1
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Bélanger S, Kramer MC, Payne HA, Hui AY, Slotkin RK, Meyers BC, Staub JM. Plastid dsRNA transgenes trigger phased small RNA-based gene silencing of nuclear-encoded genes. THE PLANT CELL 2023; 35:3398-3412. [PMID: 37309669 PMCID: PMC10473229 DOI: 10.1093/plcell/koad165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 05/16/2023] [Accepted: 06/12/2023] [Indexed: 06/14/2023]
Abstract
Plastid transformation technology has been widely used to express traits of potential commercial importance, though the technology has been limited to traits that function while sequestered in the organelle. Prior research indicates that plastid contents can escape from the organelle, suggesting a possible mechanism for engineering plastid transgenes to function in other cellular locations. To test this hypothesis, we created tobacco (Nicotiana tabacum cv. Petit Havana) plastid transformants that express a fragment of the nuclear-encoded Phytoene desaturase (PDS) gene capable of catalyzing post-transcriptional gene silencing if RNA escapes into the cytoplasm. We found multiple lines of direct evidence that plastid-encoded PDS transgenes affect nuclear PDS gene silencing: knockdown of the nuclear-encoded PDS mRNA and/or its apparent translational inhibition, biogenesis of 21-nucleotide (nt) phased small interfering RNAs (phasiRNAs), and pigment-deficient plants. Furthermore, plastid-expressed dsRNA with no cognate nuclear-encoded pairing partner also produced abundant 21-nt phasiRNAs in the cytoplasm, demonstrating that a nuclear-encoded template is not required for siRNA biogenesis. Our results indicate that RNA escape from plastids to the cytoplasm occurs generally, with functional consequences that include entry into the gene silencing pathway. Furthermore, we uncover a method to produce plastid-encoded traits with functions outside of the organelle and open additional fields of study in plastid development, compartmentalization, and small RNA biogenesis.
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Affiliation(s)
- Sébastien Bélanger
- Donald Danforth Plant Science Center, 975 N. Warson Road, St. Louis, MO 63132, USA
| | - Marianne C Kramer
- Donald Danforth Plant Science Center, 975 N. Warson Road, St. Louis, MO 63132, USA
| | - Hayden A Payne
- Donald Danforth Plant Science Center, 975 N. Warson Road, St. Louis, MO 63132, USA
| | - Alice Y Hui
- Plastomics Inc, 1100 Corporate Square Drive, St. Louis, MO 63132, USA
| | - R Keith Slotkin
- Donald Danforth Plant Science Center, 975 N. Warson Road, St. Louis, MO 63132, USA
- Division of Biological Sciences, University of Missouri, Columbia, MO 65211, USA
| | - Blake C Meyers
- Donald Danforth Plant Science Center, 975 N. Warson Road, St. Louis, MO 63132, USA
- Division of Plant Science and Technology, University of Missouri, Columbia, MO 65211, USA
| | - Jeffrey M Staub
- Plastomics Inc, 1100 Corporate Square Drive, St. Louis, MO 63132, USA
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2
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Christian R, Labbancz J, Usadel B, Dhingra A. Understanding protein import in diverse non-green plastids. Front Genet 2023; 14:969931. [PMID: 37007964 PMCID: PMC10063809 DOI: 10.3389/fgene.2023.969931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 02/24/2023] [Indexed: 03/19/2023] Open
Abstract
The spectacular diversity of plastids in non-green organs such as flowers, fruits, roots, tubers, and senescing leaves represents a Universe of metabolic processes in higher plants that remain to be completely characterized. The endosymbiosis of the plastid and the subsequent export of the ancestral cyanobacterial genome to the nuclear genome, and adaptation of the plants to all types of environments has resulted in the emergence of diverse and a highly orchestrated metabolism across the plant kingdom that is entirely reliant on a complex protein import and translocation system. The TOC and TIC translocons, critical for importing nuclear-encoded proteins into the plastid stroma, remain poorly resolved, especially in the case of TIC. From the stroma, three core pathways (cpTat, cpSec, and cpSRP) may localize imported proteins to the thylakoid. Non-canonical routes only utilizing TOC also exist for the insertion of many inner and outer membrane proteins, or in the case of some modified proteins, a vesicular import route. Understanding this complex protein import system is further compounded by the highly heterogeneous nature of transit peptides, and the varying transit peptide specificity of plastids depending on species and the developmental and trophic stage of the plant organs. Computational tools provide an increasingly sophisticated means of predicting protein import into highly diverse non-green plastids across higher plants, which need to be validated using proteomics and metabolic approaches. The myriad plastid functions enable higher plants to interact and respond to all kinds of environments. Unraveling the diversity of non-green plastid functions across the higher plants has the potential to provide knowledge that will help in developing climate resilient crops.
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Affiliation(s)
- Ryan Christian
- Department of Horticulture, Washington State University, Pullman, WA, United States
| | - June Labbancz
- Department of Horticulture, Washington State University, Pullman, WA, United States
- Department of Horticultural Sciences, Texas A&M University, College Station, TX, United States
| | | | - Amit Dhingra
- Department of Horticulture, Washington State University, Pullman, WA, United States
- Department of Horticultural Sciences, Texas A&M University, College Station, TX, United States
- *Correspondence: Amit Dhingra,
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3
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Loudya N, Maffei DPF, Bédard J, Ali SM, Devlin PF, Jarvis RP, López-Juez E. Mutations in the chloroplast inner envelope protein TIC100 impair and repair chloroplast protein import and impact retrograde signaling. THE PLANT CELL 2022; 34:3028-3046. [PMID: 35640571 PMCID: PMC9338805 DOI: 10.1093/plcell/koac153] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Accepted: 05/19/2022] [Indexed: 05/16/2023]
Abstract
Chloroplast biogenesis requires synthesis of proteins in the nucleocytoplasm and the chloroplast itself. Nucleus-encoded chloroplast proteins are imported via multiprotein translocons in the organelle's envelope membranes. Controversy exists around whether a 1-MDa complex comprising TIC20, TIC100, and other proteins constitutes the inner membrane TIC translocon. The Arabidopsis thaliana cue8 virescent mutant is broadly defective in plastid development. We identify CUE8 as TIC100. The tic100cue8 mutant accumulates reduced levels of 1-MDa complex components and exhibits reduced import of two nucleus-encoded chloroplast proteins of different import profiles. A search for suppressors of tic100cue8 identified a second mutation within the same gene, tic100soh1, which rescues the visible, 1 MDa complex-subunit abundance, and chloroplast protein import phenotypes. tic100soh1 retains but rapidly exits virescence and rescues the synthetic lethality of tic100cue8 when retrograde signaling is impaired by a mutation in the GENOMES UNCOUPLED 1 gene. Alongside the strong virescence, changes in RNA editing and the presence of unimported precursor proteins show that a strong signaling response is triggered when TIC100 function is altered. Our results are consistent with a role for TIC100, and by extension the 1-MDa complex, in the chloroplast import of photosynthetic and nonphotosynthetic proteins, a process which initiates retrograde signaling.
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Affiliation(s)
- Naresh Loudya
- Department of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK
| | - Douglas P F Maffei
- Department of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK
| | - Jocelyn Bédard
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK
| | - Sabri Mohd Ali
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK
| | - Paul F Devlin
- Department of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK
| | - R Paul Jarvis
- Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK
| | - Enrique López-Juez
- Department of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK
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4
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Ma L, Yang Y, Wang Y, Cheng K, Zhou X, Li J, Zhang J, Li R, Zhang L, Wang K, Zeng N, Gong Y, Zhu D, Deng Z, Qu G, Zhu B, Fu D, Luo Y, Zhu H. SlRBP1 promotes translational efficiency via SleIF4A2 to maintain chloroplast function in tomato. THE PLANT CELL 2022; 34:2747-2764. [PMID: 35385118 PMCID: PMC9252502 DOI: 10.1093/plcell/koac104] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Accepted: 03/05/2022] [Indexed: 06/01/2023]
Abstract
Many glycine-rich RNA-binding proteins (GR-RBPs) have critical functions in RNA processing and metabolism. Here, we describe a role for the tomato (Solanum lycopersicum) GR-RBP SlRBP1 in regulating mRNA translation. We found that SlRBP1 knockdown mutants (slrbp1) displayed reduced accumulation of total chlorophyll and impaired chloroplast ultrastructure. These phenotypes were accompanied by deregulation of the levels of numerous key transcripts associated with chloroplast functions in slrbp1. Furthermore, native RNA immunoprecipitation-sequencing (nRIP-seq) recovered 61 SlRBP1-associated RNAs, most of which are involved in photosynthesis. SlRBP1 binding to selected target RNAs was validated by nRIP-qPCR. Intriguingly, the accumulation of proteins encoded by SlRBP1-bound transcripts, but not the mRNAs themselves, was reduced in slrbp1 mutants. Polysome profiling followed by RT-qPCR assays indicated that the polysome occupancy of target RNAs was lower in slrbp1 plants than in wild-type. Furthermore, SlRBP1 interacted with the eukaryotic translation initiation factor SleIF4A2. Silencing of SlRBP1 significantly reduced SleIF4A2 binding to SlRBP1-target RNAs. Taking these observations together, we propose that SlRBP1 binds to and channels RNAs onto the SleIF4A2 translation initiation complex and promotes the translation of its target RNAs to regulate chloroplast functions.
