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Molecular Cell - Direct Regulation of the NADPH Oxidase RBOHD by the PRR-Associated Kinase BIK1 during Plant Immunity

Molecular Cell - Direct Regulation of the NADPH Oxidase RBOHD by the PRR-Associated Kinase BIK1 during Plant Immunity | Auxin | Scoop.it
HighlightsThe plasma membrane Arabidopsis NADPH oxidase RBOHD is part of the PRR complexRBOHD is directly phosphorylated by the kinase BIK1 in response to PAMP perceptionBIK1 activation and BIK1-mediated RBOHD phosphorylation are calcium independentBIK1-mediated phosphorylation of RBOHD is critical for its function in immunitySummaryThe rapid production of reactive oxygen species (ROS) burst is a conserved signaling output in immunity across kingdoms. In plants, perception of pathogen-associated molecular patterns (PAMPs) by surface-localized pattern recognition receptors (PRRs) activates the NADPH oxidase RBOHD by hitherto unknown mechanisms. Here, we show that RBOHD exists in complex with the receptor kinases EFR and FLS2, which are the PRRs for bacterial EF-Tu and flagellin, respectively. The plasma-membrane-associated kinase BIK1, which is a direct substrate of the PRR complex, directly interacts with and phosphorylates RBOHD upon PAMP perception. BIK1 phosphorylates different residues than calcium-dependent protein kinases, and both PAMP-induced BIK1 activation and BIK1-mediated phosphorylation of RBOHD are calcium independent. Importantly, phosphorylation of these residues is critical for the PAMP-induced ROS burst and antibacterial immunity. Our study reveals a rapid regulatory mechanism of a plant RBOH, which occurs in parallel with and is essential for its paradigmatic calcium-based regulation.
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Nat. Commun.: Arabidopsis WAT1 is a vacuolar auxin transport facilitator required for auxin homoeostasis (2013)

Nat. Commun.: Arabidopsis WAT1 is a vacuolar auxin transport facilitator required for auxin homoeostasis (2013) | Auxin | Scoop.it
The plant hormone auxin (indole-3-acetic acid, IAA) has a crucial role in plant development. Its spatiotemporal distribution is controlled by a combination of biosynthetic, metabolic and transport mechanisms. Four families of auxin transporters have been identified that mediate transport across the plasma or endoplasmic reticulum membrane. Here we report the discovery and the functional characterization of the first vacuolar auxin transporter. We demonstrate that WALLS ARE THIN1 (WAT1), a plant-specific protein that dictates secondary cell wall thickness of wood fibres, facilitates auxin export from isolated Arabidopsis vacuoles in yeast and in Xenopus oocytes. We unambiguously identify IAA and related metabolites in isolated Arabidopsis vacuoles, suggesting a key role for the vacuole in intracellular auxin homoeostasis. Moreover, local auxin application onto wat1 mutant stems restores fibre cell wall thickness. Our study provides new insight into the complexity of auxin transport in plants and a means to dissect auxin function during fibre differentiation. Philippe Ranocha, Oana Dima, Réka Nagy, Judith Felten, Claire Corratgé-Faillie, Ondřej Novák, Kris Morreel, Benoît Lacombe, Yves Martinez, Stephanie Pfrunder, Xu Jin, Jean-Pierre Renou, Jean-Baptiste Thibaud, Karin Ljung, Urs Fischer, Enrico Martinoia, Wout Boerjan & Deborah Goffner
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Nicolas Denancé's curator insight, October 17, 2013 4:24 AM

The last, but not least, paper on Arabidospis WAT1. That article follows previous papers showing that:

- mutation of WAT1 alters secondary cell wall formation and deregulates expression of auxin-related genes: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-313X.2010.04256.x/abstract 

- growth and cell wall, but not auxin phenotypes are partially restored by light in wat1 mutant: https://www.landesbioscience.com/journals/psb/article/13103/

- wat1 mutant exhibits an increased resistance to vascular pathogens, presumably due to a cross-regulation of salicylic acid and tryptophan/auxin/glucosinolates metabolism in roots: http://onlinelibrary.wiley.com/doi/10.1111/tpj.12027/abstract

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Simulation of organ patterning on the floral meristem using a polar auxin transport model (PLoS ONE)

