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Chen X, Ru Y, Takahashi H, Nakazono M, Shabala S, Smith SM, Yu M. Single-cell transcriptomic analysis of pea shoot development and cell-type-specific responses to boron deficiency. Plant J 2024; 117:302-322. [PMID: 37794835 DOI: 10.1111/tpj.16487] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2023] [Revised: 09/08/2023] [Accepted: 09/20/2023] [Indexed: 10/06/2023]
Abstract
Understanding how nutrient stress impacts plant growth is fundamentally important to the development of approaches to improve crop production under nutrient limitation. Here we applied single-cell RNA sequencing to shoot apices of Pisum sativum grown under boron (B) deficiency. We identified up to 15 cell clusters based on the clustering of gene expression profiles and verified cell identity with cell-type-specific marker gene expression. Different cell types responded differently to B deficiency. Specifically, the expression of photosynthetic genes in mesophyll cells (MCs) was down-regulated by B deficiency, consistent with impaired photosynthetic rate. Furthermore, the down-regulation of stomatal development genes in guard cells, including homologs of MUTE and TOO MANY MOUTHS, correlated with a decrease in stomatal density under B deficiency. We also constructed the developmental trajectory of the shoot apical meristem (SAM) cells and a transcription factor interaction network. The developmental progression of SAM to MC was characterized by up-regulation of genes encoding histones and chromatin assembly and remodeling proteins including homologs of FASCIATA1 (FAS1) and SWITCH DEFECTIVE/SUCROSE NON-FERMENTABLE (SWI/SNF) complex. However, B deficiency suppressed their expression, which helps to explain impaired SAM development under B deficiency. These results represent a major advance over bulk-tissue RNA-seq analysis in which cell-type-specific responses are lost and hence important physiological responses to B deficiency are missed. The reported findings reveal strategies by which plants adapt to B deficiency thus offering breeders a set of specific targets for genetic improvement. The reported approach and resources have potential applications well beyond P. sativum species and could be applied to various legumes to improve their adaptability to multiple nutrient or abiotic stresses.
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Affiliation(s)
- Xi Chen
- Department of Horticulture, International Research Centre for Environmental Membrane Biology, Foshan University, Foshan, 528000, China
- Tasmanian Institute of Agriculture, University of Tasmania, Hobart, TAS, 7001, Australia
- School of Biological Science, University of Western Australia, Crawley, WA, 6009, Australia
| | - Yanqi Ru
- Department of Horticulture, International Research Centre for Environmental Membrane Biology, Foshan University, Foshan, 528000, China
| | - Hirokazu Takahashi
- Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8601, Japan
| | - Mikio Nakazono
- Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8601, Japan
- School of Agriculture and Environment, University of Western Australia, Crawley, WA, 6009, Australia
| | - Sergey Shabala
- Department of Horticulture, International Research Centre for Environmental Membrane Biology, Foshan University, Foshan, 528000, China
- Tasmanian Institute of Agriculture, University of Tasmania, Hobart, TAS, 7001, Australia
- School of Biological Science, University of Western Australia, Crawley, WA, 6009, Australia
| | - Steven M Smith
- Australian Research Council Centre of Excellence for Plant Success in Nature and Agriculture, School of Natural Sciences, University of Tasmania, Hobart, TAS, 7001, Australia
| | - Min Yu
- Department of Horticulture, International Research Centre for Environmental Membrane Biology, Foshan University, Foshan, 528000, China
- School of Agriculture and Environment, University of Western Australia, Crawley, WA, 6009, Australia
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2
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Harrington SA, Franceschetti M, Balk J. Genetic basis of the historical iron-accumulating dgl and brz mutants in pea. Plant J 2024; 117:590-598. [PMID: 37882414 PMCID: PMC10952674 DOI: 10.1111/tpj.16514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2023] [Accepted: 10/12/2023] [Indexed: 10/27/2023]
Abstract
The Pisum sativum (pea) mutants degenerate leaves (dgl) and bronze (brz) accumulate large amounts of iron in leaves. First described several decades ago, the two mutants have provided important insights into iron homeostasis in plants but the underlying mutations have remained unknown. Using exome sequencing we identified an in-frame deletion associated with dgl in a BRUTUS homolog. The deletion is absent from wild type and the original parent line. BRUTUS belongs to a small family of E3 ubiquitin ligases acting as negative regulators of iron uptake in plants. The brz mutation was previously mapped to chromosome 4, and superimposing this region to the pea genome sequence uncovered a mutation in OPT3, encoding an oligopeptide transporter with a plant-specific role in metal transport. The causal nature of the mutations was confirmed by additional genetic analyses. Identification of the mutated genes rationalizes many of the previously described phenotypes and provides new insights into shoot-to-root signaling of iron deficiency. Furthermore, the non-lethal mutations in these essential genes suggest new strategies for biofortification of crops with iron.