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Affiliation(s)
- Liqun Ma
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | | | - Yuqiu Wang
- School of Advanced Agricultural Sciences and School of Life Sciences, Peking University, Beijing 100871, China
| | - Ke Cheng
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Xiwen Zhou
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Jinyan Li
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Jingyu Zhang
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | | | - Lingling Zhang
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Keru Wang
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Ni Zeng
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Yanyan Gong
- School of Advanced Agricultural Sciences and School of Life Sciences, Peking University, Beijing 100871, China
| | - Danmeng Zhu
- School of Advanced Agricultural Sciences and School of Life Sciences, Peking University, Beijing 100871, China
| | - Zhiping Deng
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Institute of Virology and Biotechnology, Zhejiang Academy of Agricultural Sciences, Hangzhou, Zhejiang 310021, China
| | - Guiqin Qu
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Benzhong Zhu
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Daqi Fu
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
| | - Yunbo Luo
- The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
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5
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Zheng XT, Wang C, Lin W, Lin C, Han D, Xie Q, Lai J, Yang C. Importation of chloroplast proteins under heat stress is facilitated by their SUMO conjugations. THE NEW PHYTOLOGIST 2022; 235:173-187. [PMID: 35347735 DOI: 10.1111/nph.18121] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2021] [Accepted: 03/12/2022] [Indexed: 06/14/2023]
Abstract
Chloroplasts are hypersensitive to heat stress (HS). SUMOylation, a critical post-translational modification, is conservatively involved in HS responses. However, the functional connection between SUMOylation and chloroplasts under HS remains to be studied. The bioinformatics, biochemistry, and cell biology analyses were used to detect the SUMOylation statuses of Arabidopsis nuclear-encoded chloroplast proteins and the effect of SUMOylation on subcellular localization of these proteins under HS. PSBR, a subunit of photosystem II, was used as an example for a detailed investigation of functional mechanisms. After a global SUMOylation site prediction of nuclear-encoded chloroplast proteins, biochemical data showed that most of the selected candidates are modified by SUMO3 in the cytoplasm. The chloroplast localization of these SUMOylation targets under long-term HS is partially maintained by the SUMO ligase AtSIZ1. The HS-induced SUMOylation on PSBR contributes to the maintenance of its chloroplast localization, which is dependent on its chloroplast importation efficiency correlated to phosphorylation. The complementation analysis provided evidence that SUMOylation is essential for the physiological function of PSBR under HS. Our study illustrated a general regulatory mechanism of SUMOylation in maintaining the chloroplast protein importation during HS and provided hints for further investigation on protein modifications associated with plant organelles under stress conditions.
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Affiliation(s)
- Xiao-Ting Zheng
- Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Science, South China Normal University, 510631, Guangzhou, China
| | - Caijuan Wang
- Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Science, South China Normal University, 510631, Guangzhou, China
| | - Wenxiong Lin
- Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Science, South China Normal University, 510631, Guangzhou, China
| | - Chufang Lin
- Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Science, South China Normal University, 510631, Guangzhou, China
| | - Danlu Han
- Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Science, South China Normal University, 510631, Guangzhou, China
| | - Qi Xie
- Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, 100101, China
| | - Jianbin Lai
- Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Science, South China Normal University, 510631, Guangzhou, China
| | - Chengwei Yang
- Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Science, South China Normal University, 510631, Guangzhou, China
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6
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Schwenkert S, Fernie AR, Geigenberger P, Leister D, Möhlmann T, Naranjo B, Neuhaus HE. Chloroplasts are key players to cope with light and temperature stress. TRENDS IN PLANT SCIENCE 2022; 27:577-587. [PMID: 35012879 DOI: 10.1016/j.tplants.2021.12.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 11/16/2021] [Accepted: 12/09/2021] [Indexed: 05/04/2023]
Abstract
Under natural environmental conditions, changes in light intensity and temperature are closely interwoven, and of all organelles, only chloroplasts react strongly upon alterations of these two parameters. We review increasing evidence indicating that changes in chloroplast metabolism are critical for the comprehensive cellular answer in a challenging environment. This cellular answer starts with rapid modifications of thylakoid-located processes, followed by modifications in the stroma and transport activities across the chloroplast envelope. We propose that the 'modulators' involved contribute to plant stress tolerance and that deciphering of their characteristics is essential to understand 'acclimation'. Especially in times of climatic changes, we must gain knowledge on physiological reactions that might become instrumental for directed breeding strategies aiming to develop stress-tolerant crop plants.
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7
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Caspari OD. Transit Peptides Often Require Downstream Unstructured Sequence for Efficient Chloroplast Import in Chlamydomonas reinhardtii. FRONTIERS IN PLANT SCIENCE 2022; 13:825797. [PMID: 35646025 PMCID: PMC9133816 DOI: 10.3389/fpls.2022.825797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 04/27/2022] [Indexed: 06/15/2023]
Abstract
The N-terminal sequence stretch that defines subcellular targeting for most nuclear encoded chloroplast proteins is usually considered identical to the sequence that is cleaved upon import. Yet here this study shows that for eight out of ten tested Chlamydomonas chloroplast transit peptides, significant additional sequence stretches past the cleavage site are required to enable efficient chloroplast import of heterologous cargo proteins. Analysis of Chlamydomonas cTPs with known cleavage sites and replacements of native post-cleavage residues with alternative sequences points to a role for unstructured sequence at mature protein N-termini.
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8
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Coordination of Chloroplast Activity with Plant Growth: Clues Point to TOR. PLANTS 2022; 11:plants11060803. [PMID: 35336685 PMCID: PMC8953291 DOI: 10.3390/plants11060803] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/14/2022] [Accepted: 03/16/2022] [Indexed: 11/17/2022]
Abstract
Photosynthesis is the defining function of most autotrophic organisms. In the plantae kingdom, chloroplasts host this function and ensure growth. However, these organelles are very sensitive to stressful conditions and the photosynthetic process can cause photooxidative damage if not perfectly regulated. In addition, their function is energivorous in terms of both chemical energy and nutrients. To coordinate chloroplast activity with the cell’s need, continuous signaling is required: from chloroplasts to cytoplasm and from nucleus to chloroplasts. In this opinion article, several mechanisms that ensure this communication are reported and the many clues that point to an important role of the Target of Rapamycin (TOR) kinase in the coordination between the eukaryotic and prokaryotic sides of plants are highlighted.
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9
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Cackett L, Luginbuehl LH, Schreier TB, Lopez-Juez E, Hibberd JM. Chloroplast development in green plant tissues: the interplay between light, hormone, and transcriptional regulation. THE NEW PHYTOLOGIST 2022; 233:2000-2016. [PMID: 34729790 DOI: 10.1111/nph.17839] [Citation(s) in RCA: 45] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Accepted: 10/09/2021] [Indexed: 05/20/2023]
Abstract
Chloroplasts are best known for their role in photosynthesis, but they also allow nitrogen and sulphur assimilation, amino acid, fatty acid, nucleotide and hormone synthesis. How chloroplasts develop is therefore relevant to these diverse and fundamental biological processes, but also to attempts at their rational redesign. Light is strictly required for chloroplast formation in all angiosperms and directly regulates the expression of hundreds of chloroplast-related genes. Light also modulates the levels of several hormones including brassinosteriods, cytokinins, auxins and gibberellins, which themselves control chloroplast development particularly during early stages of plant development. Transcription factors such as GOLDENLIKE1&2 (GLK1&2), GATA NITRATE-INDUCIBLE CARBON METABOLISM-INVOLVED (GNC) and CYTOKININ-RESPONSIVE GATA FACTOR 1 (CGA1) act downstream of both light and phytohormone signalling to regulate chloroplast development. Thus, in green tissues transcription factors, light signalling and hormone signalling form a complex network regulating the transcription of chloroplast- and photosynthesis-related genes to control the development and number of chloroplasts per cell. We use this conceptual framework to identify points of regulation that could be harnessed to modulate chloroplast abundance and increase photosynthetic efficiency of crops, and to highlight future avenues to overcome gaps in current knowledge.
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Affiliation(s)
- Lee Cackett
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
| | - Leonie H Luginbuehl
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
| | - Tina B Schreier
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
| | - Enrique Lopez-Juez
- Department of Biological Sciences, Royal Holloway University of London, Egham, TW20 0EX, UK
| | - Julian M Hibberd
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK
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10
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Zhu D, Xiong H, Wu J, Zheng C, Lu D, Zhang L, Xu X. Protein Targeting Into the Thylakoid Membrane Through Different Pathways. Front Physiol 2022; 12:802057. [PMID: 35095563 PMCID: PMC8790069 DOI: 10.3389/fphys.2021.802057] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Accepted: 12/07/2021] [Indexed: 01/19/2023] Open
Abstract
In higher plants, chloroplasts are essential semi-autonomous organelles with complex compartments. As part of these sub-organellar compartments, the sheet-like thylakoid membranes contain abundant light-absorbing chlorophylls bound to the light-harvesting proteins and to some of the reaction center proteins. About half of the thylakoid membrane proteins are encoded by nuclear genes and synthesized in the cytosol as precursors before being imported into the chloroplast. After translocation across the chloroplast envelope by the Toc/Tic system, these proteins are subsequently inserted into or translocated across the thylakoid membranes through distinct pathways. The other half of thylakoid proteins are encoded by the chloroplast genome, synthesized in the stroma and integrated into the thylakoid through a cotranslational process. Much progress has been made in identification and functional characterization of new factors involved in protein targeting into the thylakoids, and new insights into this process have been gained. In this review, we introduce the distinct transport systems mediating the translocation of substrate proteins from chloroplast stroma to the thylakoid membrane, and present the recent advances in the identification of novel components mediating these pathways. Finally, we raise some unanswered questions involved in the targeting of chloroplast proteins into the thylakoid membrane, along with perspectives for future research.
