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Extracellular Vesicle-Mediated Secretion of Protochlorophyllide in the Cyanobacterium Leptolyngbya boryana. PLANTS 2022; 11:plants11070910. [PMID: 35406890 PMCID: PMC9003413 DOI: 10.3390/plants11070910] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 03/19/2022] [Accepted: 03/25/2022] [Indexed: 11/17/2022]
Abstract
Protochlorophyllide (Pchlide) reduction in the late stage of chlorophyll a (Chl) biosynthesis is catalyzed by two enzymes: light-dependent Pchlide oxidoreductase (LPOR) and dark-operative Pchlide oxidoreductase (DPOR). The differential operation of LPOR and DPOR enables a stable supply of Chl in response to changes in light conditions and environmental oxygen levels. When a DPOR-deficient mutant (YFC2) of the cyanobacterium Leptolyngbya boryana is grown heterotrophically in the dark, Pchlide accumulates in the cells and is secreted into the culture medium. In this study, we demonstrated the extracellular vesicle-mediated secretion of Pchlide. Pchlide fractions were isolated from the culture medium using sucrose density gradient centrifugation. Mass spectrometry analysis revealed that the Pchlide fractions contained porin isoforms, TolC, and FG-GAP repeat-containing protein, which are localized in the outer membrane. Transmission electron microscopy revealed extracellular vesicle-like structures in the vicinity of YFC2 cells and the Pchlide fractions. These findings suggested that the Pchlide secretion is mediated by extracellular vesicles in dark-grown YFC2 cells.
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2
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Triacylglycerol and phytyl ester synthesis in Synechocystis sp. PCC6803. Proc Natl Acad Sci U S A 2020; 117:6216-6222. [PMID: 32123083 DOI: 10.1073/pnas.1915930117] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cyanobacteria are unicellular prokaryotic algae that perform oxygenic photosynthesis, similar to plants. The cells harbor thylakoid membranes composed of lipids related to those of chloroplasts in plants to accommodate the complexes of photosynthesis. The occurrence of storage lipids, including triacylglycerol or wax esters, which are found in plants, animals, and some bacteria, nevertheless remained unclear in cyanobacteria. We show here that the cyanobacterium Synechocystis sp. PCC6803 accumulates both triacylglycerol and wax esters (fatty acid phytyl esters). Phytyl esters accumulate in higher levels under abiotic stress conditions. The analysis of an insertional mutant revealed that the acyltransferase slr2103, with sequence similarity to plant esterase/lipase/thioesterase (ELT) proteins, is essential for triacylglycerol and phytyl ester synthesis in Synechocystis The recombinant slr2103 enzyme showed acyltransferase activity with phytol and diacylglycerol, thus producing phytyl esters and triacylglycerol. Acyl-CoA thioesters were the preferred acyl donors, while acyl-ACP (acyl carrier protein), free fatty acids, or galactolipid-bound fatty acids were poor substrates. The slr2103 protein sequence is unrelated to acyltransferases from bacteria (AtfA) or plants (DGAT1, DGAT2, PDAT), and therefore establishes an independent group of bacterial acyltransferases involved in triacylglycerol and wax ester synthesis. The identification of the gene slr2103 responsible for triacylglycerol synthesis in cyanobacteria opens the possibility of using prokaryotic photosynthetic cells in biotechnological applications.
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Fang L, Ge H, Huang X, Liu Y, Lu M, Wang J, Chen W, Xu W, Wang Y. Trophic Mode-Dependent Proteomic Analysis Reveals Functional Significance of Light-Independent Chlorophyll Synthesis in Synechocystis sp. PCC 6803. MOLECULAR PLANT 2017; 10:73-85. [PMID: 27585879 DOI: 10.1016/j.molp.2016.08.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 08/03/2016] [Accepted: 08/24/2016] [Indexed: 06/06/2023]
Abstract
The photosynthetic model organism Synechocystis sp. PCC 6803 can grow in different trophic modes, depending on the availability of light and exogenous organic carbon source. However, how the protein profile changes to facilitate the cells differentially propagate in different modes has not been comprehensively investigated. Using isobaric labeling-based quantitative proteomics, we simultaneously identified and quantified 45% Synechocystis proteome across four different trophic modes, i.e., autotrophic, heterotrophic, photoheterotrophic, and mixotrophic modes. Among the 155 proteins that are differentially expressed across four trophic modes, proteins involved in nitrogen assimilation and light-independent chlorophyll synthesis are dramatically upregulated in the mixotrophic mode, concomitant with a dramatic increase of PII phosphorylation that senses carbon and nitrogen assimilation status. Moreover, functional study using a mutant defective in light-independent chlorophyll synthesis revealed that this pathway is important for chlorophyll accumulation under a cycled light/dark illumination regime, a condition mimicking day/night cycles in certain natural habitats. Collectively, these results provide the most comprehensive information on trophic mode-dependent protein expression in cyanobacterium, and reveal the functional significance of light-independent chlorophyll synthesis in trophic growth.
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Affiliation(s)
- Longfa Fang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No.1 West Beichen Road, Beijing 100101, China
| | - Haitao Ge
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No.1 West Beichen Road, Beijing 100101, China
| | - Xiahe Huang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No.1 West Beichen Road, Beijing 100101, China
| | - Ye Liu
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No.1 West Beichen Road, Beijing 100101, China
| | - Min Lu
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No.1 West Beichen Road, Beijing 100101, China
| | - Jinlong Wang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No.1 West Beichen Road, Beijing 100101, China
| | - Weiyang Chen
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No.1 West Beichen Road, Beijing 100101, China
| | - Wu Xu
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA 70504, USA
| | - Yingchun Wang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, No.1 West Beichen Road, Beijing 100101, China.
