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Nawkar GM, Legris M, Goyal A, Schmid-Siegert E, Fleury J, Mucciolo A, De Bellis D, Trevisan M, Schueler A, Fankhauser C. Air channels create a directional light signal to regulate hypocotyl phototropism. Science 2023; 382:935-940. [PMID: 37995216 DOI: 10.1126/science.adh9384] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 10/04/2023] [Indexed: 11/25/2023]
Abstract
In plants, light direction is perceived by the phototropin photoreceptors, which trigger directional growth responses known as phototropism. The formation of a phototropin activation gradient across a photosensitive organ initiates this response. However, the optical tissue properties that functionally contribute to phototropism remain unclear. In this work, we show that intercellular air channels limit light transmittance through various organs in several species. Air channels enhance light scattering in Arabidopsis hypocotyls, thereby steepening the light gradient. This is required for an efficient phototropic response in Arabidopsis and Brassica. We identified an embryonically expressed ABC transporter required for the presence of air channels in seedlings and a structure surrounding them. Our work provides insights into intercellular air space development or maintenance and identifies a mechanism of directional light sensing in plants.
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Affiliation(s)
- Ganesh M Nawkar
- Centre for Integrative Genomics, Faculty of Biology and Medicine, Génopode Building, University of Lausanne, 1015 Lausanne, Switzerland
| | - Martina Legris
- Centre for Integrative Genomics, Faculty of Biology and Medicine, Génopode Building, University of Lausanne, 1015 Lausanne, Switzerland
| | - Anupama Goyal
- Centre for Integrative Genomics, Faculty of Biology and Medicine, Génopode Building, University of Lausanne, 1015 Lausanne, Switzerland
| | - Emanuel Schmid-Siegert
- SIB, Swiss Institute for Bioinformatics, University of Lausanne, 1015 Lausanne, Switzerland
| | - Jérémy Fleury
- EPFL Renewable Energies Cluster ENAC, 1015 Lausanne, Switzerland
| | - Antonio Mucciolo
- Electron Microscopy Facility, EMF, Faculty of Biology and Medicine, Biophore Building, University of Lausanne, 1015 Lausanne, Switzerland
| | - Damien De Bellis
- Electron Microscopy Facility, EMF, Faculty of Biology and Medicine, Biophore Building, University of Lausanne, 1015 Lausanne, Switzerland
- Department of Plant Molecular Biology, Faculty of Biology and Medicine, Biophore Building University of Lausanne, 1015 Lausanne, Switzerland
| | - Martine Trevisan
- Centre for Integrative Genomics, Faculty of Biology and Medicine, Génopode Building, University of Lausanne, 1015 Lausanne, Switzerland
| | - Andreas Schueler
- EPFL Renewable Energies Cluster ENAC, 1015 Lausanne, Switzerland
| | - Christian Fankhauser
- Centre for Integrative Genomics, Faculty of Biology and Medicine, Génopode Building, University of Lausanne, 1015 Lausanne, Switzerland
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2
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Reinert S. Quantitative genetics of pleiotropy and its potential for plant sciences. JOURNAL OF PLANT PHYSIOLOGY 2022; 276:153784. [PMID: 35944292 DOI: 10.1016/j.jplph.2022.153784] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 07/14/2022] [Accepted: 07/18/2022] [Indexed: 06/15/2023]
Affiliation(s)
- Stephan Reinert
- Friedrich-Alexander-University Erlangen-Nürnberg, Department of Biology, Division of Biochemistry, Biocomputing Lab, Staudtstraße 5, 91058, Erlangen, Germany.