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Affiliation(s)
- Dan Zhu
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng, China
| | - Haibo Xiong
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng, China
| | - Jianghao Wu
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng, China
| | - Canhui Zheng
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng, China
| | - Dandan Lu
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng, China
| | - Lixin Zhang
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng, China
| | - Xiumei Xu
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Kaifeng, China
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11
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New Insights into the Chloroplast Outer Membrane Proteome and Associated Targeting Pathways. Int J Mol Sci 2022; 23:ijms23031571. [PMID: 35163495 PMCID: PMC8836251 DOI: 10.3390/ijms23031571] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 01/24/2022] [Accepted: 01/27/2022] [Indexed: 12/04/2022] Open
Abstract
Plastids are a dynamic class of organelle in plant cells that arose from an ancient cyanobacterial endosymbiont. Over the course of evolution, most genes encoding plastid proteins were transferred to the nuclear genome. In parallel, eukaryotic cells evolved a series of targeting pathways and complex proteinaceous machinery at the plastid surface to direct these proteins back to their target organelle. Chloroplasts are the most well-characterized plastids, responsible for photosynthesis and other important metabolic functions. The biogenesis and function of chloroplasts rely heavily on the fidelity of intracellular protein trafficking pathways. Therefore, understanding these pathways and their regulation is essential. Furthermore, the chloroplast outer membrane proteome remains relatively uncharted territory in our understanding of protein targeting. Many key players in the cytosol, receptors at the organelle surface, and insertases that facilitate insertion into the chloroplast outer membrane remain elusive for this group of proteins. In this review, we summarize recent advances in the understanding of well-characterized chloroplast outer membrane protein targeting pathways as well as provide new insights into novel targeting signals and pathways more recently identified using a bioinformatic approach. As a result of our analyses, we expand the known number of chloroplast outer membrane proteins from 117 to 138.
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12
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Liang L, Wang Q, Song Z, Wu Y, Liang Q, Wang Q, Yang J, Bi Y, Zhou W, Fan LM. O-fucosylation of CPN20 by SPINDLY Derepresses Abscisic Acid Signaling During Seed Germination and Seedling Development. FRONTIERS IN PLANT SCIENCE 2021; 12:724144. [PMID: 34712252 PMCID: PMC8545988 DOI: 10.3389/fpls.2021.724144] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2021] [Accepted: 09/10/2021] [Indexed: 05/31/2023]
Abstract
SPINDLY is involved in some aspects of plant development. However, the nature of this protein as an O-fucosyltransferase was recently discovered. In this study, we show that SPINDLY (SPY) interacts with CPN20 in yeast two-hybrid and split-luc assays, and the interaction is promoted by ABA. CPN20 is a chloroplast-localized co-chaperonin that negatively regulates ABAR-mediated ABA signaling. By using Electron Transfer Dissociation-MS/MS analysis, two O-fucosylation sites, e.g., 116th and 119th threonines, were detected in ectopically expressed CPN20 in mammalian cells and in Arabidopsis. The O-fucosylation at both threonine residues was confirmed by in vitro peptide O-fucosylation assay. We further show that CPN20 accumulates in the chloroplast of spy mutants, suggesting that SPY negatively regulates CPN20 localization in the chloroplast. In vivo protein degradation assay along with CPN20 localization behavior suggest that import of CPN20 into the chloroplast is negatively regulated by SPY. Genetic analysis shows that ABA insensitive phenotypes of spy-3 in terms of seed germination and early seedling development are partially suppressed by the cpn20 mutation, suggesting that CPN20 acts downstream of SPY in this ABA signaling pathway and that there may exist other pathways in parallel with CPN20. Collectively, the above data support the notion that the O-fucosylation of CPN20 by SPY fine-tunes ABA signaling in Arabidopsis.
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Affiliation(s)
- Lin Liang
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
- PKU Core Facility of Mass Spectrometry, School of Chemistry and Molecular Engineering, Peking University, Beijing, China
| | - Qi Wang
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
| | - Zihao Song
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
| | - Yaxin Wu
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
| | - Qing Liang
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
| | - Qingsong Wang
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
| | - Jinli Yang
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
| | - Ying Bi
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
| | - Wen Zhou
- PKU Core Facility of Mass Spectrometry, School of Chemistry and Molecular Engineering, Peking University, Beijing, China
| | - Liu-Min Fan
- State Key Laboratory for Plant Gene and Protein Research, School of Life Sciences, School of Advanced Agriculture Sciences, Peking University, Beijing, China
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13
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Liu XJ, Sun J, Huang Y, Li C, Zheng P, Yuan Y, Chen H, Jan M, Zheng H, Du H, Tu J. Osj10gBTF3-Mediated Import of Chloroplast Protein Is Essential for Pollen Development in Rice. FRONTIERS IN PLANT SCIENCE 2021; 12:713544. [PMID: 34421965 PMCID: PMC8377413 DOI: 10.3389/fpls.2021.713544] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/23/2021] [Accepted: 07/13/2021] [Indexed: 06/13/2023]
Abstract
Chloroplasts are crucial organelles for the generation of fatty acids and starch required for plant development. Nascent polypeptide-associated complex (NAC) proteins have been implicated in development as transcription factors. However, their chaperone roles in chloroplasts and their relationship with pollen development in plants remain to be elucidated. Here, we demonstrated that Osj10gBTF3, a NAC protein, regulates pollen and chloroplast development in rice by coordinating with a Hsp90 family chaperone OsHSP82 to mediate chloroplast import. Knockout of Osj10gBTF3 affects pollen and chloroplast development and significantly reduces the accumulation of fertility-related chloroplast protein OsPPR676. Both Osj10gBTF3 and OsHSP82 interact with OsPPR676. Interestingly, the interaction between OsHSP82 and OsPPR676 is only found in the cytoplasm, while the interaction between Osj10gBTF3 and OsPPR676 also occurs inside the chloroplast. The chloroplast stroma chaperone OsCpn60 can also be co-precipitated with Osj10gBTF3, but not with OsHSP82. Further investigation indicates that Osj10gBTF3 enters the chloroplast stroma possibly through the inner chloroplast membrane channel protein Tic110 and then recruits OsCpn60 for the folding or assembly of OsPPR676. Our results reveal a chaperone role of Osj10gBTF3 in chloroplast import different from Hsp90 and provide a link between chloroplast transport and pollen development in rice.
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Affiliation(s)
- Xue-jiao Liu
- Institute of Crop Science, Zhejiang University, Hangzhou, China
| | - Jiaqi Sun
- Department of Biology, McGill University, Montreal, QC, Canada
| | - Yuqing Huang
- Institute of Crop Science, Zhejiang University, Hangzhou, China
| | - Chao Li
- Institute of Crop Science, Zhejiang University, Hangzhou, China
| | - Peng Zheng
- Institute of Crop Science, Zhejiang University, Hangzhou, China
| | - Yue Yuan
- Institute of Crop Science, Zhejiang University, Hangzhou, China
| | - Hao Chen
- Institute of Crop Science, Zhejiang University, Hangzhou, China
| | - Mehmood Jan
- Institute of Crop Science, Zhejiang University, Hangzhou, China
| | - Huanquan Zheng
- Department of Biology, McGill University, Montreal, QC, Canada
| | - Hao Du
- Institute of Crop Science, Zhejiang University, Hangzhou, China
- Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, China
| | - Jumin Tu
- Institute of Crop Science, Zhejiang University, Hangzhou, China
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14
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Matsuoka A, Maliga P. Prospects for Reengineering Agrobacterium tumefaciens for T-DNA Delivery to Chloroplasts. PLANT PHYSIOLOGY 2021; 186:215-220. [PMID: 33620481 PMCID: PMC8154051 DOI: 10.1093/plphys/kiab081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 02/02/2021] [Indexed: 06/12/2023]
Abstract
Targeting the phiC31 phage integrase for direct export from Agrobacterium to chloroplasts reveals the feasibility of retargeting the Agrobacterium Vir proteins for T-DNA delivery to chloroplasts.
