Plant hormones and signaling peptides
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Strigolactones positively regulate defense against root-knot nematodes in tomato | Journal of Experimental Botany | Oxford Academic

Strigolactones positively regulate defense against root-knot nematodes in tomato | Journal of Experimental Botany | Oxford Academic | Plant hormones and  signaling peptides | Scoop.it
Strigolactones (SLs) are carotenoid-derived phytohormones well known to influence various aspects of plant growth and development. As root-derived signals, SLs can enhance symbiosis between plants and arbuscular mycorrhizal fungi (AMF). However, little is known about the roles of SLs in plant defense against soil-borne pathogens. Here, we demonstrated that root-knot nematodes (RKNs; Meloidogyne incognita) infection induced SL biosynthesis in tomato roots. Silencing of SL biosynthesis genes compromised the defense, whilst the application of the SL analog racGR24 enhanced the defense against RKN. Endogenous jasmonic acid (JA) and abscisic acid (ABA) accumulation in the roots were enhanced by silencing of SLs biosynthetic genes but was suppressed by application of racGR24 in response to RKN infection. Genetic evidence showed that JA was a positive regulator while ABA was a negative regulator of RKN defense in tomato. Furthermore, racGR24 enhanced the defense against nematode in JA-deficient mutant but not in ABA-deficient mutant. In addition, silencing of SLs biosynthetic genes resulted in upregulation of MYC2, which negatively regulated the resistance. Our results demonstrated that SLs play a positive role in nematode defense. MYC2 negatively regulate nematode defense potentially by mediating the hormone crosstalk among SLs, ABA and JA.
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Lotuslactone, a non-canonical strigolactone from Lotus japonicus - ScienceDirect

Lotuslactone, a non-canonical strigolactone from Lotus japonicus - ScienceDirect | Plant hormones and  signaling peptides | Scoop.it
Root exudates from Lotus japonicus were found to contain at least three different hyphal branching-inducing compounds for the arbuscular mycorrhizal (AM) fungus Gigaspora margarita, one of which had been previously identified as (+)-5-deoxystrigol (5DS), a canonical strigolactone (SL). One of the two remaining unknown hyphal branching inducers was purified and named lotuslactone. Its structure was determined as methyl (E)-2-(3-acetoxy-2-hydroxy-7-methyl-1-oxo-1,2,3,4,5,6-hexahydroazulen-2-yl)-3-(((R)-4-methyl-5-oxo-2,5-dihydrofuran-2-yl)oxy)acrylate, by 1D and 2D NMR spectroscopy, and HR-ESI- and EI-MS. Although lotuslactone, a non-canonical SL, contains the AB-ring and the enol ether-bridged D-ring, it lacks the C-ring and has a seven-membered cycloheptadiene in the A-ring part as in medicaol, a major SL of Medicago truncatula. Lotuslactone was much less active than 5DS, but showed comparable activity to methyl carlactonoate (MeCLA) in inducing hyphal branching of G. margarita. Other natural non-canonical SLs including avenaol, heliolactone, and zealactone (methyl zealactonoate) were also found to be moderate to weak inducers of hyphal branching in the AM fungus. Lotuslactone strongly elicited seed germination in Phelipanche ramosa and Orobanche minor, but Striga hermonthica seeds were 100-fold less sensitive to this stimulant.
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Tuning of SlARF10A dosage by sly‐miR160a is critical for auxin‐mediated compound leaf and flower development - Damodharan - 2018 - The Plant Journal -

Tuning of SlARF10A dosage by sly‐miR160a is critical for auxin‐mediated compound leaf and flower development - Damodharan - 2018 - The Plant Journal - | Plant hormones and  signaling peptides | Scoop.it
miR160 adjusts auxin‐mediated development by post‐transcriptional regulation of the auxin response factors ARF10/16/17. In tomato, knockdown of miR160 (sly‐miR160) suggested that it is required for auxin‐driven leaf blade outgrowth, but whether additional developmental events are adjusted by sly‐miR160 is not clear. Here, the SlMIR160 genes and the genes of its SlARFs targets were edited by CRISPR/Cas9 resulting in the isolation of loss‐of‐function mutants. In addition, hypomorphic mutants that accumulate variable reduced levels of sly‐miR160a were isolated. We found that the loss‐of‐function mutants in SlMIR160a (CR‐slmir160a‐6/7) produced only four wiry leaves, whereas the hypomorphic mutants developed leaves and flowers with graded developmental abnormalities. Phenotypic severity correlated with the upregulation of SlARF10A. Consistent with that, double mutants in SlMIR160a and SlARF10A restored leaf and flower development indicating that over‐accumulation of SlARF10A underlay the developmental abnormalities exhibited in the CR‐slmir160a mutants. Phenotype severity also correlated with the upregulation of the SHOOT MERISTEMLESS homolog Tomato Knotted 2, which in turn activated the transcription of the cytokinin biosynthesis genes SlIPT2 and SlIPT4. However, no change in Tomato Knotted 2 was detected in the absence of SlARF10A, suggesting that it is upregulated due to auxin signaling suppression by SlARF10A. Knockout of sly‐miR160a‐targeted SlARFs showed that whereas SlARF10A is indispensable for leaf blade outgrowth and floral organ patterning, the functions of SlARF16A and SlARF17 are redundant. Taken together our results suggest that sly‐miR160a promotes blade outgrowth as well as leaf and leaflet initiation and floral organ development through the quantitative regulation of its major target SlARF10A.
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Mechanistic framework for cell-intrinsic re-establishment of PIN2 polarity after cell division

