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Strigolactone/MAX2-Induced Degradation of Brassinosteroid Transcriptional Effector BES1 Regulates Shoot Branching

Strigolactone/MAX2-Induced Degradation of Brassinosteroid Transcriptional Effector BES1 Regulates Shoot Branching | Plant hormones | Scoop.it
Belen Marquez's insight:

Strigolactones (SLs), a class of the most recently identified terpenoid phytohormones, play essential roles in plant development, specifically in suppressing shoot branching. MAX2, a subunit of an SCF E3 ligase and a positive regulator that inhibits shoot branching, is likely a key SL signaling component. Here, we provide genetic and biochemical evidence to demonstrate that BES1 interacts with MAX2 and acts as its substrate to regulate SL-responsive gene expression. Additional AtD14, a putative receptor of SLs, can promote BES1 degradation. Knockdown of BES1 and its homologs dramatically suppressed the branching phenotype of max2-1 mutant. These results portray an SL signaling cascade from the putative receptor to downstream transcription factors. In addition, we demonstrate that the SL and brassinosteroid (BR) signaling pathways distinctly regulate the same transcription factor, BES1, to control specific developmental processes.

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The shoot regeneration capacity of excised Arabidopsis cotyledons is established during the initial hours after injury and is modulated by a complex genetic network of light signalling - NAMETH - 2...

The shoot regeneration capacity of excised Arabidopsis cotyledons is established during the initial hours after injury and is modulated by a complex genetic network of light signalling - NAMETH - 2... | Plant hormones | Scoop.it
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Excised plant tissues (explants) can regenerate new shoot apical meristems in vitro, but regeneration rates can be inexplicably variable. Light affects rates of shoot regeneration, but the underlying mechanisms are poorly understood. Here, excised Arabidopsis cotyledons were dark–light shifted to define the timing of explant light sensitivity. Mutants and pharmacological agents were employed to uncover underlying physiological and genetic mechanisms. Unexpectedly, explants were most light sensitive during the initial hours post-excision with respect to shoot regeneration. Only ∼100 µmol m−2 s−1 of fluorescent light was sufficient to induce reactive oxygen species (ROS) accumulation in new explants. By 48 h post-excision, induction of ROS, or quenching of ROS by xanthophylls, increased or decreased shoot regeneration, respectively. Phytochrome A-mediated signalling suppressed light inhibition of regeneration. Early exposure to blue/UV-A wavelengths inhibited regeneration, involving photoreceptor CRY1. Downstream transcription factor HY5 mediated explant photoprotection, perhaps by promoting anthocyanin accumulation, a pigment also induced by cytokinin. Surprisingly, early light inhibition of shoot regeneration was dependent on polar auxin transport. Early exposure to ethylene stimulated dark-treated explants to regenerate, but inhibited light-treated explants. We propose that variability in long-term shoot regeneration may arise within the initial hours post-excision, from inadvertent, variable exposure of explants to light, modulated by hormones.

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Biswapriya Biswavas Misra's comment, December 31, 2013 11:31 AM
Dear Belén, Wish you a Merry Christmas and Happy New Year, 2014. I was wondering, what is the best commerical source to buy/ obtain some aliquots of 'strigolactones'. i saw your paper and was thinking about it. Thanks and regards, Biswa
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Cell Research - LATERAL ORGAN BOUNDARIES DOMAIN transcription factors direct callus formation in Arabidopsis regeneration

Cell Research - LATERAL ORGAN BOUNDARIES DOMAIN transcription factors direct callus formation in Arabidopsis regeneration | Plant hormones | Scoop.it
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The remarkable regeneration capability of plant tissues or organs under culture conditions has underlain an extensive practice for decades. The initial step in plant in vitro regeneration often involves the induction of a pluripotent cell mass termed callus, which is driven by the phytohormone auxin and occurs via a root development pathway. However, the key molecules governing callus formation remain unknown. Here we demonstrate that Arabidopsis LATERAL ORGAN BOUNDARIES DOMAIN (LBD)/ASYMMETRIC LEAVES2-LIKE (ASL) transcription factors are involved in the control of callus formation program. The four LBD genes downstream of AUXIN RESPONSE FACTORs (ARFs), LBD16, LBD17, LBD18 and LBD29, are rapidly and dramatically induced by callus-inducing medium (CIM) in multiple organs. Ectopic expression of each of the four LBD genes in Arabidopsis is sufficient to trigger spontaneous callus formation without exogenous phytohormones, whereas suppression of LBD function inhibits the callus formation induced by CIM. Moreover, the callus triggered by LBD resembles that induced by CIM by characteristics of ectopically activated root meristem genes and efficient regeneration capacity. These findings define LBD transcription factors as key regulators in the callus induction process, thereby establishing a molecular link between auxin signaling and the plant regeneration program.

