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Christian Fankhauser - One of the best experts on this subject based on the ideXlab platform.
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A phosphorylation switch turns a positive regulator of phototropism into an inhibitor of the process.
Nature communications, 2018Co-Authors: Paolo Schumacher, Martine Trevisan, Emilie Demarsy, Patrice Waridel, Laure Allenbach Petrolati, Christian FankhauserAbstract:Phototropins are light-activated protein kinases, which contribute to photosynthesis optimization both through enhancement of photon absorption when light is limiting and avoidance responses in high light. This duality is in part endowed by the presence of Phototropins with different photosensitivity (phot1 and phot2). Here we show that phot1, which senses low light to promote positive phototropism (growth towards the light), also limits the response in high light. This response depends in part on phot1-mediated phosphorylation of Phytochrome Kinase Substrate 4 (PKS4). This light-regulated phosphorylation switch changes PKS4 from a phototropism enhancer in low light to a factor limiting the process in high light. In such conditions phot1 and PKS4 phosphorylation prevent phototropic responses to shallow light gradients and limit phototropism in a natural high light environment. Hence, by modifying PKS4 activity in high light the phot1-PKS4 regulon enables appropriate physiological adaptations over a range of light intensities.
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Shade Promotes Phototropism through Phytochrome B-Controlled Auxin Production.
Current biology : CB, 2016Co-Authors: Anupama Goyal, Jorge J. Casal, Elizabeth Karayekov, Vinicius Costa Galvão, Hong Ren, Christian FankhauserAbstract:Phototropism is an asymmetric growth response enabling plants to optimally position their organs. In flowering plants, the Phototropin (phot) blue light receptors are essential to detect light gradients. In etiolated seedlings, the phototropic response is enhanced by the red/far-red (R/FR)-sensing phytochromes (phy) with a predominant function of phyA. In this study, we analyzed the influence of the phytochromes on phototropism in green (de-etiolated) Arabidopsis seedlings. Our experiments in the laboratory and outdoors revealed that, in open environments (high R/FR ratio), phyB inhibits phototropism. In contrast, under foliar shade, where access to direct sunlight becomes important, the phototropic response was strong. phyB modulates phototropism, depending on the R/FR ratio, by controlling the activity of three basic-helix-loop-helix (bHLH) transcription factors of the PHYTOCHROME INTERACTING FACTORs (PIFs) family. Promotion of phototropism depends on PIF-mediated induction of several members of the YUCCA gene family, leading to auxin production in the cotyledons. Our study identifies PIFs and YUCCAs as novel molecular players promoting phototropism in photoautotrophic, but not etiolated, seedlings. Moreover, our findings reveal fundamental differences in the phytochrome-phototropism crosstalk in etiolated versus green seedlings. We propose that in natural conditions where the light environment is not homogeneous, the uncovered phytochrome-Phototropin co-action is important for plants to adapt their growth strategy to optimize photosynthetic light capture.
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repressor of ultraviolet b photomorphogenesis function allows efficient Phototropin mediated ultraviolet b phototropism in etiolated seedlings
Plant Science, 2016Co-Authors: Lucas Vanhaelewyn, Christian Fankhauser, Paolo Schumacher, Dirk Poelman, Dominique Van Der Straeten, Filip VandenbusscheAbstract:Ultraviolet B (UV-B) light is a part of the solar radiation which has significant effects on plant morphology, even at low doses. In Arabidopsis, many of these morphological changes have been attributed to a specific UV-B receptor, UV resistance locus 8 (UVR8). Recent findings showed that next to Phototropin regulated phototropism, UVR8 mediated signaling is able of inducing directional bending towards UV-B light in etiolated seedlings of Arabidopsis, in a Phototropin independent manner. In this study, kinetic analysis of phototropic bending was used to evaluate the relative contribution of each of these pathways in UV-B mediated phototropism. Diminishing UV-B light intensity favors the importance of Phototropins. Molecular and genetic analyses suggest that UV-B is capable of inducing Phototropin signaling relying on Phototropin kinase activity and regulation of NPH3. Moreover, enhanced UVR8 responses in the UV-B hypersensitive rup1rup2 mutants interferes with the fast Phototropin mediated phototropism. Together the data suggest that Phototropins are the most important receptors for UV-B induced phototropism in etiolated seedlings, and a RUP mediated negative feedback pathway prevents UVR8 signaling to interfere with the Phototropin dependent response.