Mechanistic framework for cell-intrinsic re-establishment of PIN2 polarity after cell division | Plant hormones and  signaling peptides | Scoop.it
Cell polarity, manifested by the localization of proteins to distinct polar plasma membrane domains, is a key prerequisite of multicellular life. In plants, PIN auxin transporters are prominent polarity markers crucial for a plethora of developmental processes. Cell polarity mechanisms in plants are distinct from other eukaryotes and still largely elusive. In particular, how the cell polarities are propagated and maintained following cell division remains unknown. Plant cytokinesis is orchestrated by the cell plate—a transient centrifugally growing endomembrane compartment ultimately forming the cross wall1. Trafficking of polar membrane proteins is typically redirected to the cell plate, and these will consequently have opposite polarity in at least one of the daughter cells2,3,4,5. Here, we provide mechanistic insights into post-cytokinetic re-establishment of cell polarity as manifested by the apical, polar localization of PIN2. We show that the apical domain is defined in a cell-intrinsic manner and that re-establishment of PIN2 localization to this domain requires de novo protein secretion and endocytosis, but not basal-to-apical transcytosis. Furthermore, we identify a PINOID-related kinase WAG1, which phosphorylates PIN2 in vitro6 and is transcriptionally upregulated specifically in dividing cells, as a crucial regulator of post-cytokinetic PIN2 polarity re-establishment.
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Arabidopsis ETHYLENE RESPONSE FACTOR 8 (ERF8) has dual functions in ABA signaling and immunity | BMC Plant Biology | Full Text

Arabidopsis ETHYLENE RESPONSE FACTOR 8 (ERF8) has dual functions in ABA signaling and immunity | BMC Plant Biology | Full Text | Plant hormones and  signaling peptides | Scoop.it
Background

ETHYLENE RESPONSE FACTOR (ERF) 8 is a member of one of the largest transcription factor families in plants, the APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) superfamily. Members of this superfamily have been implicated in a wide variety of processes such as development and environmental stress responses.
Results

In this study we demonstrated that ERF8 is involved in both ABA and immune signaling. ERF8 overexpression induced programmed cell death (PCD) in Arabidopsis and Nicotiana benthamiana. This PCD was salicylic acid (SA)-independent, suggesting that ERF8 acts downstream or independent of SA. ERF8-induced PCD was abolished by mutations within the ERF-associated amphiphilic repression (EAR) motif, indicating ERF8 induces cell death through its transcriptional repression activity. Two immunity-related mitogen-activated protein kinases, MITOGEN-ACTIVATED PROTEIN KINASE 4 (MPK4) and MPK11, were identified as ERF8-interacting proteins and directly phosphorylated ERF8 in vitro. Four putative MPK phosphorylation sites were identified in ERF8, one of which (Ser103) was determined to be the predominantly phosphorylated residue in vitro, while mutation of all four putative phosphorylation sites partially suppressed ERF8-induced cell death in N. benthamiana. Genome-wide transcriptomic analysis and pathogen growth assays confirmed a positive role of ERF8 in mediating immunity, as ERF8 knockdown or overexpression lines conferred compromised or enhanced resistance against the hemibiotrophic bacterial pathogen Pseudomonas syringae, respectively.
Conclusions

Together these data reveal that the ABA-inducible transcriptional repressor ERF8 has dual roles in ABA signaling and pathogen defense, and further highlight the complex influence of ABA on plant-microbe interactions.
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EIN3-LIKE1, MYB1, and ETHYLENE RESPONSE FACTOR3 Act in a Regulatory Loop That Synergistically Modulates Ethylene Biosynthesis and Anthocyanin Accumulation