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4
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Wang J, Yu Q, Xiong H, Wang J, Chen S, Yang Z, Dai S. Proteomic Insight into the Response of Arabidopsis Chloroplasts to Darkness. PLoS One 2016; 11:e0154235. [PMID: 27137770 PMCID: PMC4854468 DOI: 10.1371/journal.pone.0154235] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 04/11/2016] [Indexed: 11/23/2022] Open
Abstract
Chloroplast function in photosynthesis is essential for plant growth and development. It is well-known that chloroplasts respond to various light conditions. However, it remains poorly understood about how chloroplasts respond to darkness. In this study, we found 81 darkness-responsive proteins in Arabidopsis chloroplasts under 8 h darkness treatment. Most of the proteins are nucleus-encoded, indicating that chloroplast darkness response is closely regulated by the nucleus. Among them, 17 ribosome proteins were obviously reduced after darkness treatment. The protein expressional patterns and physiological changes revealed the mechanisms in chloroplasts in response to darkness, e.g., (1) inhibition of photosystem II resulted in preferential cyclic electron flow around PSI; (2) promotion of starch degradation; (3) inhibition of chloroplastic translation; and (4) regulation by redox and jasmonate signaling. The results have improved our understanding of molecular regulatory mechanisms in chloroplasts under darkness.
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Affiliation(s)
- Jing Wang
- Department of Mathematics, College of Mathematics and Science, Shanghai Normal University, Shanghai, P.R. China
- Institute of Plant Gene Function, Shanghai Normal University, Shanghai, P.R. China
| | - Qingbo Yu
- Institute of Plant Gene Function, Shanghai Normal University, Shanghai, P.R. China
- Department of Biology, College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, P.R. China
| | - Haibo Xiong
- Institute of Plant Gene Function, Shanghai Normal University, Shanghai, P.R. China
- Department of Biology, College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, P.R. China
| | - Jun Wang
- Department of Mathematics, College of Mathematics and Science, Shanghai Normal University, Shanghai, P.R. China
| | - Sixue Chen
- Department of Biology, Genetics Institute, Plant Molecular and Cellular Program, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, United States of America
| | - Zhongnan Yang
- Institute of Plant Gene Function, Shanghai Normal University, Shanghai, P.R. China
- Department of Biology, College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, P.R. China
| | - Shaojun Dai
- Department of Biology, College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, P.R. China
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5
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Aoki R, Hiraide Y, Yamakawa H, Fujita Y. A novel "oxygen-induced" greening process in a cyanobacterial mutant lacking the transcriptional activator ChlR involved in low-oxygen adaptation of tetrapyrrole biosynthesis. J Biol Chem 2014; 289:1841-51. [PMID: 24297184 PMCID: PMC3894359 DOI: 10.1074/jbc.m113.495358] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 11/27/2013] [Indexed: 11/06/2022] Open
Abstract
ChlR activates the transcription of the chlAII-ho2-hemN operon in response to low-oxygen conditions in the cyanobacterium Synechocystis sp. PCC 6803. Three genes in the operon encode low-oxygen-type enzymes to bypass three oxygen-dependent reactions in tetrapyrrole biosynthesis. A chlR-lacking mutant, ΔchlR, shows poor photoautotrophic growth due to low chlorophyll (Chl) content under low-oxygen conditions, which is caused by no induction of the operon. Here, we characterized the processes of etiolation of ΔchlR cells in low-oxygen conditions and the subsequent regreening of the etiolated cells upon exposure to oxygen, by HPLC, Western blotting, and low-temperature fluorescence spectra. The Chl content of the etiolated ΔchlR cells incubated under low-oxygen conditions for 7 days was only 10% of that of the wild-type with accumulation of almost all intermediates of the magnesium branch of Chl biosynthesis. Both photosystem I (PSI) and photosystem II (PSII) were significantly decreased, accompanied by a preferential decrease of antenna Chl in PSI. Upon exposure to oxygen, the etiolated ΔchlR cells resumed to produce Chl after a short lag (∼2 h), and the level at 72 h was 80% of that of the wild-type. During this novel "oxygen-induced" greening process, the PSI and PSII contents were largely increased in parallel with the increase in Chl contents. After 72 h, the PSI content reached ∼50% of the wild-type level in contrast to the full recovery of PSII. ΔchlR provides a promising alternative system to investigate the biogenesis of PSI and PSII.
