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Tano DW, Kozlowska MA, Easter RA, Woodson JD. Multiple pathways mediate chloroplast singlet oxygen stress signaling. PLANT MOLECULAR BIOLOGY 2023; 111:167-187. [PMID: 36266500 DOI: 10.1007/s11103-022-01319-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Accepted: 10/07/2022] [Indexed: 06/16/2023]
Abstract
Chloroplast singlet oxygen initiates multiple pathways to control chloroplast degradation, cell death, and nuclear gene expression. Chloroplasts can respond to stress and changes in the environment by producing reactive oxygen species (ROS). Aside from being cytotoxic, ROS also have signaling capabilities. For example, the ROS singlet oxygen (1O2) can initiate nuclear gene expression, chloroplast degradation, and cell death. To unveil the signaling mechanisms involved, researchers have used several 1O2-producing Arabidopsis thaliana mutants as genetic model systems, including plastid ferrochelatase two (fc2), fluorescent in blue light (flu), chlorina 1 (ch1), and accelerated cell death 2 (acd2). Here, we compare these 1O2-producing mutants to elucidate if they utilize one or more signaling pathways to control cell death and nuclear gene expression. Using publicly available transcriptomic data, we demonstrate fc2, flu, and ch1 share a core response to 1O2 accumulation, but maintain unique responses, potentially tailored to respond to their specific stresses. Subsequently, we used a genetic approach to determine if these mutants share 1O2 signaling pathways by testing the ability of genetic suppressors of one 1O2 producing mutant to suppress signaling in a different 1O2 producing mutant. Our genetic analyses revealed at least two different chloroplast 1O2 signaling pathways control cellular degradation: one specific to the flu mutant and one shared by fc2, ch1, and acd2 mutants, but with life-stage-specific (seedling vs. adult) features. Overall, this work reveals chloroplast stress signaling involving 1O2 is complex and may allow cells to finely tune their physiology to environmental inputs.
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Affiliation(s)
- David W Tano
- The School of Plant Sciences, University of Arizona, 1140 E, South Campus Drive, 303 Forbes Hall, Tucson, AZ, 85721-0036, USA
| | - Marta A Kozlowska
- The School of Plant Sciences, University of Arizona, 1140 E, South Campus Drive, 303 Forbes Hall, Tucson, AZ, 85721-0036, USA
| | - Robert A Easter
- The School of Plant Sciences, University of Arizona, 1140 E, South Campus Drive, 303 Forbes Hall, Tucson, AZ, 85721-0036, USA
| | - Jesse D Woodson
- The School of Plant Sciences, University of Arizona, 1140 E, South Campus Drive, 303 Forbes Hall, Tucson, AZ, 85721-0036, USA.
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Woodson JD. Control of chloroplast degradation and cell death in response to stress. Trends Biochem Sci 2022; 47:851-864. [DOI: 10.1016/j.tibs.2022.03.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 02/25/2022] [Accepted: 03/14/2022] [Indexed: 12/16/2022]
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Bhatt M, Pandey SS, Tiwari AK, Tiwari BS. Plastid-mediated singlet oxygen in regulated cell death. PLANT BIOLOGY (STUTTGART, GERMANY) 2021; 23:686-694. [PMID: 33768665 DOI: 10.1111/plb.13260] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Accepted: 03/09/2021] [Indexed: 06/12/2023]
Abstract
Reactive oxygen species (ROS) generation within a cell is a natural process of specific subcellular components involved in redox reactions. Within a plant cell, chloroplasts are one of the major sources of ROS generation. Plastid-generated ROS molecules include singlet oxygen (1 O2 ), superoxide radical (O2 - ), hydroxyl radical (OH• ) and hydrogen peroxide (H2 O2 ), which are produced mainly during photochemical reactions of photosynthesis and chlorophyll biosynthetic process. Under normal growth and developmental, generated ROS molecules act as a secondary messenger controlling several metabolic reactions; however, perturbed environmental conditions lead to multi-fold amplification of cellular ROS that eventually kill the target cell. To maintain homeostasis between production and scavenging of ROS, the cell has instituted several enzymatic and non-enzymatic antioxidant machineries to maintain ROS at a physiological level. Among chloroplastic ROS molecules, excess generation of singlet oxygen (1 O2 ) is highly deleterious to the cell metabolic functions and survival. Interestingly, within cellular antioxidant machinery, enzymes involved in detoxification of 1 O2 are lacking. Recent studies suggest that under optimal concentrations, 1 O2 acts as a signalling molecule and drives the cell to either the acclimation pathway or regulated cell death (RCD). Stress-induced RCD is a survival mechanism for the whole plant, while the involvement of chloroplasts and chloroplast-localized molecules that execute RCD are not well understood. In this review, we advocate for participation of chloroplasts-generated 1 O2 in signalling and RCD in plants.