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3
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Sullivan S, Waksman T, Paliogianni D, Henderson L, Lütkemeyer M, Suetsugu N, Christie JM. Regulation of plant phototropic growth by NPH3/RPT2-like substrate phosphorylation and 14-3-3 binding. Nat Commun 2021; 12:6129. [PMID: 34675214 PMCID: PMC8531357 DOI: 10.1038/s41467-021-26333-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Accepted: 09/28/2021] [Indexed: 11/09/2022] Open
Abstract
Polarity underlies all directional growth responses in plants including growth towards the light (phototropism). The plasma-membrane associated protein, NON-PHOTOTROPIC HYPOCOTYL 3 (NPH3) is a key determinant of phototropic growth which is regulated by phototropin (phot) AGC kinases. Here we demonstrate that NPH3 is directly phosphorylated by phot1 within a conserved C-terminal consensus sequence (RxS) that is necessary to promote phototropism and petiole positioning in Arabidopsis. RxS phosphorylation also triggers 14-3-3 binding combined with changes in NPH3 phosphorylation and localisation status. Mutants of NPH3 that are unable to bind or constitutively bind 14-3-3 s show compromised functionality consistent with a model where phototropic curvature is established by signalling outputs arising from a gradient of NPH3 RxS phosphorylation across the stem. Our findings therefore establish that NPH3/RPT2-Like (NRL) proteins are phosphorylation targets for plant AGC kinases. Moreover, RxS phosphorylation is conserved in other members of the NRL family, suggesting a common mechanism of regulating plant growth to the prevailing light environment.
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Affiliation(s)
- Stuart Sullivan
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK.
| | - Thomas Waksman
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Dimitra Paliogianni
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Louise Henderson
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK
| | - Melanie Lütkemeyer
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK.,RNA Biology and Molecular Physiology, Faculty of Biology, Bielefeld University, 33615, Bielefeld, Germany
| | - Noriyuki Suetsugu
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK.,Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, 153-8902, Japan
| | - John M Christie
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow, G12 8QQ, UK.
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4
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Pardo-Medina J, Gutiérrez G, Limón MC, Avalos J. Impact of the White Collar Photoreceptor WcoA on the Fusarium fujikuroi Transcriptome. Front Microbiol 2021; 11:619474. [PMID: 33574802 PMCID: PMC7871910 DOI: 10.3389/fmicb.2020.619474] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Accepted: 12/18/2020] [Indexed: 01/25/2023] Open
Abstract
The proteins of the White Collar 1 family (WC) constitute a major class of flavin photoreceptors, widely distributed in fungi, that work in cooperation with a WC 2 protein forming a regulatory complex. The WC complex was investigated in great detail in Neurospora crassa, a model fungus in photobiology studies, where it controls all its major photoresponses. The fungus Fusarium fujikuroi, a model system in the production of secondary metabolites, contains a single WC-1 gene called wcoA. The best-known light response in this fungus is the photoinduction of the synthesis of carotenoids, terpenoid pigments with antioxidant properties. Loss of WcoA in F. fujikuroi results in a drastic reduction in the mRNA levels of the carotenoid genes, and a diversity of morphological and metabolic changes, including alterations in the synthesis of several secondary metabolites, suggesting a complex regulatory role. To investigate the function of WcoA, the transcriptome of F. fujikuroi was analyzed in the dark and after 15-, 60- or 240-min illumination in a wild strain and in a formerly investigated wcoA insertional mutant. Using a threshold of four-fold change in transcript levels, 298 genes were activated and 160 were repressed in the wild strain under at least one of the light exposures. Different response patterns were observed among them, with genes exhibiting either fast, intermediate, and slow photoinduction, or intermediate or slow repression. All the fast and intermediate photoresponses, and most of the slow ones, were lost in the wcoA mutant. However, the wcoA mutation altered the expression of a much larger number of genes irrespective of illumination, reaching at least 16% of the annotated genes in this fungus. Such genes include many related to secondary metabolism, as well as others related to photobiology and other cellular functions, including the production of hydrophobins. As judged by the massive transcriptomic changes exhibited by the wcoA mutant in the dark, the results point to WcoA as a master regulatory protein in F. fujikuroi, in addition to a central function as the photoreceptor responsible for most of the transcriptional responses to light in this fungus.