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Affiliation(s)
- Aki Matsuoka
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ 08854, USA
| | - Pal Maliga
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ 08854, USA
- Department of Plant Biology, Rutgers University, New Brunswick, NJ 08901, USA
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15
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Yuan H, Pawlowski EG, Yang Y, Sun T, Thannhauser TW, Mazourek M, Schnell D, Li L. Arabidopsis ORANGE protein regulates plastid pre-protein import through interacting with Tic proteins. JOURNAL OF EXPERIMENTAL BOTANY 2021; 72:1059-1072. [PMID: 33165598 DOI: 10.1093/jxb/eraa528] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 10/30/2020] [Indexed: 05/19/2023]
Abstract
Chloroplast-targeted proteins are actively imported into chloroplasts via the machinery spanning the double-layered membranes of chloroplasts. While the key translocons at the outer (TOC) and inner (TIC) membranes of chloroplasts are defined, proteins that interact with the core components to facilitate pre-protein import are continuously being discovered. A DnaJ-like chaperone ORANGE (OR) protein is known to regulate carotenoid biosynthesis as well as plastid biogenesis and development. In this study, we found that OR physically interacts with several Tic proteins including Tic20, Tic40, and Tic110 in the classic TIC core complex of the chloroplast import machinery. Knocking out or and its homolog or-like greatly affects the import efficiency of some photosynthetic and non-photosynthetic pre-proteins. Consistent with the direct interactions of OR with Tic proteins, the binding efficiency assay revealed that the effect of OR occurs at translocation at the inner envelope membrane (i.e. at the TIC complex). OR is able to reduce the Tic40 protein turnover rate through its chaperone activity. Moreover, OR was found to interfere with the interaction between Tic40 and Tic110, and reduces the binding of pre-proteins to Tic110 in aiding their release for translocation and processing. Our findings suggest that OR plays a new and regulatory role in stabilizing key translocons and in facilitating the late stage of plastid pre-protein translocation to regulate plastid pre-protein import.
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Affiliation(s)
- Hui Yuan
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
| | - Emily G Pawlowski
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
| | - Yong Yang
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
| | - Tianhu Sun
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
| | - Theodore W Thannhauser
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
| | - Michael Mazourek
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
| | - Danny Schnell
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
| | - Li Li
- Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, NY, USA
- Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
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16
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Xu X, Ouyang M, Lu D, Zheng C, Zhang L. Protein Sorting within Chloroplasts. Trends Cell Biol 2020; 31:9-16. [PMID: 33121860 DOI: 10.1016/j.tcb.2020.09.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 09/22/2020] [Accepted: 09/30/2020] [Indexed: 12/11/2022]
Abstract
Chloroplasts have multiple suborganellar membranes. Correct and efficient translocation of chloroplast proteins from their site of synthesis into or across membranes to their functional compartments are fundamental processes. In recent years, several new components and regulatory mechanisms involved in chloroplast protein import and sorting have been explored. Moreover, the formation of liquid-liquid phase transition (LLPT) has been recently reported as a novel mechanism for regulating chloroplast protein sorting. Here, we overview the recent advances of both nuclear- and chloroplast-encoded protein trafficking to their final destination within chloroplasts, and discuss the novel components and regulatory mechanisms of intrachloroplast sorting. Furthermore, we propose that LLPT may be a universal and conserved mechanism for driving organelle protein trafficking and organelle biogenesis.
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Affiliation(s)
- Xiumei Xu
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Jinming Avenue, Kaifeng 475004, China
| | - Min Ouyang
- State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan, 430062, China
| | - Dandan Lu
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Jinming Avenue, Kaifeng 475004, China
| | - Canhui Zheng
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Jinming Avenue, Kaifeng 475004, China
| | - Lixin Zhang
- State Key Laboratory of Crop Stress Adaptation and Improvement, School of Life Sciences, Henan University, Jinming Avenue, Kaifeng 475004, China.
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17
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Bhattacharya O, Ortiz I, Walling LL. Methodology: an optimized, high-yield tomato leaf chloroplast isolation and stroma extraction protocol for proteomics analyses and identification of chloroplast co-localizing proteins. PLANT METHODS 2020; 16:131. [PMID: 32983250 PMCID: PMC7513546 DOI: 10.1186/s13007-020-00667-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 09/04/2020] [Indexed: 06/09/2023]
Abstract
BACKGROUND Chloroplasts are critical organelles that perceive and convey metabolic and stress signals to different cellular components, while remaining the seat of photosynthesis and a metabolic factory. The proteomes of intact leaves, chloroplasts, and suborganellar fractions of plastids have been evaluated in the model plant Arabidopsis, however fewer studies have characterized the proteomes of plastids in crops. Tomato (Solanum lycopersicum) is an important world-wide crop and a model system for the study of wounding, herbivory and fruit ripening. While significant advances have been made in understanding proteome and metabolome changes in fruit ripening, far less is known about the tomato chloroplast proteome or its subcompartments. RESULTS With the long-term goal of understanding chloroplast proteome dynamics in response to stress, we describe a high-yielding method to isolate intact tomato chloroplasts and stromal proteins for proteomic studies. The parameters that limit tomato chloroplast yields were identified and revised to increase yields. Compared to published data, our optimized method increased chloroplast yields by 6.7- and 4.3-fold relative to published spinach and Arabidopsis leaf protocols, respectively; furthermore, tomato stromal protein yields were up to 79-fold higher than Arabidopsis stromal proteins yields. We provide immunoblot evidence for the purity of the stromal proteome isolated using our enhanced methods. In addition, we leverage our nanoliquid chromatography tandem mass spectrometry (nanoLC-MS/MS) data to assess the quality of our stromal proteome. Using strict criteria, proteins detected by 1 peptide spectral match, by one peptide, or were sporadically detected were designated as low-level contaminating proteins. A set of 254 proteins that reproducibly co-isolated with the tomato chloroplast stroma were identified. The subcellular localization, frequency of detection, normalized spectral abundance, and functions of the co-isolating proteins are discussed. CONCLUSIONS Our optimized method for chloroplast isolation increased the yields of tomato chloroplasts eightfold enabling the proteomics analysis of the chloroplast stromal proteome. The set of 254 proteins that co-isolate with the chloroplast stroma provides opportunities for developing a better understanding of the extensive and dynamic interactions of chloroplasts with other organelles. These co-isolating proteins also have the potential for expanding our knowledge of proteins that are co-localized in multiple subcellular organelles.
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Affiliation(s)
- Oindrila Bhattacharya
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California, Riverside, CA 92521 USA
| | - Irma Ortiz
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California, Riverside, CA 92521 USA
| | - Linda L. Walling
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California, Riverside, CA 92521 USA
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18
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Grabsztunowicz M, Rokka A, Farooq I, Aro EM, Mulo P. Gel-based proteomic map of Arabidopsis thaliana root plastids and mitochondria. BMC PLANT BIOLOGY 2020; 20:413. [PMID: 32887556 PMCID: PMC7650296 DOI: 10.1186/s12870-020-02635-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 08/30/2020] [Indexed: 06/11/2023]
Abstract
BACKGROUND Non-photosynthetic plastids of plants are known to be involved in a range of metabolic and biosynthetic reactions, even if they have been difficult to study due to their small size and lack of color. The morphology of root plastids is heterogeneous and also the plastid size, density and subcellular distribution varies depending on the cell type and developmental stage, and therefore the functional features have remained obscure. Although the root plastid proteome is likely to reveal specific functional features, Arabidopsis thaliana root plastid proteome has not been studied to date. RESULTS In the present study, we separated Arabidopsis root protein fraction enriched with plastids and mitochondria by 2D-PAGE and identified 84 plastid-targeted and 77 mitochondrion-targeted proteins using LC-MS/MS. The most prevalent root plastid protein categories represented amino acid biosynthesis, carbohydrate metabolism and lipid biosynthesis pathways, while the enzymes involved in starch and sucrose metabolism were not detected. Mitochondrion-targeted proteins were classified mainly into the energetics category. CONCLUSIONS This is the first study presenting gel-based map of Arabidopsis thaliana root plastid and mitochondrial proteome. Our findings suggest that Arabidopsis root plastids have broad biosynthetic capacity, and that they do not play a major role in a long-term storage of carbohydrates. The proteomic map provides a tool for further studies to compare changes in the proteome, e.g. in response to environmental cues, and emphasizes the role of root plastids in nitrogen and sulfur metabolism as well as in amino acid and fatty acid biosynthesis. The results enable taking a first step towards an integrated view of root plastid/mitochondrial proteome and metabolic functions in Arabidopsis thaliana roots.
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Affiliation(s)
| | - Anne Rokka
- Turku Bioscience Centre, University of Turku and Åbo Akademi University, 20520, Turku, Finland
| | - Irum Farooq
- Molecular Plant Biology, University of Turku, 20520, Turku, Finland
| | - Eva-Mari Aro
- Molecular Plant Biology, University of Turku, 20520, Turku, Finland
| | - Paula Mulo
- Molecular Plant Biology, University of Turku, 20520, Turku, Finland.
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19
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Protein import into chloroplasts and its regulation by the ubiquitin-proteasome system. Biochem Soc Trans 2020; 48:71-82. [PMID: 31922184 PMCID: PMC7054747 DOI: 10.1042/bst20190274] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 12/19/2019] [Accepted: 12/23/2019] [Indexed: 02/08/2023]
Abstract
Chloroplasts are photosynthetic plant organelles descended from a bacterial ancestor. The vast majority of chloroplast proteins are synthesized in the cytosol and then imported into the chloroplast post-translationally. Translocation complexes exist in the organelle's outer and inner envelope membranes (termed TOC and TIC, respectively) to facilitate protein import. These systems recognize chloroplast precursor proteins and mediate their import in an energy-dependent manner. However, many unanswered questions remain regarding mechanistic details of the import process and the participation and functions of individual components; for example, the cytosolic events that mediate protein delivery to chloroplasts, the composition of the TIC apparatus, and the nature of the protein import motor all require resolution. The flux of proteins through TOC and TIC varies greatly throughout development and in response to specific environmental cues. The import process is, therefore, tightly regulated, and it has emerged that the ubiquitin-proteasome system (UPS) plays a key role in this regard, acting at several different steps in the process. The UPS is involved in: the selective degradation of transcription factors that co-ordinate the expression of chloroplast precursor proteins; the removal of unimported chloroplast precursor proteins in the cytosol; the inhibition of chloroplast biogenesis pre-germination; and the reconfiguration of the TOC apparatus in response to developmental and environmental signals in a process termed chloroplast-associated protein degradation. In this review, we highlight recent advances in our understanding of protein import into chloroplasts and how this process is regulated by the UPS.