EIN3-LIKE1, MYB1, and ETHYLENE RESPONSE FACTOR3 Act in a Regulatory Loop That Synergistically Modulates Ethylene Biosynthesis and Anthocyanin Accumulation | Plant hormones and  signaling peptides | Scoop.it
Ethylene regulates climacteric fruit ripening, and EIN3-LIKE1 (EIL1) plays an important role in this process. In apple (Malus domestica), fruit coloration is accompanied by ethylene release during fruit ripening, but the molecular mechanism that underlies these two physiological processes is unknown. In this study, we found that ethylene treatment markedly induced fruit coloration as well as the expression of MdMYB1, a positive regulator of anthocyanin biosynthesis and fruit coloration. In addition, we found that MdEIL1 directly bound to the promoter of MdMYB1 and transcriptionally activated its expression, which resulted in anthocyanin biosynthesis and fruit coloration. Furthermore, MdMYB1 interacted with the promoter of ETHYLENE RESPONSE FACTOR3, a key regulator of ethylene biosynthesis, thereby providing a positive feedback for ethylene biosynthesis regulation. Overall, our findings provide insight into a mechanism involving the synergistic interaction of the ethylene signal with the MdMYB1 transcription factor to regulate ethylene biosynthesis and fruit coloration in apple.
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Natural genetic variation shapes root system responses to phytohormones in Arabidopsis - Ristova - 2018 - The Plant Journal -

Natural genetic variation shapes root system responses to phytohormones in Arabidopsis - Ristova - 2018 - The Plant Journal - | Plant hormones and  signaling peptides | Scoop.it
Plants adjust their architecture by modulating organ growth. This ability is largely dependent on phytohormones. While responses to phytohormones have been studied extensively, it remains unclear to which extent and how these responses are modulated in non‐reference strains. Here, we assess variation of root traits upon treatment with auxin, cytokinin and abscisic acid (ABA) in 192 Arabidopsis accessions. We identify common response patterns, uncover the extent of their modulation by specific genotypes, and find that the Col‐0 reference accession is not a good representative of the species in this regard. We conduct genome‐wide association studies and identify 114 significant associations, most of them relating to ABA treatment. The numerous ABA candidate genes are not enriched for known ABA‐associated genes, indicating that we largely uncovered unknown players. Overall, our study provides a comprehensive view of the diversity of hormone responses in the Arabidopsis thaliana species, and shows that variation of genes that are yet mostly not associated with such a role to determine natural variation of the response to phytohormones.
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Ethylene promotes cadmium‐induced root growth inhibition through EIN3 controlled XTH33 and LSU1 expression in Arabidopsis - Kong - 2018 - Plant, Cell & Environment -

Ethylene promotes cadmium‐induced root growth inhibition through EIN3 controlled XTH33 and LSU1 expression in Arabidopsis - Kong - 2018 - Plant, Cell & Environment - | Plant hormones and  signaling peptides | Scoop.it
Cadmium (Cd) stress is one of the most serious heavy metal stresses limiting plant growth and development. However, the molecular mechanisms underlying Cd‐induced root growth inhibition remain unclear. Here, we found that ethylene signalling positively regulates Cd‐induced root growth inhibition. Arabidopsis seedlings pretreated with the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid exhibited enhanced Cd‐induced root growth inhibition, whereas the addition of the ethylene biosynthesis inhibitor aminoethoxyvinyl glycine decreased Cd‐induced root growth inhibition. Consistently, ethylene‐insensitive mutants, such as ein4‐1, ein3‐1 eil1‐1 double mutant, and EBF1ox, displayed an increased tolerance to Cd. Furthermore, we also observed that Cd inhibited EIN3 protein degradation, a process that was regulated by ethylene signalling. Genetic and biochemical analyses showed that EIN3 enhanced root growth inhibition under Cd stress through direct binding to the promoters and regulating the expression of XTH33 and LSU1, which encode key regulators of cell wall extension and sulfur metabolic process, respectively. Collectively, our study demonstrates that ethylene plays a positive role in Cd‐regulated root growth inhibition through EIN3‐mediated transcriptional regulation of XTH33 and LSU1 and provides a molecular framework for the integration of environmental signals and intrinsic regulators in modulating plant root growth.
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Strigolactones in plant adaptation to abiotic stresses: An emerging avenue of plant research - Mostofa - 2018 - Plant, Cell & Environment -

