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Isopentenyltransferase-1 (IPT1) knockout in Physcomitrella together with phylogenetic analyses of IPTs provide insights into evolution of plant cytokinin biosynthesis

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chloroplast-bound IPT1 was almost exclusively responsible for the A37 prenylation of tRNA in Physcomitrella. Ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS)-based cytokinin profiling demonstrated that the total amount of all free cytokinins in tissue was almost unaffected. However, the knockout plants showed increased levels of the N 6-isopentenyladenine (iP)- andtrans-zeatin (tZ)-type cytokinins, considered to provide active forms, while cis-zeatin (cZ)-type cytokinins were reduced. The data provide evidence for an additional and unexpected tRNA-independent cytokinin biosynthetic pathway in moss. Comprehensive phylogenetic analysis indicates a diversification of tRNA-IPT-like genes in bryophytes probably related to additional functions.

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Lotus japonicus Cytokinin Receptors Work Partially Redundantly to Mediate Nodule Formation

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A Highly Selective Biosensor with Nanomolar Sensitivity Based on Cytokinin Dehydrogenase

PLOS ONE: an inclusive, peer-reviewed, open-access resource from the PUBLIC LIBRARY OF SCIENCE. Reports of well-performed scientific studies from all disciplines freely available to the whole world.
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The immobilisedZmCKX1 retained a high affinity for its preferred substrate N6-(Δ2-isopentenyl) adenine (iP), and gave the miniaturized biosensor a large linear dynamic range from 10 nM to 10 µM, a detection limit of 3.9 nM and a high sensitivity to iP of 603.3 µAmM−1cm−2 (n = 4, R2 = 0.9999). Excellent selectivity was displayed for several other aliphatic cytokinins and their ribosides, including N6-(Δ2-isopentenyl) adenine, N6-(Δ2-isopentenyl) adenosine, cis-zeatin, trans-zeatin and trans-zeatin riboside. Aromatic cytokinins and metabolites such as cytokinin glucosides were generally poor substrates.

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Expression and functional analysis of genes encoding cytokinin receptor-like histidine kinase in maize (Zea mays L.) - Online First - Springer

Expression and functional analysis of genes encoding cytokinin receptor-like histidine kinase in maize (Zea mays L.) - Online First - Springer | plant developments | Scoop.it
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the ZmHK1a2-OX transgenic line has the lowest germination rate in the dark, ZmHK1-OX and ZmHK2a2-OX can delay leaf senescence, and seed size of ZmHK1-OX, ZmHK1a2-OX, ZmHK2-OX, ZmHK3b-OX andZmHK2a2-OX was obviously reduced as compared to wild type. Additionally, ZmHK genes play opposite roles in shoot and root development; all ZmHK-OX transgenic lines display obvious shorter root length and reduced number of lateral roots, but enhanced shoot development compared with the wild type. Most notably, Arabidopsis response regulator ARR5 gene was up-regulated in ZmHK1-OX, ZmHK1a2-OX, ZmHK2-OX, ZmHK3b-OX and ZmHK2a2-OX as compared to wild type.

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Two rice histidine phosphotransfer proteins, OsAHP1 and OsAHP2, mediate cytokinin signaling and stress responses in rice

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two rice authentic HPs (OsAHP1 and OsAHP2) were knocked down simultaneously via RNA interference (RNAi), and the transgenic OsAHPs-RNAi plants exhibited phenotypes expected for a deficiency in cytokinin signaling, including dwarfism with reduced internode lengths, enhanced lateral root growth, early leaf senescence, and reduced tiller numbers and fertility under natural conditions. The OsAHPs-RNAi seedlings were also hyposensitive to exogenous cytokinin.

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Overexpression of the cytosolic cytokinin oxidase/dehydrogenase (CKX7) from Arabidopsis causes specific changes in root growth and xylem differentiation - Köllmer - The Plant Journal - Wiley Online...