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20
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Hu S, Ding Y, Zhu C. Sensitivity and Responses of Chloroplasts to Heat Stress in Plants. FRONTIERS IN PLANT SCIENCE 2020; 11:375. [PMID: 32300353 PMCID: PMC7142257 DOI: 10.3389/fpls.2020.00375] [Citation(s) in RCA: 123] [Impact Index Per Article: 30.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2019] [Accepted: 03/16/2020] [Indexed: 05/21/2023]
Abstract
Increased temperatures caused by global warming threaten agricultural production, as warmer conditions can inhibit plant growth and development or even destroy crops in extreme circumstances. Extensive research over the past several decades has revealed that chloroplasts, the photosynthetic organelles of plants, are highly sensitive to heat stress, which affects a variety of photosynthetic processes including chlorophyll biosynthesis, photochemical reactions, electron transport, and CO2 assimilation. Important mechanisms by which plant cells respond to heat stress to protect these photosynthetic organelles have been identified and analyzed. More recent studies have made it clear that chloroplasts play an important role in inducing the expression of nuclear heat-response genes during the heat stress response. In this review, we summarize these important advances in plant-based research and discuss how the sensitivity, responses, and signaling roles of chloroplasts contribute to plant heat sensitivity and tolerance.
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Affiliation(s)
| | | | - Cheng Zhu
- Key Laboratory of Marine Food Quality and Hazard Controlling Technology of Zhejiang Province, College of Life Sciences, China Jiliang University, Hangzhou, China
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21
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Li HM, Schnell D, Theg SM. Protein Import Motors in Chloroplasts: On the Role of Chaperones. THE PLANT CELL 2020; 32:536-542. [PMID: 31932485 PMCID: PMC7054032 DOI: 10.1105/tpc.19.00300] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2019] [Revised: 08/01/2019] [Accepted: 01/08/2020] [Indexed: 05/09/2023]
Affiliation(s)
- Hsou-Min Li
- Institute of Molecular Biology Academia Sinica Taipei 11529, Taiwan
| | - Danny Schnell
- Department of Plant Biology Michigan State University East Lansing, Michigan 48824
| | - Steven M Theg
- Department of Plant Biology University of California Davis, California 95616
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22
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Tadini L, Peracchio C, Trotta A, Colombo M, Mancini I, Jeran N, Costa A, Faoro F, Marsoni M, Vannini C, Aro EM, Pesaresi P. GUN1 influences the accumulation of NEP-dependent transcripts and chloroplast protein import in Arabidopsis cotyledons upon perturbation of chloroplast protein homeostasis. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2020; 101:1198-1220. [PMID: 31648387 DOI: 10.1111/tpj.14585] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2019] [Revised: 10/09/2019] [Accepted: 10/21/2019] [Indexed: 05/21/2023]
Abstract
Correct chloroplast development and function require co-ordinated expression of chloroplast and nuclear genes. This is achieved through chloroplast signals that modulate nuclear gene expression in accordance with the chloroplast's needs. Genetic evidence indicates that GUN1, a chloroplast-localized pentatricopeptide repeat (PPR) protein with a C-terminal Small MutS-Related (SMR) domain, is involved in integrating multiple developmental and stress-related signals in both young seedlings and adult leaves. Recently, GUN1 was found to interact physically with factors involved in chloroplast protein homeostasis, and with enzymes of tetrapyrrole biosynthesis in adult leaves that function in various retrograde signalling pathways. Here we show that following perturbation of chloroplast protein homeostasis: (i) by growth in lincomycin-containing medium; or (ii) in mutants defective in either the FtsH protease complex (ftsh), plastid ribosome activity (prps21-1 and prpl11-1) or plastid protein import and folding (cphsc70-1), GUN1 influences NEP-dependent transcript accumulation during cotyledon greening and also intervenes in chloroplast protein import.
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Affiliation(s)
- Luca Tadini
- Dipartimento di Bioscienze, Università degli Studi di Milano, 20133, Milano, Italy
| | - Carlotta Peracchio
- Dipartimento di Bioscienze, Università degli Studi di Milano, 20133, Milano, Italy
| | - Andrea Trotta
- Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turku, Finland
| | - Monica Colombo
- Centro Ricerca e Innovazione, Fondazione Edmund Mach, 38010, San Michele all'Adige, Italy
| | - Ilaria Mancini
- Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turku, Finland
| | - Nicolaj Jeran
- Dipartimento di Bioscienze, Università degli Studi di Milano, 20133, Milano, Italy
| | - Alex Costa
- Dipartimento di Bioscienze, Università degli Studi di Milano, 20133, Milano, Italy
| | - Franco Faoro
- Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia, Università degli Studi di Milano, 20133, Milano, Italy
| | - Milena Marsoni
- Dipartimento di Biotecnologie e Scienze della Vita, Università degli Studi dell'Insubria, via J.H. Dunant 3, 21100, Varese, Italy
| | - Candida Vannini
- Dipartimento di Biotecnologie e Scienze della Vita, Università degli Studi dell'Insubria, via J.H. Dunant 3, 21100, Varese, Italy
| | - Eva-Mari Aro
- Molecular Plant Biology, Department of Biochemistry, University of Turku, 20014, Turku, Finland
| | - Paolo Pesaresi
- Dipartimento di Bioscienze, Università degli Studi di Milano, 20133, Milano, Italy
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23
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Richardson LGL, Schnell DJ. Origins, function, and regulation of the TOC-TIC general protein import machinery of plastids. JOURNAL OF EXPERIMENTAL BOTANY 2020; 71:1226-1238. [PMID: 31730153 PMCID: PMC7031061 DOI: 10.1093/jxb/erz517] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 11/14/2019] [Indexed: 05/11/2023]
Abstract
The evolution of chloroplasts from the original endosymbiont involved the transfer of thousands of genes from the ancestral bacterial genome to the host nucleus, thereby combining the two genetic systems to facilitate coordination of gene expression and achieve integration of host and organelle functions. A key element of successful endosymbiosis was the evolution of a unique protein import system to selectively and efficiently target nuclear-encoded proteins to their site of function within the chloroplast after synthesis in the cytoplasm. The chloroplast TOC-TIC (translocon at the outer chloroplast envelope-translocon at the inner chloroplast envelope) general protein import system is conserved across the plant kingdom, and is a system of hybrid origin, with core membrane transport components adapted from bacterial protein targeting systems, and additional components adapted from host genes to confer the specificity and directionality of import. In vascular plants, the TOC-TIC system has diversified to mediate the import of specific, functionally related classes of plastid proteins. This functional diversification occurred as the plastid family expanded to fulfill cell- and tissue-specific functions in terrestrial plants. In addition, there is growing evidence that direct regulation of TOC-TIC activities plays an essential role in the dynamic remodeling of the organelle proteome that is required to coordinate plastid biogenesis with developmental and physiological events.
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Affiliation(s)
- Lynn G L Richardson
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
| | - Danny J Schnell
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA
- Correspondence:
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24
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Schnell DJ. The TOC GTPase Receptors: Regulators of the Fidelity, Specificity and Substrate Profiles of the General Protein Import Machinery of Chloroplasts. Protein J 2020; 38:343-350. [PMID: 31201619 PMCID: PMC6589150 DOI: 10.1007/s10930-019-09846-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
More than 2500 nuclear encoded preproteins are required for the function of chloroplasts in terrestrial plants. These preproteins are imported into chloroplasts via the concerted action of two multi-subunit translocons of the outer (TOC) and inner (TIC) membranes of the chloroplast envelope. This general import machinery functions to recognize and import proteins with high fidelity and efficiency to ensure that organelle biogenesis is properly coordinated with developmental and physiological events. Two components of the TOC machinery, Toc34 and Toc159, act as the primary receptors for preproteins at the chloroplast surface. They interact with the intrinsic targeting signals (transit peptides) of preproteins to mediate the selectivity of targeting, and they contribute to the quality control of import by constituting a GTP-dependent checkpoint in the import reaction. The TOC receptor family has expanded to regulate the import of distinct classes of preproteins that are required for remodeling of organelle proteomes during plastid-type transitions that accompany developmental changes. As such, the TOC receptors function as central regulators of the fidelity, specificity and selectivity of the general import machinery, thereby contributing to the integration of protein import with plastid biogenesis.
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Affiliation(s)
- Danny J Schnell
- Department of Plant Biology, Michigan State University, East Lansing, MI, USA.
