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Ballabani G, Forough M, Kessler F, Shanmugabalaji V. The journey of preproteins across the chloroplast membrane systems. Front Physiol 2023; 14:1213866. [PMID: 37324391 PMCID: PMC10267391 DOI: 10.3389/fphys.2023.1213866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 05/22/2023] [Indexed: 06/17/2023] Open
Abstract
The photosynthetic capacity of chloroplasts is vital for autotrophic growth in algae and plants. The origin of the chloroplast has been explained by the endosymbiotic theory that proposes the engulfment of a cyanobacterium by an ancestral eukaryotic cell followed by the transfer of many cyanobacterial genes to the host nucleus. As a result of the gene transfer, the now nuclear-encoded proteins acquired chloroplast targeting peptides (known as transit peptides; transit peptide) and are translated as preproteins in the cytosol. Transit peptides contain specific motifs and domains initially recognized by cytosolic factors followed by the chloroplast import components at the outer and inner envelope of the chloroplast membrane. Once the preprotein emerges on the stromal side of the chloroplast protein import machinery, the transit peptide is cleaved by stromal processing peptidase. In the case of thylakoid-localized proteins, cleavage of the transit peptides may expose a second targeting signal guiding the protein to the thylakoid lumen or allow insertion into the thylakoid membrane by internal sequence information. This review summarizes the common features of targeting sequences and describes their role in routing preproteins to and across the chloroplast envelope as well as the thylakoid membrane and lumen.
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Affiliation(s)
| | | | - Felix Kessler
- *Correspondence: Felix Kessler, ; Venkatasalam Shanmugabalaji,
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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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Caspari OD, Garrido C, Law CO, Choquet Y, Wollman FA, Lafontaine I. Converting antimicrobial into targeting peptides reveals key features governing protein import into mitochondria and chloroplasts. PLANT COMMUNICATIONS 2023:100555. [PMID: 36733255 PMCID: PMC10363480 DOI: 10.1016/j.xplc.2023.100555] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 01/18/2023] [Accepted: 01/26/2023] [Indexed: 06/18/2023]
Abstract
We asked what peptide features govern targeting to the mitochondria versus the chloroplast, using antimicrobial peptides as a starting point. This approach was inspired by the endosymbiotic hypothesis that organelle-targeting peptides derive from antimicrobial amphipathic peptides delivered by the host cell, to which organelle progenitors became resistant. To explore the molecular changes required to convert antimicrobial into targeting peptides, we expressed a set of 13 antimicrobial peptides in Chlamydomonas reinhardtii. Peptides were systematically modified to test distinctive features of mitochondrion- and chloroplast-targeting peptides, and we assessed their targeting potential by following the intracellular localization and maturation of a Venus fluorescent reporter used as a cargo protein. Mitochondrial targeting can be achieved by some unmodified antimicrobial peptide sequences. Targeting to both organelles is improved by replacing lysines with arginines. Chloroplast targeting is enabled by the presence of flanking unstructured sequences, additional constraints consistent with chloroplast endosymbiosis having occurred in a cell that already contained mitochondria. If indeed targeting peptides evolved from antimicrobial peptides, then required modifications imply a temporal evolutionary scenario with an early exchange of cationic residues and a late acquisition of chloroplast-specific motifs.
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Affiliation(s)
- Oliver D Caspari
- UMR7141 (CNRS/Sorbonne Université), Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France.
| | - Clotilde Garrido
- UMR7141 (CNRS/Sorbonne Université), Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France
| | - Chris O Law
- Centre for Microscopy and Cellular Imaging, Biology Department Loyola Campus of Concordia University, 7141 Sherbrooke W., Montréal, QC H4B 1R6, Canada
| | - Yves Choquet
- UMR7141 (CNRS/Sorbonne Université), Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France
| | - Francis-André Wollman
- UMR7141 (CNRS/Sorbonne Université), Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France
| | - Ingrid Lafontaine
- UMR7141 (CNRS/Sorbonne Université), Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France.