Strigolactones in plant adaptation to abiotic stresses: An emerging avenue of plant research - Mostofa - 2018 - Plant, Cell & Environment - | Plant hormones and  signaling peptides | Scoop.it
Phytohormones play central roles in boosting plant tolerance to environmental stresses, which negatively affect plant productivity and threaten future food security. Strigolactones (SLs), a class of carotenoid‐derived phytohormones, were initially discovered as an “ecological signal” for parasitic seed germination and establishment of symbiotic relationship between plants and beneficial microbes. Subsequent characterizations have described their functional roles in various developmental processes, including root development, shoot branching, reproductive development, and leaf senescence. SLs have recently drawn much attention due to their essential roles in the regulation of various physiological and molecular processes during the adaptation of plants to abiotic stresses. Reports suggest that the production of SLs in plants is strictly regulated and dependent on the type of stresses that plants confront at various stages of development. Recently, evidence for crosstalk between SLs and other phytohormones, such as abscisic acid, in responses to abiotic stresses suggests that SLs actively participate within regulatory networks of plant stress adaptation that are governed by phytohormones. Moreover, the prospective roles of SLs in the management of plant growth and development under adverse environmental conditions have been suggested. In this review, we provide a comprehensive discussion pertaining to SL‐mediated plant responses and adaptation to abiotic stresses.
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EIN3-LIKE1, MYB1, and ETHYLENE RESPONSE FACTOR3 Act in a Regulatory Loop That Synergistically Modulates Ethylene Biosynthesis and Anthocyanin Accumulation

EIN3-LIKE1, MYB1, and ETHYLENE RESPONSE FACTOR3 Act in a Regulatory Loop That Synergistically Modulates Ethylene Biosynthesis and Anthocyanin Accumulation | Plant hormones and  signaling peptides | Scoop.it
Ethylene regulates climacteric fruit ripening, and EIN3-LIKE1 (EIL1) plays an important role in this process. In apple (Malus domestica), fruit coloration is accompanied by ethylene release during fruit ripening, but the molecular mechanism that underlies these two physiological processes is unknown. In this study, we found that ethylene treatment markedly induced fruit coloration as well as the expression of MdMYB1, a positive regulator of anthocyanin biosynthesis and fruit coloration. In addition, we found that MdEIL1 directly bound to the promoter of MdMYB1 and transcriptionally activated its expression, which resulted in anthocyanin biosynthesis and fruit coloration. Furthermore, MdMYB1 interacted with the promoter of ETHYLENE RESPONSE FACTOR3, a key regulator of ethylene biosynthesis, thereby providing a positive feedback for ethylene biosynthesis regulation. Overall, our findings provide insight into a mechanism involving the synergistic interaction of the ethylene signal with the MdMYB1 transcription factor to regulate ethylene biosynthesis and fruit coloration in apple.
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The potato transcription factor StbZIP61 regulates dynamic biosynthesis of salicylic acid in defense against Phytophthora infestans infection - Zhou - 2018 - The Plant Journal -

The potato transcription factor StbZIP61 regulates dynamic biosynthesis of salicylic acid in defense against Phytophthora infestans infection - Zhou - 2018 - The Plant Journal - | Plant hormones and  signaling peptides | Scoop.it
Salicylic acid (SA) signalling plays an essential role in plant innate immunity. In this study, we identified a component in the SA signaling pathway in potato (Solanum tuberosum), the transcription factor StbZIP61, and characterized its function in defence against Phytophthora infestans. Expression of StbZIP61 was induced upon P. infestans infection and following exposure to the defense signaling hormones SA, ethylene and jasmonic acid. Overexpression of StbZIP61 increased the tolerance of potato plants to P. infestans while RNA interference (RNAi) increased susceptibility. Yeast two‐hybrid and pull down experiments revealed that StbZIP61 could interact with an NPR3‐like protein (StNPR3L) that inhibited its DNA‐binding and transcriptional activation activities. Moreover, StNPR3L interacted with StbZIP61 in an SA‐dependent manner. Among candidate genes involved in SA‐regulated defense responses, StbZIP61 had a significant impact on expression of StICS1, which encodes a key enzyme for SA biosynthesis. StICS1 transcription was induced upon P. infestans infection and this responsive expression to the pathogen was reduced in StbZIP61 RNAi plants. Accordingly, StICS1 expression was remarkably enhanced in StbZIP61‐overexpressing plants. Together, our data demonstrate that StbZIP61 functions in concert with StNPR3L to regulate the temporal activation of SA biosynthesis, which contributes to SA‐mediated immunity against P. infestans infection in potato.
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SUMO Suppresses the Activity of the Jasmonic Acid Receptor CORONATINE INSENSITIVE1