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25
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Eisa A, Malenica K, Schwenkert S, Bölter B. High Light Acclimation Induces Chloroplast Precursor Phosphorylation and Reduces Import Efficiency. PLANTS 2019; 9:plants9010024. [PMID: 31878089 PMCID: PMC7020187 DOI: 10.3390/plants9010024] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Revised: 12/19/2019] [Accepted: 12/22/2019] [Indexed: 12/14/2022]
Abstract
Acclimation is an essential process in plants on many levels, but especially in chloroplasts under changing light conditions. It is partially known how the photosynthetic machinery reacts upon exposure to high light intensities, including rearrangement of numerous protein complexes. Since the majority of proteins residing within chloroplasts needs to be posttranslationally imported into the organelles, we endeavored to study how this important process is regulated upon subjecting plants from pea and Arabidopsis to high light. Our results reveal that acclimation takes place on the one hand in the cytosol by differential phosphorylation of preproteins and resulting from the altered expression of the responsible kinases, and on the other hand at the level of the translocation machineries in the outer (TOC) and inner (TIC) envelope membranes. Intriguingly, while phosphorylation is more pronounced under high light, import itself shows a lower efficiency, along with a reduced accumulation of the Toc receptor proteins Toc34 and Toc159.
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26
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Moyet L, Salvi D, Bouchnak I, Miras S, Perrot L, Seigneurin-Berny D, Kuntz M, Rolland N. Calmodulin is involved in the dual subcellular location of two chloroplast proteins. J Biol Chem 2019; 294:17543-17554. [PMID: 31578278 PMCID: PMC6873194 DOI: 10.1074/jbc.ra119.010846] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Indexed: 12/02/2022] Open
Abstract
Cell compartmentalization is an essential process by which eukaryotic cells separate and control biological processes. Although calmodulins are well-known to regulate catalytic properties of their targets, we show here their involvement in the subcellular location of two plant proteins. Both proteins exhibit a dual location, namely in the cytosol in addition to their association to plastids (where they are known to fulfil their role). One of these proteins, ceQORH, a long-chain fatty acid reductase, was analyzed in more detail, and its calmodulin-binding site was identified by specific mutations. Such a mutated form is predominantly targeted to plastids at the expense of its cytosolic location. The second protein, TIC32, was also shown to be dependent on its calmodulin-binding site for retention in the cytosol. Complementary approaches (bimolecular fluorescence complementation and reverse genetics) demonstrated that the calmodulin isoform CAM5 is specifically involved in the retention of ceQORH in the cytosol. This study identifies a new role for calmodulin and sheds new light on the intriguing CaM-binding properties of hundreds of plastid proteins, despite the fact that no CaM or CaM-like proteins were identified in plastids.
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Affiliation(s)
- Lucas Moyet
- Laboratoire de Physiologie Cellulaire & Végétale, Université Grenoble Alpes, INRA, CNRS, CEA, IRIG-LPCV, 38000 Grenoble, France
| | - Daniel Salvi
- Laboratoire de Physiologie Cellulaire & Végétale, Université Grenoble Alpes, INRA, CNRS, CEA, IRIG-LPCV, 38000 Grenoble, France
| | - Imen Bouchnak
- Laboratoire de Physiologie Cellulaire & Végétale, Université Grenoble Alpes, INRA, CNRS, CEA, IRIG-LPCV, 38000 Grenoble, France
| | - Stéphane Miras
- Laboratoire de Physiologie Cellulaire & Végétale, Université Grenoble Alpes, INRA, CNRS, CEA, IRIG-LPCV, 38000 Grenoble, France
| | - Laura Perrot
- Laboratoire de Physiologie Cellulaire & Végétale, Université Grenoble Alpes, INRA, CNRS, CEA, IRIG-LPCV, 38000 Grenoble, France
| | - Daphné Seigneurin-Berny
- Laboratoire de Physiologie Cellulaire & Végétale, Université Grenoble Alpes, INRA, CNRS, CEA, IRIG-LPCV, 38000 Grenoble, France
| | - Marcel Kuntz
- Laboratoire de Physiologie Cellulaire & Végétale, Université Grenoble Alpes, INRA, CNRS, CEA, IRIG-LPCV, 38000 Grenoble, France
| | - Norbert Rolland
- Laboratoire de Physiologie Cellulaire & Végétale, Université Grenoble Alpes, INRA, CNRS, CEA, IRIG-LPCV, 38000 Grenoble, France
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Zhang T, Schneider JD, Lin C, Geng S, Ma T, Lawrence SR, Dufresne CP, Harmon AC, Chen S. MPK4 Phosphorylation Dynamics and Interacting Proteins in Plant Immunity. J Proteome Res 2019; 18:826-840. [PMID: 30632760 DOI: 10.1021/acs.jproteome.8b00345] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Arabidopsis MAP kinase 4 (MPK4) has been proposed to be a negative player in plant immunity, and it is also activated by pathogen-associated molecular patterns (PAMPs), such as flg22. The molecular mechanisms by which MPK4 is activated and regulates plant defense remain elusive. In this study, we investigated Arabidopsis defense against a bacterial pathogen Pseudomonas syringae pv tomato ( Pst) DC3000 when Brassica napus MPK4 ( BnMPK4) is overexpressed. We showed an increase in pathogen resistance and suppression of jasmonic acid (JA) signaling in the BnMPK4 overexpressing (OE) plants. We also showed that the OE plants have increased sensitivity to flg22-triggered reactive oxygen species (ROS) burst in guard cells, which resulted in enhanced stomatal closure compared to wild-type (WT). During flg22 activation, dynamic phosphorylation events within and outside of the conserved TEY activation loop were observed. To elucidate how BnMPK4 functions during the defense response, we used immunoprecipitation coupled with mass spectrometry (IP-MS) to identify BnMPK4 interacting proteins in the absence and presence of flg22. Quantitative proteomic analysis revealed a shift in the MPK4-associated protein network, providing insight into the molecular functions of MPK4 at the systems level.
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Affiliation(s)
| | | | | | | | | | | | - Craig P Dufresne
- Thermo Fisher Scientific , 1400 Northpoint Parkway , West Palm Beach , Florida 33407 , United States
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28
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Su HJ, Barkman TJ, Hao W, Jones SS, Naumann J, Skippington E, Wafula EK, Hu JM, Palmer JD, dePamphilis CW. Novel genetic code and record-setting AT-richness in the highly reduced plastid genome of the holoparasitic plant Balanophora. Proc Natl Acad Sci U S A 2019; 116:934-943. [PMID: 30598433 PMCID: PMC6338844 DOI: 10.1073/pnas.1816822116] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Plastid genomes (plastomes) vary enormously in size and gene content among the many lineages of nonphotosynthetic plants, but key lineages remain unexplored. We therefore investigated plastome sequence and expression in the holoparasitic and morphologically bizarre Balanophoraceae. The two Balanophora plastomes examined are remarkable, exhibiting features rarely if ever seen before in plastomes or in any other genomes. At 15.5 kb in size and with only 19 genes, they are among the most reduced plastomes known. They have no tRNA genes for protein synthesis, a trait found in only three other plastid lineages, and thus Balanophora plastids must import all tRNAs needed for translation. Balanophora plastomes are exceptionally compact, with numerous overlapping genes, highly reduced spacers, loss of all cis-spliced introns, and shrunken protein genes. With A+T contents of 87.8% and 88.4%, the Balanophora genomes are the most AT-rich genomes known save for a single mitochondrial genome that is merely bloated with AT-rich spacer DNA. Most plastid protein genes in Balanophora consist of ≥90% AT, with several between 95% and 98% AT, resulting in the most biased codon usage in any genome described to date. A potential consequence of its radical compositional evolution is the novel genetic code used by Balanophora plastids, in which TAG has been reassigned from stop to tryptophan. Despite its many exceptional properties, the Balanophora plastome must be functional because all examined genes are transcribed, its only intron is correctly trans-spliced, and its protein genes, although highly divergent, are evolving under various degrees of selective constraint.
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Affiliation(s)
- Huei-Jiun Su
- Department of Earth and Life Sciences, University of Taipei, 100 Taipei, Taiwan
- Department of Biology, Pennsylvania State University, University Park, PA 16802
- Institute of Molecular Evolutionary Genetics, Pennsylvania State University, University Park, PA 16802
| | - Todd J Barkman
- Department of Biological Sciences, Western Michigan University, Kalamazoo, MI 49008
| | - Weilong Hao
- Department of Biological Sciences, Wayne State University, Detroit, MI 48202
| | - Samuel S Jones
- Graduate Program in Plant Biology, Pennsylvania State University, University Park, PA 16802
| | - Julia Naumann
- Department of Biology, Pennsylvania State University, University Park, PA 16802
- Institute of Molecular Evolutionary Genetics, Pennsylvania State University, University Park, PA 16802
| | | | - Eric K Wafula
- Department of Biology, Pennsylvania State University, University Park, PA 16802
- Institute of Molecular Evolutionary Genetics, Pennsylvania State University, University Park, PA 16802
| | - Jer-Ming Hu
- Institute of Ecology and Evolutionary Biology, National Taiwan University, 106 Taipei, Taiwan
| | - Jeffrey D Palmer
- Department of Biology, Indiana University, Bloomington, IN 47405;
| | - Claude W dePamphilis
- Department of Biology, Pennsylvania State University, University Park, PA 16802;
- Institute of Molecular Evolutionary Genetics, Pennsylvania State University, University Park, PA 16802
- Graduate Program in Plant Biology, Pennsylvania State University, University Park, PA 16802
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29
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Ziehe D, Dünschede B, Schünemann D. Molecular mechanism of SRP-dependent light-harvesting protein transport to the thylakoid membrane in plants. PHOTOSYNTHESIS RESEARCH 2018; 138:303-313. [PMID: 29956039 PMCID: PMC6244792 DOI: 10.1007/s11120-018-0544-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 06/20/2018] [Indexed: 05/26/2023]
Abstract
The light-harvesting chlorophyll a/b binding proteins (LHCP) belong to a large family of membrane proteins. They form the antenna complexes of photosystem I and II and function in light absorption and transfer of the excitation energy to the photosystems. As nuclear-encoded proteins, the LHCPs are imported into the chloroplast and further targeted to their final destination-the thylakoid membrane. Due to their hydrophobicity, the formation of the so-called 'transit complex' in the stroma is important to prevent their aggregation in this aqueous environment. The posttranslational LHCP targeting mechanism is well regulated through the interaction of various soluble and membrane-associated protein components and includes several steps: the binding of the LHCP to the heterodimeric cpSRP43/cpSRP54 complex to form the soluble transit complex; the docking of the transit complex to the SRP receptor cpFtsY and the Alb3 translocase at the membrane followed by the release and integration of the LHCP into the thylakoid membrane in a GTP-dependent manner. This review summarizes the molecular mechanisms and dynamics behind the posttranslational LHCP targeting to the thylakoid membrane of Arabidopsis thaliana.
