1
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Liu H, Li Y, Peng T, Xue S. Transmembrane potential, an indicator in situ reporting cellular senescence and stress response in plant tissues. PLANT METHODS 2023; 19:27. [PMID: 36945027 PMCID: PMC10029184 DOI: 10.1186/s13007-023-01006-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 03/10/2023] [Indexed: 06/18/2023]
Abstract
BACKGROUND Plant cells usually sustain a stable membrane potential due to influx and/or efflux of charged ions across plasma membrane. With the growth and development of plants, different tissues and cells undergo systemic or local programmed decline. Whether the membrane potential of plasma membrane could report senescence signal of plant tissues and cells is unclear. RESULTS We applied a maneuverable transmembrane potential (TMP) detection method with patch-clamp setup to examine the senescence signal of leaf tissue cells in situ over the whole life cycle in Arabidopsis thaliana. The data showed that the TMPs of plant tissues and cells were varied at different growth stages, and the change of TMP was higher at the vegetative growth stage than at the reproductive stage of plant growth. The distinct change of TMP was detectable between the normal and the senescent tissues and cells in several plant species. Moreover, diverse abiotic stimuli, such as heat stress, hyperpolarized the TMP in a short time, followed by depolarized membrane potential with the senescence occurring. We further examined the TMP of plant chloroplasts, which also indicates the senescence signal in organelles. CONCLUSIONS This convenient TMP detection method can report the senescence signal of plant tissues and cells, and can also indicate the potential of plant tolerance to environmental stress.
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Affiliation(s)
- Hai Liu
- College of Life Science and Technology, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, 430070, China
| | - Yufei Li
- College of Life Science and Technology, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, 430070, China
| | - Ting Peng
- College of Agriculture, Guizhou University, Guiyang, 550025, China
| | - Shaowu Xue
- College of Life Science and Technology, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, 430070, China.
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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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Architecture of chloroplast TOC-TIC translocon supercomplex. Nature 2023; 615:349-357. [PMID: 36702157 DOI: 10.1038/s41586-023-05744-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 01/19/2023] [Indexed: 01/27/2023]
Abstract
Chloroplasts rely on the translocon complexes in the outer and inner envelope membranes (the TOC and TIC complexes, respectively) to import thousands of different nuclear-encoded proteins from the cytosol1-4. Although previous studies indicated that the TOC and TIC complexes may assemble into larger supercomplexes5-7, the overall architectures of the TOC-TIC supercomplexes and the mechanism of preprotein translocation are unclear. Here we report the cryo-electron microscopy structure of the TOC-TIC supercomplex from Chlamydomonas reinhardtii. The major subunits of the TOC complex (Toc75, Toc90 and Toc34) and TIC complex (Tic214, Tic20, Tic100 and Tic56), three chloroplast translocon-associated proteins (Ctap3, Ctap4 and Ctap5) and three newly identified small inner-membrane proteins (Simp1-3) have been located in the supercomplex. As the largest protein, Tic214 traverses the inner membrane, the intermembrane space and the outer membrane, connecting the TOC complex with the TIC proteins. An inositol hexaphosphate molecule is located at the Tic214-Toc90 interface and stabilizes their assembly. Four lipid molecules are located within or above an inner-membrane funnel formed by Tic214, Tic20, Simp1 and Ctap5. Multiple potential pathways found in the TOC-TIC supercomplex may support translocation of different substrate preproteins into chloroplasts.
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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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Gao LL, Hong ZH, Wang Y, Wu GZ. Chloroplast proteostasis: A story of birth, life, and death. PLANT COMMUNICATIONS 2023; 4:100424. [PMID: 35964157 PMCID: PMC9860172 DOI: 10.1016/j.xplc.2022.100424] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 08/02/2022] [Accepted: 08/10/2022] [Indexed: 06/02/2023]
Abstract
Protein homeostasis (proteostasis) is a dynamic balance of protein synthesis and degradation. Because of the endosymbiotic origin of chloroplasts and the massive transfer of their genetic information to the nucleus of the host cell, many protein complexes in the chloroplasts are constituted from subunits encoded by both genomes. Hence, the proper function of chloroplasts relies on the coordinated expression of chloroplast- and nucleus-encoded genes. The biogenesis and maintenance of chloroplast proteostasis are dependent on synthesis of chloroplast-encoded proteins, import of nucleus-encoded chloroplast proteins from the cytosol, and clearance of damaged or otherwise undesired "old" proteins. This review focuses on the regulation of chloroplast proteostasis, its interaction with proteostasis of the cytosol, and its retrograde control over nuclear gene expression. We also discuss significant issues and perspectives for future studies and potential applications for improving the photosynthetic performance and stress tolerance of crops.
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Affiliation(s)
- Lin-Lin Gao
- Shanghai Collaborative Innovation Center of Agri-Seeds, School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Joint Center for Single Cell Biology, School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Zheng-Hui Hong
- Shanghai Collaborative Innovation Center of Agri-Seeds, School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Joint Center for Single Cell Biology, School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Yinsong Wang
- Shanghai Collaborative Innovation Center of Agri-Seeds, School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Joint Center for Single Cell Biology, School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Guo-Zhang Wu
- Shanghai Collaborative Innovation Center of Agri-Seeds, School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Joint Center for Single Cell Biology, School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
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6
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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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Yu H, Wang Q, Zhang Z, Wu T, Yang X, Zhu X, Ye Y, Leng J, Yang S, Feng X. Genetic Mapping of the Gmpgl3 Mutant Reveals the Function of GmTic110a in Soybean Chloroplast Development. FRONTIERS IN PLANT SCIENCE 2022; 13:892077. [PMID: 35693168 PMCID: PMC9178232 DOI: 10.3389/fpls.2022.892077] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Accepted: 05/09/2022] [Indexed: 06/15/2023]
Abstract
The generation of oxygen and organic matter in plants mainly depends on photosynthesis, which directly affects plant growth and development. The chloroplast is the main organelle in which photosynthesis occurs. In this study, a Glycine max pale green leaf 3-1 (Gmpgl3-1) mutant was isolated from the soybean mutagenized population. The Gmpgl3-1 mutant presented with decreased chlorophyll contents, reduced chloroplast stroma thylakoids, reduced yields, and decreased numbers of pods per plant. Bulked segregant analysis (BSA) together with map-based cloning revealed a single-nucleotide non-synonymous mutation at the 341st nucleotide of the first exon of the chloroplast development-related GmTic110a gene. The phenotype of the knockout plants was the same as that of the mutant. The GmTic110a gene was highly expressed in the leaves at various developmental stages, and its protein was localized to the inner chloroplast membrane. Split luciferase complementation assays and coimmunoprecipitation (co-IP) experiments revealed that GmTic110a interacted with GmTic20, GmTic40a, and GmTic40b in tobacco leaves. These results indicated that the GmTic110a gene plays an important role in chloroplast development.
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Affiliation(s)
- Hui Yu
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
| | - Qiushi Wang
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
| | - Zhirui Zhang
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
- College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Tao Wu
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
- College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Xinjing Yang
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
- College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Xiaobin Zhu
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
- College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Yongheng Ye
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
- College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Jiantian Leng
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
| | - Suxin Yang
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
| | - Xianzhong Feng
- Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, China
- College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, China
- Zhejiang Lab, Hangzhou, China
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8
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Chloroplast Protein Tic55 Involved in Dark-Induced Senescence through AtbHLH/AtWRKY-ANAC003 Controlling Pathway of Arabidopsis thaliana. Genes (Basel) 2022; 13:genes13020308. [PMID: 35205352 PMCID: PMC8872272 DOI: 10.3390/genes13020308] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 01/26/2022] [Accepted: 02/02/2022] [Indexed: 12/04/2022] Open
Abstract
The chloroplast comprises the outer and inner membranes that are composed of the translocon protein complexes Toc and Tic (translocon at the outer/inner envelope membrane of chloroplasts), respectively. Tic55, a chloroplast Tic protein member, was shown to be not vital for functional protein import in Arabidopsis from previous studies. Instead, Tic55 was revealed to be a dark-induced senescence-related protein in our earlier study. To explore whether Tic55 elicits other biological functions, a tic55-II knockout mutant (SALK_086048) was characterized under different stress treatments. Abiotic stress conditions, such as cold, heat, and high osmotic pressure, did not cause visible effects on tic55-II mutant plant, when compared to the wild type (WT). In contrast, senescence was induced in the individually darkened leaves (IDLs), resulting in the differential expression of the senescence-related genes PEROXISOME DEFECTIVE 1 (PED1), BLUE COPPER-BINDING PROTEIN (BCB), SENESCENCE 1 (SEN1), and RUBISCO SMALL SUBUNIT GENE 2B (RBCS2B). The absence of Tic55 in tic55-II knockout mutant inhibited expression of the senescence-related genes PED1, BCB, and SEN1 at different stages of dark adaptation, while causing stimulation of RBCS2B gene expression at an early stage of dark response. Finally, yeast one-hybrid assays located the ANAC003 promoter region with cis-acting elements are responsible for binding to the different AtbHLH proteins, thereby causing the transactivation of an HIS3 reporter gene. ANAC003 was shown previously as a senescence-related protein and its activation would lead to expression of senescence-associated genes (SAGs), resulting in plant senescence. Thus, we propose a hypothetical model in which three signaling pathways may be involved in controlling the expression of ANAC003, followed by expression of SAGs that in turn leads to leaf senescence in Arabidopsis by this study and previous data.
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9
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Shrestha B, Gilbert LE, Ruhlman TA, Jansen RK. Rampant Nuclear Transfer and Substitutions of Plastid Genes in Passiflora. Genome Biol Evol 2021; 12:1313-1329. [PMID: 32539116 PMCID: PMC7488351 DOI: 10.1093/gbe/evaa123] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/09/2020] [Indexed: 12/15/2022] Open
Abstract
Gene losses in plastid genomes (plastomes) are often accompanied by functional transfer to the nucleus or substitution of an alternative nuclear-encoded gene. Despite the highly conserved gene content in plastomes of photosynthetic land plants, recent gene loss events have been documented in several disparate angiosperm clades. Among these lineages, Passiflora lacks several essential ribosomal genes, rps7, rps16, rpl20, rpl22, and rpl32, the two largest plastid genes, ycf1 and ycf2, and has a highly divergent rpoA. Comparative transcriptome analyses were performed to determine the fate of the missing genes in Passiflora. Putative functional transfers of rps7, rpl22, and rpl32 to nucleus were detected, with the nuclear transfer of rps7, representing a novel event in angiosperms. Plastid-encoded rps7 was transferred into the intron of a nuclear-encoded plastid-targeted thioredoxin m-type gene, acquiring its plastid transit peptide (TP). Plastid rpl20 likely experienced a novel substitution by a duplicated, nuclear-encoded mitochondrial-targeted rpl20 that has a similar gene structure. Additionally, among rosids, evidence for a third independent transfer of rpl22 in Passiflora was detected that gained a TP from a nuclear gene containing an organelle RNA recognition motif. Nuclear transcripts representing rpoA, ycf1, and ycf2 were not detected. Further analyses suggest that the divergent rpoA remains functional and that the gene is under positive or purifying selection in different clades. Comparative analyses indicate that alternative translocon and motor protein complexes may have substituted for the loss of ycf1 and ycf2 in Passiflora.