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Affiliation(s)
- Javier Pardo-Medina
- Department of Genetics, Faculty of Biology, University of Seville, Seville, Spain
| | - Gabriel Gutiérrez
- Department of Genetics, Faculty of Biology, University of Seville, Seville, Spain
| | - M Carmen Limón
- Department of Genetics, Faculty of Biology, University of Seville, Seville, Spain
| | - Javier Avalos
- Department of Genetics, Faculty of Biology, University of Seville, Seville, Spain
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5
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Legris M, Boccaccini A. Stem phototropism toward blue and ultraviolet light. PHYSIOLOGIA PLANTARUM 2020; 169:357-368. [PMID: 32208516 DOI: 10.1111/ppl.13098] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 03/05/2020] [Accepted: 03/19/2020] [Indexed: 06/10/2023]
Abstract
Positive phototropism is the process through which plants orient their organs toward a directional light source. While the blue light receptors phototropins (phot) play a major role in phototropism toward blue (B) and ultraviolet (UV) radiation, recent research showed that the UVB light receptor UVR8 also triggers phototropism toward UVB. In addition, new details of the molecular mechanisms underlying the activity of these receptors and interaction with other environmental signals have emerged in the past years. In this review, we summarize the current knowledge about hypocotyledoneous and inflorescence stem growth reorientation toward B and UVB, with a focus on the molecular mechanisms.
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Affiliation(s)
- Martina Legris
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, CH-1015, Lausanne, Switzerland
| | - Alessandra Boccaccini
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, CH-1015, Lausanne, Switzerland
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6
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Engineering the phototropin photocycle improves photoreceptor performance and plant biomass production. Proc Natl Acad Sci U S A 2019; 116:12550-12557. [PMID: 31160455 PMCID: PMC6589663 DOI: 10.1073/pnas.1902915116] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
A key challenge for plant molecular biologists is to increase plant yield by altering photosynthetic productivity to secure food, energy, and environmental sustainability. In the model plant Arabidopsis thaliana, the plasma-membrane–associated phototropin kinases, phot1 and phot2, are activated by blue light and play important roles in regulating several responses that optimize photosynthetic efficiency. However, little effort has been made to target these pathways to increase plant growth. Here, we demonstrate that modifying the photocycle of phot1 and phot2 increases their sensitivity to light. Plants with these engineered phototropins exhibit more rapid and robust chloroplast movement responses and improved leaf positioning and expansion, leading to improved biomass accumulation under light-limiting conditions. The ability to enhance photosynthetic capacity remains a recognized bottleneck to improving plant productivity. Phototropin blue light receptors (phot1 and phot2) optimize photosynthetic efficiency in Arabidopsis thaliana by coordinating multiple light-capturing processes. In this study, we explore the potential of using protein engineering to improve photoreceptor performance and thereby plant growth. We demonstrate that targeted mutagenesis can decrease or increase the photocycle lifetime of Arabidopsis phototropins in vitro and show that these variants can be used to reduce or extend the duration of photoreceptor activation in planta. Our findings show that slowing the phototropin photocycle enhanced several light-capturing responses, while accelerating it reduced phototropin’s sensitivity for chloroplast accumulation movement. Moreover, plants engineered to have a slow-photocycling variant of phot1 or phot2 displayed increased biomass production under low-light conditions as a consequence of their improved sensitivity. Together, these findings demonstrate the feasibility of engineering photoreceptors to manipulate plant growth and offer additional opportunities to enhance photosynthetic competence, particularly under suboptimal light regimes.