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Affiliation(s)
- M Bhatt
- Institute of Advanced Research, Gandhinagar, Gujrat, India
| | - S S Pandey
- Biotechnology Division, CSIR-Institute of Himalayan Bioresource Technology, Palampur, H.P., India
| | - A K Tiwari
- Institute of Advanced Research, Gandhinagar, Gujrat, India
| | - B S Tiwari
- Institute of Advanced Research, Gandhinagar, Gujrat, India
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Ambastha V, Chauhan G, Tiwari BS, Tripathy BC. Execution of programmed cell death by singlet oxygen generated inside the chloroplasts of Arabidopsis thaliana. PROTOPLASMA 2020; 257:841-851. [PMID: 31909436 DOI: 10.1007/s00709-019-01467-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Accepted: 12/04/2019] [Indexed: 06/10/2023]
Abstract
Absorption of excess excitation energy induces overproduction of singlet oxygen (1O2) in plants. The major sources of singlet oxygen production are chlorophyll and its intermediates located in the chloroplast. Over-accumulation of the chlorophyll biosynthetic intermediate protochlorophyllide by the exogenous application of 5-aminolevulinic acid (ALA), the precursor of tetrapyrrole, induced singlet oxygen production in the plastidic membranes. Over-expression of protochlorophyllide oxidoreductase C (PORC) in Arabidopsis thaliana resulted in efficient light-induced photo-transformation of protochlorophyllide to chlorophyllide that limited the accumulation of protochlorophyllide. Consequently, the 1O2 generation decreased in the PORC overexpressors (PORCx) and their cell death was minimal. Conversely, porC-2 over-accumulated protochlorophyllide in response to ALA treatment and generated higher amounts of 1O2 in light and had highest cell death as monitored by Evans blue staining. The protoplasts isolated from PORCx plants, when treated with ALA, generated minimal amounts of 1O2 as revealed by singlet oxygen sensor green (SOSG) fluorescence emission from chloroplasts. Conversely, the protoplasts of porC-2 mutants under identical conditions generated the maximum SOSG fluorescence in their chloroplasts and cytosol surrounding the chloroplasts most likely due to the leakage from the organelle. The membrane blebbing, a hallmark of programmed cell death, was clearly visible in WT and porC-2 protoplasts. Similarly, the nick end labelling (TUNEL) assay revealed nicks in the DNA. The TUNEL-positive nuclei after 30 min of light exposure were highest in porC-2 and lowest in PORCx protoplasts. The results demonstrate that higher amounts of singlet oxygen produced in the chloroplasts play an important role in programmed cell death.
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Affiliation(s)
- Vivek Ambastha
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Garima Chauhan
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Budhi Sagar Tiwari
- School of Biological Sciences and Biotechnology, Institute of Advanced Research, Koba, Gandhinagar, Gujarat, 382007, India
| | - Baishnab C Tripathy
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India.
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Wu X, Liang C. Enhancing tolerance of rice (Oryza sativa) to simulated acid rain by exogenous abscisic acid. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2017; 24:4860-4870. [PMID: 27987126 DOI: 10.1007/s11356-016-8219-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 12/07/2016] [Indexed: 06/06/2023]
Abstract
Abscisic acid (ABA) regulates much important plant physiological and biochemical processes and induces tolerance to different stresses. Here, we studied the regulation of exogenous ABA on adaptation of rice seedlings to simulated acid rain (SAR) stress by measuring biomass dry weight, stomatal conductance, net photosynthesis rate, nutrient elements, and endogenous hormones. The application of 10 μM ABA alleviated the SAR-induced inhibition on growth, stomatal conductance, net photosynthesis rate, and decreases in contents of nutrient (K, Mg, N, and P) and hormone (auxin, gibberellins, and zeatin). Moreover, 10 μM ABA could stimulate the Ca content as signaling molecules under SAR stress. Contrarily, the application of 100 μM ABA aggravated the SAR-induced inhibition on growth, stomatal conductance, net photosynthesis rate, and contents of nutrient and hormone. The results got after a 5-day recovery (without SAR) show that exogenous 10 μM ABA can promote self-restoration process in rice whereas 100 μM ABA hindered the restoration by increasing deficiency of nutrients and disturbing the balance of hormones. These results confirmed that exogenous ABA at proper concentration could enhance the tolerance of rice to SAR stress.