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4
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Kim DB, Na C, Hwang I, Lee DW. Understanding protein translocation across chloroplast membranes: Translocons and motor proteins. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2023; 65:408-416. [PMID: 36223071 DOI: 10.1111/jipb.13385] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 10/11/2022] [Indexed: 06/16/2023]
Abstract
Subcellular organelles in eukaryotes are surrounded by lipid membranes. In an endomembrane system, vesicle trafficking is the primary mechanism for the delivery of organellar proteins to specific organelles. However, organellar proteins for chloroplasts, mitochondria, the nucleus, and peroxisomes that are translated in the cytosol are directly imported into their target organelles. Chloroplasts are a plant-specific organelle with outer and inner envelope membranes, a dual-membrane structure that is similar to mitochondria. Interior chloroplast proteins translated by cytosolic ribosomes are thus translocated through TOC and TIC complexes (translocons in the outer and inner envelope of chloroplasts, respectively), with stromal ATPase motor proteins playing a critical role in pulling pre-proteins through these import channels. Over the last three decades, the identity and function of TOC/TIC components and stromal motor proteins have been actively investigated, which has shed light on the action mechanisms at a molecular level. However, there remains some disagreement over the exact composition of TIC complexes and genuine stromal motor proteins. In this review, we discuss recent findings on the mechanisms by which proteins are translocated through TOC/TIC complexes and discuss future prospects for this field of research.
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Affiliation(s)
- Da Been Kim
- Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju, 61186, Korea
| | - Changhee Na
- Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju, 61186, Korea
| | - Inhwan Hwang
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, 37673, Korea
| | - Dong Wook Lee
- Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju, 61186, Korea
- Department of Bioenergy Science and Technology, Chonnam National University, Gwangju, 61186, Korea
- Kumho Life Science Laboratory, Chonnam National University, Gwangju, 61186, Korea
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5
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Structure of a TOC-TIC supercomplex spanning two chloroplast envelope membranes. Cell 2022; 185:4788-4800.e13. [PMID: 36413996 DOI: 10.1016/j.cell.2022.10.030] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2022] [Revised: 09/07/2022] [Accepted: 10/28/2022] [Indexed: 11/23/2022]
Abstract
The TOC and TIC complexes are essential translocons that facilitate the import of the nuclear genome-encoded preproteins across the two envelope membranes of chloroplast, but their exact molecular identities and assembly remain unclear. Here, we report a cryoelectron microscopy structure of TOC-TIC supercomplex from Chlamydomonas, containing a total of 14 identified components. The preprotein-conducting pore of TOC is a hybrid β-barrel co-assembled by Toc120 and Toc75, while the potential translocation path of TIC is formed by transmembrane helices from Tic20 and YlmG, rather than a classic model of Tic110. A rigid intermembrane space (IMS) scaffold bridges two chloroplast membranes, and a large hydrophilic cleft on the IMS scaffold connects TOC and TIC, forming a pathway for preprotein translocation. Our study provides structural insights into the TOC-TIC supercomplex composition, assembly, and preprotein translocation mechanism, and lays a foundation to interpret the evolutionary conservation and diversity of this fundamental translocon machinery.
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Zhao X, Higa T, Nakai M. Tic12, a 12-kDa essential component of the translocon at the inner envelope membrane of chloroplasts in Arabidopsis. THE PLANT CELL 2022; 34:4569-4582. [PMID: 35929083 PMCID: PMC9614449 DOI: 10.1093/plcell/koac240] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 07/15/2022] [Indexed: 06/15/2023]
Abstract
The complexes translocon at the outer envelope membrane of chloroplasts and translocon at the inner envelope membrane of chloroplasts (TIC) mediate preprotein translocation across the chloroplast outer and inner envelope membranes, respectively. Tic20, Tic56, Tic100, and Tic214 form a stable one-megadalton TIC whose function is essential for Arabidopsis thaliana and Chlamydomonas reinhardtii. Tic20 plays a central role in preprotein translocation by forming a protein-conducting channel. Tic56, Tic100, and Tic214 are also indispensable for TIC function, but whether other components are required for this process remain unclear. Here, we demonstrate that a 12-kDa protein named Tic12 is part of the TIC in A. thaliana and participates in preprotein translocation across the inner envelope membrane. Tic12 was tightly associated with the TIC but disassociated under high-salt conditions in combination with Triton X-100. Site-specific UV crosslinking experiments revealed that Tic12 and Tic20 directly interact with the transit peptide of a translocating preprotein. The tic12 null mutants are albino and seedling lethal, similar to the other tic null mutants. Tic12 and Tic20 were also involved in preprotein translocation in (Pisum sativum) pea chloroplasts. Thus, Tic12 is an essential constituent that forms the functional core together with Tic20 in the one-megadalton TIC.