SUMO Suppresses the Activity of the Jasmonic Acid Receptor CORONATINE INSENSITIVE1 | Plant hormones and  signaling peptides | Scoop.it
Plants respond rapidly to sudden environmental cues, often responding prior to changes in the hormone levels that coordinate these responses. How this is achieved is not fully understood. The integrative role of the phytohormone jasmonic acid (JA) relies upon the plant’s ability to control the levels of JASMONATE ZIM (JAZ) domain-containing repressor proteins. Here, we demonstrate that regardless of intrinsic JA levels, Small Ubiquitin-like Modifier (SUMO)-conjugated JAZ proteins inhibit the JA receptor CORONATINE INSENSITIVE1 (COI1) from mediating non-SUMOylated JAZ degradation. The SUMO-deconjugating proteases OVERLY TOLERANT TO SALT1 (OTS1) and OTS2 regulate JAZ protein SUMOylation and stability. The ots1 ots2 double mutants accumulate SUMOylated and non-SUMOylated JAZ repressor proteins but show no change in endogenous JA levels compared with wild-type plants. SUMO1-conjugated JAZ proteins bind to COI1 independently of the JA mimic coronatine. SUMO inhibits JAZ binding to COI1. We identify the SUMO interacting motif in COI1 and demonstrate that this is vital to SUMO-dependent inhibition of COI1. Necrotroph infection of Arabidopsis thaliana promotes SUMO protease degradation, and this increases JAZ SUMOylation and abundance, which in turn inhibits JA signaling. This study reveals a mechanism for rapidly regulating JA responses, allowing plants to adapt to environmental changes.
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It starts with TIRs

It starts with TIRs | Plant hormones and  signaling peptides | Scoop.it
The canonical auxin receptor complex mediates gene expression, but it is also necessary for responses far too rapid to be mediated by transcription. An innovative setup that uses advanced microscopy and microfluidics can record auxin-induced changes within 30 seconds during root growth.
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ABRE‐BINDING FACTORS play a role in the feedback regulation of ABA signaling by mediating rapid ABA induction of ABA co‐receptor genes - Wang - 2019 - New Phytologist -

ABRE‐BINDING FACTORS play a role in the feedback regulation of ABA signaling by mediating rapid ABA induction of ABA co‐receptor genes - Wang - 2019 - New Phytologist - | Plant hormones and  signaling peptides | Scoop.it
Group A protein phosphatase 2Cs (PP2Cs) are abscisic acid (ABA) co‐receptors that negatively regulate the ABA signaling pathway by inhibiting the downstream SnRK2 protein kinases. It has long been observed that exogenous ABA treatments dramatically induce the expression of group A PP2C genes, but the underlying molecular mechanisms and the biological significance remain largely unknown.
Here, by using GUS reporter transgenic lines in which various lengths of ABI1 and ABI2 promoters were used to drive GUS gene expression, we defined the promoter fragments that confer ABA inducibility to ABI1 and ABI2. We further showed that ABRE‐binding factors (ABFs), the bZIP family transcription factors, directly bind to the promoters of group A PP2C genes, and mediate rapid induction of their expression on exogenous ABA treatments.
Moreover, our data indicated that ABA dramatically induces the expression of ABF genes and the accumulation of endogenous ABF proteins, and that ABFs themselves are involved in this induction, thus providing another layer of ABA regulation towards ABF proteins in addition to the well‐characterized ABA‐induced phosphorylation by SnRK2 protein kinases.
Together, our data demonstrate that ABFs mediate rapid ABA induction of group A PP2C genes, thus playing a role in the negative feedback regulation of ABA signaling.
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Long-distance signaling in plant stress response - ScienceDirect

Long-distance signaling in plant stress response - ScienceDirect | Plant hormones and  signaling peptides | Scoop.it
Vascular plants respond to various environmental stresses by integrating and transmitting environmental information perceived by roots and leaves, respectively. Long-distance signaling plays a crucial role in plant adaptation to and subsequent survival to severe environmental conditions. Recent studies have elucidated that various mobile molecules, such as small proteins, peptides, RNAs, metabolites, and second messengers, transmit extracellular stimuli from sensing tissues to target organs. Plants have unique and complex mechanisms for accurately connecting various organs despite the lack of a nervous system. In this short review, we summarize the current knowledge of plant molecules involved in long-distance signaling for optimal growth and stress response, with special focus on mobile peptides.
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Accumulation of endogenous peptides triggers a pathogen stress response in Arabidopsis thaliana - Kmiec - 2018 - The Plant Journal -

Accumulation of endogenous peptides triggers a pathogen stress response in Arabidopsis thaliana - Kmiec - 2018 - The Plant Journal - | Plant hormones and  signaling peptides | Scoop.it
The stepwise degradation of peptides to amino acids in plant mitochondria and chloroplasts is catalyzed by a network of oligopeptidases (presequence protease PreP, organellar oligopeptidase OOP) and aminopeptidases. In the present report, we show that the lack of oligopeptidase activity in Arabidopsis thaliana results in the accumulation of endogenous free peptides, mostly of chloroplastic origin (targeting peptides and degradation products). Using mRNA sequencing and deep coverage proteomics, allowing for the identification of 17 000 transcripts and 11 000 proteins, respectively, we uncover a peptide‐stress response occurring in plants lacking PreP and OOP oligopeptidase activity. The peptide‐stress response results in the activation of the classical plant defense pathways in the absence of pathogenic challenge. The constitutive activation of the pathogen‐defense pathways imposes a strong growth penalty and a reduction of the plants reproductive fitness. Our results indicate that the absence of organellar oligopeptidases PreP1/2 and OOP results in the accumulation of peptides that are perceived as pathogenic effectors and activate the signaling pathways of plant‐defense response.
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The CLE9/10 secretory peptide regulates stomatal and vascular development through distinct receptors