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Affiliation(s)
| | | | - Janneke Balk
- Department of Biochemistry and MetabolismJohn Innes CentreNorwichNR4 7UHUK
- School of Biological SciencesUniversity of East AngliaNorwichNR4 7TJUK
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Pandey J, Devadasu E, Saini D, Dhokne K, Marriboina S, Raghavendra AS, Subramanyam R. Reversible changes in structure and function of photosynthetic apparatus of pea ( Pisum sativum) leaves under drought stress. Plant J 2023; 113:60-74. [PMID: 36377283 DOI: 10.1111/tpj.16034] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Accepted: 11/08/2022] [Indexed: 06/16/2023]
Abstract
The effects of drought on photosynthesis have been extensively studied, whereas those on thylakoid organization are limited. We observed a significant decline in gas exchange parameters of pea (Pisum sativum) leaves under progressive drought stress. Chl a fluorescence kinetics revealed the reduction of photochemical efficiency of photosystem (PS)II and PSI. The non-photochemical quenching (NPQ) and the levels of PSII subunit PSBS increased. Furthermore, the light-harvesting complexes (LHCs) and some of the PSI and PSII core proteins were disassembled in drought conditions, whereas these complexes were reassociated during recovery. By contrast, the abundance of supercomplexes of PSII-LHCII and PSII dimer were reduced, whereas LHCII monomers increased following the change in the macro-organization of thylakoids. The stacks of thylakoids were loosely arranged in drought-affected plants, which could be attributed to changes in the supercomplexes of thylakoids. Severe drought stress caused a reduction of both LHCI and LHCII and a few reaction center proteins of PSI and PSII, indicating significant disorganization of the photosynthetic machinery. After 7 days of rewatering, plants recovered well, with restored chloroplast thylakoid structure and photosynthetic efficiency. The correlation of structural changes with leaf reactive oxygen species levels indicated that these changes were associated with the production of reactive oxygen species.
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Affiliation(s)
- Jayendra Pandey
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500046, India
| | - Elsinraju Devadasu
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500046, India
| | - Deepak Saini
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500046, India
| | - Kunal Dhokne
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500046, India
| | - Sureshbabu Marriboina
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500046, India
| | - Agepati S Raghavendra
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500046, India
| | - Rajagopal Subramanyam
- Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500046, India
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Blicharz S, Beemster GT, Ragni L, De Diego N, Spíchal L, Hernándiz AE, Marczak Ł, Olszak M, Perlikowski D, Kosmala A, Malinowski R. Phloem exudate metabolic content reflects the response to water-deficit stress in pea plants ( Pisum sativum L.). Plant J 2021; 106:1338-1355. [PMID: 33738886 PMCID: PMC8360158 DOI: 10.1111/tpj.15240] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Revised: 03/09/2021] [Accepted: 03/15/2021] [Indexed: 05/31/2023]
Abstract
Drought stress impacts the quality and yield of Pisum sativum. Here, we show how short periods of limited water availability during the vegetative stage of pea alters phloem sap content and how these changes are connected to strategies used by plants to cope with water deficit. We have investigated the metabolic content of phloem sap exudates and explored how this reflects P. sativum physiological and developmental responses to drought. Our data show that drought is accompanied by phloem-mediated redirection of the components that are necessary for cellular respiration and the proper maintenance of carbon/nitrogen balance during stress. The metabolic content of phloem sap reveals a shift from anabolic to catabolic processes as well as the developmental plasticity of P. sativum plants subjected to drought. Our study underlines the importance of phloem-mediated transport for plant adaptation to unfavourable environmental conditions. We also show that phloem exudate analysis can be used as a useful proxy to study stress responses in plants. We propose that the decrease in oleic acid content within phloem sap could be considered as a potential marker of early signalling events mediating drought response.