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Affiliation(s)
- Rina Aoki
- From the Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
| | - Yuto Hiraide
- From the Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
| | - Hisanori Yamakawa
- From the Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
| | - Yuichi Fujita
- From the Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
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6
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Kopečná J, Sobotka R, Komenda J. Inhibition of chlorophyll biosynthesis at the protochlorophyllide reduction step results in the parallel depletion of Photosystem I and Photosystem II in the cyanobacterium Synechocystis PCC 6803. PLANTA 2013; 237:497-508. [PMID: 23011568 DOI: 10.1007/s00425-012-1761-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Accepted: 09/03/2012] [Indexed: 05/07/2023]
Abstract
In most oxygenic phototrophs, including cyanobacteria, two independent enzymes catalyze the reduction of protochlorophyllide to chlorophyllide, which is the penultimate step in chlorophyll (Chl) biosynthesis. One is light-dependent NADPH:protochlorophyllide oxidoreductase (LPOR) and the second type is dark-operative protochlorophyllide oxidoreductase (DPOR). To clarify the roles of both enzymes, we assessed synthesis and accumulation of Chl-binding proteins in mutants of cyanobacterium Synechocystis PCC 6803 that either completely lack LPOR or possess low levels of the active enzyme due to its ectopic regulatable expression. The LPOR-less mutant grew photoautotrophically in moderate light and contained a maximum of 20 % of the wild-type (WT) Chl level. Both Photosystem II (PSII) and Photosystem I (PSI) were reduced to the same degree. Accumulation of PSII was mostly limited by the synthesis of antennae CP43 and especially CP47 as indicated by the accumulation of reaction center assembly complexes. The phenotype of the LPOR-less mutant was comparable to the strain lacking DPOR that also contained <25 % of the wild-type level of PSII and PSI when cultivated under light-activated heterotrophic growth conditions. However, in the latter case, we detected no reaction center assembly complexes, indicating that synthesis was almost completely inhibited for all Chl-proteins, including the D1 and D2 proteins.
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Affiliation(s)
- Jana Kopečná
- Department of Phototrophic Microorganisms, Institute of Microbiology, Academy of Sciences, Opatovický mlýn, Třeboň, Czech Republic
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7
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Shpilyov AV, Zinchenko VV, Grimm B, Lokstein H. Chlorophyll a phytylation is required for the stability of photosystems I and II in the cyanobacterium Synechocystis sp. PCC 6803. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2013; 73:336-346. [PMID: 23039123 DOI: 10.1111/tpj.12044] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2011] [Revised: 09/28/2012] [Accepted: 10/02/2012] [Indexed: 06/01/2023]
Abstract
In oxygenic phototrophic organisms, the phytyl 'tail' of chlorophyll a is formed from a geranylgeranyl residue by the enzyme geranylgeranyl reductase. Additionally, in oxygenic phototrophs, phytyl residues are the tail moieties of tocopherols and phylloquinone. A mutant of the cyanobacterium Synechocystis sp. PCC 6803 lacking geranylgeranyl reductase, ΔchlP, was compared to strains with specific deficiencies in either tocopherols or phylloquinone to assess the role of chlorophyll a phytylatation (versus geranylgeranylation). The tocopherol-less Δhpt strain grows indistinguishably from the wild-type under 'standard' light photoautotrophic conditions, and exhibited only a slightly enhanced rate of photosystem I degradation under strong irradiation. The phylloquinone-less ΔmenA mutant also grows photoautotrophically, albeit rather slowly and only at low light intensities. Under strong irradiation, ΔmenA retained its chlorophyll content, indicative of stable photosystems. ΔchlP may only be cultured photomixotrophically (due to the instability of both photosystems I and II). The increased accumulation of myxoxanthophyll in ΔchlP cells indicates photo-oxidative stress even under moderate illumination. Under high-light conditions, ΔchlP exhibited rapid degradation of photosystems I and II. In conclusion, the results demonstrate that chlorophyll a phytylation is important for the (photo)stability of photosystems I and II, which, in turn, is necessary for photoautotrophic growth and tolerance of high light in an oxygenic environment.
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Affiliation(s)
- Alexey V Shpilyov
- Biology Division, Genetics Department, Lomonosov Moscow State University, Moscow, 119899, Russia
- Institut für Biologie/Pflanzenphysiologie, Humboldt-Universität zu Berlin, Unter den Linden 6, D-10099, Berlin, Germany
| | - Vladislav V Zinchenko
- Biology Division, Genetics Department, Lomonosov Moscow State University, Moscow, 119899, Russia
| | - Bernhard Grimm
- Institut für Biologie/Pflanzenphysiologie, Humboldt-Universität zu Berlin, Unter den Linden 6, D-10099, Berlin, Germany
| | - Heiko Lokstein
- Institut für Biologie/Pflanzenphysiologie, Humboldt-Universität zu Berlin, Unter den Linden 6, D-10099, Berlin, Germany
- Institut für Biologie III, Albert-Ludwigs-Universität Freiburg, Schänzlestraße 1, D-79104, Freiburg, Germany
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8
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Yao DCI, Brune DC, Vavilin D, Vermaas WFJ. Photosystem II component lifetimes in the cyanobacterium Synechocystis sp. strain PCC 6803: small Cab-like proteins stabilize biosynthesis intermediates and affect early steps in chlorophyll synthesis. J Biol Chem 2011; 287:682-692. [PMID: 22090028 DOI: 10.1074/jbc.m111.320994] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To gain insight in the lifetimes of photosystem II (PSII) chlorophyll and proteins, a combined stable isotope labeling (15N)/mass spectrometry method was used to follow both old and new pigments and proteins. Photosystem I-less Synechocystis cells were grown to exponential or post-exponential phase and then diluted in BG-11 medium with [15N]ammonium and [15N]nitrate. PSII was isolated, and the masses of PSII protein fragments and chlorophyll were determined. Lifetimes of PSII components ranged from 1.5 to 40 h, implying that at least some of the proteins and chlorophyll turned over independently from each other. Also, a significant amount of nascent PSII components accumulated in thylakoids when cells were in post-exponential growth phase. In a mutant lacking small Cab-like proteins (SCPs), most PSII protein lifetimes were unaffected, but the lifetime of chlorophyll and the amount of nascent PSII components that accumulated were decreased. In the absence of SCPs, one of the PSII biosynthesis intermediates, the monomeric PSII complex without CP43, was missing. Therefore, SCPs may stabilize nascent PSII protein complexes. Moreover, upon SCP deletion, the rate of chlorophyll synthesis and the accumulation of early tetrapyrrole precursors were drastically reduced. When [14N]aminolevulinic acid (ALA) was supplemented to 15N-BG-11 cultures, the mutant lacking SCPs incorporated much more exogenous ALA into chlorophyll than the control demonstrating that ALA biosynthesis was impaired in the absence of SCPs. This illustrates the major effects that nonstoichiometric PSII components such as SCPs have on intermediates and assembly but not on the lifetime of PSII proteins.