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Plant Callus: Mechanisms of Induction and Repression

Plant Callus: Mechanisms of Induction and Repression | Plant hormones | Scoop.it
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Plants develop unorganized cell masses like callus and tumors in response to various biotic and abiotic stimuli. Since the historical discovery that the combination of two growth-promoting hormones, auxin and cytokinin, induces callus from plant explants in vitro, this experimental system has been used extensively in both basic research and horticultural applications. The molecular basis of callus formation has long been obscure, but we are finally beginning to understand how unscheduled cell proliferation is suppressed during normal plant development and how genetic and environmental cues override these repressions to induce callus formation. In this review, we will first provide a brief overview of callus development in nature and in vitro and then describe our current knowledge of genetic and epigenetic mechanisms underlying callus formation.

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PLOS Genetics: DNA Methylation and Histone Modifications Regulate De Novo Shoot Regeneration in Arabidopsis by Modulating WUSCHEL Expression and Auxin Signaling

PLOS Genetics: DNA Methylation and Histone Modifications Regulate De Novo Shoot Regeneration in Arabidopsis by Modulating WUSCHEL Expression and Auxin Signaling | Plant hormones | Scoop.it
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DAD2 Is an α/β Hydrolase likely to Be Involved in the Perception of the Plant Branching Hormone, Strigolactone

DAD2 Is an α/β Hydrolase likely to Be Involved in the Perception of the Plant Branching Hormone, Strigolactone | Plant hormones | Scoop.it

Strigolactones are a recently discovered class of plant hormone involved in branching, leaf senescence, root development, and plant-microbe interactions [1,2,3,4,5,6]. They are carotenoid-derived lactones, synthesized in the roots and transported acropetally to modulate axillary bud outgrowth (i.e., branching) [1,2]. However, a receptor for strigolactones has not been identified. We have identified the DAD2 gene from petunia, an ortholog of the rice and Arabidopsis D14 genes, and present evidence for its roles in strigolactone perception and signaling. DAD2 acts in the strigolactone pathway, and the dad2 mutant is insensitive to the strigolactone analog GR24. The crystal structure of DAD2 reveals an α/β hydrolase fold containing a canonical catalytic triad with a large internal cavity capable of accommodating strigolactones. In the presence of GR24 DAD2 interacts with PhMAX2A, a central component of strigolactone signaling, in a GR24 concentration-dependent manner. DAD2 can hydrolyze GR24, with mutants of the catalytic triad abolishing both this activity and the ability of DAD2 to interact with PhMAX2A. The hydrolysis products can neither stimulate the protein-protein interaction nor modulate branching. These observations suggest that DAD2 acts to bind the mobile strigolactone signal and then interacts with PhMAX2A during catalysis to initiate an SCF-mediated signal transduction pathway.


Via GMI Vienna
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D14-SCFD3-dependent degradation of D53 regulates strigolactone signalling : Nature

D14-SCFD3-dependent degradation of D53 regulates strigolactone signalling : Nature | Plant hormones | Scoop.it