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Affiliation(s)
- Bikash Shrestha
- Department of Integrative Biology, University of Texas, Austin
| | - Lawrence E Gilbert
- Faculty of Science, Department of Biological Sciences, Centre of Excellence in Bionanoscience Research, King Abdulaziz University, Jeddah, Saudi Arabia
| | | | - Robert K Jansen
- Department of Integrative Biology, University of Texas, Austin.,Faculty of Science, Department of Biological Sciences, Centre of Excellence in Bionanoscience Research, King Abdulaziz University, Jeddah, Saudi Arabia
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10
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Miyazaki S, Chitama BYA, Kagaya W, Lucky AB, Zhu X, Yahata K, Morita M, Takashima E, Tsuboi T, Kaneko O. Plasmodium falciparum SURFIN 4.1 forms an intermediate complex with PTEX components and Pf113 during export to the red blood cell. Parasitol Int 2021; 83:102358. [PMID: 33901679 DOI: 10.1016/j.parint.2021.102358] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 04/08/2021] [Accepted: 04/14/2021] [Indexed: 02/04/2023]
Abstract
Plasmodium falciparum malaria parasites export several hundred proteins to the cytoplasm of infected red blood cells (RBCs) to modify the cell environment suitable for their growth. A Plasmodium translocon of exported proteins (PTEX) is necessary for both soluble and integral membrane proteins to cross the parasitophorous vacuole (PV) membrane surrounding the parasite inside the RBC. However, the molecular composition of the translocation complex for integral membrane proteins is not fully characterized, especially at the parasite plasma membrane. To examine the translocation complex, here we used mini-SURFIN4.1, consisting of a short N-terminal region, a transmembrane region, and a cytoplasmic region of an exported integral membrane protein SURFIN4.1. We found that mini-SURFIN4.1 forms a translocation intermediate complex with core PTEX components, EXP2, HSP101, and PTEX150. We also found that several proteins are exposed to the PV space, including Pf113, an uncharacterized PTEX-associated protein. We determined that Pf113 localizes in dense granules at the merozoite stage and on the parasite periphery after RBC invasion. Using an inducible translocon-clogged mini-SURFIN4.1, we found that a stable translocation intermediate complex forms at the parasite plasma membrane and contains EXP2 and a processed form of Pf113. These results suggest a potential role of Pf113 for the translocation step of mini-SURFIN4.1, providing further insights into the translocation mechanisms for parasite integral membrane proteins.
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Affiliation(s)
- Shinya Miyazaki
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | - Ben-Yeddy Abel Chitama
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan; Program for Nurturing Global Leaders in Tropical and Emerging Infectious Diseases, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
| | - Wataru Kagaya
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan; Department of Environmental Parasitology, Graduate School of Tokyo Medical and Dental University, Tokyo, Japan
| | - Amuza Byaruhanga Lucky
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan; Program for Nurturing Global Leaders in Tropical and Emerging Infectious Diseases, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
| | - Xiaotong Zhu
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | - Kazuhide Yahata
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | - Masayuki Morita
- Division of Malaria Research, Proteo-Science Center, Ehime University, Ehime, Japan
| | - Eizo Takashima
- Division of Malaria Research, Proteo-Science Center, Ehime University, Ehime, Japan
| | - Takafumi Tsuboi
- Division of Malaria Research, Proteo-Science Center, Ehime University, Ehime, Japan
| | - Osamu Kaneko
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan; Program for Nurturing Global Leaders in Tropical and Emerging Infectious Diseases, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
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11
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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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12
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Ramundo S, Asakura Y, Salomé PA, Strenkert D, Boone M, Mackinder LCM, Takafuji K, Dinc E, Rahire M, Crèvecoeur M, Magneschi L, Schaad O, Hippler M, Jonikas MC, Merchant S, Nakai M, Rochaix JD, Walter P. Coexpressed subunits of dual genetic origin define a conserved supercomplex mediating essential protein import into chloroplasts. Proc Natl Acad Sci U S A 2020; 117:32739-32749. [PMID: 33273113 PMCID: PMC7768757 DOI: 10.1073/pnas.2014294117] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
In photosynthetic eukaryotes, thousands of proteins are translated in the cytosol and imported into the chloroplast through the concerted action of two translocons-termed TOC and TIC-located in the outer and inner membranes of the chloroplast envelope, respectively. The degree to which the molecular composition of the TOC and TIC complexes is conserved over phylogenetic distances has remained controversial. Here, we combine transcriptomic, biochemical, and genetic tools in the green alga Chlamydomonas (Chlamydomonas reinhardtii) to demonstrate that, despite a lack of evident sequence conservation for some of its components, the algal TIC complex mirrors the molecular composition of a TIC complex from Arabidopsis thaliana. The Chlamydomonas TIC complex contains three nuclear-encoded subunits, Tic20, Tic56, and Tic100, and one chloroplast-encoded subunit, Tic214, and interacts with the TOC complex, as well as with several uncharacterized proteins to form a stable supercomplex (TIC-TOC), indicating that protein import across both envelope membranes is mechanistically coupled. Expression of the nuclear and chloroplast genes encoding both known and uncharacterized TIC-TOC components is highly coordinated, suggesting that a mechanism for regulating its biogenesis across compartmental boundaries must exist. Conditional repression of Tic214, the only chloroplast-encoded subunit in the TIC-TOC complex, impairs the import of chloroplast proteins with essential roles in chloroplast ribosome biogenesis and protein folding and induces a pleiotropic stress response, including several proteins involved in the chloroplast unfolded protein response. These findings underscore the functional importance of the TIC-TOC supercomplex in maintaining chloroplast proteostasis.
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Affiliation(s)
- Silvia Ramundo
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
- Howard Hughes Medical Institute, Chevy Chase, MD 20815
| | - Yukari Asakura
- Laboratory of Organelle Biology, Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Patrice A Salomé
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095
| | - Daniela Strenkert
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095
| | - Morgane Boone
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143
- Howard Hughes Medical Institute, Chevy Chase, MD 20815
| | - Luke C M Mackinder
- Department of Biology, University of York, York YO10 5DD, United Kingdom
| | - Kazuaki Takafuji
- Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
| | - Emine Dinc
- Department of Molecular Biology, University of Geneva, Geneva CH-1211, Switzerland
- Department of Plant Biology, University of Geneva, Geneva CH-1211, Switzerland
| | - Michèle Rahire
- Department of Molecular Biology, University of Geneva, Geneva CH-1211, Switzerland
- Department of Plant Biology, University of Geneva, Geneva CH-1211, Switzerland
| | - Michèle Crèvecoeur
- Department of Molecular Biology, University of Geneva, Geneva CH-1211, Switzerland
- Department of Plant Biology, University of Geneva, Geneva CH-1211, Switzerland
| | - Leonardo Magneschi
- Institute of Plant Biology and Biotechnology, University of Münster, Münster 48143, Germany
| | - Olivier Schaad
- Department of Biochemistry, University of Geneva, Geneva CH-1211, Switzerland
| | - Michael Hippler
- Institute of Plant Biology and Biotechnology, University of Münster, Münster 48143, Germany
- Institute of Plant Science and Resources, Okayama University, Kurashiki 710-0046, Japan
| | - Martin C Jonikas
- Department of Molecular Biology, Princeton University, Princeton, NJ 08540
- Howard Hughes Medical Institute, Chevy Chase, MD 20815
| | - Sabeeha Merchant
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095
| | - Masato Nakai
- Laboratory of Organelle Biology, Institute for Protein Research, Osaka University, Osaka 565-0871, Japan;
| | - Jean-David Rochaix
- Department of Molecular Biology, University of Geneva, Geneva CH-1211, Switzerland;
- Department of Plant Biology, University of Geneva, Geneva CH-1211, Switzerland
| | - Peter Walter
- Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143;
- Howard Hughes Medical Institute, Chevy Chase, MD 20815
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13
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Hakimi H, Templeton TJ, Sakaguchi M, Yamagishi J, Miyazaki S, Yahata K, Uchihashi T, Kawazu SI, Kaneko O, Asada M. Novel Babesia bovis exported proteins that modify properties of infected red blood cells. PLoS Pathog 2020; 16:e1008917. [PMID: 33017449 PMCID: PMC7561165 DOI: 10.1371/journal.ppat.1008917] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 10/15/2020] [Accepted: 08/20/2020] [Indexed: 11/19/2022] Open
Abstract
Babesia bovis causes a pathogenic form of babesiosis in cattle. Following invasion of red blood cells (RBCs) the parasite extensively modifies host cell structural and mechanical properties via the export of numerous proteins. Despite their crucial role in virulence and pathogenesis, such proteins have not been comprehensively characterized in B. bovis. Here we describe the surface biotinylation of infected RBCs (iRBCs), followed by proteomic analysis. We describe a multigene family (mtm) that encodes predicted multi-transmembrane integral membrane proteins which are exported and expressed on the surface of iRBCs. One mtm gene was downregulated in blasticidin-S (BS) resistant parasites, suggesting an association with BS uptake. Induced knockdown of a novel exported protein encoded by BBOV_III004280, named VESA export-associated protein (BbVEAP), resulted in a decreased growth rate, reduced RBC surface ridge numbers, mis-localized VESA1, and abrogated cytoadhesion to endothelial cells, suggesting that BbVEAP is a novel virulence factor for B. bovis.