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Affiliation(s)
- Sara Blicharz
- Integrative Plant Biology TeamInstitute of Plant Genetics Polish Academy of Sciencesul. Strzeszyńska 34Poznań60‐479Poland
| | - Gerrit T.S. Beemster
- Laboratory for Integrated Molecular Plant Physiology Research (IMPRES)Department of BiologyUniversity of AntwerpGroenenborgerlaan 171Antwerpen2020Belgium
| | - Laura Ragni
- ZMBP‐Center for Plant Molecular BiologyUniversity of TübingenTübingenGermany
| | - Nuria De Diego
- Department of Chemical Biology and GeneticsCentre of the Region Haná for Biotechnological and Agricultural ResearchFaculty of SciencePalacký UniversityOlomoucCzech Republic
| | - Lukas Spíchal
- Department of Chemical Biology and GeneticsCentre of the Region Haná for Biotechnological and Agricultural ResearchFaculty of SciencePalacký UniversityOlomoucCzech Republic
| | - Alba E. Hernándiz
- Department of Chemical Biology and GeneticsCentre of the Region Haná for Biotechnological and Agricultural ResearchFaculty of SciencePalacký UniversityOlomoucCzech Republic
| | - Łukasz Marczak
- Institute of Bioorganic Chemistry Polish Academy of SciencesNoskowskiego 12/14Poznan61‐704Poland
| | - Marcin Olszak
- Department of Plant BiochemistryInstitute of Biochemistry and Biophysics Polish Academy of Sciencesul. Pawińskiego 5aWarsaw02‐106Poland
| | - Dawid Perlikowski
- Plant Physiology TeamInstitute of Plant Genetics Polish Academy of Sciencesul. Strzeszyńska 34Poznań60‐479Poland
| | - Arkadiusz Kosmala
- Plant Physiology TeamInstitute of Plant Genetics Polish Academy of Sciencesul. Strzeszyńska 34Poznań60‐479Poland
| | - Robert Malinowski
- Integrative Plant Biology TeamInstitute of Plant Genetics Polish Academy of Sciencesul. Strzeszyńska 34Poznań60‐479Poland
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5
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Wittmiß M, Mikkat S, Hagemann M, Bauwe H. Stoichiometry of two plant glycine decarboxylase complexes and comparison with a cyanobacterial glycine cleavage system. Plant J 2020; 103:801-813. [PMID: 32311173 DOI: 10.1111/tpj.14773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2019] [Revised: 04/01/2020] [Accepted: 04/07/2020] [Indexed: 06/11/2023]
Abstract
The multienzyme glycine cleavage system (GCS) converts glycine and tetrahydrofolate to the one-carbon compound 5,10-methylenetetrahydrofolate, which is of vital importance for most if not all organisms. Photorespiring plant mitochondria contain very high levels of GCS proteins organised as a fragile glycine decarboxylase complex (GDC). The aim of this study is to provide mass spectrometry-based stoichiometric data for the plant leaf GDC and examine whether complex formation could be a general property of the GCS in photosynthesizing organisms. The molar ratios of the leaf GDC component proteins are 1L2 -4P2 -8T-26H and 1L2 -4P2 -8T-20H for pea and Arabidopsis, respectively, as determined by mass spectrometry. The minimum mass of the plant leaf GDC ranges from 1550 to 1650 kDa, which is larger than previously assumed. The Arabidopsis GDC contains four times more of the isoforms GCS-P1 and GCS-L1 in comparison with GCS-P2 and GCS-L2, respectively, whereas the H-isoproteins GCS-H1 and GCS-H3 are fully redundant as indicated by their about equal amounts. Isoform GCS-H2 is not present in leaf mitochondria. In the cyanobacterium Synechocystis sp. PCC 6803, GCS proteins concentrations are low but above the complex formation threshold reported for pea leaf GDC. Indeed, formation of a cyanobacterial GDC from the individual recombinant GCS proteins in vitro could be demonstrated. Presence and metabolic significance of a Synechocystis GDC in vivo remain to be examined but could involve multimers of the GCS H-protein that dynamically crosslink the three GCS enzyme proteins, facilitating glycine metabolism by the formation of multienzyme metabolic complexes. Data are available via ProteomeXchange with identifier PXD018211.