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7
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Sullivan S, Kharshiing E, Laird J, Sakai T, Christie JM. Deetiolation Enhances Phototropism by Modulating NON-PHOTOTROPIC HYPOCOTYL3 Phosphorylation Status. PLANT PHYSIOLOGY 2019; 180:1119-1131. [PMID: 30918082 PMCID: PMC6548275 DOI: 10.1104/pp.19.00206] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Accepted: 03/22/2019] [Indexed: 05/23/2023]
Abstract
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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Affiliation(s)
- Stuart Sullivan
- Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Eros Kharshiing
- Department of Botany, St. Edmund's College, Shillong 793003, Meghalaya, India
| | - Janet Laird
- Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Tatsuya Sakai
- Institute of Science and Technology, Niigata University, Ikarashi, Nishiku, Niigata 950-2181, Japan
| | - John M Christie
- Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
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8
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ZINC-FINGER interactions mediate transcriptional regulation of hypocotyl growth in Arabidopsis. Proc Natl Acad Sci U S A 2018; 115:E4503-E4511. [PMID: 29686058 PMCID: PMC5948964 DOI: 10.1073/pnas.1718099115] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Light coordinates energy production, growth, and survival throughout plant development. In Arabidopsis, light stimulates transcriptional reprogramming during developmental transitions such as photomorphogenesis and flowering through the action of photoreceptors, transcription factors, and signaling components. Here we assign a function to a member of the zinc-finger homeodomain (ZFHD) transcription factor family in regulating light-induced development. Our findings reveal ZFHD10 to be a missing link in understanding how the recently discovered integrator of light and photoperiodic flowering, TANDEM ZINC-FINGER PLUS3 (TZP), controls the expression of growth-promoting transcriptional regulators via direct association with light-regulated promoter elements. Elucidating how such novel protein complexes coordinate gene expression will allow scientists and breeders to optimize plant growth and development in response to unfavorable environmental conditions. Integration of environmental signals and interactions among photoreceptors and transcriptional regulators is key in shaping plant development. TANDEM ZINC-FINGER PLUS3 (TZP) is an integrator of light and photoperiodic signaling that promotes flowering in Arabidopsis thaliana. Here we elucidate the molecular role of TZP as a positive regulator of hypocotyl elongation. We identify an interacting partner for TZP, the transcription factor ZINC-FINGER HOMEODOMAIN 10 (ZFHD10), and characterize its function in coregulating the expression of blue-light–dependent transcriptional regulators and growth-promoting genes. By employing a genome-wide approach, we reveal that ZFHD10 and TZP coassociate with promoter targets enriched in light-regulated elements. Furthermore, using a targeted approach, we show that ZFHD10 recruits TZP to the promoters of key coregulated genes. Our findings not only unveil the mechanism of TZP action in promoting hypocotyl elongation at the transcriptional level but also assign a function to an uncharacterized member of the ZFHD transcription factor family in promoting plant growth.
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9
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Schnabel J, Hombach P, Waksman T, Giuriani G, Petersen J, Christie JM. A chemical genetic approach to engineer phototropin kinases for substrate labeling. J Biol Chem 2018; 293:5613-5623. [PMID: 29475950 DOI: 10.1074/jbc.ra118.001834] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Revised: 02/05/2018] [Indexed: 12/18/2022] Open
Abstract
Protein kinases (PKs) control many aspects of plant physiology by regulating signaling networks through protein phosphorylation. Phototropins (phots) are plasma membrane-associated serine/threonine PKs that control a range of physiological processes that collectively serve to optimize photosynthetic efficiency in plants. These include phototropism, leaf positioning and flattening, chloroplast movement, and stomatal opening. Despite their identification over two decades ago, only a handful of substrates have been identified for these PKs. Progress in this area has been hampered by the lack of a convenient means to confirm the identity of potential substrate candidates. Here we demonstrate that the kinase domain of Arabidopsis phot1 and phot2 can be successfully engineered to accommodate non-natural ATP analogues by substituting the bulky gatekeeper residue threonine for glycine. This approach circumvents the need for radioactivity to track phot kinase activity and follow light-induced receptor autophosphorylation in vitro by incorporating thiophosphate from N6-benzyl-ATPγS. Consequently, thiophosphorylation of phot substrate candidates can be readily monitored when added or co-expressed with phots in vitro Furthermore, gatekeeper-modified phot1 retained its functionality and its ability to accommodate N6-benzyl-ATPγS as a phosphodonor when expressed in Arabidopsis We therefore anticipate that this chemical genetic approach will provide new opportunities for labeling and identifying substrates for phots and other related AGC kinases under in vitro and near-native in vivo conditions.