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Affiliation(s)
- Hassan Hakimi
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
- National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan
- * E-mail: (HH); (MA)
| | - Thomas J. Templeton
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | - Miako Sakaguchi
- Central Laboratory, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | - Junya Yamagishi
- Division of Collaboration and Education, Research Center for Zoonosis Control, Hokkaido University, Sapporo, Japan
- International Collaboration Unit, Research Center for Zoonosis Control, Hokkaido University, Sapporo, Japan
| | - Shinya Miyazaki
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | - Kazuhide Yahata
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | | | - Shin-ichiro Kawazu
- National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan
| | - Osamu Kaneko
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
| | - Masahito Asada
- Department of Protozoology, Institute of Tropical Medicine (NEKKEN), Nagasaki University, Nagasaki, Japan
- National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan
- * E-mail: (HH); (MA)
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14
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Pentatricopeptide repeat protein MID1 modulates nad2 intron 1 splicing and Arabidopsis development. Sci Rep 2020; 10:2008. [PMID: 32029763 PMCID: PMC7005036 DOI: 10.1038/s41598-020-58495-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 01/15/2020] [Indexed: 12/13/2022] Open
Abstract
As one of the best-studied RNA binding proteins in plant, pentatricopeptide repeats (PPRs) protein are mainly targeted to mitochondria and/or chloroplasts for RNA processing to regulate the biogenesis and function of the organelles, but its molecular mechanism and role in development remain to be further revealed. Here, we identified a mitochondria-localized P-type small PPR protein, MITOCHONDRION-MEDIATED GROWTH DEFECT 1 (MID1) that is crucial for Arabidopsis development. Mutation in MID1 causes retarded embryo development and stunted plant growth with defects in cell expansion and proliferation. Molecular experiments showed that MID1 is required for the splicing of the nad2 intron 1 in mitochondria. Consistently, mid1 plants display significant reduction in the abundance and activity of mitochondrial respiration complex I, accompanied by abnormal mitochondrial morphology and energy metabolism. Furthermore, MID1 is associated with other trans-factors involved in NICOTINAMIDE ADENINE DINUCLEOTIDE HYDROGEN (NADH) DEHYDROGENASE SUBUNIT 2 (nad2) intron 1 splicing, and interacts directly with itself and MITOCHONDRIAL STABILITY FACTOR 1 (MTSF1). This suggests that MID1 most likely functions as a dimer for nad2 intron 1 splicing. Together, we characterized a novel PPR protein MID1 for nad2 intron 1 splicing.
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15
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Novák Vanclová AMG, Zoltner M, Kelly S, Soukal P, Záhonová K, Füssy Z, Ebenezer TE, Lacová Dobáková E, Eliáš M, Lukeš J, Field MC, Hampl V. Metabolic quirks and the colourful history of the Euglena gracilis secondary plastid. THE NEW PHYTOLOGIST 2020; 225:1578-1592. [PMID: 31580486 DOI: 10.1111/nph.16237] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Accepted: 09/25/2019] [Indexed: 05/20/2023]
Abstract
Euglena spp. are phototrophic flagellates with considerable ecological presence and impact. Euglena gracilis harbours secondary green plastids, but an incompletely characterised proteome precludes accurate understanding of both plastid function and evolutionary history. Using subcellular fractionation, an improved sequence database and MS we determined the composition, evolutionary relationships and hence predicted functions of the E. gracilis plastid proteome. We confidently identified 1345 distinct plastid protein groups and found that at least 100 proteins represent horizontal acquisitions from organisms other than green algae or prokaryotes. Metabolic reconstruction confirmed previously studied/predicted enzymes/pathways and provided evidence for multiple unusual features, including uncoupling of carotenoid and phytol metabolism, a limited role in amino acid metabolism, and dual sets of the SUF pathway for FeS cluster assembly, one of which was acquired by lateral gene transfer from Chlamydiae. Plastid paralogues of trafficking-associated proteins potentially mediating fusion of transport vesicles with the outermost plastid membrane were identified, together with derlin-related proteins, potential translocases across the middle membrane, and an extremely simplified TIC complex. The Euglena plastid, as the product of many genomes, combines novel and conserved features of metabolism and transport.
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Affiliation(s)
| | - Martin Zoltner
- Faculty of Science, Charles University, BIOCEV, Vestec, 252 50, Czechia
- School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Steven Kelly
- Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK
| | - Petr Soukal
- Faculty of Science, Charles University, BIOCEV, Vestec, 252 50, Czechia
| | - Kristína Záhonová
- Faculty of Science, Charles University, BIOCEV, Vestec, 252 50, Czechia
- Faculty of Science, University of Ostrava, Ostrava, 710 00, Czechia
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, 370 05, Czechia
| | - Zoltán Füssy
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, 370 05, Czechia
| | - ThankGod E Ebenezer
- School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK
| | - Eva Lacová Dobáková
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, 370 05, Czechia
| | - Marek Eliáš
- Faculty of Science, University of Ostrava, Ostrava, 710 00, Czechia
| | - Julius Lukeš
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, 370 05, Czechia
- Faculty of Science, University of South Bohemia, České Budějovice, 370 05, Czechia
| | - Mark C Field
- School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, 370 05, Czechia
| | - Vladimír Hampl
- Faculty of Science, Charles University, BIOCEV, Vestec, 252 50, Czechia
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16
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Chen Z, Wang X, Li S, Yao J, Shao Z, Duan D. Verification of the Saccharina japonica Translocon Tic20 and its Localization in the Chloroplast Membrane in Diatoms. Int J Mol Sci 2019; 20:E4000. [PMID: 31426420 PMCID: PMC6720183 DOI: 10.3390/ijms20164000] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 08/01/2019] [Accepted: 08/15/2019] [Indexed: 12/21/2022] Open
Abstract
Tic20 is an important translocon protein that plays a role in protein transport in the chloroplast. The sequence of Tic20 was determined in the lower brown alga Saccharina japonica. Structural analysis of SjTic20 revealed a noncanonical structure consisting of an N-terminal non-cyanobacterium-originated EF-hand domain (a helix-loop-helix structural domain) and a C-terminal cyanobacterium-originated Tic20 domain. Subcellular localization and transmembrane analysis indicated that SjTic20 featured an "M"-type Nin-Cin-terminal orientation, with four transmembrane domains in the innermost membrane of the chloroplast in the microalga Phaeodactylum tricornutum, and the EF-hand domain was entirely extruded into the chloroplast stroma. Our study provides information on the structure, localization, and topological features of SjTic20, and further functional analysis of SjTic20 in S. japonica is needed.
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Affiliation(s)
- Zhihang Chen
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
- University of Chinese Academy of Sciences, Beijing 100093, China
| | - Xiuliang Wang
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China.
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China.
| | - Shuang Li
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
- University of Chinese Academy of Sciences, Beijing 100093, China
| | - Jianting Yao
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
| | - Zhanru Shao
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
| | - Delin Duan
- Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China.
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China.
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17
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Schäfer P, Helm S, Köhler D, Agne B, Baginsky S. Consequences of impaired 1-MDa TIC complex assembly for the abundance and composition of chloroplast high-molecular mass protein complexes. PLoS One 2019; 14:e0213364. [PMID: 30865669 PMCID: PMC6415892 DOI: 10.1371/journal.pone.0213364] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Accepted: 02/20/2019] [Indexed: 12/28/2022] Open
Abstract
We report a systematic analysis of chloroplast high-molecular mass protein complexes using a combination of native gel electrophoresis and absolute protein quantification by MSE. With this experimental setup, we characterized the effect of the tic56-3 mutation in the 1-MDa inner envelope translocase (TIC) on the assembly of the chloroplast proteome. We show that the tic56-3 mutation results in a reduction of the 1-MDa TIC complex to approximately 10% of wildtype levels. Hierarchical clustering confirmed the association of malate dehydrogenase (MDH) with an envelope-associated FtsH/FtsHi complex and suggested the association of a glycine-rich protein with the 1-MDa TIC complex. Depletion of this complex leads to a reduction of chloroplast ATPase to approx. 75% of wildtype levels, while the abundance of the FtsH/FtsHi complex is increased to approx. 140% of wildtype. The accumulation of the major photosynthetic complexes is not affected by the mutation, suggesting that tic56-3 plants can sustain a functional photosynthetic machinery despite a significant reduction of the 1-MDa TIC complex. Together our analysis expands recent efforts to catalogue the native molecular masses of chloroplast proteins and provides information on the consequences of impaired accumulation of the 1-MDa TIC translocase for chloroplast proteome assembly.
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Affiliation(s)
- Peter Schäfer
- Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, Halle (Saale), Germany
| | - Stefan Helm
- Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, Halle (Saale), Germany
| | - Daniel Köhler
- Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, Halle (Saale), Germany
| | - Birgit Agne
- Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, Halle (Saale), Germany
| | - Sacha Baginsky
- Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Biozentrum, Halle (Saale), Germany
- * E-mail:
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18
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Voith von Voithenberg L, Park J, Stübe R, Lux C, Lee Y, Philippar K. A Novel Prokaryote-Type ECF/ABC Transporter Module in Chloroplast Metal Homeostasis. FRONTIERS IN PLANT SCIENCE 2019; 10:1264. [PMID: 31736987 PMCID: PMC6828968 DOI: 10.3389/fpls.2019.01264] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 09/11/2019] [Indexed: 05/18/2023]
Abstract
During evolution, chloroplasts, which originated by endosymbiosis of a prokaryotic ancestor of today's cyanobacteria with a eukaryotic host cell, were established as the site for photosynthesis. Therefore, chloroplast organelles are loaded with transition metals including iron, copper, and manganese, which are essential for photosynthetic electron transport due to their redox capacity. Although transport, storage, and cofactor-assembly of metal ions in chloroplasts are tightly controlled and crucial throughout plant growth and development, knowledge on the molecular nature of chloroplast metal-transport proteins is still fragmentary. Here, we characterized the soluble, ATP-binding ABC-transporter subunits ABCI10 and ABCI11 in Arabidopsis thaliana, which show similarities to components of prokaryotic, multisubunit ABC transporters. Both ABCI10 and ABCI11 proteins appear to be strongly attached to chloroplast-intrinsic membranes, most likely inner envelopes for ABCI10 and possibly plastoglobuli for ABCI11. Loss of ABCI10 and ABCI11 gene products in Arabidopsis leads to extremely dwarfed, albino plants showing impaired chloroplast biogenesis and deregulated metal homeostasis. Further, we identified the membrane-intrinsic protein ABCI12 as potential interaction partner for ABCI10 in the inner envelope. Our results suggest that ABCI12 inserts into the chloroplast inner envelope membrane most likely with five predicted α-helical transmembrane domains and represents the membrane-intrinsic subunit of a prokaryotic-type, energy-coupling factor (ECF) ABC-transporter complex. In bacteria, these multisubunit ECF importers are widely distributed for the uptake of nickel and cobalt metal ions as well as for import of vitamins and several other metabolites. Therefore, we propose that ABCI10 (as the ATPase A-subunit) and ABCI12 (as the membrane-intrinsic, energy-coupling T-subunit) are part of a novel, chloroplast envelope-localized, AAT energy-coupling module of a prokaryotic-type ECF transporter, most likely involved in metal ion uptake.