Strigolactones (SLs), a newly discovered class of carotenoid-derived phytohormones, are essential for developmental processes that shape plant architecture and interactions with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Despite the rapid progress in elucidating the SL biosynthetic pathway, the perception and signalling mechanisms of SL remain poorly understood. Here we show that DWARF 53 (D53) acts as a repressor of SL signalling and that SLs induce its degradation. We find that the rice (Oryza sativa) d53 mutant, which produces an exaggerated number of tillers compared to wild-type plants, is caused by a gain-of-function mutation and is insensitive to exogenous SL treatment. The D53 gene product shares predicted features with the class I Clp ATPase proteins and can form a complex with the α/β hydrolase protein DWARF 14 (D14) and the F-box protein DWARF 3 (D3), two previously identified signalling components potentially responsible for SL perception. We demonstrate that, in a D14- and D3-dependent manner, SLs induce D53 degradation by the proteasome and abrogate its activity in promoting axillary bud outgrowth. Our combined genetic and biochemical data reveal that D53 acts as a repressor of the SL signalling pathway, whose hormone-induced degradation represents a key molecular link between SL perception and responses


Via Christophe Jacquet
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Strigolactones fine-tune the root system - Springer

Strigolactones fine-tune the root system - Springer | Plant hormones | Scoop.it

Strigolactones were originally discovered to be involved in parasitic weed germination, in mycorrhizal association and in the control of shoot architecture. Despite their clear role in rhizosphere signaling, comparatively less attention has been given to the belowground function of strigolactones on plant development. However, research has revealed that strigolactones play a key role in the regulation of the root system including adventitious roots, primary root length, lateral roots, root hairs and nodulation. Here, we review the recent progress regarding strigolactone regulation of the root system and the antagonism and interplay with other hormones.


Via Francis Martin
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Molecular Plant Pathology - Do strigolactones contribute to plant defence?

Molecular Plant Pathology - Do strigolactones contribute to plant defence? | Plant hormones | Scoop.it

Abstract

Strigolactones are multifunctional molecules involved in several processes outside and within the plant. As signalling molecules in the rhizosphere, they favour arbuscular mycorrhizal symbiosis establishment, but they also act as host detection cues for root parasitic plants. As phytohormones, they are involved in the regulation of plant architecture, adventitious rooting, secondary growth and reproductive development, and novel roles are emerging continuously. In the present study, the possible involvement of strigolactones in plant defence responses was investigated. For that purpose, the resistance/susceptibility of the strigolactone-deficient tomato mutant Slccd8 against the foliar fungal pathogens Botrytis cinerea and Alternaria alternata was assessed. Slccd8 was more susceptible to both pathogens, pointing to a new role for strigolactones in plant defence. A reduction on the content of the defence-related hormones jasmonic acid, salicylic acid, and abscisic acid was detected by HPLC-MS/MS in the Slccd8 mutant, suggesting that hormone homeostasis is altered in the mutant. Moreover, the expression level of the jasmonate-dependent gene PinII, involved in resistance of tomato to B. cinerea, was lower than in the corresponding wild-type. We propose here that strigolactones play a role in the regulation of plant defences through their interaction with other defence-related hormones, especially with the jasmonic acid signalling pathway.


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Strigolactones...more than enough to keep plant scientists occupied

For instance, strigolactones are known to promote root hair elongation, inhibit shoot branching, promote hyphae branching in Arbuscular Mycorrhiza Fungi and to stimulate the germination of parasitic plants (hence their strong ...
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CUC2 as an early marker for regeneration competence in Arabidopsis root explants

CUC2 as an early marker for regeneration competence in Arabidopsis root explants | Plant hormones | Scoop.it
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CUP SHAPED COTELYDON 2 (CUC2) was tested as a marker for shoot induction to monitor and facilitate the optimization of in vitro regeneration of Arabidopsis thaliana. The expression of a pCUC2::3XVENUS-N7 fluorescent marker allowed the observation of early steps in the initiation and development of shoots on root explants. The explants were first incubated on an auxin-rich callus induction medium (CIM) and then transferred to a cytokinin-rich shoot induction medium (SIM). CUC2-expression occurred prior to visible shoot formation during the incubation of the root explant on CIM. Shoot formation was invariably preceded by the accumulation of CUC2 expression at dispersed sites along the root explant. These patches of CUC2-expression also marked the site of lateral root primordium formation in root explants that were transferred to hormone free medium. Thus, CUC2 is a predictive marker for the acquisition of root explant competence for root and shoot organogenesis.