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Affiliation(s)
- Danny C I Yao
- School of Life Sciences and Center for Bioenergy and Photosynthesis, Arizona State University, Tempe, Arizona 85287-4501
| | - Daniel C Brune
- School of Life Sciences and Center for Bioenergy and Photosynthesis, Arizona State University, Tempe, Arizona 85287-4501
| | - Dmitri Vavilin
- School of Life Sciences and Center for Bioenergy and Photosynthesis, Arizona State University, Tempe, Arizona 85287-4501
| | - Wim F J Vermaas
- School of Life Sciences and Center for Bioenergy and Photosynthesis, Arizona State University, Tempe, Arizona 85287-4501.
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Nixon PJ, Michoux F, Yu J, Boehm M, Komenda J. Recent advances in understanding the assembly and repair of photosystem II. ANNALS OF BOTANY 2010; 106:1-16. [PMID: 20338950 PMCID: PMC2889791 DOI: 10.1093/aob/mcq059] [Citation(s) in RCA: 382] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Revised: 02/01/2010] [Accepted: 02/09/2010] [Indexed: 05/18/2023]
Abstract
BACKGROUND Photosystem II (PSII) is the light-driven water:plastoquinone oxidoreductase of oxygenic photosynthesis and is found in the thylakoid membrane of chloroplasts and cyanobacteria. Considerable attention is focused on how PSII is assembled in vivo and how it is repaired following irreversible damage by visible light (so-called photoinhibition). Understanding these processes might lead to the development of plants with improved growth characteristics especially under conditions of abiotic stress. SCOPE Here we summarize recent results on the assembly and repair of PSII in cyanobacteria, which are excellent model organisms to study higher plant photosynthesis. CONCLUSIONS Assembly of PSII is highly co-ordinated and proceeds through a number of distinct assembly intermediates. Associated with these assembly complexes are proteins that are not found in the final functional PSII complex. Structural information and possible functions are beginning to emerge for several of these 'assembly' factors, notably Ycf48/Hcf136, Psb27 and Psb28. A number of other auxiliary proteins have been identified that appear to have evolved since the divergence of chloroplasts and cyanobacteria. The repair of PSII involves partial disassembly of the damaged complex, the selective replacement of the damaged sub-unit (predominantly the D1 sub-unit) by a newly synthesized copy, and reassembly. It is likely that chlorophyll released during the repair process is temporarily stored by small CAB-like proteins (SCPs). A model is proposed in which damaged D1 is removed in Synechocystis sp. PCC 6803 by a hetero-oligomeric complex composed of two different types of FtsH sub-unit (FtsH2 and FtsH3), with degradation proceeding from the N-terminus of D1 in a highly processive reaction. It is postulated that a similar mechanism of D1 degradation also operates in chloroplasts. Deg proteases are not required for D1 degradation in Synechocystis 6803 but members of this protease family might play a supplementary role in D1 degradation in chloroplasts under extreme conditions.
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Affiliation(s)
- Peter J Nixon
- Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.
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10
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Masuda T. Recent overview of the Mg branch of the tetrapyrrole biosynthesis leading to chlorophylls. PHOTOSYNTHESIS RESEARCH 2008; 96:121-43. [PMID: 18273690 DOI: 10.1007/s11120-008-9291-4] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2007] [Accepted: 01/29/2008] [Indexed: 05/20/2023]
Abstract
In plants, chlorophylls (chlorophyll a and chlorophyll b) are the most abundant tetrapyrrole molecules and are essential for photosynthesis. The first committed step of chlorophyll biosynthesis is the insertion of Mg(2+) into protoporphyrin IX, and thus subsequent steps of the biosynthesis are called the Mg branch. As the Mg branch in higher plants is complex, it was not until the last decade--after many years of intensive research--that most of the genes encoding the enzymes for the pathway were identified. Biochemical and molecular genetic analyses have certainly modified the classic metabolic map of tetrapyrrole biosynthesis, and only recently have the molecular mechanisms of regulatory pathways governing chlorophyll metabolism been elucidated. As a result, novel functions of tetrapyrroles and biosynthetic enzymes have been proposed. In this review, I summarize the recent findings on enzymes involved in the Mg branch, mainly in higher plants.
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Affiliation(s)
- Tatsuru Masuda
- Graduate School of Arts and Sciences, The University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan.