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Affiliation(s)
| | - Jiyoung Park
- Department of Life Science, Pohang University of Science and Technology, Pohang, South Korea
| | - Roland Stübe
- Plant Biochemistry and Physiology, Department of Biology I, LMU München, Planegg-Martinsried, Germany
| | - Christopher Lux
- Plant Biology, Center for Human and Molecular Biology (ZHMB), Saarland University, Saarbrücken, Germany
| | - Youngsook Lee
- Department of Life Science, Pohang University of Science and Technology, Pohang, South Korea
| | - Katrin Philippar
- Plant Biology, Center for Human and Molecular Biology (ZHMB), Saarland University, Saarbrücken, Germany
- *Correspondence: Katrin Philippar,
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19
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Voith von Voithenberg L, Park J, Stübe R, Lux C, Lee Y, Philippar K. A Novel Prokaryote-Type ECF/ABC Transporter Module in Chloroplast Metal Homeostasis. FRONTIERS IN PLANT SCIENCE 2019; 10:1264. [PMID: 31736987 DOI: 10.3389/fpls201901264] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 09/11/2019] [Indexed: 05/22/2023]
Abstract
During evolution, chloroplasts, which originated by endosymbiosis of a prokaryotic ancestor of today's cyanobacteria with a eukaryotic host cell, were established as the site for photosynthesis. Therefore, chloroplast organelles are loaded with transition metals including iron, copper, and manganese, which are essential for photosynthetic electron transport due to their redox capacity. Although transport, storage, and cofactor-assembly of metal ions in chloroplasts are tightly controlled and crucial throughout plant growth and development, knowledge on the molecular nature of chloroplast metal-transport proteins is still fragmentary. Here, we characterized the soluble, ATP-binding ABC-transporter subunits ABCI10 and ABCI11 in Arabidopsis thaliana, which show similarities to components of prokaryotic, multisubunit ABC transporters. Both ABCI10 and ABCI11 proteins appear to be strongly attached to chloroplast-intrinsic membranes, most likely inner envelopes for ABCI10 and possibly plastoglobuli for ABCI11. Loss of ABCI10 and ABCI11 gene products in Arabidopsis leads to extremely dwarfed, albino plants showing impaired chloroplast biogenesis and deregulated metal homeostasis. Further, we identified the membrane-intrinsic protein ABCI12 as potential interaction partner for ABCI10 in the inner envelope. Our results suggest that ABCI12 inserts into the chloroplast inner envelope membrane most likely with five predicted α-helical transmembrane domains and represents the membrane-intrinsic subunit of a prokaryotic-type, energy-coupling factor (ECF) ABC-transporter complex. In bacteria, these multisubunit ECF importers are widely distributed for the uptake of nickel and cobalt metal ions as well as for import of vitamins and several other metabolites. Therefore, we propose that ABCI10 (as the ATPase A-subunit) and ABCI12 (as the membrane-intrinsic, energy-coupling T-subunit) are part of a novel, chloroplast envelope-localized, AAT energy-coupling module of a prokaryotic-type ECF transporter, most likely involved in metal ion uptake.
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Affiliation(s)
| | - Jiyoung Park
- Department of Life Science, Pohang University of Science and Technology, Pohang, South Korea
| | - Roland Stübe
- Plant Biochemistry and Physiology, Department of Biology I, LMU München, Planegg-Martinsried, Germany
| | - Christopher Lux
- Plant Biology, Center for Human and Molecular Biology (ZHMB), Saarland University, Saarbrücken, Germany
| | - Youngsook Lee
- Department of Life Science, Pohang University of Science and Technology, Pohang, South Korea
| | - Katrin Philippar
- Plant Biology, Center for Human and Molecular Biology (ZHMB), Saarland University, Saarbrücken, Germany
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20
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LaBrant E, Barnes AC, Roston RL. Lipid transport required to make lipids of photosynthetic membranes. PHOTOSYNTHESIS RESEARCH 2018; 138:345-360. [PMID: 29961189 DOI: 10.1007/s11120-018-0545-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Accepted: 06/20/2018] [Indexed: 05/21/2023]
Abstract
Photosynthetic membranes provide much of the usable energy for life on earth. To produce photosynthetic membrane lipids, multiple transport steps are required, including fatty acid export from the chloroplast stroma to the endoplasmic reticulum, and lipid transport from the endoplasmic reticulum to the chloroplast envelope membranes. Transport of hydrophobic molecules through aqueous space is energetically unfavorable and must be catalyzed by dedicated enzymes, frequently on specialized membrane structures. Here, we review photosynthetic membrane lipid transport to the chloroplast in the context of photosynthetic membrane lipid synthesis. We independently consider the identity of transported lipids, the proteinaceous transport components, and membrane structures which may allow efficient transport. Recent advances in lipid transport of chloroplasts, bacteria, and other systems strongly suggest that lipid transport is achieved by multiple mechanisms which include membrane contact sites with specialized protein machinery. This machinery is likely to include the TGD1, 2, 3 complex with the TGD5 and TGD4/LPTD1 systems, and may also include a number of proteins with domains similar to other membrane contact site lipid-binding proteins. Importantly, the likelihood of membrane contact sites does not preclude lipid transport by other mechanisms including vectorial acylation and vesicle transport. Substantial progress is needed to fully understand all photosynthetic membrane lipid transport processes and how they are integrated.
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Affiliation(s)
- Evan LaBrant
- Department of Biochemistry, University of Nebraska-Lincoln, 1901 Vine St, Lincoln, NE, 68588, USA
| | - Allison C Barnes
- Department of Biochemistry, University of Nebraska-Lincoln, 1901 Vine St, Lincoln, NE, 68588, USA
| | - Rebecca L Roston
- Department of Biochemistry, University of Nebraska-Lincoln, 1901 Vine St, Lincoln, NE, 68588, USA.
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21
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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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22
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Peculiar features of the plastids of the colourless alga Euglena longa and photosynthetic euglenophytes unveiled by transcriptome analyses. Sci Rep 2018; 8:17012. [PMID: 30451959 PMCID: PMC6242988 DOI: 10.1038/s41598-018-35389-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Accepted: 11/02/2018] [Indexed: 12/17/2022] Open
Abstract
Euglenophytes are a familiar algal group with green alga-derived secondary plastids, but the knowledge of euglenophyte plastid function and evolution is still highly incomplete. With this in mind we sequenced and analysed the transcriptome of the non-photosynthetic species Euglena longa. The transcriptomic data confirmed the absence of genes for the photosynthetic machinery, but provided candidate plastid-localised proteins bearing N-terminal bipartite topogenic signals (BTSs) of the characteristic euglenophyte type. Further comparative analyses including transcriptome assemblies available for photosynthetic euglenophytes enabled us to unveil salient aspects of the basic euglenophyte plastid infrastructure, such as plastidial targeting of several proteins as C-terminal translational fusions with other BTS-bearing proteins or replacement of the conventional eubacteria-derived plastidial ribosomal protein L24 by homologs of archaeo-eukaryotic origin. Strikingly, no homologs of any key component of the TOC/TIC system and the plastid division apparatus are discernible in euglenophytes, and the machinery for intraplastidial protein targeting has been simplified by the loss of the cpSRP/cpFtsY system and the SEC2 translocon. Lastly, euglenophytes proved to encode a plastid-targeted homolog of the termination factor Rho horizontally acquired from a Lambdaproteobacteria-related donor. Our study thus further documents a substantial remodelling of the euglenophyte plastid compared to its green algal progenitor.
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23
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Kikuchi S, Asakura Y, Imai M, Nakahira Y, Kotani Y, Hashiguchi Y, Nakai Y, Takafuji K, Bédard J, Hirabayashi-Ishioka Y, Mori H, Shiina T, Nakai M. A Ycf2-FtsHi Heteromeric AAA-ATPase Complex Is Required for Chloroplast Protein Import. THE PLANT CELL 2018; 30:2677-2703. [PMID: 30309901 PMCID: PMC6305978 DOI: 10.1105/tpc.18.00357] [Citation(s) in RCA: 100] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Revised: 08/16/2018] [Accepted: 10/01/2018] [Indexed: 05/20/2023]
Abstract
Chloroplasts import thousands of nucleus-encoded preproteins synthesized in the cytosol through the TOC and TIC translocons on the outer and inner envelope membranes, respectively. Preprotein translocation across the inner membrane requires ATP; however, the import motor has remained unclear. Here, we report that a 2-MD heteromeric AAA-ATPase complex associates with the TIC complex and functions as the import motor, directly interacting with various translocating preproteins. This 2-MD complex consists of a protein encoded by the previously enigmatic chloroplast gene ycf2 and five related nuclear-encoded FtsH-like proteins, namely, FtsHi1, FtsHi2, FtsHi4, FtsHi5, and FtsH12. These components are each essential for plant viability and retain the AAA-type ATPase domain, but only FtsH12 contains the zinc binding active site generally conserved among FtsH-type metalloproteases. Furthermore, even the FtsH12 zinc binding site is dispensable for its essential function. Phylogenetic analyses suggest that all AAA-type members of the Ycf2/FtsHi complex including Ycf2 evolved from the chloroplast-encoded membrane-bound AAA-protease FtsH of the ancestral endosymbiont. The Ycf2/FtsHi complex also contains an NAD-malate dehydrogenase, a proposed key enzyme for ATP production in chloroplasts in darkness or in nonphotosynthetic plastids. These findings advance our understanding of this ATP-driven protein translocation system that is unique to the green lineage of photosynthetic eukaryotes.