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Affiliation(s)
- Maria Wittmiß
- Department of Plant Physiology, University of Rostock, Albert-Einstein-Straße 3, D-18059, Rostock, Germany
| | - Stefan Mikkat
- Core Facility Proteome Analysis, Rostock University Medical Center, Schilling-Allee 69, D-18057, Rostock, Germany
| | - Martin Hagemann
- Department of Plant Physiology, University of Rostock, Albert-Einstein-Straße 3, D-18059, Rostock, Germany
| | - Hermann Bauwe
- Department of Plant Physiology, University of Rostock, Albert-Einstein-Straße 3, D-18059, Rostock, Germany
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Boivin S, Ait Lahmidi N, Sherlock D, Bonhomme M, Dijon D, Heulin‐Gotty K, Le‐Queré A, Pervent M, Tauzin M, Carlsson G, Jensen E, Journet E, Lopez‐Bellido R, Seidenglanz M, Marinkovic J, Colella S, Brunel B, Young P, Lepetit M. Host-specific competitiveness to form nodules in Rhizobium leguminosarum symbiovar viciae. New Phytol 2020; 226:555-568. [PMID: 31873949 PMCID: PMC7687279 DOI: 10.1111/nph.16392] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Accepted: 12/09/2019] [Indexed: 05/07/2023]
Abstract
Fabeae legumes such as pea and faba bean form symbiotic nodules with a large diversity of soil Rhizobium leguminosarum symbiovar viciae (Rlv) bacteria. However, bacteria competitive to form root nodules (CFN) are generally not the most efficient to fix dinitrogen, resulting in a decrease in legume crop yields. Here, we investigate differential selection by host plants on the diversity of Rlv. A large collection of Rlv was collected by nodule trapping with pea and faba bean from soils at five European sites. Representative genomes were sequenced. In parallel, diversity and abundance of Rlv were estimated directly in these soils using metabarcoding. The CFN of isolates was measured with both legume hosts. Pea/faba bean CFN were associated to Rlv genomic regions. Variations of bacterial pea and/or faba bean CFN explained the differential abundance of Rlv genotypes in pea and faba bean nodules. No evidence was found for genetic association between CFN and variations in the core genome, but variations in specific regions of the nod locus, as well as in other plasmid loci, were associated with differences in CFN. These findings shed light on the genetic control of CFN in Rlv and emphasise the importance of host plants in controlling Rhizobium diversity.
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Affiliation(s)
- Stéphane Boivin
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | - Nassima Ait Lahmidi
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | | | - Maxime Bonhomme
- Laboratoire de Recherche en Sciences Végétales, CNRS, UPSUniversité de Toulouse31326Castanet‐TolosanFrance
| | - Doriane Dijon
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | - Karine Heulin‐Gotty
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | - Antoine Le‐Queré
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | - Marjorie Pervent
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | - Marc Tauzin
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | - Georg Carlsson
- Department of Biosystems and TechnologySwedish University of Agricultural SciencesSE‐230 53AlnarpSweden
| | - Erik Jensen
- Department of Biosystems and TechnologySwedish University of Agricultural SciencesSE‐230 53AlnarpSweden
| | - Etienne‐Pascal Journet
- AGroécologie, Innovation et teRritoires (AGIR) INRAEENSAT31326Castanet‐TolosanFrance
- Laboratoire des Interactions Plantes MicrorganismesUniversité de Toulouse, INRAE, CNRS31326Castanet‐TolosanFrance
| | - Raphael Lopez‐Bellido
- Departamento de Ciencias y Recursos Agrícolas y ForestalesUniversity of Córdoba14071CórdobaSpain
| | | | | | - Stefano Colella
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | - Brigitte Brunel
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
| | - Peter Young
- Department of BiologyUniversity of YorkYorkYO10 5DDUK
| | - Marc Lepetit
- Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM) INRAE, IRD, CIRADUniversity of MontpellierMontpellier SupAgro34398Montpellier cedex 5France
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Albanese P, Manfredi M, Re A, Marengo E, Saracco G, Pagliano C. Thylakoid proteome modulation in pea plants grown at different irradiances: quantitative proteomic profiling in a non-model organism aided by transcriptomic data integration. Plant J 2018; 96:786-800. [PMID: 30118564 DOI: 10.1111/tpj.14068] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 08/03/2018] [Accepted: 08/13/2018] [Indexed: 05/02/2023]
Abstract
Plant thylakoid membranes contain hundreds of proteins that closely interact to cope with ever-changing environmental conditions. We investigated how Pisum sativum L. (pea) grown at different irradiances optimizes light-use efficiency through the differential accumulation of thylakoid proteins. Thylakoid membranes from plants grown under low (LL), moderate (ML) and high (HL) light intensity were characterized by combining chlorophyll fluorescence measurements with quantitative label-free proteomic analysis. Protein sequences retrieved from available transcriptomic data considerably improved thylakoid proteome profiling, increasing the quantifiable proteins from 63 to 194. The experimental approach used also demonstrates that this integrative omics strategy is powerful for unravelling protein isoforms and functions that are still unknown in non-model organisms. We found that the different growth irradiances affect the electron transport kinetics but not the relative abundance of photosystems (PS) I and II. Two acclimation strategies were evident. The behaviour of plants acclimated to LL was compared at higher irradiances: (i) in ML, plants turn on photoprotective responses mostly modulating the PSII light-harvesting capacity, either accumulating Lhcb4.3 or favouring the xanthophyll cycle; (ii) in HL, plants reduce the pool of light-harvesting complex II and enhance the PSII repair cycle. When growing at ML and HL, plants accumulate ATP synthase, boosting both cyclic and linear electron transport by finely tuning the ΔpH across the membrane and optimizing protein trafficking by adjusting the thylakoid architecture. Our results provide a quantitative snapshot of how plants coordinate light harvesting, electron transport and protein synthesis by adjusting the thylakoid membrane proteome in a light-dependent manner.