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reduced phototropism in pks mutants may be due to altered auxin regulated gene expression or reduced lateral auxin transport
Plant Journal, 2014Co-Authors: Chitose Kami, Melina Zourelidou, Kotaro T. Yamamoto, Claus Schwechheimer, Laure Allenbach, Karin Ljung, Frederic Schutz, Erika Isono, Masaaki K Watahiki, Christian FankhauserAbstract:Phototropism allows plants to orient their photosynthetic organs towards the light. In Arabidopsis, Phototropins 1 and 2 sense directional blue light such that phot1 triggers phototropism in response to low fluence rates, while both phot1 and phot2 mediate this response under higher light conditions. Phototropism results from asymmetric growth in the hypocotyl elongation zone that depends on an auxin gradient across the embryonic stem. How Phototropin activation leads to this growth response is still poorly understood. Members of the phytochrome kinase substrate (PKS) family may act early in this pathway, because PKS1, PKS2 and PKS4 are needed for a normal phototropic response and they associate with phot1 in vivo. Here we show that PKS proteins are needed both for phot1- and phot2-mediated phototropism. The phototropic response is conditioned by the developmental asymmetry of dicotyledonous seedlings, such that there is a faster growth reorientation when cotyledons face away from the light compared with seedlings whose cotyledons face the light. The molecular basis for this developmental effect on phototropism is unknown; here we show that PKS proteins play a role at the interface between development and phototropism. Moreover, we present evidence for a role of PKS genes in hypocotyl gravi-reorientation that is independent of photoreceptors. pks mutants have normal levels of auxin and normal polar auxin transport, however they show altered expression patterns of auxin marker genes. This situation suggests that PKS proteins are involved in auxin signaling and/or lateral auxin redistribution.
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Defining the site of light perception and initiation of phototropism in Arabidopsis.
Current biology : CB, 2013Co-Authors: Tobias Preuten, Sven Bergmann, Tim Hohm, Christian FankhauserAbstract:Phototropism is an adaptive response allowing plants to optimize photosynthetic light capture. This is achieved by asymmetric growth between the shaded and lit sides of the stimulated organ. In grass seedlings, the site of Phototropin-mediated light perception is distinct from the site of bending; however, in dicotyledonous plants (e.g., Arabidopsis), spatial aspects of perception remain debatable. We use morphological studies and genetics to show that phototropism can occur in the absence of the root, lower hypocotyl, hypocotyl apex, and cotyledons. Tissue-specific expression of the Phototropin1 (phot1) photoreceptor demonstrates that light sensing occurs in the upper hypocotyl and that expression of phot1 in the hypocotyl elongation zone is sufficient to enable a normal phototropic response. Moreover, we show that efficient phototropism occurs when phot1 is expressed from endodermal, cortical, or epidermal cells and that its local activation rapidly leads to a global response throughout the seedling. We propose that spatial aspects in the steps leading from light perception to growth reorientation during phototropism differ between grasses and dicots. These results are important to properly interpret genetic experiments and establish a model connecting light perception to the growth response, including cellular and morphological aspects.
John T M Kennis - One of the best experts on this subject based on the ideXlab platform.
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helical contributions mediate light activated conformational change in the lov2 domain of avena sativa Phototropin 1
ACS omega, 2019Co-Authors: Josiah P Zayner, Tilo Mathes, Tobin R Sosnick, John T M KennisAbstract:Algae, plants, bacteria, and fungi contain flavin-binding light-oxygen-voltage (LOV) domains that function as blue light sensors to control cellular responses to light. In the second LOV domain of Phototropins, called LOV2 domains, blue light illumination leads to covalent bond formation between protein and flavin that induces the dissociation and unfolding of a C-terminally attached α helix (Jα) and the N-terminal helix (A′α). To date, the majority of studies on these domains have focused on versions that contain truncations in the termini, which creates difficulties when extrapolating to the much larger proteins that contain these domains. Here, we study the influence of deletions and extensions of the A′α helix of the LOV2 domain of Avena sativa Phototropin 1 (AsLOV2) on the light-triggered structural response of the protein by Fourier-transform infrared difference spectroscopy. Deletion of the A′α helix abolishes the light-induced unfolding of Jα, whereas extensions of the A′α helix lead to an attenua...