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Affiliation(s)
- Shingo Kikuchi
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Yukari Asakura
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Midori Imai
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Yoichi Nakahira
- College of Agriculture, Ibaraki University, Ami-cho, Inashiki, Ibaraki 300-0393, Japan
| | - Yoshiko Kotani
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | - Yasuyuki Hashiguchi
- Department of Biology, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan
| | - Yumi Nakai
- Department of Biochemistry, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan
| | - Kazuaki Takafuji
- CoMIT Omics Center, Graduate School of Medicine, Osaka University, Osaka 565-0871, Japan
| | - Jocelyn Bédard
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
| | | | - Hitoshi Mori
- Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
| | - Takashi Shiina
- School of Human Environment Science, Kyoto Prefectural University, Sakyo-ku, Kyoto 606-8522, Japan
| | - Masato Nakai
- Institute for Protein Research, Osaka University, Osaka 565-0871, Japan
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24
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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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25
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The Direct Involvement of Dark-Induced Tic55 Protein in Chlorophyll Catabolism and Its Indirect Role in the MYB108-NAC Signaling Pathway during Leaf Senescence in Arabidopsis thaliana. Int J Mol Sci 2018; 19:ijms19071854. [PMID: 29937503 PMCID: PMC6073118 DOI: 10.3390/ijms19071854] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Revised: 06/19/2018] [Accepted: 06/21/2018] [Indexed: 11/23/2022] Open
Abstract
The chloroplast relies on proteins encoded in the nucleus, synthesized in the cytosol and subsequently transported into chloroplast through the protein complexes Toc and Tic (Translocon at the outer/inner membrane of chloroplasts). A Tic complex member, Tic55, contains a redox-related motif essential for protein import into chloroplasts in peas. However, Tic55 is not crucial for protein import in Arabidopsis. Here, a tic55-II-knockout mutant of Arabidopsis thaliana was characterized for Tic55 localization, its relationship with other translocon proteins, and its association with plant leaf senescence when compared to the wild type. Individually darkened leaves (IDLs) obtained through dark-induced leaf senescence were used to demonstrate chlorophyll breakdown and its relationship with plant senescence in the tic55-II-knockout mutant. The IDLs of the tic55-II-knockout mutant contained higher chlorophyll concentrations than those of the wild type. Our microarray analysis of IDLs during leaf senescence identified seven senescence-associated genes (SAGs) that were downregulated in the tic55-II-knockout mutant: ASP3, APG7, DIN2, DIN11, SAG12, SAG13, and YLS9. Real-time quantitative PCR confirmed the reliability of microarray analysis by showing the same expression patterns with those of the microarray data. Thus, Tic55 functions in dark-induced aging in A. thaliana by indirectly regulating downstream SAGs expression. In addition, the expression of four NAC genes, including ANAC003, ANAC010, ANAC042, and ANAC075 of IDL treated tic55-II-knockout mutant appeared to be downregulated. Yeast one hybrid assay revealed that only ANAC003 promoter region can be bound by MYB108, suggesting that a MYB-NAC regulatory network is involved in dark-stressed senescence.
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26
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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: 52] [Impact Index Per Article: 8.7] [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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27
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Lee DW, Hwang I. Evolution and Design Principles of the Diverse Chloroplast Transit Peptides. Mol Cells 2018; 41:161-167. [PMID: 29487274 PMCID: PMC5881089 DOI: 10.14348/molcells.2018.0033] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Accepted: 02/06/2018] [Indexed: 11/27/2022] Open
Abstract
Chloroplasts are present in organisms belonging to the kingdom Plantae. These organelles are thought to have originated from photosynthetic cyanobacteria through endosymbiosis. During endosymbiosis, most cyanobacterial genes were transferred to the host nucleus. Therefore, most chloroplast proteins became encoded in the nuclear genome and must return to the chloroplast after translation. The N-terminal cleavable transit peptide (TP) is necessary and sufficient for the import of nucleus-encoded interior chloroplast proteins. Over the past decade, extensive research on the TP has revealed many important characteristic features of TPs. These studies have also shed light on the question of how the many diverse TPs could have evolved to target specific proteins to the chloroplast. In this review, we summarize the characteristic features of TPs. We also highlight recent advances in our understanding of TP evolution and provide future perspectives about this important research area.
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Affiliation(s)
- Dong Wook Lee
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 37673,
Korea
| | - Inhwan Hwang
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 37673,
Korea
- Department of Life Sciences, Pohang University of Science and Technology, Pohang 37673,
Korea
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28
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Lee DW, Yoo YJ, Razzak MA, Hwang I. Prolines in Transit Peptides Are Crucial for Efficient Preprotein Translocation into Chloroplasts. PLANT PHYSIOLOGY 2018; 176:663-677. [PMID: 29158328 PMCID: PMC5761803 DOI: 10.1104/pp.17.01553] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Accepted: 11/17/2017] [Indexed: 05/20/2023]
Abstract
Chloroplasts import many preproteins that can be classified based on their physicochemical properties. The cleavable N-terminal transit peptide (TP) of chloroplast preproteins contains all the information required for import into chloroplasts through Toc/Tic translocons. The question of whether and how the physicochemical properties of preproteins affect TP-mediated import into chloroplasts has not been elucidated. Here, we present evidence that Pro residues in TP mediate efficient translocation through the chloroplast envelope membranes for proteins containing transmembrane domains (TMDs) or proteins prone to aggregation. By contrast, the translocation of soluble proteins through the chloroplast envelope membranes is less dependent on TP prolines. Proless TPs failed to mediate protein translocation into chloroplasts; instead, these mutant TPs led to protein mistargeting to the chloroplast envelope membranes or nonspecific protein aggregation during import into chloroplasts. The mistargeting of TMD-containing proteins caused by Pro-less TPs in wild-type protoplasts was mimicked by wild-type TPs in hsp93-V protoplasts, in which preprotein translocation is compromised. We propose that the physicochemical properties of chloroplast proteins affect protein translocation through the chloroplast envelope, and prolines in TP have a crucial role in the efficient translocation of TMD-containing proteins.
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Affiliation(s)
- Dong Wook Lee
- Division of Integrative Biosciences and Biotechnology, and Department of Life Sciences, Pohang University of Science and Technology, Pohang, 37673, Korea
| | - Yun-Joo Yoo
- Division of Integrative Biosciences and Biotechnology, and Department of Life Sciences, Pohang University of Science and Technology, Pohang, 37673, Korea
| | - Md Abdur Razzak
- Division of Integrative Biosciences and Biotechnology, and Department of Life Sciences, Pohang University of Science and Technology, Pohang, 37673, Korea
| | - Inhwan Hwang
- Division of Integrative Biosciences and Biotechnology, and Department of Life Sciences, Pohang University of Science and Technology, Pohang, 37673, Korea
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29
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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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30
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Chen LJ, Li HM. Stable megadalton TOC-TIC supercomplexes as major mediators of protein import into chloroplasts. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2017; 92:178-188. [PMID: 28745032 DOI: 10.1111/tpj.13643] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2017] [Accepted: 07/21/2017] [Indexed: 05/12/2023]
Abstract
Preproteins are believed to be imported into chloroplasts through membrane contact sites where the translocon complexes of the outer (TOC) and inner (TIC) envelope membranes are assembled together. However, a single TOC-TIC supercomplex containing preproteins undergoing active import has not yet been directly observed. We optimized the blue native polyacrylamide gel electrophoresis (PAGE) (BN-PAGE) system to detect and resolve megadalton (MD)-sized complexes. Using this optimized system, the outer-membrane channel Toc75 from pea chloroplasts was found in at least two complexes: the 880-kD TOC complex and a previously undetected 1-MD complex. Two-dimensional BN-PAGE immunoblots further showed that Toc75, Toc159, Toc34, Tic20, Tic56 and Tic110 were all located in the 880-kD to 1.3-MD region. During active preprotein import, preproteins were transported mostly through the 1-MD complex and a smaller amount of preproteins was also detected in a complex of 1.25 MD. Antibody-shift assays showed that the 1-MD complex is a TOC-TIC supercomplex containing at least Toc75, Toc159, Toc34 and Tic110. Results from crosslinking and import with Arabidopsis chloroplasts suggest that the 1.25-MD complex is also a supercomplex. Our data provide direct evidence supporting that chloroplast preproteins are imported through TOC-TIC supercomplexes, and also provide the first size estimation of these supercomplexes. Furthermore, unlike in mitochondria where translocon supercomplexes are only transiently assembled during preprotein import, in chloroplasts at least some of the supercomplexes are preassembled stable structures.
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Affiliation(s)
- Lih-Jen Chen
- Institute of Molecular Biology, Academia Sinica, Taipei, 11529, Taiwan
| | - Hsou-Min Li
- Institute of Molecular Biology, Academia Sinica, Taipei, 11529, Taiwan
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31
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Sjuts I, Soll J, Bölter B. Import of Soluble Proteins into Chloroplasts and Potential Regulatory Mechanisms. FRONTIERS IN PLANT SCIENCE 2017; 8:168. [PMID: 28228773 PMCID: PMC5296341 DOI: 10.3389/fpls.2017.00168] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 01/26/2017] [Indexed: 05/20/2023]
Abstract
Chloroplasts originated from an endosymbiotic event in which a free-living cyanobacterium was engulfed by an ancestral eukaryotic host. During evolution the majority of the chloroplast genetic information was transferred to the host cell nucleus. As a consequence, proteins formerly encoded by the chloroplast genome are now translated in the cytosol and must be subsequently imported into the chloroplast. This process involves three steps: (i) cytosolic sorting procedures, (ii) binding to the designated receptor-equipped target organelle and (iii) the consecutive translocation process. During import, proteins have to overcome the two barriers of the chloroplast envelope, namely the outer envelope membrane (OEM) and the inner envelope membrane (IEM). In the majority of cases, this is facilitated by two distinct multiprotein complexes, located in the OEM and IEM, respectively, designated TOC and TIC. Plants are constantly exposed to fluctuating environmental conditions such as temperature and light and must therefore regulate protein composition within the chloroplast to ensure optimal functioning of elementary processes such as photosynthesis. In this review we will discuss the recent models of each individual import stage with regard to short-term strategies that plants might use to potentially acclimate to changes in their environmental conditions and preserve the chloroplast protein homeostasis.
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Affiliation(s)
- Inga Sjuts
- Department Biologie I-Botanik, Ludwig-Maximilians-UniversitätPlanegg-Martinsried, Germany
| | - Jürgen Soll
- Department Biologie I-Botanik, Ludwig-Maximilians-UniversitätPlanegg-Martinsried, Germany
- Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-UniversitätMunich, Germany
| | - Bettina Bölter
- Department Biologie I-Botanik, Ludwig-Maximilians-UniversitätPlanegg-Martinsried, Germany
- Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-UniversitätMunich, Germany
- *Correspondence: Bettina Bölter,
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32
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Wagner R, von Sydow L, Aigner H, Netotea S, Brugière S, Sjögren L, Ferro M, Clarke A, Funk C. Deletion of FtsH11 protease has impact on chloroplast structure and function in Arabidopsis thaliana when grown under continuous light. PLANT, CELL & ENVIRONMENT 2016; 39:2530-2544. [PMID: 27479913 DOI: 10.1111/pce.12808] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 07/12/2016] [Accepted: 07/17/2016] [Indexed: 05/20/2023]
Abstract
The membrane-integrated metalloprotease FtsH11 of Arabidopsis thaliana is proposed to be dual-targeted to mitochondria and chloroplasts. A bleached phenotype was observed in ftsh11 grown at long days or continuous light, pointing to disturbances in the chloroplast. Within the chloroplast, FtsH11 was found to be located exclusively in the envelope. Two chloroplast-located proteins of unknown function (Tic22-like protein and YGGT-A) showed significantly higher abundance in envelope membranes and intact chloroplasts of ftsh11 and therefore qualify as potential substrates for the FtsH11 protease. No proteomic changes were observed in the mitochondria of 6-week-old ftsh11 compared with wild type, and FtsH11 was not immunodetected in these organelles. The abundance of plastidic proteins, especially of photosynthetic proteins, was altered even during standard growth conditions in total leaves of ftsh11. At continuous light, the amount of photosystem I decreased relative to photosystem II, accompanied by a drastic change of the chloroplast morphology and a drop of non-photochemical quenching. FtsH11 is crucial for chloroplast structure and function during growth in prolonged photoperiod.