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Affiliation(s)
- Dominik Ziehe
- Molecular Biology of Plant Organelles, Ruhr-University Bochum, Universitätsstraße 150, 44780, Bochum, Germany
| | - Beatrix Dünschede
- Molecular Biology of Plant Organelles, Ruhr-University Bochum, Universitätsstraße 150, 44780, Bochum, Germany
| | - Danja Schünemann
- Molecular Biology of Plant Organelles, Ruhr-University Bochum, Universitätsstraße 150, 44780, Bochum, Germany.
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Bölter B. En route into chloroplasts: preproteins' way home. PHOTOSYNTHESIS RESEARCH 2018; 138:263-275. [PMID: 29943212 DOI: 10.1007/s11120-018-0542-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 06/20/2018] [Indexed: 06/08/2023]
Abstract
Chloroplasts are the characteristic endosymbiotic organelles of plant cells which during the course of evolution lost most of their genetic information to the nucleus. Thus, they critically depend on the host cell for allocation of nearly their complete protein supply. This includes gene expression, translation, protein targeting, and transport-all of which need to be tightly regulated and perfectly coordinated to accommodate the cells' needs. To this end, multiple signaling pathways have been implemented that interchange information between the different cellular compartments. One of the most complex and energy consuming processes is the translocation of chloroplast-destined proteins into their target organelle. It is a concerted effort from chaperones, receptor proteins, channels, and regulatory elements to ensure correct targeting, efficient transport, and subsequent folding. Although we have discovered and learned a lot about protein import into chloroplasts in the last decades, there are still many open questions and debates about the roles of individual proteins as well as the mechanistic details. In this review, I will summarize and discuss the published data with a focus on the translocation complex in the chloroplast inner envelope membrane.
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Affiliation(s)
- Bettina Bölter
- Department Biologie I, Botanik, Ludwig-Maximilians-Universität, Planegg-Martinsried, Germany.
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31
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Richardson LGL, Small EL, Inoue H, Schnell DJ. Molecular Topology of the Transit Peptide during Chloroplast Protein Import. THE PLANT CELL 2018; 30:1789-1806. [PMID: 29991536 PMCID: PMC6139696 DOI: 10.1105/tpc.18.00172] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Revised: 06/26/2018] [Accepted: 07/06/2018] [Indexed: 05/04/2023]
Abstract
Chloroplast protein import is directed by the interaction of the targeting signal (transit peptide) of nucleus-encoded preproteins with translocons at the outer (TOC) and inner (TIC) chloroplast envelope membranes. Studies of the energetics and determinants of transit peptide binding have led to the hypothesis that import occurs through sequential recognition of transit peptides by components of TOC and TIC during protein import. To test this hypothesis, we employed a site-specific cross-linking approach to map transit peptide topology in relation to TOC-TIC components at specific stages of import in Arabidopsis thaliana and pea (Pisum sativum). We demonstrate that the transit peptide is in contact with Tic20 at the inner envelope in addition to TOC complex components at the earliest stages of chloroplast binding. Low levels of ATP hydrolysis catalyze the commitment of the preprotein to import by promoting further penetration across the envelope membranes and stabilizing the association of the preprotein with TOC-TIC. GTP hydrolysis at the TOC receptors serves as a checkpoint to regulate the ATP-dependent commitment of the preprotein to import and is not essential to drive preprotein import. Our results demonstrate the close cooperativity of the TOC and TIC machinery at each stage of transit peptide recognition and membrane translocation during protein import.
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Affiliation(s)
- Lynn G L Richardson
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Eliana L Small
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Hitoshi Inoue
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Danny J Schnell
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
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32
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Nakai M. New Perspectives on Chloroplast Protein Import. PLANT & CELL PHYSIOLOGY 2018; 59:1111-1119. [PMID: 29684214 DOI: 10.1093/pcp/pcy083] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 04/13/2018] [Indexed: 05/21/2023]
Abstract
Virtually all chloroplasts in extant photosynthetic eukaryotes derive from a single endosymbiotic event that probably occurred more than a billion years ago between a host eukaryotic cell and a cyanobacterium-like ancestor. Many endosymbiont genes were subsequently transferred to the host nuclear genome, concomitant with the establishment of a system for protein transport through the chloroplast double-membrane envelope. Presently, 2,000-3,000 different nucleus-encoded chloroplast proteins must be imported into the chloroplast following their synthesis in the cytosol. The TOC (translocon at the outer envelope membrane of chloroplasts) and TIC (translocon at the inner envelope membrane of chloroplasts) complexes are protein translocation machineries at the outer and inner envelope membranes, respectively, that facilitate this chloroplast protein import with the aid of a TIC-associated ATP-driven import motor. All the essential components of this protein import system seemed to have been identified through biochemical analyses and subsequent genetic studies that initiated in the late 1990s. However, in 2013, the Nakai group reported a novel inner envelope membrane TIC complex, for which a novel ATP-driven import motor associated with this TIC complex is likely to exist. In this mini review, I will summarize these recent discoveries together with new, or reanalyzed, data presented by other groups in recent years. Whereas the precise concurrent view of chloroplast protein import is still a matter of some debate, it is anticipated that the entire TOC/TIC/ATP motor system, including any novel components, will be conclusively established in the next decade. Such findings may lead to an extensively revised view of the evolution and molecular mechanisms of chloroplast protein import.
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Affiliation(s)
- Masato Nakai
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871 Japan
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33
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Matic S, Muders V, Meisinger C. Tuning the mitochondrial protein import machinery by reversible phosphorylation: from metabolic switches to cell cycle regulation. CURRENT OPINION IN PHYSIOLOGY 2018. [DOI: 10.1016/j.cophys.2018.02.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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34
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Aigner H, Wilson RH, Bracher A, Calisse L, Bhat JY, Hartl FU, Hayer-Hartl M. Plant RuBisCo assembly in E. coli with five chloroplast chaperones including BSD2. Science 2018; 358:1272-1278. [PMID: 29217567 DOI: 10.1126/science.aap9221] [Citation(s) in RCA: 130] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 10/17/2017] [Indexed: 01/06/2023]
Abstract
Plant RuBisCo, a complex of eight large and eight small subunits, catalyzes the fixation of CO2 in photosynthesis. The low catalytic efficiency of RuBisCo provides strong motivation to reengineer the enzyme with the goal of increasing crop yields. However, genetic manipulation has been hampered by the failure to express plant RuBisCo in a bacterial host. We achieved the functional expression of Arabidopsis thaliana RuBisCo in Escherichia coli by coexpressing multiple chloroplast chaperones. These include the chaperonins Cpn60/Cpn20, RuBisCo accumulation factors 1 and 2, RbcX, and bundle-sheath defective-2 (BSD2). Our structural and functional analysis revealed the role of BSD2 in stabilizing an end-state assembly intermediate of eight RuBisCo large subunits until the small subunits become available. The ability to produce plant RuBisCo recombinantly will facilitate efforts to improve the enzyme through mutagenesis.
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Affiliation(s)
- H Aigner
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - R H Wilson
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - A Bracher
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - L Calisse
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - J Y Bhat
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - F U Hartl
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - M Hayer-Hartl
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany.
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35
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Structural components involved in plastid protein import. Essays Biochem 2018; 62:65-75. [DOI: 10.1042/ebc20170093] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 01/24/2018] [Accepted: 01/29/2018] [Indexed: 02/04/2023]
Abstract
Import of preproteins into chloroplasts is an essential process, requiring two major multisubunit protein complexes that are embedded in the outer and inner chloroplast envelope membrane. Both the translocon of the outer chloroplast membrane (Toc), as well as the translocon of the inner chloroplast membrane (Tic) have been studied intensively with respect to their individual subunit compositions, functions and regulations. Recent advances in crystallography have increased our understanding of the operation of these proteins in terms of their interactions and regulation by conformational switching. Several subdomains of components of the Toc translocon have been studied at the structural level, among them the polypeptide transport-associated (POTRA) domain of the channel protein Toc75 and the GTPase domain of Toc34. In this review, we summarize and discuss the insight that has been gained from these structural analyses. In addition, we present the crystal structure of the Toc64 tetratrico-peptide repeat (TPR) domain in complex with the C-terminal domains of the heat-shock proteins (Hsp) Hsp90 and Hsp70.