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LBD29 regulates the cell cycle progression in response to auxin during lateral root formation in Arabidopsis thaliana

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Abstract

Background and Aims LATERAL ORGAN BOUNDARIES DOMAIN 29 (LBD29), an important molecule downstream of auxin response factors ARF7 and ARF19, has a critical role in lateral root formation in Arabidopsis thaliana. The cell cycle activation of pericycle cells and their specification triggered by auxin are crucial for the initiation of lateral roots. In this study, we attempted to determine whether LBD29 is involved in auxin signalling and/or cell cycle regulation and to characterize the roles of LBD29 in these processes.

Methods The impact of LBD29 on cell cycling progression in pericycle cells was investigated in lbd29 loss-of-function mutant or LBD29-over-expressing plants. The cell cycle was determined by measuring the expression of some cell cycle-related genes using in situ hybridization and quantitative real-time reverse transcription–PCR (qRT-PCR). Furthermore, the cell division in the root explants from either the lbd29 mutant, LBD29-over-expressing plants or the wild type grown in auxin-rich media was also analysed and compared by the distribution of DR5:β-glucuronidase (GUS) in the primordia or by the expression of PIN-FORMED (PIN) members and PLETHROA 1 (PLT1) which represented the auxin response by the pericycle cells.

Key Results lbd29 mutation resulted in reduced numbers of lateral roots and primordia, whereas LBD29 over-expression resulted in more lateral root and primordia formation than in the wild type. More importantly, the level of LBD29 expression was found to be positively correlated with the level of expression of cell cycle-related genes and correlated with the numbers of subcellular organelles found in pericycle cells in the maturation zone. In addition, an in vitro experiment using root explants demonstrated that the presence of LBD29 was required for the maintenance of the cell division capacity of the pericycle. Furthermore, LBD29 appeared to modify PIN-dependent auxin signalling in the primordia since there was a correlated association between the expression of PINs, PLT1 and DR5:GUS and the expression of LBD29.

Conclusions The ability of LBD29 to regulate lateral root initiation is associated with its maintenance of the cell division capacity of the pericycle in response to auxin and its involvement in the auxin signalling pathway.

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Pluripotency of Arabidopsis xylem pericycle underlies shoot regeneration from root and hypocotyl explants grown in vitro - Atta - 2008 - The Plant Journal - Wiley Online Library

Pluripotency of Arabidopsis xylem pericycle underlies shoot regeneration from root and hypocotyl explants grown in vitro - Atta - 2008 - The Plant Journal - Wiley Online Library | Plant hormones | Scoop.it

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-313X.2008.03715.x/abstract;jsessionid=602B71722D1E4A415E8E58F0AD796030.f01t01

Belen Marquez's insight:

We have established a detailed framework for the process of shoot regeneration from Arabidopsis root and hypocotyl explants grown in vitro. Using transgenic plant lines in which the GUS or GFP genes were fused to promoters of developmental genes (WUS, CLV1, CLV3, STM, CUC1, PLT1, RCH1, QC25), or to promoters of genes encoding indicators of the auxin response (DR5) or transport (PIN1), cytokinin (CK) response (ARR5) or synthesis (IPT5), or mitotic activity (CYCB1), we showed that regenerated shoots originated directly or indirectly from the pericycle cells adjacent to xylem poles. In addition, shoot regeneration appeared to be partly similar to the formation of lateral root meristems (LRMs). During pre-culture on a 2, 4-dichlorophenoxyacetic acid (2, 4-D)-rich callus-inducing medium (CIM), xylem pericycle reactivation established outgrowths that were not true calli but had many characteristics of LRMs. Transfer to a CK-rich shoot-inducing medium (SIM) resulted in early LRM-like primordia changing to shoot meristems. Direct origin of shoots from the xylem pericycle occurred upon direct culture on CK-containing media without prior growth on CIM. Thus, it appeared that the xylem pericycle is more pluripotent than previously thought. This pluripotency was accompanied by the ability of pericycle derivatives to retain diploidy, even after several rounds of cell division. In contrast, the phloem pericycle did not display such developmental plasticity, and responded to CKs with only periclinal divisions. Such observations reinforce the view that the pericycle is an ‘extended meristem’ that comprises two types of cell populations. They also suggest that the founder cells for LRM initiation are not initially fully specified for this developmental pathway.