The CLE9/10 secretory peptide regulates stomatal and vascular development through distinct receptors | Plant hormones and  signaling peptides | Scoop.it

The frequency and orientation of cell division are regulated by intercellular signalling molecules; however, tissue-specific regulatory systems for cell divisions are only partially understood. Here, we report that the peptide hormone CLAVATA3/ESR-RELATED 9/10 (CLE9/10) regulates two different developmental processes, stomatal lineage development and xylem development, through two distinct receptor systems in Arabidopsis thaliana. We show that the receptor kinase HAESA-LIKE 1 (HSL1) is a CLE9/10 receptor that regulates stomatal lineage cell division, and BARELY NO MERISTEM (BAM) class receptor kinases are CLE9/10 receptors that regulate periclinal cell division of xylem precursor cells. Both HSL1 and BAM1 bind to CLE9/10, but only HSL1 recruits SOMATIC EMBRYOGENESIS RECEPTOR KINASES as co-receptors in the presence of CLE9/10, suggesting different signalling modes for these receptor systems.

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JAZ repressors of metabolic defense promote growth and reproductive fitness in Arabidopsis

JAZ repressors of metabolic defense promote growth and reproductive fitness in Arabidopsis | Plant hormones and  signaling peptides | Scoop.it
Plant immune responses mediated by the hormone jasmonoyl-l-isoleucine (JA-Ile) are metabolically costly and often linked to reduced growth. Although it is known that JA-Ile activates defense responses by triggering the degradation of JASMONATE ZIM DOMAIN (JAZ) transcriptional repressor proteins, expansion of the JAZ gene family in vascular plants has hampered efforts to understand how this hormone impacts growth and other physiological tasks over the course of ontogeny. Here, we combined mutations within the 13-member Arabidopsis JAZ gene family to investigate the effects of chronic JAZ deficiency on growth, defense, and reproductive output. A higher-order mutant (jaz decuple, jazD) defective in 10 JAZ genes (JAZ1–7, -9, -10, and -13) exhibited robust resistance to insect herbivores and fungal pathogens, which was accompanied by slow vegetative growth and poor reproductive performance. Metabolic phenotypes of jazD discerned from global transcript and protein profiling were indicative of elevated carbon partitioning to amino acid-, protein-, and endoplasmic reticulum body-based defenses controlled by the JA-Ile and ethylene branches of immunity. Resource allocation to a strong defense sink in jazD leaves was associated with increased respiration and hallmarks of carbon starvation but no overt changes in photosynthetic rate. Depletion of the remaining JAZ repressors in jazD further exaggerated growth stunting, nearly abolished seed production and, under extreme conditions, caused spreading necrotic lesions and tissue death. Our results demonstrate that JAZ proteins promote growth and reproductive success at least in part by preventing catastrophic metabolic effects of an unrestrained immune response.
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ZmbZIP4 Contributes to Stress Resistance in Maize by Regulating ABA Synthesis and Root Development

ZmbZIP4 Contributes to Stress Resistance in Maize by Regulating ABA Synthesis and Root Development | Plant hormones and  signaling peptides | Scoop.it
In plants, bZIP (basic leucine zipper) transcription factors regulate diverse processes such as development and stress responses. However, few of these transcription factors have been functionally characterized in maize (Zea mays). In this study, we characterized the bZIP transcription factor gene ZmbZIP4 from maize. ZmbZIP4 was differentially expressed in various organs of maize and was induced by high salinity, drought, heat, cold, and abscisic acid treatment in seedlings. A transactivation assay in yeast demonstrated that ZmbZIP4 functioned as a transcriptional activator. A genome-wide screen for ZmbZIP4 targets by immunoprecipitation sequencing revealed that ZmbZIP4 could positively regulate a number of stress response genes, such as ZmLEA2, ZmRD20, ZmRD21, ZmRab18, ZmNHX3, ZmGEA6, and ZmERD, and some abscisic acid synthesis-related genes, including NCED, ABA1, AAO3, and LOS5. In addition, ZmbZIP4 targets some root development-related genes, including ZmLRP1, ZmSCR, ZmIAA8, ZmIAA14, ZmARF2, and ZmARF3, and overexpression of ZmbZIP4 resulted in an increased number of lateral roots, longer primary roots, and an improved root system. Increased abscisic acid synthesis by overexpression of ZmbZIP4 also can increase the plant’s ability to resist abiotic stress. Thus, ZmbZIP4 is a positive regulator of plant abiotic stress responses and is involved in root development in maize.
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Ethylene signaling regulates natural variation in the abundance of antifungal acetylated diferuloylsucroses and Fusarium graminearum resistance in maize seedling roots - Zhou - - New Phytologist - ..