Simulation of organ patterning on the floral meristem using a polar auxin transport model (PLoS ONE) | Auxin | Scoop.it
An intriguing phenomenon in plant development is the timing and positioning of lateral organ initiation, which is a fundamental aspect of plant architecture. Although important progress has been made in elucidating the role of auxin transport in the vegetative shoot to explain the phyllotaxis of leaf formation in a spiral fashion, a model study of the role of auxin transport in whorled organ patterning in the expanding floral meristem is not available yet. We present an initial simulation approach to study the mechanisms that are expected to play an important role. Starting point is a confocal imaging study of Arabidopsis floral meristems at consecutive time points during flower development. These images reveal auxin accumulation patterns at the positions of the organs, which strongly suggests that the role of auxin in the floral meristem is similar to the role it plays in the shoot apical meristem. This is the basis for a simulation study of auxin transport through a growing floral meristem, which may answer the question whether auxin transport can in itself be responsible for the typical whorled floral pattern. We combined a cellular growth model for the meristem with a polar auxin transport model. The model predicts that sepals are initiated by auxin maxima arising early during meristem outgrowth. These form a pre-pattern relative to which a series of smaller auxin maxima are positioned, which partially overlap with the anlagen of petals, stamens, and carpels. We adjusted the model parameters corresponding to properties of floral mutants and found that the model predictions agree with the observed mutant patterns. The predicted timing of the primordia outgrowth and the timing and positioning of the sepal primordia show remarkable similarities with a developing flower in nature.
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Auxin biosynthesis and storage forms

Auxin biosynthesis and storage forms | Auxin | Scoop.it
The plant hormone auxin drives plant growth and morphogenesis. The levels and distribution of the active auxin indole-3-acetic acid (IAA) are tightly controlled through synthesis, inactivation, and transport. Many auxin precursors and modified auxin forms, used to regulate auxin homeostasis, have been identified; however, very little is known about the integration of multiple auxin biosynthesis and inactivation pathways. This review discusses the many ways auxin levels are regulated through biosynthesis, storage forms, and inactivation, and the potential roles modified auxins play in regulating the bioactive pool of auxin to affect plant growth and development.
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Auxin Biosynthesis

Auxin Biosynthesis | Auxin | Scoop.it
“Yunde Zhao (2014) Auxin Biosynthesis. The Arabidopsis Book: Vol. , No. , pp. null. doi: http://dx.doi.org/10.1199/tab.0173”
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Simulation of organ patterning on the floral meristem using a polar auxin transport model (PLoS ONE)

Simulation of organ patterning on the floral meristem using a polar auxin transport model (PLoS ONE) | Auxin | Scoop.it
An intriguing phenomenon in plant development is the timing and positioning of lateral organ initiation, which is a fundamental aspect of plant architecture. Although important progress has been made in elucidating the role of auxin transport in the vegetative shoot to explain the phyllotaxis of leaf formation in a spiral fashion, a model study of the role of auxin transport in whorled organ patterning in the expanding floral meristem is not available yet. We present an initial simulation approach to study the mechanisms that are expected to play an important role. Starting point is a confocal imaging study of Arabidopsis floral meristems at consecutive time points during flower development. These images reveal auxin accumulation patterns at the positions of the organs, which strongly suggests that the role of auxin in the floral meristem is similar to the role it plays in the shoot apical meristem. This is the basis for a simulation study of auxin transport through a growing floral meristem, which may answer the question whether auxin transport can in itself be responsible for the typical whorled floral pattern. We combined a cellular growth model for the meristem with a polar auxin transport model. The model predicts that sepals are initiated by auxin maxima arising early during meristem outgrowth. These form a pre-pattern relative to which a series of smaller auxin maxima are positioned, which partially overlap with the anlagen of petals, stamens, and carpels. We adjusted the model parameters corresponding to properties of floral mutants and found that the model predictions agree with the observed mutant patterns. The predicted timing of the primordia outgrowth and the timing and positioning of the sepal primordia show remarkable similarities with a developing flower in nature.
Via GMI Vienna
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The main auxin biosynthesis pathway in Arabidopsis (PNAS)