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Developmental Cell - Strigolactone/MAX2-Induced Degradation of Brassinosteroid Transcriptional Effector BES1 Regulates Shoot Branching

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Nature: Witchcraft and destruction (protein degradation and strigolactone signaling)

Nature: Witchcraft and destruction (protein degradation and strigolactone signaling) | Plant hormones | Scoop.it
The discovery of a protein that is targeted for degradation by the 'witch' hormones called strigolactones reveals a mechanism by which shoot architecture is controlled in rice plants.

 

An overview of two articles in Nature advanced online.


Via Mary Williams, Jennifer Mach
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D14-SCFD3-dependent degradation of D53 regulates strigolactone signalling

D14-SCFD3-dependent degradation of D53 regulates strigolactone signalling | Plant hormones | Scoop.it

Strigolactones (SLs), a newly discovered class of carotenoid-derived phytohormones, are essential for developmental processes that shape plant architecture and interactions with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Despite the rapid progress in elucidating the SL biosynthetic pathway, the perception and signalling mechanisms of SL remain poorly understood. Here we show that DWARF 53 (D53) acts as a repressor of SL signalling and that SLs induce its degradation. We find that the rice (Oryza sativa) d53 mutant, which produces an exaggerated number of tillers compared to wild-type plants, is caused by a gain-of-function mutation and is insensitive to exogenous SL treatment. The D53 gene product shares predicted features with the class I Clp ATPase proteins and can form a complex with the α/β hydrolase protein DWARF 14 (D14) and the F-box protein DWARF 3 (D3), two previously identified signalling components potentially responsible for SL perception. We demonstrate that, in a D14- and D3-dependent manner, SLs induce D53 degradation by the proteasome and abrogate its activity in promoting axillary bud outgrowth. Our combined genetic and biochemical data reveal that D53 acts as a repressor of the SL signalling pathway, whose hormone-induced degradation represents a key molecular link between SL perception and responses.


Via Francis Martin, Jean-Michel Ané
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Jean-Michel Ané's curator insight, December 12, 2013 10:34 AM

This one is for strigolactone fans!

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Trends in Plant Science - The biology of strigolactones


Via Biswapriya Biswavas Misra
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Biswapriya Biswavas Misra's curator insight, February 6, 2013 2:15 PM
Summary

The strigolactones are rhizosphere signaling molecules as well as a new class of plant hormones with a still increasing number of biological functions being uncovered. Here, we review a recent major breakthrough in our understanding of strigolactone biosynthesis, which has revealed the unexpected simplicity of the originally postulated complex pathway. Moreover, the discovery and localization of a strigolactone exporter sheds new light on putative strigolactone fluxes to the rhizosphere as well as within the plant. The combination of these data with information on the expression and regulation of strigolactone biosynthetic and downstream signaling genes provides new insights into how strigolactones control the many different aspects of plant development and how their rhizosphere signaling role may have evolved.

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Cytokinins can act as suppressors of nitric oxide in Arabidopsis


Via Andres Zurita, Biswapriya Biswavas Misra
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Andres Zurita's curator insight, January 27, 2013 7:25 PM

Maintaining nitric oxide (NO) homeostasis is essential for normal plant physiological processes. However, very little is known about the mechanisms of NO modulation in plants. Here, we report a unique mechanism for the catabolism of NO based on the reaction with the plant hormone cytokinin. We screened for NO-insensitive mutants in Arabidopsis and isolated two allelic lines, cnu1-1 and 1–2 (continuous NO-unstressed 1), that were identified as the previously reported altered meristem program 1 (amp1) and as having elevated levels of cytokinins. A double mutant of cnu1-2 and nitric oxide overexpression 1 (nox1) reduced the severity of the phenotypes ascribed to excess NO levels as did treating the nox1 line with trans-zeatin, the predominant form of cytokinin in Arabidopsis. We further showed that peroxinitrite, an active NO derivative, can react with zeatin in vitro, which together with the results in vivo suggests that cytokinins suppress the action of NO most likely through direct interaction between them, leading to the reduction of endogenous NO levels. These results provide insights into NO signaling and regulation of its bioactivity in plants.