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36
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Abstract
The plastids, including chloroplasts, are a group of interrelated organelles that confer photoautotrophic growth and the unique metabolic capabilities that are characteristic of plant systems. Plastid biogenesis relies on the expression, import, and assembly of thousands of nuclear encoded preproteins. Plastid proteomes undergo rapid remodeling in response to developmental and environmental signals to generate functionally distinct plastid types in specific cells and tissues. In this review, we will highlight the central role of the plastid protein import system in regulating and coordinating the import of functionally related sets of preproteins that are required for plastid-type transitions and maintenance.
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37
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Rolland V, Rae BD, Long BM. Setting sub-organellar sights: accurate targeting of multi-transmembrane-domain proteins to specific chloroplast membranes. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:5013-5016. [PMID: 29106623 PMCID: PMC5853405 DOI: 10.1093/jxb/erx351] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
This article comments on: Singhal R, Fernandez DE. 2017. Sorting of SEC translocase SCY components to different membranes in chloroplasts. Journal of Experimental Botany 68, 5029–5043.
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Affiliation(s)
| | - Benjamin D Rae
- ARC Centre of Excellence for Translational Photosynthesis, Division of Plant Science, Research School of Biology, The Australian National University, Acton ACT, Australia
| | - Benedict M Long
- ARC Centre of Excellence for Translational Photosynthesis, Division of Plant Science, Research School of Biology, The Australian National University, Acton ACT, Australia
- Correspondence:
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38
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Singhal R, Fernandez DE. Sorting of SEC translocase SCY components to different membranes in chloroplasts. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:5029-5043. [PMID: 28992187 PMCID: PMC5853536 DOI: 10.1093/jxb/erx318] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Accepted: 08/15/2017] [Indexed: 05/20/2023]
Abstract
Membrane proteins that are imported into chloroplasts must be accurately routed in order to establish and maintain the highly differentiated membranes characteristic of these organelles. Little is known about the targeting information or pathways involved, especially in the case of proteins with multiple transmembrane domains. We have studied targeting of the SCY components of the two SEC translocases in chloroplasts. SCY1 and SCY2 share a similar, highly conserved structure with 10 transmembrane domains, but are targeted to different membranes: the thylakoids and inner envelope, respectively. We used protoplast transfections and a confocal microscopy imaging assay in combination with a domain-swapping approach to investigate sorting pathways and identify important targeting elements in these proteins. We show that the N-terminal region of SCY1 contains targeting determinants that allow SCY1 to be recruited to the signal-recognition particle pathway. In addition, substituting the N-terminal region of SCY1 for the N-terminal region of SCY2 causes SCY2 to be displaced out of the inner envelope. The region of SCY2 that contains transmembrane domains 3 and 4 is necessary for localization to the inner envelope and may serve as a membrane anchor, enhancing the integration of other transmembrane domains via either stop-transfer or post-import mechanisms.
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Affiliation(s)
- Rajneesh Singhal
- Department of Botany, University of Wisconsin-Madison, Madison, WI, USA
| | - Donna E Fernandez
- Department of Botany, University of Wisconsin-Madison, Madison, WI, USA
- Correspondence:
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Ries F, Carius Y, Rohr M, Gries K, Keller S, Lancaster CRD, Willmund F. Structural and molecular comparison of bacterial and eukaryotic trigger factors. Sci Rep 2017; 7:10680. [PMID: 28878399 PMCID: PMC5587573 DOI: 10.1038/s41598-017-10625-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Accepted: 08/11/2017] [Indexed: 12/04/2022] Open
Abstract
A considerably small fraction of approximately 60–100 proteins of all chloroplast proteins are encoded by the plastid genome. Many of these proteins are major subunits of complexes with central functions within plastids. In comparison with other subcellular compartments and bacteria, many steps of chloroplast protein biogenesis are not well understood. We report here on the first study of chloroplast-localised trigger factor. In bacteria, this molecular chaperone is known to associate with translating ribosomes to facilitate the folding of newly synthesized proteins. Chloroplast trigger factors of the unicellular green algae Chlamydomonas reinhardtii and the vascular land plant Arabidopsis thaliana were characterized by biophysical and structural methods and compared to the Escherichia coli isoform. We show that chloroplast trigger factor is mainly monomeric and displays only moderate stability against thermal unfolding even under mild heat-stress conditions. The global shape and conformation of these proteins were determined in solution by small-angle X-ray scattering and subsequent ab initio modelling. As observed for bacteria, plastidic trigger factors have a dragon-like structure, albeit with slightly altered domain arrangement and flexibility. This structural conservation despite low amino acid sequence homology illustrates a remarkable evolutionary robustness of chaperone conformations across various kingdoms of life.
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Affiliation(s)
- Fabian Ries
- Molecular Genetics of Eukaryotes, University of Kaiserslautern, Erwin-Schrödinger-Str. 70, 67663, Kaiserslautern, Germany
| | - Yvonne Carius
- Department of Structural Biology, Saarland University, Center of Human and Molecular Biology (ZHMB), Faculty of Medicine Building 60, 66421, Homburg, Germany
| | - Marina Rohr
- Molecular Genetics of Eukaryotes, University of Kaiserslautern, Erwin-Schrödinger-Str. 70, 67663, Kaiserslautern, Germany
| | - Karin Gries
- Molecular Genetics of Eukaryotes, University of Kaiserslautern, Erwin-Schrödinger-Str. 70, 67663, Kaiserslautern, Germany
| | - Sandro Keller
- Molecular Biophysics, University of Kaiserslautern, Erwin-Schrödinger-Str. 13, 67663, Kaiserslautern, Germany
| | - C Roy D Lancaster
- Department of Structural Biology, Saarland University, Center of Human and Molecular Biology (ZHMB), Faculty of Medicine Building 60, 66421, Homburg, Germany.
| | - Felix Willmund
- Molecular Genetics of Eukaryotes, University of Kaiserslautern, Erwin-Schrödinger-Str. 70, 67663, Kaiserslautern, Germany.
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40
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Denkert N, Schendzielorz AB, Barbot M, Versemann L, Richter F, Rehling P, Meinecke M. Cation selectivity of the presequence translocase channel Tim23 is crucial for efficient protein import. eLife 2017; 6. [PMID: 28857742 PMCID: PMC5578737 DOI: 10.7554/elife.28324] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 07/31/2017] [Indexed: 01/09/2023] Open
Abstract
Virtually all mitochondrial matrix proteins and a considerable number of inner membrane proteins carry a positively charged, N-terminal presequence and are imported by the TIM23 complex (presequence translocase) located in the inner mitochondrial membrane. The voltage-regulated Tim23 channel constitutes the actual protein-import pore wide enough to allow the passage of polypeptides with a secondary structure. In this study, we identify amino acids important for the cation selectivity of Tim23. Structure based mutants show that selectivity is provided by highly conserved, pore-lining amino acids. Mutations of these amino acid residues lead to reduced selectivity properties, reduced protein import capacity and they render the Tim23 channel insensitive to substrates. We thus show that the cation selectivity of the Tim23 channel is a key feature for substrate recognition and efficient protein import. The cells of animals, plants and other eukaryotic organisms contain compartments known as organelles that play many different roles. For example, compartments called mitochondria are responsible for supplying the chemical energy cells need to survive and grow. Two membranes surround each mitochondrion and energy is converted on the surface of the inner one. Mitochondria contain over 1,000 different proteins, most of which are produced in the main part of the cell and have to be transported into the mitochondria. A transport protein called Tim23 is part of a larger group or ‘complex’ of proteins that helps to import many other proteins into the mitochondria. This complex sits in the inner membrane, with the Tim23 protein forming a large, water-filled pore through its core that provides a route for proteins to pass through the membrane. Proteins are made of building blocks called amino acids. The proteins transported by the complex containing Tim23 all have a short chain of amino acids at one end known as an N-terminal presequence. However, it is not clear how the inside of the Tim23 channel identifies and transports this presequence to allow the right proteins to pass through the inner membrane. Denkert, Schendzielorz et al. studied the normal and mutant versions of a Tim23 channel from yeast to find out which parts of the protein are involved in detecting the N-terminal presequence after it enters the pore. The experiments show that there are several amino acids in Tim23 that play important roles in this process. Furthermore, mitochondria containing mutant Tim23 channels, that are less able to identify the N-terminal presequence, are impaired in their ability to import proteins. Tim23 proteins in humans and other organisms also contain most or all of the specific amino acids identified in this study, suggesting that the findings of Denkert, Schendzielorz et al. will also apply to other species. Furthermore, the experimental strategy used in this study could be adapted to investigate transport proteins in other cell compartments.
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Affiliation(s)
- Niels Denkert
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany
| | | | - Mariam Barbot
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany
| | - Lennart Versemann
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany
| | - Frank Richter
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany
| | - Peter Rehling
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany.,Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Göttinger Zentrum für Molekulare Biowissenschaften, Göttingen, Germany
| | - Michael Meinecke
- Department of Cellular Biochemistry, University Medical Center Göttingen, Göttingen, Germany.,Göttinger Zentrum für Molekulare Biowissenschaften, Göttingen, Germany.,European Neuroscience Institute Göttingen, Göttingen, Germany
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