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Affiliation(s)
- Raik Wagner
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
| | - Lotta von Sydow
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
| | - Harald Aigner
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
| | - Sergiu Netotea
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden
- Bioinformatics Infrastructure for Life Sciences (BILS), Linköping, Sweden
| | - Sabine Brugière
- U1038 INSERM/CEA/UJ, Institut de Recherches en Technologies et Sciences pour le Vivant, Grenoble, Cedex 9, France
| | - Lars Sjögren
- Department of Biological and Environmental Sciences, Gothenburg University, 40530, Gothenburg, Sweden
| | - Myriam Ferro
- U1038 INSERM/CEA/UJ, Institut de Recherches en Technologies et Sciences pour le Vivant, Grenoble, Cedex 9, France
| | - Adrian Clarke
- Department of Biological and Environmental Sciences, Gothenburg University, 40530, Gothenburg, Sweden
| | - Christiane Funk
- Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden.
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33
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Bölter B, Soll J. Once upon a Time - Chloroplast Protein Import Research from Infancy to Future Challenges. MOLECULAR PLANT 2016; 9:798-812. [PMID: 27142186 DOI: 10.1016/j.molp.2016.04.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 04/25/2016] [Accepted: 04/27/2016] [Indexed: 05/08/2023]
Abstract
Protein import into chloroplasts has been a focus of research for several decades. The first publications dealing with this fascinating topic appeared in the 1970s. From the initial realization that many plastid proteins are being encoded for in the nucleus and require transport into their target organelle to the identification of import components in the cytosol, chloroplast envelopes, and stroma, as well as elucidation of some mechanistic details, more fascinating aspects are still being unraveled. With this overview, we present a survey of the beginnings of chloroplast protein import research, the first steps on this winding road, and end with a glimpse into the future.
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Affiliation(s)
- Bettina Bölter
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhaderner Straße 2-4, 82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, 81377 Munich, Germany.
| | - Jürgen Soll
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhaderner Straße 2-4, 82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
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34
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López-Millán AF, Duy D, Philippar K. Chloroplast Iron Transport Proteins - Function and Impact on Plant Physiology. FRONTIERS IN PLANT SCIENCE 2016; 7:178. [PMID: 27014281 DOI: 10.3389/fpls201600178] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 02/02/2016] [Indexed: 05/22/2023]
Abstract
Chloroplasts originated about three billion years ago by endosymbiosis of an ancestor of today's cyanobacteria with a mitochondria-containing host cell. During evolution chloroplasts of higher plants established as the site for photosynthesis and thus became the basis for all life dependent on oxygen and carbohydrate supply. To fulfill this task, plastid organelles are loaded with the transition metals iron, copper, and manganese, which due to their redox properties are essential for photosynthetic electron transport. In consequence, chloroplasts for example represent the iron-richest system in plant cells. However, improvement of oxygenic photosynthesis in turn required adaptation of metal transport and homeostasis since metal-catalyzed generation of reactive oxygen species (ROS) causes oxidative damage. This is most acute in chloroplasts, where radicals and transition metals are side by side and ROS-production is a usual feature of photosynthetic electron transport. Thus, on the one hand when bound by proteins, chloroplast-intrinsic metals are a prerequisite for photoautotrophic life, but on the other hand become toxic when present in their highly reactive, radical generating, free ionic forms. In consequence, transport, storage and cofactor-assembly of metal ions in plastids have to be tightly controlled and are crucial throughout plant growth and development. In the recent years, proteins for iron transport have been isolated from chloroplast envelope membranes. Here, we discuss their putative functions and impact on cellular metal homeostasis as well as photosynthetic performance and plant metabolism. We further consider the potential of proteomic analyses to identify new players in the field.
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Affiliation(s)
- Ana F López-Millán
- Department of Pediatrics, Children's Nutrition Research Center, Baylor College of Medicine, United States Department of Agriculture/Agricultural Research Service, Houston TX, USA
| | - Daniela Duy
- Plastid Fatty Acid and Iron Transport - Plant Biochemistry and Physiology, Department Biology I, Ludwig-Maximilians-University of Munich Munich, Germany
| | - Katrin Philippar
- Plastid Fatty Acid and Iron Transport - Plant Biochemistry and Physiology, Department Biology I, Ludwig-Maximilians-University of Munich Munich, Germany
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35
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López-Millán AF, Duy D, Philippar K. Chloroplast Iron Transport Proteins - Function and Impact on Plant Physiology. FRONTIERS IN PLANT SCIENCE 2016; 7:178. [PMID: 27014281 PMCID: PMC4780311 DOI: 10.3389/fpls.2016.00178] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 02/02/2016] [Indexed: 05/08/2023]
Abstract
Chloroplasts originated about three billion years ago by endosymbiosis of an ancestor of today's cyanobacteria with a mitochondria-containing host cell. During evolution chloroplasts of higher plants established as the site for photosynthesis and thus became the basis for all life dependent on oxygen and carbohydrate supply. To fulfill this task, plastid organelles are loaded with the transition metals iron, copper, and manganese, which due to their redox properties are essential for photosynthetic electron transport. In consequence, chloroplasts for example represent the iron-richest system in plant cells. However, improvement of oxygenic photosynthesis in turn required adaptation of metal transport and homeostasis since metal-catalyzed generation of reactive oxygen species (ROS) causes oxidative damage. This is most acute in chloroplasts, where radicals and transition metals are side by side and ROS-production is a usual feature of photosynthetic electron transport. Thus, on the one hand when bound by proteins, chloroplast-intrinsic metals are a prerequisite for photoautotrophic life, but on the other hand become toxic when present in their highly reactive, radical generating, free ionic forms. In consequence, transport, storage and cofactor-assembly of metal ions in plastids have to be tightly controlled and are crucial throughout plant growth and development. In the recent years, proteins for iron transport have been isolated from chloroplast envelope membranes. Here, we discuss their putative functions and impact on cellular metal homeostasis as well as photosynthetic performance and plant metabolism. We further consider the potential of proteomic analyses to identify new players in the field.
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Affiliation(s)
- Ana F. López-Millán
- Department of Pediatrics, Children’s Nutrition Research Center, Baylor College of Medicine, United States Department of Agriculture/Agricultural Research Service, HoustonTX, USA
| | - Daniela Duy
- Plastid Fatty Acid and Iron Transport – Plant Biochemistry and Physiology, Department Biology I, Ludwig-Maximilians-University of MunichMunich, Germany
| | - Katrin Philippar
- Plastid Fatty Acid and Iron Transport – Plant Biochemistry and Physiology, Department Biology I, Ludwig-Maximilians-University of MunichMunich, Germany
- *Correspondence: Katrin Philippar,
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Lee DW, Woo S, Geem KR, Hwang I. Sequence Motifs in Transit Peptides Act as Independent Functional Units and Can Be Transferred to New Sequence Contexts. PLANT PHYSIOLOGY 2015; 169:471-84. [PMID: 26149569 PMCID: PMC4577419 DOI: 10.1104/pp.15.00842] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 07/02/2015] [Indexed: 05/04/2023]
Abstract
A large number of nuclear-encoded proteins are imported into chloroplasts after they are translated in the cytosol. Import is mediated by transit peptides (TPs) at the N termini of these proteins. TPs contain many small motifs, each of which is critical for a specific step in the process of chloroplast protein import; however, it remains unknown how these motifs are organized to give rise to TPs with diverse sequences. In this study, we generated various hybrid TPs by swapping domains between Rubisco small subunit (RbcS) and chlorophyll a/b-binding protein, which have highly divergent sequences, and examined the abilities of the resultant TPs to deliver proteins into chloroplasts. Subsequently, we compared the functionality of sequence motifs in the hybrid TPs with those of wild-type TPs. The sequence motifs in the hybrid TPs exhibited three different modes of functionality, depending on their domain composition, as follows: active in both wild-type and hybrid TPs, active in wild-type TPs but inactive in hybrid TPs, and inactive in wild-type TPs but active in hybrid TPs. Moreover, synthetic TPs, in which only three critical motifs from RbcS or chlorophyll a/b-binding protein TPs were incorporated into an unrelated sequence, were able to deliver clients to chloroplasts with a comparable efficiency to RbcS TP. Based on these results, we propose that diverse sequence motifs in TPs are independent functional units that interact with specific translocon components at various steps during protein import and can be transferred to new sequence contexts.
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Affiliation(s)
- Dong Wook Lee
- Division of Integrative Biosciences and Biotechnology (D.W.L., S.W., I.H.) and Department of Life Sciences (K.R.G., I.H.), Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Seungjin Woo
- Division of Integrative Biosciences and Biotechnology (D.W.L., S.W., I.H.) and Department of Life Sciences (K.R.G., I.H.), Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Kyoung Rok Geem
- Division of Integrative Biosciences and Biotechnology (D.W.L., S.W., I.H.) and Department of Life Sciences (K.R.G., I.H.), Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Inhwan Hwang
- Division of Integrative Biosciences and Biotechnology (D.W.L., S.W., I.H.) and Department of Life Sciences (K.R.G., I.H.), Pohang University of Science and Technology, Pohang 790-784, Korea
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Nakai M. YCF1: A Green TIC: Response to the de Vries et al. Commentary. THE PLANT CELL 2015; 27:1834-8. [PMID: 26071422 PMCID: PMC4531358 DOI: 10.1105/tpc.15.00363] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Revised: 06/01/2015] [Accepted: 06/02/2015] [Indexed: 05/07/2023]
Abstract
This response to a recent Commentary article by de Vries et al. highlights critical errors in the annotation and identification of Ycf1 homologs in the sequenced chloroplast genomes. Contrary to what is reported by de Vries et al., the majority of chloroplast genomes sequenced to date appear to have retained a typical Ycf1 sequence (i.e., including the N-terminal 6TM domain and a variable hydrophilic C-terminal domain) as my group previously reported. Our evidence continues to support the model that Ycf1 forms an essential component of a "green TIC" that is largely conserved among the Chlorophyta and land plants. Since the establishment of this green TIC with Tic20 as the core component, some cases of loss of Ycf1 during the evolution of the green lineages might be regarded as modifications or alterations of the complex. Here, I discuss our working model that the presence of an alternative "nonphotosynthetic-type" or "ancestral-type" TIC might explain other (or specific) cases of the lack of Ycf1, not only in early lineages, including Glaucophyta and Rhodophyta, but also in the grasses.