The main auxin biosynthesis pathway in Arabidopsis (PNAS) | Auxin | Scoop.it
The phytohormone auxin plays critical roles in the regulation of plant growth and development. Indole-3-acetic acid (IAA) has been recognized as the major auxin for more than 70 y. Although several pathways have been proposed, how auxin is synthesized in plants is still unclear. Previous genetic and enzymatic studies demonstrated that both TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA) and YUCCA (YUC) flavin monooxygenase-like proteins are required for biosynthesis of IAA during plant development, but these enzymes were placed in two independent pathways. In this article, we demonstrate that the TAA family produces indole-3-pyruvic acid (IPA) and the YUC family functions in the conversion of IPA to IAA in Arabidopsis (Arabidopsis thaliana) by a quantification method of IPA using liquid chromatography–electrospray ionization–tandem MS. We further show that YUC protein expressed in Escherichia coli directly converts IPA to IAA. Indole-3-acetaldehyde is probably not a precursor of IAA in the IPA pathway. Our results indicate that YUC proteins catalyze a rate-limiting step of the IPA pathway, which is the main IAA biosynthesis pathway in Arabidopsis.
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Cytokinin modulates endocytic trafficking of PIN1 auxin efflux carrier to control plant organogenesis (Developmental Cell)

Cytokinin modulates endocytic trafficking of PIN1 auxin efflux carrier to control plant organogenesis (Developmental Cell) | Auxin | Scoop.it
Cytokinin is an important regulator of plant growth and development. In Arabidopsis thaliana, the two-component phosphorelay mediated through a family of histidine kinases and response regulators is recognized as the principal cytokinin signal transduction mechanism activating the complex transcriptional response to control various developmental processes. Here, we identified an alternative mode of cytokinin action that uses endocytic trafficking as a means to direct plant organogenesis. This activity occurs downstream of known cytokinin receptors but through a branch of the cytokinin signaling pathway that does not involve transcriptional regulation. We show that cytokinin regulates endocytic recycling of the auxin efflux carrier PINFORMED1 (PIN1) by redirecting it for lytic degradation in vacuoles. Stimulation of the lytic PIN1 degradation is not a default effect for general downregulation of proteins from plasma membranes, but a specific mechanism to rapidly modulate the auxin distribution in cytokinin-mediated developmental processes.
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Cytokinin modulates endocytic trafficking of PIN1 auxin efflux carrier to control plant organogenesis (Developmental Cell)

Cytokinin modulates endocytic trafficking of PIN1 auxin efflux carrier to control plant organogenesis (Developmental Cell) | Auxin | Scoop.it
Cytokinin is an important regulator of plant growth and development. In Arabidopsis thaliana, the two-component phosphorelay mediated through a family of histidine kinases and response regulators is recognized as the principal cytokinin signal transduction mechanism activating the complex transcriptional response to control various developmental processes. Here, we identified an alternative mode of cytokinin action that uses endocytic trafficking as a means to direct plant organogenesis. This activity occurs downstream of known cytokinin receptors but through a branch of the cytokinin signaling pathway that does not involve transcriptional regulation. We show that cytokinin regulates endocytic recycling of the auxin efflux carrier PINFORMED1 (PIN1) by redirecting it for lytic degradation in vacuoles. Stimulation of the lytic PIN1 degradation is not a default effect for general downregulation of proteins from plasma membranes, but a specific mechanism to rapidly modulate the auxin distribution in cytokinin-mediated developmental processes.
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Membrane Trafficking Pathways and their Roles in Plant-Microbe Interactions

Membrane Trafficking Pathways and their Roles in Plant-Microbe Interactions | Auxin | Scoop.it
Membrane trafficking functions in the delivery of proteins that are newly synthesized in the endoplasmic reticulum (ER) to their final destinations, such as the plasma membrane (PM) and the vacuole, and in the internalization of extracellular components or PM-associated proteins for recycling or degradative regulation. These trafficking pathways play pivotal roles in the rapid responses to environmental stimuli such as challenges by microorganisms. In this review, we provide an overview of the current knowledge of plant membrane trafficking and its roles in plant-microbe interactions. Although there is little information regarding the mechanism of pathogenic modulation of plant membrane trafficking thus far, recent research has identified many membrane trafficking factors as possible targets of microbial modulation.
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Structure - Structural Basis for Proteasome Formation Controlled by an Assembly Chaperone Nas2