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Affiliation(s)
- Xueyang Zhao
- Institute for Protein Research, Osaka University, Suita, 565-0871, Japan
| | - Takeshi Higa
- Institute for Protein Research, Osaka University, Suita, 565-0871, Japan
| | - Masato Nakai
- Institute for Protein Research, Osaka University, Suita, 565-0871, Japan
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7
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Rozov SM, Deineko EV. Increasing the Efficiency of the Accumulation of Recombinant Proteins in Plant Cells: The Role of Transport Signal Peptides. PLANTS (BASEL, SWITZERLAND) 2022; 11:2561. [PMID: 36235427 PMCID: PMC9572730 DOI: 10.3390/plants11192561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 09/23/2022] [Accepted: 09/26/2022] [Indexed: 06/16/2023]
Abstract
The problem with increasing the yield of recombinant proteins is resolvable using different approaches, including the transport of a target protein to cell compartments with a low protease activity. In the cell, protein targeting involves short-signal peptide sequences recognized by intracellular protein transport systems. The main systems of the protein transport across membranes of the endoplasmic reticulum and endosymbiotic organelles are reviewed here, as are the major types and structure of the signal sequences targeting proteins to the endoplasmic reticulum and its derivatives, to plastids, and to mitochondria. The role of protein targeting to certain cell organelles depending on specific features of recombinant proteins and the effect of this targeting on the protein yield are discussed, in addition to the main directions of the search for signal sequences based on their primary structure. This knowledge makes it possible not only to predict a protein localization in the cell but also to reveal the most efficient sequences with potential biotechnological utility.
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8
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Jeong J, Moon B, Hwang I, Lee DW. GREEN FLUORESCENT PROTEIN variants with enhanced folding are more efficiently imported into chloroplasts. PLANT PHYSIOLOGY 2022; 190:238-249. [PMID: 35699510 PMCID: PMC9434181 DOI: 10.1093/plphys/kiac291] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Accepted: 06/05/2022] [Indexed: 06/15/2023]
Abstract
Chloroplasts and mitochondria are subcellular organelles that evolved from cyanobacteria and α-proteobacteria, respectively. Although they have their own genomes, the majority of their proteins are encoded by nuclear genes, translated by cytosolic ribosomes, and imported via outer and inner membrane translocon complexes. The unfolding of mature regions of proteins is thought to be a prerequisite for the import of the proteins into these organelles. However, it is not fully understood how protein folding properties affect their import into these organelles. In this study, we examined the import behavior of chloroplast and mitochondrial reporters with normal green fluorescent protein (GFP) and two GFP variants with enhanced folding propensity, superfolder GFP (sfGFP) and extra-superfolder GFP (esGFP), which is folded better than sfGFP. sfGFP and esGFP were less dependent on the sequence motifs of the transit peptide (TP) and import machinery during protein import into Arabidopsis (Arabidopsis thaliana) chloroplasts, compared with normal GFP. sfGFP and esGFP were efficiently imported into chloroplasts by a mutant TP with an alanine substitution in the N-terminal MLM motif, whereas the same mutant TP showed a defect in importing normal GFP into chloroplasts. Moreover, sfGFP and esGFP were efficiently imported into plastid protein import 2 (ppi2) and heat shock protein 93-V (hsp93-V) plants, which have mutations in atToc159 and Hsp93-V, respectively. In contrast, the presequence-mediated mitochondrial import of sfGFP and esGFP was severely impaired. Based on these results, we propose that the chloroplast import machinery is more tolerant to different folding states of preproteins, whereas the mitochondrial machinery is more specialized in the translocation of unfolded preproteins.