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the primary photophysics of the avena sativa Phototropin 1 lov2 domain observed with time resolved emission spectroscopy
Photochemistry and Photobiology, 2011Co-Authors: Ivo H M Van Stokkum, Magdalena Gauden, Sean Crosson, Rienk Van Grondelle, Keith Moffat, John T M KennisAbstract:The Phototropins are blue-light receptors that base their lightdependent action on the reversible formation of a covalent bond between a flavin mononucleotide (FMN) cofactor and a conserved cysteine in light, oxygen or voltage (LOV) domains. The primary reactions of the Avena sativa Phototropin 1 LOV2 domain were investigated by means of time-resolved and lowtemperature fluorescence spectroscopy. Synchroscan streak camera experiments revealed a fluorescence lifetime of 2.2 ns in LOV2. A weak long-lived component with emission intensity from 600 to 650 nm was assigned to phosphorescence from the reactive FMN triplet state. This observation allowed determination of the LOV2 triplet state energy level at physiological temperature at 16600 cm )1 . FMN dissolved in aqueous solution showed pH-dependent fluorescence lifetimes of 2.7 ns at pH 2 and 3.9)4.1 ns at pH 3–8. Here, too, a weak phosphorescence band was observed. The fluorescence quantum yield of LOV2 increased from 0.13 to 0.41 upon cooling the sample from 293 to 77 K. A pronounced phosphorescence emission around 600 nm was observed in the LOV2 domain between 77 and 120 K in the steady-state emission.
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conformational heterogeneity and propagation of structural changes in the lov2 jα domain from avena sativa Phototropin 1 as recorded by temperature dependent ftir spectroscopy
Biophysical Journal, 2009Co-Authors: Maxime T A Alexandre, Rienk Van Grondelle, Klaas J Hellingwerf, John T M KennisAbstract:Phototropins control phototropism, chloroplast movement, stomatal opening, and leaf expansion in plants. Phototropin 1 (phot1) is composed of a kinase domain linked to two blue light-sensing domains, LOV2 and LOV1, which bind flavin mononucleotide. Disruption of the interaction between the LOV2 domain and a helical segment named Jα, joining LOV to the kinase domain, induces the subsequent kinase activity of Phototropin 1 and further-downstream signal transduction. Here we study the effects of temperature and hydration on the light-triggered signal propagation in the phot1 LOV2 domain of Avena sativa (AsLOV2/Jα), using Fourier transform infrared spectroscopy to unravel part of the molecular mechanism of Phototropin 1. We report that AsLOV2/Jα shows an intense signal in the amide I and II regions, arising mainly from β-sheet changes and the unbinding of the Jα helix from the Per-ARNT-Sim core and its subsequent partial unfolding. Importantly, these structural changes only occur under conditions of full hydration and at temperatures above 280 K. We characterized a newly isolated low-hydration intermediate that shows a downshift of high-frequency amide I signals and that possibly corresponds to loop tightening, without large β-sheet or Jα structural changes. In addition, we report a heterogeneity in AsLOV2/Jα involving two different C(4)=O conformer populations, coexisting in the dark state and characterized by C(4)=O carbonyl frequencies at 1712 cm−1 and 1694 cm−1 that are attributable to a single H-bond and two H-bonds at this site, respectively. Such conformers display slightly shifted absorption spectra and cause a splitting of the 475-nm band in the ultraviolet/visible spectra of LOV domains at low temperature.
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a base catalyzed mechanism for dark state recovery in the avena sativa Phototropin 1 lov2 domain
Biochemistry, 2007Co-Authors: Maxime T A Alexandre, Rienk Van Grondelle, Klaas J Hellingwerf, Jos C Arents, John T M KennisAbstract:Phototropins are autophosphorylating serine/threonine kinases responsible for blue-light perception in plants; their action gives rise to phototropism, chloroplast relocation, and opening of stomatal guard cells. The kinase domain constitutes the C-terminal part of Avena sativa Phototropin 1. The N-terminal part contains two light, oxygen, or voltage (LOV) sensing domains, LOV1 and LOV2; each binds a flavin mononucleotide (FMN) chromophore (λmax = 447 nm, termed D447) and forms the light-sensitive domains, of which LOV2 is the principal component. Blue-light absorption produces a covalent adduct between a very conserved nearby cysteine residue and the C(4a) atom of the FMN moiety via the triplet state of the flavin. The covalent adduct thermally decays to regenerate the D447 dark state, with a rate that may vary by several orders of magnitude between different species. We report that the imidazole base can act as a very efficient enhancer of the dark recovery of A. sativa phot1 LOV2 (AsLOV2) and some othe...