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Affiliation(s)
- Xi Wu
- State Key Laboratory of Food Science and Technology, Jiangsu Key Laboratory of Anaerobic Biotechnology, College of Environment and Civil Engineering, Jiangnan University, Wuxi, 214122, China
| | - Chanjuan Liang
- State Key Laboratory of Food Science and Technology, Jiangsu Key Laboratory of Anaerobic Biotechnology, College of Environment and Civil Engineering, Jiangnan University, Wuxi, 214122, China.
- Jiangsu Cooperative Innovation Center of Technology and Material of Water Treatment, Wuxi, 214122, China.
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Klasek L, Inoue K. Dual Protein Localization to the Envelope and Thylakoid Membranes Within the Chloroplast. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 323:231-63. [PMID: 26944623 DOI: 10.1016/bs.ircmb.2015.12.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The chloroplast houses various metabolic processes essential for plant viability. This organelle originated from an ancestral cyanobacterium via endosymbiosis and maintains the three membranes of its progenitor. Among them, the outer envelope membrane functions mainly in communication with cytoplasmic components while the inner envelope membrane houses selective transport of various metabolites and the biosynthesis of several compounds, including membrane lipids. These two envelope membranes also play essential roles in import of nuclear-encoded proteins and in organelle division. The third membrane, the internal membrane system known as the thylakoid, houses photosynthetic electron transport and chemiosmotic phosphorylation. The inner envelope and thylakoid membranes share similar lipid composition. Specific targeting pathways determine their defined proteomes and, thus, their distinct functions. Nonetheless, several proteins have been shown to exist in both the envelope and thylakoid membranes. These proteins include those that play roles in protein transport, tetrapyrrole biosynthesis, membrane dynamics, or transport of nucleotides or inorganic phosphate. In this review, we summarize the current knowledge about proteins localized to both the envelope and thylakoid membranes in the chloroplast, discussing their roles in each membrane and potential mechanisms of their dual localization. Addressing the unanswered questions about these dual-localized proteins should help advance our understanding of chloroplast development, protein transport, and metabolic regulation.
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Affiliation(s)
- Laura Klasek
- Department of Plant Sciences, University of California at Davis, Davis, CA, United States of America
| | - Kentaro Inoue
- Department of Plant Sciences, University of California at Davis, Davis, CA, United States of America.
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Turan S, Tripathy BC. Salt-stress induced modulation of chlorophyll biosynthesis during de-etiolation of rice seedlings. PHYSIOLOGIA PLANTARUM 2015; 153:477-91. [PMID: 25132047 DOI: 10.1111/ppl.12250] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Accepted: 05/19/2014] [Indexed: 05/08/2023]
Abstract
Chlorophyll biosynthesis in plants is subjected to modulation by various environmental factors. To understand the modulation of the chlorophyll (Chl) biosynthesis during greening process by salt, 100-200 mM NaCl was applied to the roots of etiolated rice seedlings 12 h prior to the transfer to light. Application of 200 mM NaCl to rice seedlings that were grown in light for further 72 h resulted in reduced dry matter production (-58%) and Chl accumulation (-66%). Ionic imbalance due to salinity stress resulted in additional downregulation (41-45%) of seedling dry weight, Chl and carotenoid contents over and above that of similar osmotic stress induced by polyethylene glycol. Downregulation of Chl biosynthesis may be attributed to decreased activities of Chl biosynthetic pathway enzymes, i.e. 5-aminolevulinic acid (ALA) dehydratase (EC-2.4.1.24), porphobilinogen deaminase (EC-4.3.1.8), coproporphyrinogen III oxidase (EC-1.3.3.3), protoporphyrinogen IX oxidase (EC-1.3.3.4), Mg-protoporphyrin IX chelatase (EC-6.6.1.1) and protochlorophyllide oxidoreductase (EC-1.3.33.1). Reduced enzymatic activities were due to downregulation of their protein abundance and/or gene expression in salt-stressed seedlings. The extent of downregulation of ALA biosynthesis nearly matched with that of protochlorophyllide and Chl to prevent the accumulation of highly photosensitive photodynamic tetrapyrroles that generates singlet oxygen under stress conditions. Although, ALA synthesis decreased, the gene/protein expression of glutamyl-tRNA reductase (EC-1.2.1.70) increased suggesting it may play a role in acclimation to salt stress. The similar downregulation of both early and late Chl biosynthesis intermediates in salt-stressed seedlings suggests a regulatory network of genes involved in tetrapyrrole biosynthesis.