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11
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Vermaas WFJ, Timlin JA, Jones HDT, Sinclair MB, Nieman LT, Hamad SW, Melgaard DK, Haaland DM. In vivo hyperspectral confocal fluorescence imaging to determine pigment localization and distribution in cyanobacterial cells. Proc Natl Acad Sci U S A 2008; 105:4050-5. [PMID: 18316743 PMCID: PMC2268818 DOI: 10.1073/pnas.0708090105] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2007] [Indexed: 11/18/2022] Open
Abstract
Hyperspectral confocal fluorescence imaging provides the opportunity to obtain individual fluorescence emission spectra in small ( approximately 0.03-microm(3)) volumes. Using multivariate curve resolution, individual fluorescence components can be resolved, and their intensities can be calculated. Here we localize, in vivo, photosynthesis-related pigments (chlorophylls, phycobilins, and carotenoids) in wild-type and mutant cells of the cyanobacterium Synechocystis sp. PCC 6803. Cells were excited at 488 nm, exciting primarily phycobilins and carotenoids. Fluorescence from phycocyanin, allophycocyanin, allophycocyanin-B/terminal emitter, and chlorophyll a was resolved. Moreover, resonance-enhanced Raman signals and very weak fluorescence from carotenoids were observed. Phycobilin emission was most intense along the periphery of the cell whereas chlorophyll fluorescence was distributed more evenly throughout the cell, suggesting that fluorescing phycobilisomes are more prevalent along the outer thylakoids. Carotenoids were prevalent in the cell wall and also were present in thylakoids. Two chlorophyll fluorescence components were resolved: the short-wavelength component originates primarily from photosystem II and is most intense near the periphery of the cell; and the long-wavelength component that is attributed to photosystem I because it disappears in mutants lacking this photosystem is of higher relative intensity toward the inner rings of the thylakoids. Together, the results suggest compositional heterogeneity between thylakoid rings, with the inner thylakoids enriched in photosystem I. In cells depleted in chlorophyll, the amount of both chlorophyll emission components was decreased, confirming the accuracy of the spectral assignments. These results show that hyperspectral fluorescence imaging can provide unique information regarding pigment organization and localization in the cell.
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Affiliation(s)
- Wim F. J. Vermaas
- *School of Life Sciences and Center for Bioenergy and Photosynthesis, Arizona State University, Box 874501, Tempe, AZ 85287-4501; and
| | | | | | | | | | - Sawsan W. Hamad
- *School of Life Sciences and Center for Bioenergy and Photosynthesis, Arizona State University, Box 874501, Tempe, AZ 85287-4501; and
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12
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Liu X, Zhao J, Wu Q. Sorbitol regulates energy transfer from allophycocyanin to the terminal emitter within phycobilisomes in Synechocystis sp. Biotechnol Lett 2006; 29:253-9. [PMID: 17091373 DOI: 10.1007/s10529-006-9225-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Revised: 10/02/2006] [Accepted: 10/02/2006] [Indexed: 10/23/2022]
Abstract
The effects of sorbitol on energy transfer of phycobilisomes (PBSs) in vivo were investigated in a chlN deletion mutant of Synechocystis sp. PCC 6803. When the mutant was grown in the dark, it contained intact and functional PBSs but essentially no chlorophyll or photosystems. Therefore, the structural and functional changes of the mutant PBSs in vivo can be detected by measurement of low temperature (77 K) and room temperature fluorescence emission spectra. Our results, for the first time, demonstrate that sorbitol decreases the energy transfer from allophycocyanin to the terminal emitter, indicating the site for osmotic regulation of excitation transfer in PBSs.
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Affiliation(s)
- Xingguo Liu
- Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, China
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13
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Liu X, Zhao J, Wu Q. Biogenesis of chlorophyll-binding proteins under iron stress in Synechocystis sp. PCC 6803. BIOCHEMISTRY (MOSCOW) 2006; 71 Suppl 1:S101-4. [PMID: 16487060 DOI: 10.1134/s0006297906130177] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The biogenesis of chlorophyll-binding proteins under iron stress has been investigated in vivo in a chlN deletion mutant of Synechocystis sp. PCC 6803. The chlN gene encodes one subunit of the light-independent protochlorophyllide reductase. The mutant is unable to synthesis chlorophyll in darkness, causing chlorophyll biosynthesis to become light dependent. When the mutant was propagated in darkness, essentially no chlorophyll and photosystems were detected. Upon return of the chlN deletion mutant to light, 77 K fluorescence emission spectra and oxygen evolution of greening cells under iron-sufficient or -deficient conditions were measured. The gradual blue shift of the photosystem I (PS I) peak upon greening under iron stress suggested the structural alteration of newly synthesized PS I. Furthermore, the rate of biogenesis of PS II was delayed under iron stress, which might be due to the presence of IsiA.
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Affiliation(s)
- X Liu
- Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, P R China
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14
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Heyes DJ, Hunter CN. Making light work of enzyme catalysis: protochlorophyllide oxidoreductase. Trends Biochem Sci 2005; 30:642-9. [PMID: 16182531 DOI: 10.1016/j.tibs.2005.09.001] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2005] [Revised: 08/08/2005] [Accepted: 09/12/2005] [Indexed: 10/25/2022]
Abstract
In the chlorophyll biosynthetic pathway, the enzyme protochlorophyllide oxidoreductase (POR) catalyses a key light-driven reaction that triggers a profound transformation in plant development. Because POR is activated by light, it can provide information on the way in which light energy can be harnessed to power enzyme reactions and it presents us with a unique opportunity to study catalysis at low temperatures and on ultrafast timescales that are not accessible for most analyses of enzyme function. Recent advances in our understanding of the catalytic mechanism of POR illustrate why it is an important generic model for studying enzyme catalysis and reaction dynamics.