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primary reactions of the lov2 domain of Phototropin a plant blue light photoreceptor
Biochemistry, 2003Co-Authors: John T M Kennis, Magdalena Gauden, Sean Crosson, Keith Moffat, Ivo H M Van Stokkum, Rienk Van GrondelleAbstract:The Phototropins constitute an important class of plant photoreceptor kinases that control a range of physiological responses, including phototropism, light-directed chloroplast movement, and light-induced stomatal opening. The LOV2 domain of Phototropin binds a molecule of flavin mononucleotide (FMN) and undergoes a photocycle involving light-driven covalent adduct formation between a conserved cysteine residue and the C(4a) atom of FMN. This product state promotes C-terminal kinase activation and downstream signal transduction. Here, we report the primary photophysics and photochemistry of LOV2 domains of Phototropin 1 of Avena sativa (oat) and of the phy3 photoreceptor of Adiantum capillus-veneris (maidenhair fern). In agreement with earlier reports [Swartz, T. E., et al. (2001) J. Biol. Chem. 276, 36493−36500], we find that the FMN triplet state is the reactive species from which the photoreaction occurs. We demonstrate that the triplet state is the primary photoproduct in the LOV2 photocycle, generat...
John M. Christie - One of the best experts on this subject based on the ideXlab platform.
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Regulation of plant phototropic growth by NPH3/RPT2-like substrate phosphorylation and 14-3-3 binding
'Springer Science and Business Media LLC', 2021Co-Authors: Stuart Sullivan, Noriyuki Suetsugu, Thomas Waksman, Dimitra Paliogianni, Louise Henderson, Melanie Lütkemeyer, John M. ChristieAbstract:The plasma membrane-localized NPH3 protein is required for phototropic growth in Arabidopsis. Here the authors show that Phototropin 1 phosphorylates NPH3 at a conserved C-terminal sequence motif triggering binding of 14-3-3 proteins to NPH3 that is necessary for the phototropic response
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Deetiolation Enhances Phototropism by Modulating NON-PHOTOTROPIC HYPOCOTYL3 Phosphorylation Status.
Plant physiology, 2019Co-Authors: Stuart Sullivan, Eros Kharshiing, Tatsuya Sakai, Janet Laird, John M. ChristieAbstract:Phototropin (phot) receptor kinases play important roles in promoting plant growth by controlling light-capturing processes, such as phototropism. Phototropism is mediated through the action of NON-PHOTOTROPIC HYPOCOTYL3 (NPH3), which is dephosphorylated following phot activation. However, the functional significance of this early signaling event remains unclear. Here, we show that the onset of phototropism in dark-grown (etiolated) seedlings of Arabidopsis (Arabidopsis thaliana) and tomato (Solanum lycopersicum) is enhanced by greening (deetiolation). Red and blue light were equally effective in promoting phototropism in Arabidopsis, consistent with our observations that deetiolation by phytochrome or cryptochrome was sufficient to enhance phototropism. Increased responsiveness did not result from an enhanced sensitivity to the phytohormone auxin, nor does it involve the phot-interacting protein, ROOT PHOTOTROPISM2. Instead, deetiolated seedlings showed attenuated levels of NPH3 dephosphorylation and diminished relocalization of NPH3 from the plasma membrane during phototropism. Likewise, etiolated seedlings that lack the PHYTOCHROME-INTERACTING FACTORS (PIFs) PIF1, PIF3, PIF4, and PIF5 displayed reduced NPH3 dephosphorylation and enhanced phototropism, consistent with their constitutive photomorphogenic phenotype in darkness. Phototropic enhancement could also be achieved in etiolated seedlings by lowering the light intensity to diminish NPH3 dephosphorylation. Thus, phototropism is enhanced following deetiolation through the modulation of a phosphorylation rheostat, which in turn sustains the activity of NPH3. We propose that this dynamic mode of regulation enables young seedlings to maximize their establishment under changing light conditions, depending on their photoautotrophic capacity.