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Affiliation(s)
- Pascal Albanese
- Applied Science and Technology Department-BioSolar Lab, Politecnico di Torino, Environment Park, Via Livorno 60, 10144, Torino, Italy
| | - Marcello Manfredi
- ISALIT-Department of Science and Technological Innovation, University of Eastern Piedmont, Viale T. Michel 11, 15121, Alessandria, Italy
- Department of Science and Technological Innovation, University of Eastern Piedmont, Viale T. Michel 11, 15121, Alessandria, Italy
| | - Angela Re
- Center for Sustainable Future Technologies-CSFT@POLITO, Istituto Italiano di Tecnologia, Corso Trento 21, 10129, Torino, Italy
| | - Emilio Marengo
- Department of Science and Technological Innovation, University of Eastern Piedmont, Viale T. Michel 11, 15121, Alessandria, Italy
| | - Guido Saracco
- Applied Science and Technology Department-BioSolar Lab, Politecnico di Torino, Environment Park, Via Livorno 60, 10144, Torino, Italy
| | - Cristina Pagliano
- Applied Science and Technology Department-BioSolar Lab, Politecnico di Torino, Environment Park, Via Livorno 60, 10144, Torino, Italy
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Chen LJ, Li HM. Stable megadalton TOC-TIC supercomplexes as major mediators of protein import into chloroplasts. Plant J 2017; 92:178-188. [PMID: 28745032 DOI: 10.1111/tpj.13643] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2017] [Accepted: 07/21/2017] [Indexed: 05/12/2023]
Abstract
Preproteins are believed to be imported into chloroplasts through membrane contact sites where the translocon complexes of the outer (TOC) and inner (TIC) envelope membranes are assembled together. However, a single TOC-TIC supercomplex containing preproteins undergoing active import has not yet been directly observed. We optimized the blue native polyacrylamide gel electrophoresis (PAGE) (BN-PAGE) system to detect and resolve megadalton (MD)-sized complexes. Using this optimized system, the outer-membrane channel Toc75 from pea chloroplasts was found in at least two complexes: the 880-kD TOC complex and a previously undetected 1-MD complex. Two-dimensional BN-PAGE immunoblots further showed that Toc75, Toc159, Toc34, Tic20, Tic56 and Tic110 were all located in the 880-kD to 1.3-MD region. During active preprotein import, preproteins were transported mostly through the 1-MD complex and a smaller amount of preproteins was also detected in a complex of 1.25 MD. Antibody-shift assays showed that the 1-MD complex is a TOC-TIC supercomplex containing at least Toc75, Toc159, Toc34 and Tic110. Results from crosslinking and import with Arabidopsis chloroplasts suggest that the 1.25-MD complex is also a supercomplex. Our data provide direct evidence supporting that chloroplast preproteins are imported through TOC-TIC supercomplexes, and also provide the first size estimation of these supercomplexes. Furthermore, unlike in mitochondria where translocon supercomplexes are only transiently assembled during preprotein import, in chloroplasts at least some of the supercomplexes are preassembled stable structures.
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Affiliation(s)
- Lih-Jen Chen
- Institute of Molecular Biology, Academia Sinica, Taipei, 11529, Taiwan
| | - Hsou-Min Li
- Institute of Molecular Biology, Academia Sinica, Taipei, 11529, Taiwan
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