Structure - Structural Basis for Proteasome Formation Controlled by an Assembly Chaperone Nas2 | Auxin | Scoop.it
HighlightsAn assembly chaperone Nas2 bivalently binds the proteasome Rpt5 subunit.The Nas2 N-terminal helical domain masks the Rpt1-interacting surface of Rpt5.The Nas2 C-terminal PDZ domain caps the proteasome-activating motif of Rpt5.The structural data provide the missing link in proteasome assembly mechanisms.SummaryProteasome formation does not occur due to spontaneous self-organization but results from a highly ordered process assisted by several assembly chaperones. The assembly of the proteasome ATPase subunits is assisted by four client-specific chaperones, of which three have been structurally resolved. Here, we provide the structural basis for the working mechanisms of the last, hereto structurally uncharacterized assembly chaperone, Nas2. We revealed that Nas2 binds to the Rpt5 subunit in a bivalent mode: the N-terminal helical domain of Nas2 masks the Rpt1-interacting surface of Rpt5, whereas its C-terminal PDZ domain caps the C-terminal proteasome-activating motif. Thus, Nas2 operates as a proteasome activation blocker, offering a checkpoint during the formation of the 19S ATPase prior to its docking onto the proteolytic 20S core particle.
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Current Biology: Local Auxin Sources Orient the Apical-Basal Axis in Arabidopsis Embryos

Current Biology: Local Auxin Sources Orient the Apical-Basal Axis in Arabidopsis Embryos | Auxin | Scoop.it
SUMMARY: Establishment of the embryonic axis foreshadows the main body axis of adults both in plants and in animals, but underlying mechanisms are considered distinct. Plants utilize directional, cell-to-cell transport of the growth hormone auxin [1 and 2] to generate an asymmetric auxin response that specifies the embryonic apical-basal axis [3, 4, 5 and 6]. The auxin flow directionality depends on the polarized subcellular localization of PIN-FORMED (PIN) auxin transporters [7 and 8]. It remains unknown which mechanisms and spatial cues guide cell polarization and axis orientation in early embryos. Herein, we provide conceptually novel insights into the formation of embryonic axis in Arabidopsis by identifying a crucial role of localized tryptophan-dependent auxin biosynthesis [ 9, 10, 11 and 12]. Local auxin production at the base of young embryos and the accompanying PIN7-mediated auxin flow toward the proembryo are required for the apical auxin response maximum and the specification of apical embryonic structures. Later in embryogenesis, the precisely timed onset of localized apical auxin biosynthesis mediates PIN1 polarization, basal auxin response maximum, and specification of the root pole. Thus, the tight spatiotemporal control of distinct local auxin sources provides a necessary, non-cell-autonomous trigger for the coordinated cell polarization and subsequent apical-basal axis orientation during embryogenesis and, presumably, also for other polarization events during postembryonic plant life [ 13 and 14].
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The Arabidopsis ROP GTPase AtROP6 functions in developmental and pathogen response pathways

The Arabidopsis ROP GTPase AtROP6 functions in developmental and pathogen response pathways | Auxin | Scoop.it
How plants coordinate developmental processes and environmental stress responses is a pressing question. Here, we show that Arabidopsis AtROP6 integrates developmental and pathogen response signaling. AtROP6 expression is induced by auxin and detected in the root meristem, lateral root initials, and leaf hydathodes. Plants expressing a dominant negative AtROP6 (rop6DN) under regulation of its endogenous promoter are small, have multiple inflorescence stems, twisted leaves, deformed leaf epidermis pavement cells, and differentially organized cytoskeleton. Microarrays analyses of rop6DN plants revealed that major changes in gene expression are associated with constitutive salicylic acid (SA)-mediated defense responses. In agreement, the free and total SA levels resembled that of wild-type plants inoculated with a virulent powdery mildew pathogen. The constitutive SA-associated response in rop6DN was suppressed in mutant backgrounds defective in SA signaling (npr1) or biosynthesis (sid2). However, the rop6DN npr1 or rop6DN sid2 double mutants retained the aberrant developmental phenotypes, indicating that the constitutive SA response can be uncoupled from ROP function(s) in development. rop6DN plants exhibited enhanced pre-invasive defense responses to a host-adapted virulent powdery mildew fungus, but were impaired in pre-invasive defenses upon inoculation with a non-adapted powdery mildew. The host-adapted powdery mildew had a reduced reproductive fitness on rop6DN plants, which was retained in mutant backgrounds defective in SA biosynthesis or signaling. Our findings indicate that both the morphological aberrations and altered sensitivity to powdery mildews of rop6DN plants result from perturbations that are independent from the SA-associated response. These perturbations uncouple SA-dependent defense signaling from disease resistance execution.
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Cytokinin modulates endocytic trafficking of PIN1 auxin efflux carrier to control plant organogenesis (Developmental Cell)