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phytochrome a mediates blue light enhancement of second positive phototropism in arabidopsis
Frontiers in Plant Science, 2016Co-Authors: Stuart Sullivan, Jaynee E Hart, Patrick Rasch, Catriona H Walker, John M. ChristieAbstract:Hypocotyl phototropism of etiolated Arabidopsis seedlings is primarily mediated by the blue-light receptor kinase Phototropin 1 (phot1). Phot1-mediated curvature to continuous unilateral blue light irradiation (0.5 µmol m-2 s-1) is enhanced by overhead pre-treatment with red light (20 µmol m-2 s-1 for 15 min) through the action of phytochrome (phyA). Here, we show that pre-treatment with blue light is equally as effective in eliciting phototropic enhancement and is dependent on phyA. Although blue pre-treatment was sufficient to activate early phot1 signalling events, phot1 autophosphorylation in vivo was not found to be saturated, as assessed by subsequently measuring phot1 kinase activity in vitro. However, enhancement effects to red and blue pre-treatment were not observed at higher intensities of phototropic stimulation (10 µmol m-2 s-1). Phototropic enhancement to red and blue pre-treatments to 0.5 µmol m-2 s-1 unilateral blue light irradiation was also lacking in transgenic Arabidopsis where PHOT1 expression was restricted to the epidermis. Together, these findings indicate that phyA-mediated effects on phot1 signalling are restricted to low intensities of phototropic stimulation and originate from tissues other than the epidermis.
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functional characterization of ostreococcus tauri Phototropin
New Phytologist, 2016Co-Authors: Stuart Sullivan, Jan Petersen, Lisa Blackwood, Maria Papanatsiou, John M. ChristieAbstract:Phototropins (phots) regulate a range of adaptive processes in plants that serve to optimize photosynthetic efficiency and promote growth. Light sensing by Arabidopsis thaliana phots is predominantly mediated by the Light, Oxygen and Voltage sensing 2 (LOV2) flavin-binding motif located within the N-terminus of the photoreceptor. Here we characterize the photochemical and biochemical properties of phot from the marine picoalga Ostreococcus tauri Phototropin (Otphot) and examine its ability to replace phot-mediated function in Arabidopsis. Photochemical properties of Otphot rely on both LOV1 and LOV2. Yet, biochemical analysis indicates that light-dependent receptor autophosphorylation is primarily dependent on LOV2. As found for Arabidopsis phots, Otphot associates with the plasma membrane and partially internalizes, albeit to a limited extent, in response to blue-light irradiation. Otphot is able to elicit a number of phot-regulated processes in Arabidopsis, including petiole positioning, leaf expansion, stomatal opening and chloroplast accumulation movement. However, Otphot is unable to restore phototropism and chloroplast avoidance movement. Consistent with its lack of phototropic function in Arabidopsis, Otphot does not associate with or trigger dephosphorylation of the phototropic signalling component Non-Phototropic Hypocotyl 3 (NPH3). Taken together, these findings indicate that the mechanism of action of plant and evolutionarily distant algal phots is less well conserved than previously thought.
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phot1 inhibition of abcb19 primes lateral auxin fluxes in the shoot apex required for phototropism
PLOS Biology, 2011Co-Authors: John M. Christie, Stuart Sullivan, Haibing Yang, Gregory L Richter, Catriona E Thomson, Jinshan Lin, Boosaree Titapiwatanakun, Margaret Ennis, Eirini Kaiserli, Ok Ran LeeAbstract:It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase Phototropin 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperms.
Masamitsu Wada - One of the best experts on this subject based on the ideXlab platform.
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a c terminal membrane association domain of Phototropin 2 is necessary for chloroplast movement
Plant and Cell Physiology, 2013Co-Authors: Sam-geun Kong, Takatoshi Kagawa, Masamitsu Wada, Akira NagataniAbstract:: Phototropins (phot1 and phot2), plant-specific blue light receptor kinases, mediate a range of physiological responses in Arabidopsis, including phototropism, chloroplast photorelocation movement, stomatal opening and leaf flattening. Phototropins consist of two photoreceptive domains at their N-terminus, LOV1 (light, oxygen or voltage 1) and LOV2, and a serine/threonine kinase domain at their C-terminus. Here, we determined the molecular moiety for the membrane association of Phototropins using the yeast CytoTrap and Arabidopsis protoplast systems. We then examined the physiological significance of the membrane association of Phototropins. This detailed study with serial deletions narrowed down the association domain to a relatively small part of the C-terminal domain of Phototropin. The functional analysis of phot2 deletion mutants in the phot2-deficient Adiantum and Arabidopsis mutants revealed that the ability to mediate the chloroplast avoidance response correlated well with phot2's membrane association, especially with the Golgi apparatus. Taken together, our data suggest that a small part of the C-terminal domain of Phototropins is necessary not only for membrane association but also for the physiological activities that elicit Phototropin-specific responses.