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Affiliation(s)
- Masato Nakai
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
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Köhler D, Montandon C, Hause G, Majovsky P, Kessler F, Baginsky S, Agne B. Characterization of chloroplast protein import without Tic56, a component of the 1-megadalton translocon at the inner envelope membrane of chloroplasts. PLANT PHYSIOLOGY 2015; 167:972-90. [PMID: 25588737 PMCID: PMC4348784 DOI: 10.1104/pp.114.255562] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2014] [Accepted: 01/14/2015] [Indexed: 05/17/2023]
Abstract
We report on the characterization of Tic56, a unique component of the recently identified 1-MD translocon at the inner envelope membrane of chloroplasts (TIC) in Arabidopsis (Arabidopsis thaliana) comprising Tic20, Tic100, and Tic214. We isolated Tic56 by copurification with Tandem Affinity Purification-tagged Toc159 in the absence of precursor protein, indicating spontaneous and translocation-independent formation of the translocon at the outer envelope membrane of chloroplasts (TOC) and TIC supercomplexes. Tic56 mutant plants have an albino phenotype and are unable to grow without an external carbon source. Using specific enrichment of protein amino termini, we analyzed the tic56-1 and plastid protein import2 (toc159) mutants to assess the in vivo import capacity of plastids in mutants of an outer and inner envelope component of the anticipated TOC-TIC supercomplex. Inboth mutants, we observed processing of several import substrates belonging to various pathways. Our results suggest that despite the severe developmental defects, protein import into Tic56-deficient plastids is functional to a considerable degree, indicating the existence of alternative translocases at the inner envelope membrane.
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The TIC complex uncovered: The alternative view on the molecular mechanism of protein translocation across the inner envelope membrane of chloroplasts. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:957-67. [PMID: 25689609 DOI: 10.1016/j.bbabio.2015.02.011] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Revised: 01/19/2015] [Accepted: 02/07/2015] [Indexed: 12/29/2022]
Abstract
Chloroplasts must import thousands of nuclear-encoded preproteins synthesized in the cytosol through two successive protein translocons at the outer and inner envelope membranes, termed TOC and TIC, respectively, to fulfill their complex physiological roles. The molecular identity of the TIC translocon had long remained controversial; two proteins, namely Tic20 and Tic110, had been proposed to be central to protein translocation across the inner envelope membrane. Tic40 also had long been considered to be another central player in this process. However, recently, a novel 1-megadalton complex consisting of Tic20, Tic56, Tic100, and Tic214 was identified at the chloroplast inner membrane of Arabidopsis and was demonstrated to constitute a general TIC translocon which functions in concert with the well-characterized TOC translocon. On the other hand, direct interaction between this novel TIC transport system and Tic110 or Tic40 was hardly observed. Consequently, the molecular model for protein translocation across the inner envelope membrane of chloroplasts might need to be extensively revised. In this review article, I intend to propose such alternative view regarding the TIC transport system in contradistinction to the classical view. I also would emphasize importance of reevaluation of previous works in terms of with what methods these classical Tic proteins such as Tic110 or Tic40 were picked up as TIC constituents at the very beginning as well as what actual evidence there were to support their direct and specific involvement in chloroplast protein import. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
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Bölter B, Soll J, Schwenkert S. Redox meets protein trafficking. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:949-56. [PMID: 25626173 DOI: 10.1016/j.bbabio.2015.01.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 01/16/2015] [Accepted: 01/19/2015] [Indexed: 11/15/2022]
Abstract
After the engulfment of two prokaryotic organisms, the thus emerged eukaryotic cell needed to establish means of communication and signaling to properly integrate the acquired organelles into its metabolism. Regulatory mechanisms had to evolve to ensure that chloroplasts and mitochondria smoothly function in accordance with all other cellular processes. One essential process is the post-translational import of nuclear encoded organellar proteins, which needs to be adapted according to the requirements of the plant. The demand for protein import is constantly changing depending on varying environmental conditions, as well as external and internal stimuli or different developmental stages. Apart from long-term regulatory mechanisms such as transcriptional/translation control, possibilities for short-term acclimation are mandatory. To this end, protein import is integrated into the cellular redox network, utilizing the recognition of signals from within the organelles and modifying the efficiency of the translocon complexes. Thereby, cellular requirements can be communicated throughout the whole organism. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
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Affiliation(s)
- Bettina Bölter
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhadernerstr. 2-4, D-82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany
| | - Jürgen Soll
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhadernerstr. 2-4, D-82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany.
| | - Serena Schwenkert
- Department Biologie I-Botanik, Ludwig-Maximilians-Universität, Großhadernerstr. 2-4, D-82152 Planegg-Martinsried, Germany; Munich Center for Integrated Protein Science CiPSM, Ludwig-Maximilians-Universität, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany
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Abstract
Eukaryotic cells contain a multitude of membrane structures that are connected through a highly dynamic and complex exchange of their constituents. The vibrant instability of these structures challenges the classical view of defined, static compartments that are connected by different types of vesicles. Despite this astonishing complexity, proteins and lipids are accurately transported into the different intracellular membrane systems. Over the past few decades many factors have been identified that either mediate or regulate intracellular membrane trafficking. Like in a modern parcel sorting system of a logistics center, the cargo typically passes through several sequential sorting stations until it finally reaches the location that is specified by its individual address label. While each membrane system employs specific sets of factors, the transport processes typically operate on common principles. With the advent of genome- and proteome-wide screens, the availability of mutant collections, exciting new developments in microscope technology and sophisticated methods to study their dynamics, the future promises a broad and comprehensive picture of the processes by which eukaryotic cells sort their proteins.
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Campbell JH, Hoang T, Jelokhani-Niaraki M, Smith MD. Folding and self-association of atTic20 in lipid membranes: implications for understanding protein transport across the inner envelope membrane of chloroplasts. BMC BIOCHEMISTRY 2014; 15:29. [PMID: 25551276 PMCID: PMC4307631 DOI: 10.1186/s12858-014-0029-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Accepted: 12/12/2014] [Indexed: 11/24/2022]
Abstract
Background The Arabidopsis thaliana protein atTic20 is a key component of the protein import machinery at the inner envelope membrane of chloroplasts. As a component of the TIC complex, it is believed to form a preprotein-conducting channel across the inner membrane. Results We report a method for producing large amounts of recombinant atTic20 using a codon-optimized strain of E. coli coupled with an autoinduction method of protein expression. This method resulted in the recombinant protein being directed to the bacterial membrane without the addition of a bacterial targeting sequence. Using biochemical and biophysical approaches, we were able to demonstrate that atTic20 homo-oligomerizes in vitro when solubilized in detergents or reconstituted into liposomes. Furthermore, we present evidence that the extramembranous N-terminus of the mature protein displays characteristics that are consistent with it being an intrinsically disordered protein domain. Conclusion Our work strengthens the hypothesis that atTic20 functions similarly to other small α-helical integral membrane proteins, such as Tim23, that are involved in protein transport across membranes. Electronic supplementary material The online version of this article (doi:10.1186/s12858-014-0029-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- James H Campbell
- Department of Biology, Wilfrid Laurier University, 75 University Avenue West, Waterloo, ON, N2L 3C5, Canada. .,Current address: Department of Biology, University of Waterloo, Waterloo, ON, Canada.
| | - Tuan Hoang
- Department of Chemistry & Biochemistry, Wilfrid Laurier University, Waterloo, ON, Canada. .,Biophysics Interdepartmental Group, University of Guelph, Guelph, ON, Canada.
| | - Masoud Jelokhani-Niaraki
- Department of Chemistry & Biochemistry, Wilfrid Laurier University, Waterloo, ON, Canada. .,Biophysics Interdepartmental Group, University of Guelph, Guelph, ON, Canada.
| | - Matthew D Smith
- Department of Biology, Wilfrid Laurier University, 75 University Avenue West, Waterloo, ON, N2L 3C5, Canada. .,Biophysics Interdepartmental Group, University of Guelph, Guelph, ON, Canada.
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Simmerman RF, Dave AM, Bruce BD. Structure and function of POTRA domains of Omp85/TPS superfamily. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2014; 308:1-34. [PMID: 24411168 DOI: 10.1016/b978-0-12-800097-7.00001-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The Omp85/TPS (outer-membrane protein of 85 kDa/two-partner secretion) superfamily is a ubiquitous and major class of β-barrel proteins. This superfamily is restricted to the outer membranes of gram-negative bacteria, mitochondria, and chloroplasts. The common architecture, with an N-terminus consisting of repeats of soluble polypeptide-transport-associated (POTRA) domains and a C-terminal β-barrel pore is highly conserved. The structures of multiple POTRA domains and one full-length TPS protein have been solved, yet discovering roles of individual POTRA domains has been difficult. This review focuses on similarities and differences between POTRA structures, emphasizing POTRA domains in autotrophic organisms including plants and cyanobacteria. Unique roles, specific for certain POTRA domains, are examined in the context of POTRA location with respect to their attachment to the β-barrel pore, and their degree of biological dispensability. Finally, because many POTRA domains may have the ability to interact with thousands of partner proteins, possible modes of these interactions are also explored.
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Affiliation(s)
- Richard F Simmerman
- Department of Biochemistry and Cellular and Molecular Biology, Knoxville, Tennessee, USA
| | - Ashita M Dave
- Department of Biochemistry and Cellular and Molecular Biology, Knoxville, Tennessee, USA
| | - Barry D Bruce
- Department of Biochemistry and Cellular and Molecular Biology, Knoxville, Tennessee, USA; Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA.