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Affiliation(s)
- Jonathan Schnabel
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom and
| | - Peter Hombach
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom and.,RNA Biology and Molecular Physiology, Faculty of Biology, Bielefeld University, 33615 Bielefeld, Germany
| | - Thomas Waksman
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom and
| | - Giovanni Giuriani
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom and
| | - Jan Petersen
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom and
| | - John M Christie
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom and
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10
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Christie JM, Suetsugu N, Sullivan S, Wada M. Shining Light on the Function of NPH3/RPT2-Like Proteins in Phototropin Signaling. PLANT PHYSIOLOGY 2018; 176:1015-1024. [PMID: 28720608 PMCID: PMC5813532 DOI: 10.1104/pp.17.00835] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Accepted: 07/12/2017] [Indexed: 05/05/2023]
Abstract
NRL proteins coordinate different aspects of phototropin signaling through signaling processes that are conserved in land plants and algae.
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Affiliation(s)
- John M Christie
- Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Noriyuki Suetsugu
- Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
- Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
| | - Stuart Sullivan
- Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Masamitsu Wada
- Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo 192-0397, Japan
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11
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Harmer SL, Brooks CJ. Growth-mediated plant movements: hidden in plain sight. CURRENT OPINION IN PLANT BIOLOGY 2018; 41:89-94. [PMID: 29107827 PMCID: PMC5826749 DOI: 10.1016/j.pbi.2017.10.003] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 10/13/2017] [Accepted: 10/17/2017] [Indexed: 05/18/2023]
Abstract
While fast plant movements are spectacular but rare, almost all plants exhibit relatively slow, growth-mediated tropic movements that are key to their survival in the natural world. In this brief review, we discuss recent insights into the molecular mechanisms underlying phototropism, gravitropism, hydrotropism, and autostraightening. Careful molecular genetic and physiological studies have helped confirm the importance of lateral auxin gradients in gravitropic and phototropic responses. However, auxin signaling does not explain all tropisms: recent work has shown that abscisic acid signaling mediates root hydrotropism and has implicated mechanosensing in autostraightening, the organ straightening process recently modeled as a proprioceptive response. The interactions between distinct tropic signaling pathways and other internal and external sensory processes are also now being untangled.
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Affiliation(s)
- Stacey L Harmer
- Department of Plant Biology, University of California, One Shields Avenue, Davis, CA 95616, USA.
| | - Christopher J Brooks
- Department of Plant Biology, University of California, One Shields Avenue, Davis, CA 95616, USA
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12
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Petersen J, Inoue SI, Kelly SM, Sullivan S, Kinoshita T, Christie JM. Functional characterization of a constitutively active kinase variant of Arabidopsis phototropin 1. J Biol Chem 2017; 292:13843-13852. [PMID: 28663371 PMCID: PMC5566536 DOI: 10.1074/jbc.m117.799643] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Revised: 06/21/2017] [Indexed: 01/14/2023] Open
Abstract
Phototropins (phots) are plasma membrane–associated serine/threonine kinases that coordinate a range of processes linked to optimizing photosynthetic efficiency in plants. These photoreceptors contain two light-, oxygen-, or voltage-sensing (LOV) domains within their N terminus, with each binding one molecule of flavin mononucleotide as a UV/blue light–absorbing chromophore. Although phots contain two LOV domains, light-induced activation of the C-terminal kinase domain and subsequent receptor autophosphorylation is controlled primarily by the A′α-LOV2-Jα photosensory module. Mutations that disrupt interactions between the LOV2 core and its flanking helical segments can uncouple this mode of light regulation. However, the impact of these mutations on phot function in Arabidopsis has not been explored. Here we report that histidine substitution of Arg-472 located within the A′α-helix of Arabidopsis phot1 constitutively activates phot1 kinase activity in vitro without affecting LOV2 photochemistry. Expression analysis of phot1 R472H in the phot-deficient mutant confirmed that it is autophosphorylated in darkness in vivo but unable to initiate phot1 signaling in the absence of light. Instead, we found that phot1 R472H is poorly functional under low-light conditions but can restore phototropism, chloroplast accumulation, stomatal opening, and leaf positioning and expansion at higher light intensities. Our findings suggest that Arabidopsis can adapt to the elevated phosphorylation status of the phot1 R472H mutant in part by reducing its stability, whereas the activity of the mutant under high-light conditions can be attributed to additional increases in LOV2-mediated photoreceptor autophosphorylation.