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antagonistic regulation of leaf flattening by phytochrome b and Phototropin in arabidopsis thaliana
Plant and Cell Physiology, 2013Co-Authors: Toshiaki Kozuka, Noriyuki Suetsugu, Masamitsu Wada, Akira NagataniAbstract:Light is one of the most important environmental factors regulating the growth and development of leaves. As the primary photosynthetic organs, leaves have a laminar structure in many dicotyledonous plants. The regulation of leaf flatness is a key mechanism for the efficient absorption of light under low light conditions. In the present study, we demonstrated that phytochrome B (phyB) promoted the development of curled leaves. Wild-type leaves gently curled downwards under white light, whereas the phyB-deficient mutant (phyB) constitutively exhibited flatter leaves. In the wild type, leaf flattening was promoted by end-of-day far-red light (EODFR) treatment, which rapidly eliminates the active Pfr phytochrome. Interestingly, the curled-leaf phenotype in a Phototropin-deficient mutant was almost completely suppressed by the phyB mutation as well as by EODFR. Thus, Phototropin promotes leaf flattening by suppressing the leaf-curling activity of phyB. We examined the downstream components of phyB and Phototropin to assess their antagonistic regulation of leaf flatness further. Consequently, we found that a Phototropin signaling transducer, NON-PHOTOTROPIC HYPOCOTYL 3 (NPH3), was required to promote leaf flattening in phyB. The present study provides new insights into a mechanism in which leaf flatness is regulated in response to different light environmental cues.
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blue light induced phototropism of inflorescence stems and petioles is mediated by Phototropin family members phot1 and phot2
Plant and Cell Physiology, 2009Co-Authors: Takatoshi Kagawa, Masamitsu Wada, Mitsuhiro KimuraAbstract:Phototropin family photoreceptors, phot1 and phot2, in Arabidopsis thaliana control the blue light (BL)-mediated phototropic responses of the hypocotyl, chloroplast relocation movement and stomatal opening. Phototropic responses in dark-grown tissues have been well studied but those in de-etiolated green plants are not well understood. Here, we analyzed phototropic responses of inflorescence stems and petioles of wild-type and Phototropin mutant plants of A. thaliana. Similar to the results obtained from dark-grown seedlings, inflorescence stems and petioles in wild-type and phot2 mutant plants showed phototropic bending towards low fluence BL, while in phot1 mutant plants, a high fluence rate of BL was required. phot1 phot2 double mutant plants did not show any phototropic responses even under very high fluence rates of BL. We further studied the photoreceptive sites for phototropic responses of stems and petioles by partial tissue irradiation. The whole part of the inflorescence stem is sensitive to BL and shows phototropism, but in the petiole only the irradiated abaxial side is sensitive. Similar to dark-grown etiolated seedlings, phot1 plays a major role in phototropic responses under weak light, but phot2 functions under high fluence rate conditions in green plants.
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an auxilin like j domain protein jac1 regulates Phototropin mediated chloroplast movement in arabidopsis
Plant Physiology, 2005Co-Authors: Noriyuki Suetsugu, Takatoshi Kagawa, Masamitsu WadaAbstract:The ambient-light conditions mediate chloroplast relocation in plant cells. Under the low-light conditions, chloroplasts accumulate in the light (accumulation response), while under the high-light conditions, they avoid the light (avoidance response). In Arabidopsis (Arabidopsis thaliana), the accumulation response is mediated by two blue-light receptors, termed Phototropins (phot1 and phot2) that act redundantly, and the avoidance response is mediated by phot2 alone. A mutant, J-domain protein required for chloroplast accumulation response 1 (jac1), lacks the accumulation response under weak blue light but shows a normal avoidance response under strong blue light. In dark-adapted wild-type cells, chloroplasts accumulate on the bottom of cells. Both the jac1 and phot2 mutants are defective in this chloroplast movement in darkness. Positional cloning of JAC1 reveals that this gene encodes a J-domain protein, resembling clathrin-uncoating factor auxilin at its C terminus. The amounts of JAC1 transcripts and JAC1 proteins are not regulated by light and by Phototropins. A green fluorescent protein-JAC1 fusion protein showed a similar localization pattern to green fluorescent protein alone in a transient expression assay using Arabidopsis mesophyll cells and onion (Allium cepa) epidermal cells, suggesting that the JAC1 protein may be a soluble cytosolic protein. Together, these results suggest that JAC1 is an essential component of Phototropin-mediated chloroplast movement.