Cytokinin modulates endocytic trafficking of PIN1 auxin efflux carrier to control plant organogenesis (Developmental Cell) | Auxin | Scoop.it
Cytokinin is an important regulator of plant growth and development. In Arabidopsis thaliana, the two-component phosphorelay mediated through a family of histidine kinases and response regulators is recognized as the principal cytokinin signal transduction mechanism activating the complex transcriptional response to control various developmental processes. Here, we identified an alternative mode of cytokinin action that uses endocytic trafficking as a means to direct plant organogenesis. This activity occurs downstream of known cytokinin receptors but through a branch of the cytokinin signaling pathway that does not involve transcriptional regulation. We show that cytokinin regulates endocytic recycling of the auxin efflux carrier PINFORMED1 (PIN1) by redirecting it for lytic degradation in vacuoles. Stimulation of the lytic PIN1 degradation is not a default effect for general downregulation of proteins from plasma membranes, but a specific mechanism to rapidly modulate the auxin distribution in cytokinin-mediated developmental processes.
Via GMI Vienna, Edith Ma
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Different auxin response machineries control distinct cell fates in the early plant embryo (Developmental Cell)

Different auxin response machineries control distinct cell fates in the early plant embryo (Developmental Cell) | Auxin | Scoop.it
The cell types of the plant root are first specified early during embryogenesis and are maintained throughout plant life. Auxin plays an essential role in embryonic root initiation, in part through the action of the ARF5/MP transcription factor and its auxin-labile inhibitor IAA12/BDL. MP and BDL function in embryonic cells but promote auxin transport to adjacent extraembryonic suspensor cells, including the quiescent center precursor (hypophysis). Here we show that a cell-autonomous auxin response within this cell is required for root meristem initiation. ARF9 and redundant ARFs, and their inhibitor IAA10, act in suspensor cells to mediate hypophysis specification and, surprisingly, also to prevent transformation to embryo identity. ARF misexpression, and analysis of the short suspensor mutant, demonstrates that lineage-specific expression of these ARFs is required for normal embryo development. These results imply the existence of a prepattern for a cell-type-specific auxin response that underlies the auxin-dependent specification of embryonic cell types.
Via GMI Vienna, Edith Ma
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Alternative splicing of the auxin biosynthesis gene YUCCA4 determines its subcellular compartmentation (Plant Journal)

Alternative splicing of the auxin biosynthesis gene YUCCA4 determines its subcellular compartmentation (Plant Journal) | Auxin | Scoop.it
Auxin is a major growth hormone in plants, and recent studies have elucidated many of the molecular mechanisms underlying its action, including transport, perception and signal transduction. However, major gaps remain in our knowledge of auxin biosynthetic control, partly due to the complexity and probable redundancy of multiple pathways that involve the YUCCA family of flavin-dependent mono-oxygenases. This study reveals the differential localization of YUCCA4 alternative splice variants to the endoplasmic reticulum and the cytosol, which depends on tissue-specific splicing. One isoform is restricted to flowers, and is anchored to the cytosolic face of the endoplasmic reticulum membrane via a hydrophobic C-terminal transmembrane domain. The other isoform is present in all tissues and is distributed throughout the cytosol. These findings are consistent with previous observations of yucca4 phenotypes in flowers, and suggest a role for intracellular compartmentation in auxin biosynthesis.
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Auxin biosynthesis and storage forms