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Organization, function and substrates of the essential Clp protease system in plastids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1847:915-30. [PMID: 25482260 DOI: 10.1016/j.bbabio.2014.11.012] [Citation(s) in RCA: 128] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 11/20/2014] [Indexed: 01/21/2023]
Abstract
Intra-plastid proteolysis is essential in plastid biogenesis, differentiation and plastid protein homeostasis (proteostasis). We provide a comprehensive review of the Clp protease system present in all plastid types and we draw lessons from structural and functional information of bacterial Clp systems. The Clp system plays a central role in plastid development and function, through selective removal of miss-folded, aggregated, or otherwise unwanted proteins. The Clp system consists of a tetradecameric proteolytic core with catalytically active ClpP and inactive ClpR subunits, hexameric ATP-dependent chaperones (ClpC,D) and adaptor protein(s) (ClpS1) enhancing delivery of subsets of substrates. Many structural and functional features of the plastid Clp system are now understood though extensive reverse genetics analysis combined with biochemical analysis, as well as large scale quantitative proteomics for loss-of-function mutants of Clp core, chaperone and ClpS1 subunits. Evolutionary diversification of Clp system across non-photosynthetic and photosynthetic prokaryotes and organelles is illustrated. Multiple substrates have been suggested based on their direct interaction with the ClpS1 adaptor or screening of different loss-of-function protease mutants. The main challenge is now to determine degradation signals (degrons) in Clp substrates and substrate delivery mechanisms, as well as functional interactions of Clp with other plastid proteases. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
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Demarsy E, Lakshmanan AM, Kessler F. Border control: selectivity of chloroplast protein import and regulation at the TOC-complex. FRONTIERS IN PLANT SCIENCE 2014; 5:483. [PMID: 25278954 PMCID: PMC4166117 DOI: 10.3389/fpls.2014.00483] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Accepted: 09/01/2014] [Indexed: 05/25/2023]
Abstract
Plants have evolved complex and sophisticated molecular mechanisms to regulate their development and adapt to their surrounding environment. Particularly the development of their specific organelles, chloroplasts and other plastid-types, is finely tuned in accordance with the metabolic needs of the cell. The normal development and functioning of plastids require import of particular subsets of nuclear encoded proteins. Most preproteins contain a cleavable sequence at their N terminal (transit peptide) serving as a signal for targeting to the organelle and recognition by the translocation machinery TOC-TIC (translocon of outer membrane complex-translocon of inner membrane complex) spanning the dual membrane envelope. The plastid proteome needs constant remodeling in response to developmental and environmental factors. Therefore selective regulation of preprotein import plays a crucial role in plant development. In this review we describe the diversity of transit peptides and TOC receptor complexes, and summarize the current knowledge and potential directions for future research concerning regulation of the different Toc isoforms.
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Affiliation(s)
| | | | - Felix Kessler
- *Correspondence: Felix Kessler, Laboratory of Plant Physiology, Université de Neuchâtel, UniMail, Rue Emile Argand 11, 2000 Neuchâtel, Switzerland e-mail:
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Paila YD, Richardson LGL, Schnell DJ. New insights into the mechanism of chloroplast protein import and its integration with protein quality control, organelle biogenesis and development. J Mol Biol 2014; 427:1038-1060. [PMID: 25174336 DOI: 10.1016/j.jmb.2014.08.016] [Citation(s) in RCA: 92] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 08/20/2014] [Accepted: 08/23/2014] [Indexed: 01/04/2023]
Abstract
The translocons at the outer (TOC) and the inner (TIC) envelope membranes of chloroplasts mediate the targeting and import of several thousand nucleus-encoded preproteins that are required for organelle biogenesis and homeostasis. The cytosolic events in preprotein targeting remain largely unknown, although cytoplasmic chaperones have been proposed to facilitate delivery to the TOC complex. Preprotein recognition is mediated by the TOC GTPase receptors Toc159 and Toc34. The receptors constitute a GTP-regulated switch, which initiates membrane translocation via Toc75, a member of the Omp85 (outer membrane protein 85)/TpsB (two-partner secretion system B) family of bacterial, plastid and mitochondrial β-barrel outer membrane proteins. The TOC receptor systems have diversified to recognize distinct sets of preproteins, thereby maximizing the efficiency of targeting in response to changes in gene expression during developmental and physiological events that impact organelle function. The TOC complex interacts with the TIC translocon to allow simultaneous translocation of preproteins across the envelope. Both the two inner membrane complexes, the Tic110 and 1 MDa complexes, have been implicated as constituents of the TIC translocon, and it remains to be determined how they interact to form the TIC channel and assemble the import-associated chaperone network in the stroma that drives import across the envelope membranes. This review will focus on recent developments in our understanding of the mechanisms and diversity of the TOC-TIC systems. Our goal is to incorporate these recent studies with previous work and present updated or revised models for the function of TOC-TIC in protein import.
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Affiliation(s)
- Yamuna D Paila
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
| | - Lynn G L Richardson
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
| | - Danny J Schnell
- Department of Biochemistry and Molecular Biology, Life Sciences Laboratories Room N431, 240 Thatcher Rd, University of Massachusetts, Amherst MA 01003-9364, USA
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Tsai JY, Chu CC, Yeh YH, Chen LJ, Li HM, Hsiao CD. Structural characterizations of the chloroplast translocon protein Tic110. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2013; 75:847-57. [PMID: 23711301 PMCID: PMC3823011 DOI: 10.1111/tpj.12249] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Revised: 05/07/2013] [Accepted: 05/14/2013] [Indexed: 05/07/2023]
Abstract
Tic110 is a major component of the chloroplast protein import translocon. Two functions with mutually exclusive structures have been proposed for Tic110: a protein-conducting channel with six transmembrane domains and a scaffold with two N-terminal transmembrane domains followed by a large soluble domain for binding transit peptides and other stromal translocon components. To investigate the structure of Tic110, Tic110 from Cyanidioschyzon merolae (CmTic110) was characterized. We constructed three fragments, CmTic110A , CmTic110B and CmTic110C , with increasing N-terminal truncations, to perform small-angle X-ray scattering (SAXS) and X-ray crystallography analyses and Dali structural comparison. Here we report the molecular envelope of CmTic110B and CmTic110C determined by SAXS, and the crystal structure of CmTic110C at 4.2 Å. Our data indicate that the C-terminal half of CmTic110 possesses a rod-shaped helix-repeat structure that is too flattened and elongated to be a channel. The structure is most similar to the HEAT-repeat motif that functions as scaffolds for protein-protein interactions.
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Behrens C, Blume C, Senkler M, Eubel H, Peterhänsel C, Braun HP. The 'protein complex proteome' of chloroplasts in Arabidopsis thaliana. J Proteomics 2013; 91:73-83. [PMID: 23851315 DOI: 10.1016/j.jprot.2013.07.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 06/19/2013] [Accepted: 07/02/2013] [Indexed: 01/30/2023]
Abstract
UNLABELLED Here, a first GelMap of the chloroplast "protein complex proteome" of Arabidopsis thaliana is presented. The GelMap software tool allows assigning multiple proteins to gel spots, thereby taking advantage of the high sensitivity of state-of-the-art mass spectrometry systems. Furthermore, the software allows functional annotation of all identified proteins. If applied to a 2D blue native (BN)/SDS gel, GelMap can selectively display protein complexes of low abundance. For the chloroplast GelMap, highly purified organelles were separated by 2D BN/SDS PAGE and spots were automatically detected using Delta 2D software. Within 287 spots, a total of 1841 proteins were identified (on average 6.4 proteins per spot), representing a set of 436 non redundant proteins. Most of these proteins form part of protein complexes. The quality of the map is reflected by its inclusion of a more or less complete set of protein complexes described for chloroplasts in the literature. The GelMap is publically available at www.gelmap.de/arabidopsis-chloro and may be used as a resource for identifying novel protein complexes within any of its functional categories. BIOLOGICAL SIGNIFICANCE The chloroplast GelMap represents a data resource for the definition of protein complexes in the model plant A. thaliana. It should be useful for in depth understanding of chloroplast biochemistry, as illustrated by the discovery of so far unknown protein complexes. The GelMap is publically available at www.gelmap.de/arabidopsis-chloro.
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Affiliation(s)
- Christof Behrens
- Institute of Plant Genetics, Faculty of Natural Sciences, Leibniz Universität Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany
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Abstract
Plasmodium and Toxoplasma are genera of apicomplexan parasites that infect millions of people each year. The former causes malaria, and the latter causes neurotropic infections associated with a weakened or developing immune system. These parasites harbor a peculiar organelle, the apicoplast. The apicoplast is the product of an ancient endosymbiosis between a heterotrophic and a photosynthetic protist. We explore the cellular and molecular mechanisms that enabled a stable union of two previously independent organisms. These include the exchange of metabolites, transfer of genes, transport of proteins, and overall coordination of biogenesis and proliferation. These mechanisms are still active today and can be exploited to treat parasite infection. They were shaped by the dramatic changes that occurred in the evolution of the phylum Apicomplexa--including the gain and loss of photosynthesis, adaptation to symbiosis and parasitism, and the explosion of animal diversity-that ultimately provided an aquatic alga access to every biotope on this planet.
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Affiliation(s)
- Giel G van Dooren
- Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia;
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50
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Yamasaki K, Motomura Y, Yagi Y, Nomura H, Kikuchi S, Nakai M, Shiina T. Chloroplast envelope localization of EDS5, an essential factor for salicylic acid biosynthesis in Arabidopsis thaliana. PLANT SIGNALING & BEHAVIOR 2013; 8:e23603. [PMID: 23333976 PMCID: PMC7030283 DOI: 10.4161/psb.23603] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Chloroplasts are responsible for biosynthesis of salicylic acid (SA) an important signal molecule in plant immunity. EDS5 is a homolog of the MATE (multidrug and toxic compound extrusion) family of transporters, and is essential for SA biosynthesis. It has been speculated that EDS5 would be involved in the export of SA from chloroplasts. However, the subcellular localization of EDS5 remains largely uncharacterized. We demonstrate here that EDS5 is specifically localized to the chloroplast envelope membrane in Arabidopsis. In addition, we found that EDS5 is preferentially expressed in epidermal cells. These findings suggest that EDS5 is responsible for transport of SA from chloroplasts to the cytoplasm in epidermal cells.
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Affiliation(s)
- Kanako Yamasaki
- Graduate School of Life and Environmental Sciences; Kyoto Prefectural University; Kyoto, Japan
| | - Yukiya Motomura
- Graduate School of Life and Environmental Sciences; Kyoto Prefectural University; Kyoto, Japan
| | - Yusuke Yagi
- Faculty of Agriculture; Kyushu University; Fukuoka, Japan
| | - Hironari Nomura
- Organization of Advanced Science and Technology; Kobe University; Kobe, Japan
| | - Shingo Kikuchi
- Institute for Protein Research; Osaka University; Osaka, Japan
| | - Masato Nakai
- Institute for Protein Research; Osaka University; Osaka, Japan
| | - Takashi Shiina
- Graduate School of Life and Environmental Sciences; Kyoto Prefectural University; Kyoto, Japan
- Correspondence to: Takashi Shiina,
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