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blue light activates calcium permeable channels in arabidopsis mesophyll cells via the Phototropin signaling pathway
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Sonja Stoelzle, Takatoshi Kagawa, Masamitsu Wada, Rainer Hedrich, Petra DietrichAbstract:Light is a central regulator of plant growth and development. Among the processes triggered by blue and UV-A light, phototropism, stomatal movement, and chloroplast orientation rely on the activation of blue-light receptors known as Phototropins. So far, these photoreceptors constitute a class of light receptor kinases unique to the plant kingdom. In Arabidopsis thaliana, the two members phot1 and phot2 have been shown to display partially overlapping functions. Up to now little is known about the signaling cascade, which links these Phototropins to the physiological responses downstream of blue-light perception. Here, we show that on illumination with blue light, but not red light, voltage-dependent and calcium-permeable channels activate in the plasma membrane of mesophyll cells. Blue-light stimulation in the presence of the photosynthetic electron transport inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicates that blue-light receptors rather than photosynthesis control channel activity. Sensitivity toward the protein kinase inhibitor K252a further pointed to the possible involvement of light receptor kinases. In support of this hypothesis, in the photoreceptor mutant phot1-5, blue-light induction of calcium currents was dramatically reduced and was eliminated in the double mutant phot1-5 phot2-1. By contrast, in cry1-304 cry2-1, an Arabidopsis mutant lacking another class of plant blue-light receptors, the channel remained sensitive to blue light. We thus conclude that blue light triggers calcium fluxes via the Phototropin-activated calcium-permeable channel.
Roger P. Hangarter - One of the best experts on this subject based on the ideXlab platform.
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Gravitational and Space Biology Bulletin 16(2) June 2003 55 ROOT PHOTOTROPISM: HOW LIGHT AND GRAVITY INTERACT IN SHAPING PLANT FORM
2015Co-Authors: John Z Kiss, Roger P. Hangarter, Jack L. Mullen, Melanie J. Correll, Richard E. EdelmannAbstract:The interactions among tropisms can be critical in determining the final growth form of plants and plant organs. We have studied tropistic responses in roots as an example of these type of interactions. While gravitropism is the predominant tropistic response in roots, phototropism also plays a role in the oriented growth in this organ in flowering plants. In blue or white light, roots exhibit negative phototropism, but red light induces positive phototropism. In the flowering plant Arabidopsis, the photosensitve pigments phytochrome A (phyA) and phytochrome B (phyB) mediate this positive red-light-based photoresponse in roots since single mutants (and the double phyAB mutant) were severely impaired in this response. While blue-light-based negative phototropism is primarily mediated by the Phototropin family of photoreceptors, the phyA and phyAB mutants (but not phyB) were inhibited in this response relative to the WT. The differences observed in phototropic responses were not due to growth limitations since the growth rates among all the mutants tested were not significantly different from that of the WT. Thus, our study shows that the blue-light and red-light systems interact in plants and that phytochrome plays a key role in integrating multiple environmental stimuli. ___________________________________________________
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d6pk agcviii kinases are required for auxin transport and phototropic hypocotyl bending in arabidopsis
The Plant Cell, 2013Co-Authors: Bjorn C Willige, Melina Zourelidou, Siv Ahlers, Ines C R Barbosa, Martine Trevisan, Philip A Davis, Rob M G Roelfsema, Emilie Demarsy, Roger P. Hangarter, Christian FankhauserAbstract:Phototropic hypocotyl bending in response to blue light excitation is an important adaptive process that helps plants to optimize their exposure to light. In Arabidopsis thaliana, phototropic hypocotyl bending is initiated by the blue light receptors and protein kinases Phototropin1 (phot1) and phot2. Phototropic responses also require auxin transport and were shown to be partially compromised in mutants of the PIN-FORMED (PIN) auxin efflux facilitators. We previously described the D6 PROTEIN KINASE (D6PK) subfamily of AGCVIII kinases, which we proposed to directly regulate PIN-mediated auxin transport. Here, we show that phototropic hypocotyl bending is strongly dependent on the activity of D6PKs and the PIN proteins PIN3, PIN4, and PIN7. While early blue light and phot-dependent signaling events are not affected by the loss of D6PKs, we detect a gradual loss of PIN3 phosphorylation in d6pk mutants of increasing complexity that is most severe in the d6pk d6pkl1 d6pkl2 d6pkl3 quadruple mutant. This is accompanied by a reduction of basipetal auxin transport in the hypocotyls of d6pk as well as in pin mutants. Based on our data, we propose that D6PK-dependent PIN regulation promotes auxin transport and that auxin transport in the hypocotyl is a prerequisite for phot1-dependent hypocotyl bending.