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Affiliation(s)
- Derren J Heyes
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
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Liu XG, Zhao JJ, Wu QY. Oxidative stress and metal ions effects on the cores of phycobilisomes inSynechocystissp. PCC 6803. FEBS Lett 2005; 579:4571-6. [PMID: 16098525 DOI: 10.1016/j.febslet.2005.07.020] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2005] [Accepted: 07/13/2005] [Indexed: 11/24/2022]
Abstract
Inactivation of the chlN gene in Synechocystis sp. PCC 6803 resulted in no chlorophyll and photosystems when the mutant was grown in darkness, providing an in vivo system to study the structure and function of phycobilisomes (PBSs). The effects of hydrogen peroxide (H2O2) and metal ions on the mutant PBSs in vivo were investigated by low temperature fluorescence emission measurement. H2O2 induced an obvious disassembly of the cores of PBSs and interruption of energy transfer from allophycocyanin to the terminal emitter. Among many metal ions only silver induced disassembly of the cores of PBSs. Our results demonstrated for the first time that the cores of PBSs act as targets in vivo for oxidative stress or silver induced damage.
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Affiliation(s)
- Xing-Guo Liu
- Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, PR China
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Ishikawa Y, Schröder WP, Funk C. Functional analysis of the PsbP-like protein (sll1418) in Synechocystis sp. PCC 6803. PHOTOSYNTHESIS RESEARCH 2005; 84:257-62. [PMID: 16049783 DOI: 10.1007/s11120-005-0477-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2004] [Accepted: 01/12/2005] [Indexed: 05/03/2023]
Abstract
A recent proteomic analysis of the thylakoid lumen of Arabidopsis thaliana revealed the presence of several PsbP-like proteins, and a homologue to this gene family was detected in the genome of the cyanobacterium Synechocystis sp. PCC 6803 (Schubert M, Petersson UA, Haas BJ, Funk C, Schröder WP, Kieselbach T (2002) J Biol Chem 277, 8354-8365). Using a peptide-directed antibody against this cyanobacterial PsbP-like protein (sll1418) we could show that it was localized in the thylakoid membrane and associated with Photosystem II. While salt washes did not remove the PsbP-like protein from the thylakoid membrane, it was partially lost during the detergent-based isolation of PSII membrane fractions. In total cell extracts this protein is present in the same amount as the extrinsic PsbO protein. We did not see any significant functional difference between the wild-type and a PsbP-like insertion mutant.
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Affiliation(s)
- Yasuo Ishikawa
- Department of Biochemistry, Umeå University, 90187, Umeå, Sweden
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Xu H, Vavilin D, Funk C, Vermaas W. Multiple Deletions of Small Cab-like Proteins in the Cyanobacterium Synechocystis sp. PCC 6803. J Biol Chem 2004; 279:27971-9. [PMID: 15107425 DOI: 10.1074/jbc.m403307200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Deletion of the genes for four or five small Cab-like proteins (SCPs) in photosystem (PS) I-less and PS I-less/PS II-less strains of Synechocystis sp. PCC 6803 caused a large decrease in the chlorophyll and carotenoid content of the cells without accumulation of early intermediates in the chlorophyll biosynthesis pathway, suggesting limited chlorophyll availability. The PS II/PS I ratio increased upon deletion of multiple SCPs in a wild type background, similar to what is observed in the presence of subsaturating concentrations of gabaculin, an inhibitor of an early step in the tetrapyrrole biosynthesis pathway. Upon deletion of multiple SCPs, neither 77 K fluorescence emission properties of phycobilisomeless thylakoids from the PS I-less/PS II-less strain nor the energy trapping efficiency of PS II were affected, indicating that under steady-state conditions SCPs do not bind much chlorophyll and do not serve as PS II antenna. Under conditions where protochlorophyllide reduction and thus chlorophyll synthesis were inhibited, chlorophyll disappeared quickly in a mutant lacking all five SCPs. This implies a role of SCPs in stabilization of chlorophyll-binding proteins and/or in reuse of chlorophylls. Under these conditions of inhibited reduction of protochlorophyllide, the accumulation kinetics of this intermediate were greatly altered in the absence of the five SCPs. This indicates an alteration of tetrapyrrole biosynthesis kinetics by SCPs. Based on this and other evidence, we propose that SCPs bind carotenoids and transiently bind chlorophyll, aiding in the supply of chlorophyll to nascent or reassembling photosynthetic complexes, and regulate the tetrapyrrole biosynthesis pathway as a function of the demand for chlorophyll.
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Affiliation(s)
- Hong Xu
- School of Life Sciences and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, AZ 85287-4501, USA
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18
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Mao HB, Li GF, Li DH, Wu QY, Gong YD, Zhang XF, Zhao NM. Effects of glycerol and high temperatures on structure and function of phycobilisomes inSynechocystissp. PCC 6803. FEBS Lett 2003; 553:68-72. [PMID: 14550548 DOI: 10.1016/s0014-5793(03)00973-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of glycerol and high temperatures on structure and function of phycobilisomes (PBSs) in vivo were investigated in a chlL deletion mutant of the cyanobacterium Synechocystis sp. PCC 6803. When the mutant was grown under light-activated heterotrophic growth conditions, it contained intact and functional PBSs, but essentially no chlorophyll and photosystems. So the structural and functional changes of the mutant PBSs in vivo can be handily detected by measurement of low temperature (77 K) fluorescence emission spectra. High concentration glycerol induced an obvious disassembly of PBSs and the dissociation of phycocyanins in the rod substructures into their oligomers and monomers. PBSs also disassembled at high temperatures and allophycocyanins were more sensitive to heat stress than phycocyanins. Our results demonstrate that the chlL(-) mutant strain is an advantageous model for studying the mechanisms of assembly and disassembly of protein complexes in vivo.