Auxin biosynthesis and storage forms | Auxin | Scoop.it
The plant hormone auxin drives plant growth and morphogenesis. The levels and distribution of the active auxin indole-3-acetic acid (IAA) are tightly controlled through synthesis, inactivation, and transport. Many auxin precursors and modified auxin forms, used to regulate auxin homeostasis, have been identified; however, very little is known about the integration of multiple auxin biosynthesis and inactivation pathways. This review discusses the many ways auxin levels are regulated through biosynthesis, storage forms, and inactivation, and the potential roles modified auxins play in regulating the bioactive pool of auxin to affect plant growth and development.
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Alternative splicing of the auxin biosynthesis gene YUCCA4 determines its subcellular compartmentation (Plant Journal)

Alternative splicing of the auxin biosynthesis gene YUCCA4 determines its subcellular compartmentation (Plant Journal) | Auxin | Scoop.it
Auxin is a major growth hormone in plants, and recent studies have elucidated many of the molecular mechanisms underlying its action, including transport, perception and signal transduction. However, major gaps remain in our knowledge of auxin biosynthetic control, partly due to the complexity and probable redundancy of multiple pathways that involve the YUCCA family of flavin-dependent mono-oxygenases. This study reveals the differential localization of YUCCA4 alternative splice variants to the endoplasmic reticulum and the cytosol, which depends on tissue-specific splicing. One isoform is restricted to flowers, and is anchored to the cytosolic face of the endoplasmic reticulum membrane via a hydrophobic C-terminal transmembrane domain. The other isoform is present in all tissues and is distributed throughout the cytosol. These findings are consistent with previous observations of yucca4 phenotypes in flowers, and suggest a role for intracellular compartmentation in auxin biosynthesis.
Via GMI Vienna
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Different auxin response machineries control distinct cell fates in the early plant embryo (Developmental Cell)

Different auxin response machineries control distinct cell fates in the early plant embryo (Developmental Cell) | Auxin | Scoop.it
The cell types of the plant root are first specified early during embryogenesis and are maintained throughout plant life. Auxin plays an essential role in embryonic root initiation, in part through the action of the ARF5/MP transcription factor and its auxin-labile inhibitor IAA12/BDL. MP and BDL function in embryonic cells but promote auxin transport to adjacent extraembryonic suspensor cells, including the quiescent center precursor (hypophysis). Here we show that a cell-autonomous auxin response within this cell is required for root meristem initiation. ARF9 and redundant ARFs, and their inhibitor IAA10, act in suspensor cells to mediate hypophysis specification and, surprisingly, also to prevent transformation to embryo identity. ARF misexpression, and analysis of the short suspensor mutant, demonstrates that lineage-specific expression of these ARFs is required for normal embryo development. These results imply the existence of a prepattern for a cell-type-specific auxin response that underlies the auxin-dependent specification of embryonic cell types.
Via GMI Vienna
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Rescooped by Edith Ma from Microbes, plant immunity, and crop science
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Nat. Commun.: Arabidopsis WAT1 is a vacuolar auxin transport facilitator required for auxin homoeostasis (2013)

Nat. Commun.: Arabidopsis WAT1 is a vacuolar auxin transport facilitator required for auxin homoeostasis (2013) | Auxin | Scoop.it
The plant hormone auxin (indole-3-acetic acid, IAA) has a crucial role in plant development. Its spatiotemporal distribution is controlled by a combination of biosynthetic, metabolic and transport mechanisms. Four families of auxin transporters have been identified that mediate transport across the plasma or endoplasmic reticulum membrane. Here we report the discovery and the functional characterization of the first vacuolar auxin transporter. We demonstrate that WALLS ARE THIN1 (WAT1), a plant-specific protein that dictates secondary cell wall thickness of wood fibres, facilitates auxin export from isolated Arabidopsis vacuoles in yeast and in Xenopus oocytes. We unambiguously identify IAA and related metabolites in isolated Arabidopsis vacuoles, suggesting a key role for the vacuole in intracellular auxin homoeostasis. Moreover, local auxin application onto wat1 mutant stems restores fibre cell wall thickness. Our study provides new insight into the complexity of auxin transport in plants and a means to dissect auxin function during fibre differentiation. Philippe Ranocha, Oana Dima, Réka Nagy, Judith Felten, Claire Corratgé-Faillie, Ondřej Novák, Kris Morreel, Benoît Lacombe, Yves Martinez, Stephanie Pfrunder, Xu Jin, Jean-Pierre Renou, Jean-Baptiste Thibaud, Karin Ljung, Urs Fischer, Enrico Martinoia, Wout Boerjan & Deborah Goffner
Via Nicolas Denancé
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Nicolas Denancé's curator insight, October 17, 2013 4:24 AM