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the arabidopsis phytochrome kinase substrate2 protein is a Phototropin signaling element that regulates leaf flattening and leaf positioning
Plant Physiology, 2010Co-Authors: Matthieu De Carbonnel, Patricia Lariguet, Isabelle Schepens, Rob M G Roelfsema, Roger P. Hangarter, Phillip A Davis, Shinichiro Inoue, Markus Geisler, Kenichiro Shimazaki, Christian FankhauserAbstract:In Arabidopsis (Arabidopsis thaliana), the blue light photoreceptor Phototropins (phot1 and phot2) fine-tune the photosynthetic status of the plant by controlling several important adaptive processes in response to environmental light variations. These processes include stem and petiole phototropism (leaf positioning), leaf flattening, stomatal opening, and chloroplast movements. The PHYTOCHROME KINASE SUBSTRATE (PKS) protein family comprises four members in Arabidopsis (PKS1-PKS4). PKS1 is a novel phot1 signaling element during phototropism, as it interacts with phot1 and the important signaling element NONPHOTOTROPIC HYPOCOTYL3 (NPH3) and is required for normal phot1-mediated phototropism. In this study, we have analyzed more globally the role of three PKS members (PKS1, PKS2, and PKS4). Systematic analysis of mutants reveals that PKS2 (and to a lesser extent PKS1) act in the same subset of Phototropin-controlled responses as NPH3, namely leaf flattening and positioning. PKS1, PKS2, and NPH3 coimmunoprecipitate with both phot1-green fluorescent protein and phot2-green fluorescent protein in leaf extracts. Genetic experiments position PKS2 within phot1 and phot2 pathways controlling leaf positioning and leaf flattening, respectively. NPH3 can act in both phot1 and phot2 pathways, and synergistic interactions observed between pks2 and nph3 mutants suggest complementary roles of PKS2 and NPH3 during Phototropin signaling. Finally, several observations further suggest that PKS2 may regulate leaf flattening and positioning by controlling auxin homeostasis. Together with previous findings, our results indicate that the PKS proteins represent an important family of Phototropin signaling proteins.
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a brassinosteroid hypersensitive mutant of bak1 indicates that a convergence of photomorphogenic and hormonal signaling modulates phototropism
Plant Physiology, 2005Co-Authors: Craig W Whippo, Roger P. HangarterAbstract:The phototropic response of Arabidopsis (Arabidopsis thaliana) is induced by the Phototropin photoreceptors and modulated by the cryptochrome and phytochrome photoreceptors. Downstream of these photoreceptors, asymmetric lateral redistribution of auxin underlies the differential growth, which results in phototropism. Historical physiological evidence and recent analysis of hormone-induced gene expression demonstrate that auxin and brassinosteroid signaling function interdependently. Similarly, in this study we report evidence that interactions between brassinosteroids and auxin signaling modulate phototropic responsiveness. We found that elongated, a previously identified photomorphogenesis mutant, enhances high-light phototropism and represents a unique allele of BAK1/SERK3, a receptor kinase implicated in brassinosteroid perception. Altogether, our results support the hypothesis that phototropic responsiveness is modulated by inputs that influence control of auxin response factor-mediated transcription.
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phytochrome modulation of blue light induced phototropism
Plant Cell and Environment, 2004Co-Authors: Craig W Whippo, Roger P. HangarterAbstract:Red light enhances hypocotyl phototropism toward unilateral blue light through a phytochrome-mediated response. This study demonstrates how the phytochromes modulate blue-light-induced phototropism in the absence of a red light pre-treatment. It was found that phytochromes A, B, and D have conditionally overlapping functions in the promotion of blue-light-induced phototropism. Under very low blue light intensities (0.01 µmol m−2 s−1) phyA activity is necessary for the progression of a normal phototropic response, whereas above 1.0 µmol m−1 s−2 phyB and phyD have functional redundancy with phyA to promote phototropism. PhyA also contributes to attenuation of phototropism under high fluence rates of unilateral blue light, which was previously shown to be dependent on the Phototropins and cryptochromes. From these results, it appears that phytochromes are required to develop a robust phototropic response under low fluence rates, whereas under high irradiances where phototropism may be less important, phyA suppresses phototropism.