Ethylene signaling regulates natural variation in the abundance of antifungal acetylated diferuloylsucroses and Fusarium graminearum resistance in maize seedling roots - Zhou - - New Phytologist - .. | Plant hormones and  signaling peptides | Scoop.it
The production and regulation of defensive specialized metabolites play a central role in pathogen resistance in maize (Zea mays) and other plants. Therefore, identification of genes involved in plant specialized metabolism can contribute to improved disease resistance.
We used comparative metabolomics to identify previously unknown antifungal metabolites in maize seedling roots, and investigated the genetic and physiological mechanisms underlying their natural variation using quantitative trait locus mapping and comparative transcriptomics approaches.
Two maize metabolites, smilaside A (3,6‐diferuloyl‐3′,6′‐diacetylsucrose) and smiglaside C (3,6‐diferuloyl‐2′,3′,6′‐triacetylsucrose), were identified that could contribute to maize resistance against Fusarium graminearum and other fungal pathogens. Elevated expression of an ethylene signaling gene, ETHYLENE INSENSITIVE 2 (ZmEIN2), co‐segregated with a decreased smilaside A : smiglaside C ratio. Pharmacological and genetic manipulation of ethylene availability and sensitivity in vivo indicated that, whereas ethylene was required for the production of both metabolites, the smilaside A : smiglaside C ratio was negatively regulated by ethylene sensitivity. This ratio, rather than the absolute abundance of these two metabolites, was important for maize seedling root defense against F. graminearum.
Ethylene signaling regulates the relative abundance of the two F. graminearum‐resistance‐related metabolites and affects resistance against F. graminearum in maize seedling roots.
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Genome‐wide association study reveals novel players in defense hormone crosstalk in Arabidopsis - Proietti - 2018 - Plant, Cell & Environment -

Genome‐wide association study reveals novel players in defense hormone crosstalk in Arabidopsis - Proietti - 2018 - Plant, Cell & Environment - | Plant hormones and  signaling peptides | Scoop.it
Jasmonic acid (JA) regulates plant defenses against necrotrophic pathogens and insect herbivores. Salicylic acid (SA) and abscisic acid (ABA) can antagonize JA‐regulated defenses, thereby modulating pathogen or insect resistance. We performed a genome‐wide association (GWA) study on natural genetic variation in Arabidopsis thaliana for the effect of SA and ABA on the JA pathway. We treated 349 Arabidopsis accessions with methyl JA (MeJA), or a combination of MeJA and either SA or ABA, after which expression of the JA‐responsive marker gene PLANT DEFENSIN1.2 (PDF1.2) was quantified as a readout for GWA analysis. Both hormones antagonized MeJA‐induced PDF1.2 in the majority of the accessions but with a large variation in magnitude. GWA mapping of the SA‐ and ABA‐affected PDF1.2 expression data revealed loci associated with crosstalk. GLYI4 (encoding a glyoxalase) and ARR11 (encoding an Arabidopsis response regulator involved in cytokinin signalling) were confirmed by T‐DNA insertion mutant analysis to affect SA–JA crosstalk and resistance against the necrotroph Botrytis cinerea. In addition, At1g16310 (encoding a cation efflux family protein) was confirmed to affect ABA–JA crosstalk and susceptibility to Mamestra brassicae herbivory. Collectively, this GWA study identified novel players in JA hormone crosstalk with potential roles in the regulation of pathogen or insect resistance.
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Three Auxin Response Factors Promote Hypocotyl Elongation

Three Auxin Response Factors Promote Hypocotyl Elongation | Plant hormones and  signaling peptides | Scoop.it
The hormone auxin regulates growth largely by affecting gene expression. By studying Arabidopsis (Arabidopsis thaliana) mutants deficient in AUXIN RESPONSE FACTORS (ARFs), we have identified three ARF proteins that are required for auxin-responsive hypocotyl elongation. Plants deficient in these factors have reduced responses to environmental conditions that increase auxin levels, including far-red-enriched light and high temperature. Despite having decreased auxin responses, the ARF-deficient plants responded to brassinosteroid and gibberellin, indicating that different hormones can act partially independently. Aux/IAA proteins, encoded by IAA genes, interact with ARF proteins to repress auxin response. Silencing expression of multiple IAA genes increased hypocotyl elongation, suggesting that Aux/IAA proteins modulate ARF activity in hypocotyls in a potential negative feedback loop.
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The Interaction between DELLA and ARF/IAA Mediates Crosstalk between Gibberellin and Auxin Signaling to Control Fruit Initiation in Tomato