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Affiliation(s)
- Hai-Bin Mao
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, PR China
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Xu H, Vavilin D, Vermaas W. The presence of chlorophyll b in Synechocystis sp. PCC 6803 disturbs tetrapyrrole biosynthesis and enhances chlorophyll degradation. J Biol Chem 2002; 277:42726-32. [PMID: 12207014 DOI: 10.1074/jbc.m205237200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Both chlorophyll (Chl) a and b accumulate in the light in a Synechocystis sp. PCC 6803 strain that expresses higher plant genes coding for a light-harvesting complex II protein and Chl a oxygenase. This cyanobacterial strain also lacks photosystem (PS) I and cannot synthesize Chl in darkness because of the lack of chlL. When this PS I-less/chlL(-)/lhcb(+)/cao(+) strain was grown in darkness, small amounts of two unusual tetrapyrroles, protochlorophyllide (PChlide) b and pheophorbide (pheide) b, were identified. Accumulation of PChlide b trailed that of PChlide a by several days, suggesting that PChlide a is an inefficient substrate of Chl a oxygenase. The presence of pheide b in this organism suggests a breakdown of Chl b via a pathway that does not involve conversion to a-type pigments. When the PS I-less/chlL(-) control strain was grown in darkness, Chl degradation was much slower than in the PS I-less/chlL(-)/lhcb(+)/cao(+) strain, suggesting that the presence of Chl b leads to more rapid turnover of Chl-binding proteins and/or a more active Chl degradation pathway. Levels and biosynthesis kinetics of Chl and of its biosynthetic intermediates are very different in the PS I-less/chlL(-)/lhcb(+)/cao(+) strain versus in the control. Moreover, when grown in darkness for 14 days, upon the addition of delta-aminolevulinic acid, the level of magnesium-protoporphyrin IX increased 60-fold in the PS I-less/chlL(-)/lhcb(+)/cao(+) strain (only approximately 2-fold in the PS I-less/chlL(-) control strain), whereas the PChlide and protoheme levels remained fairly constant. We propose that a b-type PChlide, Chl, or pheide in the PS I-less/chlL(-)/lhcb(+)/cao(+) strain may bind to tetrapyrrole biosynthesis regulatory protein(s) (for example, the small Cab-like proteins) and thus affect the regulation of this pathway.
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Affiliation(s)
- Hong Xu
- Department of Plant Biology and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, USA
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Xu H, Vavilin D, Vermaas W. Chlorophyll b can serve as the major pigment in functional photosystem II complexes of cyanobacteria. Proc Natl Acad Sci U S A 2001; 98:14168-73. [PMID: 11717469 PMCID: PMC61186 DOI: 10.1073/pnas.251530298] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
An Arabidopsis thaliana chlorophyll(ide) a oxygenase gene (cao), which is responsible for chlorophyll b synthesis from chlorophyll a, was introduced and expressed in a photosystem I-less strain of the cyanobacterium Synechocystis sp. PCC 6803. In this strain, most chlorophyll is associated with the photosystem II complex. In line with observations by Satoh et al. [Satoh, S., Ikeuchi, M., Mimuro, M. & Tanaka, A. (2001) J. Biol. Chem. 276, 4293-4297], chlorophyll b was made but accounted for less than 10% of total chlorophyll. However, when lhcb encoding light-harvesting complex (LHC)II from pea was present in the same strain (lhcb(+)/cao(+)), chlorophyll b accumulated in the cell to levels exceeding those of chlorophyll a, although LHCII did not accumulate. In the lhcb(+)/cao(+) strain, the total amount of chlorophyll, the number of chlorophylls per photosystem II center, and the oxygen-evolving activity on a per-chlorophyll basis were similar to those in the photosystem I-less strain. Furthermore, the chlorophyll a/b ratio of photosystem II core particles (retaining CP47 and CP43) and of whole cells of the lhcb(+)/cao(+) strain was essentially identical, and PS II activity could be obtained efficiently by chlorophyll b excitation. These data indicate that chlorophyll b functionally substitutes for chlorophyll a in photosystem II. Therefore, the availability of chlorophylls, rather than their binding specificity, may determine which chlorophyll is incorporated at many positions of photosystem II. We propose that the transient presence of a LHCII/chlorophyll(ide) a oxygenase complex in the lhcb(+)/cao(+) strain leads to a high abundance of available chlorophyll b that is subsequently incorporated into photosystem II complexes. The apparent LHCII requirement for high chlorophyll(ide) a oxygenase activity may be instrumental to limit the occurrence of chlorophyll b in plants to LHC proteins.