The last, but not least, paper on Arabidospis WAT1. That article follows previous papers showing that:

- mutation of WAT1 alters secondary cell wall formation and deregulates expression of auxin-related genes: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-313X.2010.04256.x/abstract 

- growth and cell wall, but not auxin phenotypes are partially restored by light in wat1 mutant: https://www.landesbioscience.com/journals/psb/article/13103/

- wat1 mutant exhibits an increased resistance to vascular pathogens, presumably due to a cross-regulation of salicylic acid and tryptophan/auxin/glucosinolates metabolism in roots: http://onlinelibrary.wiley.com/doi/10.1111/tpj.12027/abstract

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The shifting paradigms of auxin biosynthesis

The shifting paradigms of auxin biosynthesis | Auxin | Scoop.it
Auxins are an important group of hormones found in all land plants and several soil-dwelling microbes. Although auxin was the first phytohormone identified, its biosynthesis remained unclear until recently. In the past few years, our understanding of auxin biosynthesis has improved dramatically, to the stage where many believe there is a single predominant pathway in Arabidopsis (Arabidopsis thaliana L.). However, there is still uncertainty over the applicability of these findings to other plant species. Indeed, it appears that in certain organs of some species, other pathways can operate. Here we review the key advances that have led to our current understanding of auxin biosynthesis and its many proposed pathways.
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Molecular Cell - Direct Regulation of the NADPH Oxidase RBOHD by the PRR-Associated Kinase BIK1 during Plant Immunity

Molecular Cell - Direct Regulation of the NADPH Oxidase RBOHD by the PRR-Associated Kinase BIK1 during Plant Immunity | Auxin | Scoop.it
HighlightsThe plasma membrane Arabidopsis NADPH oxidase RBOHD is part of the PRR complexRBOHD is directly phosphorylated by the kinase BIK1 in response to PAMP perceptionBIK1 activation and BIK1-mediated RBOHD phosphorylation are calcium independentBIK1-mediated phosphorylation of RBOHD is critical for its function in immunitySummaryThe rapid production of reactive oxygen species (ROS) burst is a conserved signaling output in immunity across kingdoms. In plants, perception of pathogen-associated molecular patterns (PAMPs) by surface-localized pattern recognition receptors (PRRs) activates the NADPH oxidase RBOHD by hitherto unknown mechanisms. Here, we show that RBOHD exists in complex with the receptor kinases EFR and FLS2, which are the PRRs for bacterial EF-Tu and flagellin, respectively. The plasma-membrane-associated kinase BIK1, which is a direct substrate of the PRR complex, directly interacts with and phosphorylates RBOHD upon PAMP perception. BIK1 phosphorylates different residues than calcium-dependent protein kinases, and both PAMP-induced BIK1 activation and BIK1-mediated phosphorylation of RBOHD are calcium independent. Importantly, phosphorylation of these residues is critical for the PAMP-induced ROS burst and antibacterial immunity. Our study reveals a rapid regulatory mechanism of a plant RBOH, which occurs in parallel with and is essential for its paradigmatic calcium-based regulation.
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Plasma Membranes Are Subcompartmentalized into a Plethora of Coexisting and Diverse Microdomains in Arabidopsis and Nicotiana benthamiana