The Interaction between DELLA and ARF/IAA Mediates Crosstalk between Gibberellin and Auxin Signaling to Control Fruit Initiation in Tomato | Plant hormones and  signaling peptides | Scoop.it
Fruit initiation following fertilization in angiosperms is strictly regulated by phytohormones. In tomato (Solanum lycopersicum), auxin and gibberellin (GA) play central roles in promoting fruit initiation. Without fertilization, elevated GA or auxin signaling can induce parthenocarpy (seedless fruit production). The GA-signaling repressor SlDELLA and auxin-signaling components SlIAA9 and SlARF7 repress parthenocarpy, but the underlying mechanism is unknown. Here, we show that SlDELLA and the SlARF7/SlIAA9 complex mediate crosstalk between GA and auxin pathways to regulate fruit initiation. Yeast-two-hybrid and coimmunoprecipitation assays showed that SlARF7 and additional activator SlARFs interact with SlDELLA and SlIAA9 through distinct domains. SlARF7/SlIAA9 and SlDELLA antagonistically modulate the expression of feedback-regulated genes involved in GA and auxin metabolism, whereas SlARF7/SlIAA9 and SlDELLA coregulate the expression of fruit growth-related genes. Analysis of procera (della), SlARF7 RNAi (with downregulated expression of multiple activator SlARFs), and entire (iaa9) single and double mutants indicated that these genes additively affect parthenocarpy, supporting the notion that the SlARFs/SlIAA9 and SlDELLA interaction plays an important role in regulating fruit initiation. Analysis of the GA-deficient mutant gib1 showed that active GA biosynthesis and signaling are required for auxin-induced fruit initiation. Our study reveals how direct crosstalk between auxin- and GA-signaling components is critical for tomato fruit initiation.
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Frontiers | Mitogen-Activated Protein Kinase Cascades in Plant Hormone Signaling | Plant Science

Frontiers | Mitogen-Activated Protein Kinase Cascades in Plant Hormone Signaling | Plant Science | Plant hormones and  signaling peptides | Scoop.it
Mitogen-activated protein kinase (MAPK) modules play key roles in the transduction of environmental and developmental signals through phosphorylation of downstream signaling targets, including other kinases, enzymes, cytoskeletal proteins or transcription factors, in all eukaryotic cells. A typical MAPK cascade consists of at least three sequentially acting serine/threonine kinases, a MAP kinase kinase kinase (MAPKKK), a MAP kinase kinase (MAPKK) and finally, the MAP kinase (MAPK) itself, with each phosphorylating, and hence activating, the next kinase in the cascade. Recent advances in our understanding of hormone signaling pathways have led to the discovery of new regulatory systems. In particular, this research has revealed the emerging role of crosstalk between the protein components of various signaling pathways and the involvement of this crosstalk in multiple cellular processes. Here we provide an overview of current models and mechanisms of hormone signaling with a special emphasis on the role of MAPKs in cell signaling networks.
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Integrated Regulation of Apical Hook Development by Transcriptional Coupling of EIN3/EIL1 and PIFs in Arabidopsis

Integrated Regulation of Apical Hook Development by Transcriptional Coupling of EIN3/EIL1 and PIFs in Arabidopsis | Plant hormones and  signaling peptides | Scoop.it
The apical hook protects the meristems of dicot seedlings as they protrude through the soil; multiple factors, including phytohormones and light, mediate apical hook development. HOOKLESS1 (HLS1) plays an indispensable role, as HLS1 mutations cause a hookless phenotype. The ETHYLENE INSENSITIVE3 (EIN3) and EIN3-LIKE1 (EIL1) transcription factors integrate multiple signals (ethylene, gibberellins, and jasmonate) and activate HLS1 expression to enhance hook development. Here, we found that Arabidopsis thaliana PHYTOCHROME INTERACTING FACTOR (PIF) transcription factors act in parallel with EIN3/EIL1 and promote hook curvature by activating HLS1 transcription at a distinct binding motif. EIN3/EIL1 and PIFs can promote hook formation in the absence of the other. Jasmonate represses PIF function to inhibit hook development. Like EIN3 and EIL1, MYC2 interacts with PIF4 and hampers its activity. Acting together, EIN3/EIL1 and PIFs alleviate the negative effects of jasmonate/light and facilitate the positive effects of ethylene/gibberellins. Mutating EIN3/EIL1 and PIFs causes a complete hookless phenotype, marginal HLS1 expression, and insensitivity to upstream signals. Transcriptome profiling revealed that EIN3/EIL1 and PIFs additively and distinctly regulate a wide array of processes, including apical hook development. Together, our findings identify an integrated framework underlying the regulation of apical hook development and show that EIN3/EIL1 and PIFs fine-tune adaptive growth in response to hormone and light signals.
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