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Affiliation(s)
- Jinseung Jeong
- Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju 61186, South Korea
| | - Byeongho Moon
- Department of Life Sciences, Pohang University of Science and Technology, Pohang 37673, South Korea
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9
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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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10
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Doyle MT, Bernstein HD. Function of the Omp85 Superfamily of Outer Membrane Protein Assembly Factors and Polypeptide Transporters. Annu Rev Microbiol 2022; 76:259-279. [PMID: 35650668 DOI: 10.1146/annurev-micro-033021-023719] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The Omp85 protein superfamily is found in the outer membrane (OM) of all gram-negative bacteria and eukaryotic organelles of bacterial origin. Members of the family catalyze both the membrane insertion of β-barrel proteins and the translocation of proteins across the OM. Although the mechanism(s) by which these proteins function is unclear, striking new insights have emerged from recent biochemical and structural studies. In this review we discuss the entire Omp85 superfamily but focus on the function of the best-studied member, BamA, which is an essential and highly conserved component of the bacterial barrel assembly machinery (BAM). Because BamA has multiple functions that overlap with those of other Omp85 proteins, it is likely the prototypical member of the Omp85 superfamily. Furthermore, BamA has become a protein of great interest because of the recent discovery of small-molecule inhibitors that potentially represent an important new class of antibiotics. Expected final online publication date for the Annual Review of Microbiology, Volume 76 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Matthew Thomas Doyle
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA; ,
| | - Harris D Bernstein
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA; ,
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11
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Jeong J, Hwang I, Lee DW. Functional Organization of Sequence Motifs in Diverse Transit Peptides of Chloroplast Proteins. Front Physiol 2021; 12:795156. [PMID: 34880786 PMCID: PMC8645953 DOI: 10.3389/fphys.2021.795156] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Accepted: 10/28/2021] [Indexed: 11/17/2022] Open
Abstract
Although the chloroplasts in plants are characterized by an inherent genome, the chloroplast proteome is composed of proteins encoded by not only the chloroplast genome but also the nuclear genome. Nuclear-encoded chloroplast proteins are synthesized on cytosolic ribosomes and post-translationally targeted to the chloroplasts. In the latter process, an N-terminal cleavable transit peptide serves as a targeting signal required for the import of nuclear-encoded chloroplast interior proteins. This import process is mediated via an interaction between the sequence motifs in transit peptides and the components of the TOC/TIC (translocon at the outer/inner envelope of chloroplasts) translocons. Despite a considerable diversity in primary structures, several common features have been identified among transit peptides, including N-terminal moderate hydrophobicity, multiple proline residues dispersed throughout the transit peptide, preferential usage of basic residues over acidic residues, and an absence of N-terminal arginine residues. In this review, we will recapitulate and discuss recent progress in our current understanding of the functional organization of sequence elements commonly present in diverse transit peptides, which are essential for the multi-step import of chloroplast proteins.
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Affiliation(s)
- Jinseung Jeong
- Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju, South Korea
| | - Inhwan Hwang
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, South Korea
| | - Dong Wook Lee
- Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju, South Korea.,Department of Bioenergy Science and Technology, Chonnam National University, Gwangju, South Korea
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12
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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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13
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Yang F, Xiao K, Pan H, Liu J. Chloroplast: The Emerging Battlefield in Plant-Microbe Interactions. FRONTIERS IN PLANT SCIENCE 2021; 12:637853. [PMID: 33747017 PMCID: PMC7966814 DOI: 10.3389/fpls.2021.637853] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Accepted: 01/28/2021] [Indexed: 05/08/2023]
Abstract
Higher plants and some algae convert the absorbed light into chemical energy through one of the most important organelles, chloroplast, for photosynthesis and store it in the form of organic compounds to supply their life activities. However, more and more studies have shown that the role of chloroplasts is more than a factory for photosynthesis. In the process of light conversion to chemical energy, any damage to the components of chloroplast may affect the photosynthesis efficiency and promote the production of by-products, reactive oxygen species, that are mainly produced in the chloroplasts. Substantial evidence show that chloroplasts are also involved in the battle of plants and microbes. Chloroplasts are important in integrating a variety of external environmental stimuli and regulate plant immune responses by transmitting signals to the nucleus and other cell compartments through retrograde signaling pathways. Besides, chloroplasts can also regulate the biosynthesis and signal transduction of phytohormones, including salicylic acid and jasmonic acid, to affect the interaction between the plants and microbes. Since chloroplasts play such an important role in plant immunity, correspondingly, chloroplasts have become the target of pathogens. Different microbial pathogens target the chloroplast and affect its functions to promote their colonization in the host plants.
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Affiliation(s)
| | | | | | - Jinliang Liu
- College of Plant Sciences, Jilin University, Changchun, China
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14
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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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15
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Christian RW, Hewitt SL, Nelson G, Roalson EH, Dhingra A. Plastid transit peptides-where do they come from and where do they all belong? Multi-genome and pan-genomic assessment of chloroplast transit peptide evolution. PeerJ 2020; 8:e9772. [PMID: 32913678 PMCID: PMC7456531 DOI: 10.7717/peerj.9772] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 07/30/2020] [Indexed: 01/22/2023] Open
Abstract
Subcellular relocalization of proteins determines an organism's metabolic repertoire and thereby its survival in unique evolutionary niches. In plants, the plastid and its various morphotypes import a large and varied number of nuclear-encoded proteins to orchestrate vital biochemical reactions in a spatiotemporal context. Recent comparative genomics analysis and high-throughput shotgun proteomics data indicate that there are a large number of plastid-targeted proteins that are either semi-conserved or non-conserved across different lineages. This implies that homologs are differentially targeted across different species, which is feasible only if proteins have gained or lost plastid targeting peptides during evolution. In this study, a broad, multi-genome analysis of 15 phylogenetically diverse genera and in-depth analyses of pangenomes from Arabidopsis and Brachypodium were performed to address the question of how proteins acquire or lose plastid targeting peptides. The analysis revealed that random insertions or deletions were the dominant mechanism by which novel transit peptides are gained by proteins. While gene duplication was not a strict requirement for the acquisition of novel subcellular targeting, 40% of novel plastid-targeted genes were found to be most closely related to a sequence within the same genome, and of these, 30.5% resulted from alternative transcription or translation initiation sites. Interestingly, analysis of the distribution of amino acids in the transit peptides of known and predicted chloroplast-targeted proteins revealed monocot and eudicot-specific preferences in residue distribution.