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Affiliation(s)
- Satpal Turan
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
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Response of Mature, Developing and Senescing Chloroplasts to Environmental Stress. PLASTID DEVELOPMENT IN LEAVES DURING GROWTH AND SENESCENCE 2013. [DOI: 10.1007/978-94-007-5724-0_28] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Tripathy BC, Oelmüller R. Reactive oxygen species generation and signaling in plants. PLANT SIGNALING & BEHAVIOR 2012; 7:1621-33. [PMID: 23072988 PMCID: PMC3578903 DOI: 10.4161/psb.22455] [Citation(s) in RCA: 332] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The introduction of molecular oxygen into the atmosphere was accompanied by the generation of reactive oxygen species (ROS) as side products of many biochemical reactions. ROS are permanently generated in plastids, peroxisomes, mitochiondria, the cytosol and the apoplast. Imbalance between ROS generation and safe detoxification generates oxidative stress and the accumulating ROS are harmful for the plants. On the other hand, specific ROS function as signaling molecules and activate signal transduction processes in response to various stresses. Here, we summarize the generation of ROS in the different cellular compartments and the signaling processes which are induced by ROS.
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Dalal VK, Tripathy BC. Modulation of chlorophyll biosynthesis by water stress in rice seedlings during chloroplast biogenesis. PLANT, CELL & ENVIRONMENT 2012; 35:1685-703. [PMID: 22494411 DOI: 10.1111/j.1365-3040.2012.02520.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
To understand the impact of water stress on the greening process, water stress was applied to 6-day-old etiolated seedlings of a drought-sensitive cultivar of rice (Oryza sativa), Pusa Basmati-1 by immersing their roots in 40 mm polyethylene glycol (PEG) 6000 (-0.69 MPa) or 50 mm PEG 6000 (-1.03 MPa) dissolved in half-strength Murashige and Skoog (MS)-nutrient-solution, 16 h prior to transfer to cool-white-fluorescent + incandescent light. Chlorophyll (Chl) accumulation substantially declined in developing water-stressed seedlings. Reduced Chl synthesis was due to decreased accumulation of chlorophyll biosynthetic intermediates, that is, glutamate-1-semialdehyde (GSA), 5-aminolevulinic acid, Mg-protoporphyrin IX monomethylester and protochlorophyllide. Although 5-aminolevulinic acid synthesis decreased, the gene expression and protein abundance of the enzyme responsible for its synthesis, GSA aminotransferase, increased, suggesting its crucial role in the greening process in stressful environment. The biochemical activities of Chl biosynthetic enzymes, that is, 5-aminolevulinic acid dehydratase, porphobilinogen deaminase, coproporphyrinogen III oxidase, porphyrinogen IX oxidase, Mg-chelatase and protochlorophyllide oxidoreductase, were down-regulated due to their reduced protein abundance/gene expression in water-stressed seedlings. Down-regulation of protochlorophyllide oxidoreductase resulted in impaired Shibata shift. Our results demonstrate that reduced synthesis of early intermediates, that is, GSA and 5-aminolevulinic acid, could modulate the gene expression of later enzymes of Chl biosynthesis pathway.
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Affiliation(s)
- Vijay K Dalal
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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Pattanayak GK, Tripathy BC. Overexpression of protochlorophyllide oxidoreductase C regulates oxidative stress in Arabidopsis. PLoS One 2011; 6:e26532. [PMID: 22031838 PMCID: PMC3198771 DOI: 10.1371/journal.pone.0026532] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Accepted: 09/28/2011] [Indexed: 12/31/2022] Open
Abstract
Light absorbed by colored intermediates of chlorophyll biosynthesis is not utilized in photosynthesis; instead, it is transferred to molecular oxygen, generating singlet oxygen (1O2). As there is no enzymatic detoxification mechanism available in plants to destroy 1O2, its generation should be minimized. We manipulated the concentration of a major chlorophyll biosynthetic intermediate i.e., protochlorophyllide in Arabidopsis by overexpressing the light-inducible protochlorophyllide oxidoreductase C (PORC) that effectively phototransforms endogenous protochlorophyllide to chlorophyllide leading to minimal accumulation of the photosensitizer protochlorophyllide in light-grown plants. In PORC overexpressing (PORCx) plants exposed to high-light, the 1O2 generation and consequent malonedialdehyde production was minimal and the maximum quantum efficiency of photosystem II remained unaffected demonstrating that their photosynthetic apparatus and cellular organization were intact. Further, PORCx plants treated with 5-aminolevulinicacid when exposed to light, photo-converted over-accumulated protochlorophyllide to chlorophyllide, reduced the generation of 1O2 and malonedialdehyde production and reduced plasma membrane damage. So PORCx plants survived and bolted whereas, the 5-aminolevulinicacid-treated wild-type plants perished. Thus, overexpression of PORC could be biotechnologically exploited in crop plants for tolerance to 1O2-induced oxidative stress, paving the use of 5-aminolevulinicacid as a selective commercial light-activated biodegradable herbicide. Reduced protochlorophyllide content in PORCx plants released the protochlorophyllide-mediated feed-back inhibition of 5-aminolevulinicacid biosynthesis that resulted in higher 5-aminolevulinicacid production. Increase of 5-aminolevulinicacid synthesis upregulated the gene and protein expression of several downstream chlorophyll biosynthetic enzymes elucidating a regulatory net work of expression of genes involved in 5-aminolevulinicacid and tetrapyrrole biosynthesis.