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Affiliation(s)
- H Xu
- Department of Plant Biology and Center of the Study of Early Events in Photosynthesis, Arizona State University, Box 871601, Tempe, AZ 85287-1601, USA
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21
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He Q, Schlich T, Paulsen H, Vermaas W. Expression of a higher plant light-harvesting chlorophyll a/b-binding protein in Synechocystis sp. PCC 6803. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 263:561-70. [PMID: 10406967 DOI: 10.1046/j.1432-1327.1999.00526.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A chimeric lhcb gene, coding for Lhcb, a higher plant chlorophyll a/b-binding light-harvesting complex of photosystem II (LHCII), was constructed using the Synechocystis sp. PCC 6803 psbA3 promoter and a modified lhcb gene from pea. This construct drives synthesis of full-length, mature Lhcb under the control of the strong psbA3 promoter that usually drives expression of the D1 protein of photosystem II. This chimeric gene was transformed into a photosystem I-less/chlL(-) Synechocystis sp. PCC 6803 strain that is unable to synthesize chlorophyll in darkness. In the resulting strain, a high level of lhcb transcript was detected and transcript accumulation was enhanced by addition of exogenous Zn-chlorophyllide b. The chimeric lhcb gene was translated to produce full-length Lhcb as demonstrated by pulse-labeling: a new radioactively labeled band of a size corresponding to full-length Lhcb was visible on autoradiograms. Using Triton X-114 phase fractionation, this labeled protein band was found to partition to the phase containing integral membrane proteins, indicating that the pulse-labeled Lhcb is readily integrated into the membrane. However, Lhcb was rapidly degraded and did not accumulate in thylakoid membranes to levels that were detectable other than by pulse labeling. Upon immunological detection with LHCII antibodies, a small protein (approximately 8 kDa) was found specifically in the lhcb-containing mutant. We interpret this protein to be a degradation product of the full-length Lhcb. This fragment was stabilized by supplementing cells with xanthophylls, which incorporated into thylakoid membranes only in the mutant carrying lhcb. The lutein/chlorophyll ratio of thylakoids of this mutant was about 1 : 10. These results indicate that in this cyanobacterial system Lhcb is synthesized, integrated into the membrane, and then degraded to a approximately 8 kDa fragment that is stabilized by pigment binding and does not require the presence of chlorophyll b.
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Affiliation(s)
- Q He
- Department of Plant Biology and Center for the Study of Early Events in Photosynthesis, Arizona State University, Box 871601, Tempe, AZ 85287-1601, USA
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22
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He Q, Vermaas W. Chlorophyll a availability affects psbA translation and D1 precursor processing in vivo in Synechocystis sp. PCC 6803. Proc Natl Acad Sci U S A 1998; 95:5830-5. [PMID: 9576970 PMCID: PMC20465 DOI: 10.1073/pnas.95.10.5830] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Transcript accumulation and translation of psbA as well as processing of the D1 precursor protein were investigated in relation to chlorophyll availability in vivo in cyanobacterial strains lacking photosystem I (PS I). The psbA transcript level was almost independent of chlorophyll availability and was approximately 3-fold lower in darkness than in continuous light (5 microE m-2 s-1). Upon illumination, it reached a steady-state level within several hours. Upon growth under light-activated heterotrophic growth conditions (LAHG) in the PS I-less strain, D1 synthesis occurred immediately upon illumination. However, in PS I-less/chlL- cells, which lacked the light-independent chlorophyll biosynthesis pathway and had very low chlorophyll levels after LAHG growth, very little D1 synthesis occurred upon illumination, and the synthesis rate increased with time. This result suggests a translational control of D1 biosynthesis related to chlorophyll availability. Upon illumination, initially a high level of the nonprocessed D1 precursor was observed by pulse labeling and immunodetection in LAHG-grown PS I-less/chlL- cells but not in PS I-less cells. A significant amount of the D1 precursor eventually was processed to mature D1, and the half-life of the D1 precursor decreased as the chlorophyll content of the cells increased. The D1 processing enzyme CtpA was found to be present at similar levels regardless illumination or chlorophyll levels. We conclude that, directly or indirectly, chlorophyll availability is needed for D1 translation as well as for efficient processing of the D1 precursor.
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Affiliation(s)
- Q He
- Department of Plant Biology and Center for the Study of Early Events in Photosynthesis, Arizona State University, Box 871601, Tempe, AZ 85287-1601, USA
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Armstrong GA. Greening in the dark: light-independent chlorophyll biosynthesis from anoxygenic photosynthetic bacteria to gymnosperms. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 1998. [DOI: 10.1016/s1011-1344(98)00063-3] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Khudyakov I, Wolk CP. hetC, a gene coding for a protein similar to bacterial ABC protein exporters, is involved in early regulation of heterocyst differentiation in Anabaena sp. strain PCC 7120. J Bacteriol 1997; 179:6971-8. [PMID: 9371442 PMCID: PMC179636 DOI: 10.1128/jb.179.22.6971-6978.1997] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Transposon-generated mutant C3 of Anabaena sp. strain PCC 7120 is unable to form heterocysts upon deprivation of combined nitrogen but forms a pattern of spaced, weakly fluorescent cells after 2 days of deprivation. Sequence analysis of chromosomal DNA adjacent to the ends of transposon Tn5-1058 in mutant C3 showed a 1,044-amino-acid open reading frame, designated hetC, whose predicted protein product throughout its C-terminal two-thirds has extensive similarity to the HlyB family of bacterial protein exporters. Its N-terminal third is unique and does not resemble any known protein. hetC lies 1,165 bp 5' from the previously described gene hetP. Reconstruction of the C3 mutation and its complementation in trans with a wild-type copy of hetC confirmed that hetC has an essential regulatory role early in heterocyst development. hetC is induced ca. 4 h after nitrogen stepdown, hours after induction of hetR. Expression of hetC depends on HetR and may depend on HetC. Highly similar sequences are present 5' from the initiation codons and in the 3' untranslated regions of hetC and of two heterocyst-specific genes, devA and hetP.
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Affiliation(s)
- I Khudyakov
- MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing 48824, USA
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