Plasma Membranes Are Subcompartmentalized into a Plethora of Coexisting and Diverse Microdomains in Arabidopsis and Nicotiana benthamiana | Auxin | Scoop.it
Eukaryotic plasma membranes are highly compartmentalized structures. So far, only a few individual proteins that function in a wide range of cellular processes have been shown to segregate into microdomains. However, the biological roles of most microdomain-associated proteins are unknown. Here, we investigated the heterogeneity of distinct microdomains and the complexity of their coexistence. This diversity was determined in living cells of intact multicellular tissues using 20 different marker proteins from Arabidopsis thaliana, mostly belonging to the Remorin protein family. These proteins associate with microdomains at the cytosolic leaflet of the plasma membrane. We characterized these membrane domains and determined their lateral dynamics by extensive quantitative image analysis. Systematic colocalization experiments with an extended subset of marker proteins tested in 45 different combinations revealed the coexistence of highly distinct membrane domains on individual cell surfaces. These data provide valuable tools to study the lateral segregation of membrane proteins and their biological functions in living plant cells. They also demonstrate that widely used biochemical approaches such as detergent-resistant membranes cannot resolve this biological complexity of membrane compartmentalization in vivo.
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Rescooped by Edith Ma from MycorWeb Plant-Microbe Interactions
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Auxin conjugated to fluorescent dyes – a tool for the analysis of auxin transport pathways

Auxin conjugated to fluorescent dyes – a tool for the analysis of auxin transport pathways | Auxin | Scoop.it
Auxin is a small molecule involved in most processes related to plant growth and development. Its effect usually depends on the distribution in tissues and the formation of concentration gradients. Until now there has been no tool for the direct tracking of auxin transport at the cellular and tissue level; therefore the majority of studies have been based on various indirect methods. However, due to their various restrictions, relatively little is known about the relationship between various pathways of auxin transport and specific developmental processes. We present a new research tool: fluorescently labelled auxin in the form of a conjugate with two different fluorescent tracers, FITC and RITC, which allows direct observation of auxin transport in plant tissues. Chemical analysis and biological tests have shown that our conjugates have auxin-like biological activity and transport; therefore they can be used in all experimental systems as an alternative to IAA. In addition, the conjugates are a universal tool that can be applied in studies of all plant groups and species. The conjugation procedure presented in this paper can be adapted to other fluorescent dyes, which are constantly being improved. In our opinion, the conjugates greatly expand the possibilities of research concerning the role of auxin and its transport in different developmental processes in plants.
Via Francis Martin
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Rescooped by Edith Ma from Plant-microbe interaction
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Arabidopsis HSP90 protein modulates RPP4-mediated temperature-dependent cell death and defense responses

Arabidopsis HSP90 protein modulates RPP4-mediated temperature-dependent cell death and defense responses | Auxin | Scoop.it
Plant defense responses are regulated by temperature. In Arabidopsis, the chilling-sensitive mutant chs2-1 (rpp4-1d) contains a gain-of-function mutation in the TIR-NB-LRR (Toll and interleukin 1 transmembrane receptor-nucleotide binding-leucine-rich repeat) gene, RPP4 (RECOGNITION OF PERONOSPORA PARASITICA 4), which leads to constitutive activation of the defense response at low temperatures.Here, we identified and characterized two suppressors of rpp4-1d from a genetic screen, hsp90.2 and hsp90.3, which carry point mutations in the cytosolic heat shock proteins HSP90.2 and HSP90.3, respectively.The hsp90 mutants suppressed the chilling sensitivity of rpp4-1d, including seedling lethality, activation of the defense responses and cell death under chilling stress. The hsp90 mutants exhibited compromised RPM1 (RESISTANCE TO PSEUDOMONAS MACULICOLA 1)-, RPS4 (RIBOSOMAL PROTEIN S4)- and RPP4-mediated pathogen resistance. The wild-type RPP4 and the mutated form rpp4 could interact with HSP90 to form a protein complex. Furthermore, RPP4 and rpp4 proteins accumulated in the cytoplasm and nucleus at normal temperatures, whereas the nuclear accumulation of the mutated rpp4 was decreased at low temperatures. Genetic analysis of the intragenic suppressors of rpp4-1d revealed the important functions of the NB-ARC and LRR domains of RPP4 in temperature-dependent defense signaling. In addition, the rpp4-1d-induced chilling sensitivity was largely independent of the WRKY70 or MOS (modifier of snc1) genes.This study reveals that Arabidopsis HSP90 regulates RPP4-mediated temperature-dependent cell death and defense responses.
Via Suayib Üstün
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