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Affiliation(s)
- Ryan W. Christian
- Molecular Plant Sciences, Washington State University, Pullman, WA, USA
| | - Seanna L. Hewitt
- Molecular Plant Sciences, Washington State University, Pullman, WA, USA
| | - Grant Nelson
- Molecular Plant Sciences, Washington State University, Pullman, WA, USA
| | - Eric H. Roalson
- Molecular Plant Sciences, Washington State University, Pullman, WA, USA
- School of Biological Sciences, Washington State University, Pullman, WA, USA
| | - Amit Dhingra
- Molecular Plant Sciences, Washington State University, Pullman, WA, USA
- Department of Horticulture, Washington State University, Pullman, WA, USA
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16
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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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17
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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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18
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Nakai M. Reply: The Revised Model for Chloroplast Protein Import. THE PLANT CELL 2020; 32:543-546. [PMID: 31937598 PMCID: PMC7054026 DOI: 10.1105/tpc.19.00821] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Revised: 01/10/2020] [Accepted: 01/13/2020] [Indexed: 05/17/2023]
Affiliation(s)
- Masato Nakai
- Institute for Protein Research Osaka University Suita 565-0871, Japan
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19
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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
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20
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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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21
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Ganesan I, Theg SM. Structural considerations of folded protein import through the chloroplast TOC/TIC translocons. FEBS Lett 2019; 593:565-572. [PMID: 30775779 DOI: 10.1002/1873-3468.13342] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Revised: 02/13/2019] [Accepted: 02/15/2019] [Indexed: 11/11/2022]
Abstract
Protein import into chloroplasts is carried out by the protein translocons at the outer and inner envelope membranes (TOC and TIC). Detailed structures for these translocons are lacking, with only a low-resolution TOC complex structure available. Recently, we showed that the TOC/TIC translocons can import folded proteins, a rather unique feat for a coupled double membrane system. We also determined the maximum functional TOC/TIC pore size to be 30-35 Å. Here, we discuss how such large pores could form and compare the structural dynamics of the pore-forming Toc75 subunit to its bacterial/mitochondrial Omp85 family homologs. We put forward structural models that can be empirically tested and also briefly review the pore dynamics of other protein translocons with known structures.
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Affiliation(s)
- Iniyan Ganesan
- Department of Plant Biology, University of California Davis, CA, USA
| | - Steven M Theg
- Department of Plant Biology, University of California Davis, CA, USA
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22
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Yang X, Li Y, Qi M, Liu Y, Li T. Targeted Control of Chloroplast Quality to Improve Plant Acclimation: From Protein Import to Degradation. FRONTIERS IN PLANT SCIENCE 2019; 10:958. [PMID: 31402924 PMCID: PMC6670758 DOI: 10.3389/fpls.2019.00958] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2019] [Accepted: 07/09/2019] [Indexed: 05/07/2023]
Abstract
The chloroplast is an important energy-producing organelle acting as an environmental sensor for the plant cell. The normal turnover of the entire damaged chloroplast and its specific components is required for efficient photosynthesis and other metabolic reactions under stress conditions. Nuclear-encoded proteins must be imported into the chloroplast through different membrane transport complexes, and the orderly protein import plays an important role in plant adaptive regulation. Under adverse environmental conditions, the damaged chloroplast or its specific components need to be degraded efficiently to ensure normal cell function. In this review, we discuss the molecular mechanism of protein import and degradation in the chloroplast. Specifically, quality control of chloroplast from protein import to degradation and associated regulatory pathways are discussed to better understand how plants adapt to environmental stress by fine-tuning chloroplast homeostasis, which will benefit breeding approaches to improve crop yield.
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23
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Tee EE. Tic-Tac-Toe: How TIC and TOC Coordinate Getting Proteins across the Line. THE PLANT CELL 2018; 30:1666-1667. [PMID: 30111614 PMCID: PMC6139676 DOI: 10.1105/tpc.18.00618] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
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