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Affiliation(s)
- Jan Petersen
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Bower Building, Glasgow G12 8QQ, United Kingdom
| | | | - Sharon M Kelly
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Bower Building, Glasgow G12 8QQ, United Kingdom
| | - Stuart Sullivan
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Bower Building, Glasgow G12 8QQ, United Kingdom
| | - Toshinori Kinoshita
- the Division of Biological Science, Graduate School of Science and.,Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya 464-8602, Japan
| | - John M Christie
- From the Institute of Molecular, Cell, and Systems Biology, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Bower Building, Glasgow G12 8QQ, United Kingdom,
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13
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Kim J, Song K, Park E, Kim K, Bae G, Choi G. Epidermal Phytochrome B Inhibits Hypocotyl Negative Gravitropism Non-Cell-Autonomously. THE PLANT CELL 2016; 28:2770-2785. [PMID: 27758895 PMCID: PMC5155346 DOI: 10.1105/tpc.16.00487] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 09/27/2016] [Accepted: 10/06/2016] [Indexed: 05/20/2023]
Abstract
Seedling hypocotyls display negative gravitropism in the dark but agravitropism in the light. The Arabidopsis thaliana pif quadruple mutant (pifQ), which lacks four PHYTOCHROME-INTERACTING FACTORS (PIFs), is agravitropic in the dark. Endodermis-specific expression of PIF1 rescues gravitropism in pifQ mutant seedlings. Since phytochromes induce light responses by inhibiting PIFs and the COP1-SPA ubiquitin E3 ligase complex in the nucleus, we asked whether phyB can cell autonomously inhibit hypocotyl negative gravitropism in the endodermis. We found that while epidermis-specific expression of PHYB rescues hypocotyl negative gravitropism and all other phyB mutant phenotypes, endodermis-specific expression of PHYB does not. Epidermal phyB induces the phosphorylation and degradation of endodermal PIFs in response to red light. This induces a global gene expression pattern similar to that induced by red light treatment of seedlings expressing PHYB under the control of its own endogenous promoter. Our results imply that epidermal phyB generates an unidentified mobile signal that travels to the endodermis where it promotes PIF degradation and inhibits hypocotyl negative gravitropism.
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Affiliation(s)
- Jaewook Kim
- Department of Biological Sciences, KAIST, Daejeon 34141, Korea
| | - Kijong Song
- Department of Biological Sciences, KAIST, Daejeon 34141, Korea
| | - Eunae Park
- Department of Biological Sciences, KAIST, Daejeon 34141, Korea
| | - Keunhwa Kim
- Department of Biological Sciences, KAIST, Daejeon 34141, Korea
| | - Gabyong Bae
- Department of Biological Sciences, KAIST, Daejeon 34141, Korea
| | - Giltsu Choi
- Department of Biological Sciences, KAIST, Daejeon 34141, Korea
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Hofmann NR. Do Phytochromes and Phytochrome-Interacting Factors Need to Interact? THE PLANT CELL 2016; 28:2698-2699. [PMID: 27956584 PMCID: PMC5155350 DOI: 10.1105/tpc.16.00833] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
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