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pCKX7:GUS expression was detected in the vasculature, the transmitting tissue and the mature embryo sac. A CKX7-GFP fusion protein localized to the cytosol which is unique among all CKX family members. 35S:CKX7-expressing plants developed short, early-terminating primary roots with smaller apical meristems contrasting with plants overexpressing other CKX genes. The vascular bundles of 35S:CKX7 primary roots contained only protoxylem elements, thus resembling the wol mutant of the CRE1/AHK4receptor gene. We show that CRE1/AHK4 activity is required to establish the CKX7 overexpression phenotype. Several cytokinin metabolites, in particular cis-zeatin (cZ) and N-glucoside cytokinins, were depleted stronger in 35S:CKX7 plants compared to plants overexpressing other CKX genes. Interestingly, enhanced protoxylem formation together with reduced primary root growth was also found in the cZ-deficient tRNA isopentenyltransferase mutant ipt2,9, However, different cytokinins were similarly efficient in suppressing35S:CKX7 and ipt2,9 vascular phenotypes. Therefore, we hypothesize that the pool of cytosolic cytokinins is particularly relevant in the root procambium where it mediates vascular tissue differentiation through CRE1/AHK4. Taken together, the distinct consequences of CKX7overexpression indicate that the cellular compartmentation of cytokinin degradation and substrate preference of CKX isoforms are relevant parameters defining the activities of the hormone.

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A new subfamily of putative cytokinin receptors is revealed by an analysis of the evolution of the two-component signaling system of plants

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a novel subfamily of cytokinin receptors with members only from the early diverging land plants Marchantia polymorpha and Physcomitrella patens and then experimentally characterized two members of this subfamily. HTPs of charophyceae seemed to be more closely related to those of land plants than to other groups of green algae. Further down the signaling pathway, the type-B RRs were found across all plant clades, but many members lack either the canonical Asp residue or the DNA-binding domain. In contrast, the type-A RRs seemed to be limited to land plants. Finally, the analysis provided hints that one additional group of RRs, the type-C RRs, might be degenerated receptors and thus evolutionary of a different origin than bona fide response regulators.

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Structural Basis for DNA Binding Specificity by the Auxin-Dependent ARF Transcription Factors

Structural Basis for DNA Binding Specificity by the Auxin-Dependent ARF Transcription Factors | plant developments | Scoop.it
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Finally structural basis of ARFs for DNA binding is now revealed.

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WOX5–IAA17 Feedback Circuit-Mediated Cellular Auxin Response Is Crucial for the Patterning of Root Stem Cell Niches in Arabidopsis

WOX5–IAA17 Feedback Circuit-Mediated Cellular Auxin Response Is Crucial for the Patterning of Root Stem Cell Niches in Arabidopsis | plant developments | Scoop.it
PMG's insight:

feedback loop linking WOX5-mediated auxin production to IAA17-dependent repression of auxin responses. This WOX5–IAA17 feedback circuit further assures the maintenance of auxin response maximum in the root tip and thereby contributes to the maintenance of distal stem cell (DSC) populations. Our experimental studies and in silico computer simulations both demonstrate that the WOX5–IAA17 feedback circuit is essential for the maintenance of auxin gradient in the root tip and the auxin-mediated root DSC differentiation.

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Arabidopsis KANADI1 Acts as a Transcriptional Repressor by Interacting with a Specific cis-Element and Regulates Auxin Biosynthesis, Transport, and Signaling in Opposition to HD-ZIPIII Factors

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Myb-like domain in KAN1 binds the 6-bp motif GNATA(A/T) and that this motif alone is sufficient to squelch transcription of a linked reporter in vivo. In addition, we report that KAN1 acts as a transcriptional repressor. Among its targets are genes involved in auxin biosynthesis, auxin transport, and auxin response. Furthermore, we find that the adaxializing HD-ZIPIII transcription factor REVOLUTA has opposing effects on multiple components of the auxin pathway. We hypothesize that HD-ZIPIII and KANADI transcription factors pattern auxin accumulation and responsiveness in the embryo. Specifically, we propose the opposing actions of KANADI and HD-ZIPIII factors on cotyledon formation (KANADI represses and HD-ZIPIII promotes cotyledon formation) occur through their opposing actions on genes acting at multiple steps in the auxin pathway.

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A novel protective function for cytokinin in the light stress response is mediated by the AHK2 and AHK3 receptors

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The efficiency of photoprotective mechanisms, such as non-enzymatic and enzymatic scavenging systems, was decreased in plants with a reduced cytokinin status which could be a cause for the increased photodamage and subsequent D1 degradation. Mutant analysis revealed that the protective function of cytokinin during light stress depends on the AHK2 and AHK3 receptors and the type-B response regulators ARR1 and ARR12. We conclude that proper cytokinin signaling and regulation of specific target genes is necessary to protect plants efficiently from light stress.

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