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Affiliation(s)
| | - Baishnab C. Tripathy
- School of Life Sciences, Jawaharlal Nehru University, New Delphi, India
- * E-mail:
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Adhikari ND, Froehlich JE, Strand DD, Buck SM, Kramer DM, Larkin RM. GUN4-porphyrin complexes bind the ChlH/GUN5 subunit of Mg-Chelatase and promote chlorophyll biosynthesis in Arabidopsis. THE PLANT CELL 2011; 23:1449-67. [PMID: 21467578 PMCID: PMC3101535 DOI: 10.1105/tpc.110.082503] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 02/24/2011] [Accepted: 03/17/2011] [Indexed: 05/19/2023]
Abstract
The GENOMES UNCOUPLED4 (GUN4) protein stimulates chlorophyll biosynthesis by activating Mg-chelatase, the enzyme that commits protoporphyrin IX to chlorophyll biosynthesis. This stimulation depends on GUN4 binding the ChlH subunit of Mg-chelatase and the porphyrin substrate and product of Mg-chelatase. After binding porphyrins, GUN4 associates more stably with chloroplast membranes and was proposed to promote interactions between ChlH and chloroplast membranes-the site of Mg-chelatase activity. GUN4 was also proposed to attenuate the production of reactive oxygen species (ROS) by binding and shielding light-exposed porphyrins from collisions with O₂. To test these proposals, we first engineered Arabidopsis thaliana plants that express only porphyrin binding-deficient forms of GUN4. Using these transgenic plants and particular mutants, we found that the porphyrin binding activity of GUN4 and Mg-chelatase contribute to the accumulation of chlorophyll, GUN4, and Mg-chelatase subunits. Also, we found that the porphyrin binding activity of GUN4 and Mg-chelatase affect the associations of GUN4 and ChlH with chloroplast membranes and have various effects on the expression of ROS-inducible genes. Based on our findings, we conclude that ChlH and GUN4 use distinct mechanisms to associate with chloroplast membranes and that mutant alleles of GUN4 and Mg-chelatase genes cause sensitivity to intense light by a mechanism that is potentially complex.
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Affiliation(s)
- Neil D. Adhikari
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
- Genetics Program, Michigan State University, East Lansing, Michigan 48824
| | - John E. Froehlich
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
| | - Deserah D. Strand
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824
| | - Stephanie M. Buck
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
| | - David M. Kramer
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
| | - Robert M. Larkin
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
- Address correspondence to
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Adhikari ND, Orler R, Chory J, Froehlich JE, Larkin RM. Porphyrins promote the association of GENOMES UNCOUPLED 4 and a Mg-chelatase subunit with chloroplast membranes. J Biol Chem 2009; 284:24783-96. [PMID: 19605356 PMCID: PMC2757182 DOI: 10.1074/jbc.m109.025205] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 05/26/2009] [Indexed: 11/29/2022] Open
Abstract
In plants, chlorophylls and other tetrapyrroles are synthesized from a branched pathway that is located within chloroplasts. GUN4 (GENOMES UNCOUPLED 4) stimulates chlorophyll biosynthesis by activating Mg-chelatase, the enzyme that commits porphyrins to the chlorophyll branch. GUN4 stimulates Mg-chelatase by a mechanism that involves binding the ChlH subunit of Mg-chelatase, as well as a substrate (protoporphyrin IX) and product (Mg-protoporphyrin IX) of Mg-chelatase. We chose to test whether GUN4 might also affect interactions between Mg-chelatase and chloroplast membranes, the site of chlorophyll biosynthesis. To test this idea, we induced chlorophyll precursor levels in purified pea chloroplasts by feeding these chloroplasts with 5-aminolevulinic acid, determined the relative levels of GUN4 and Mg-chelatase subunits in soluble and membrane-containing fractions derived from these chloroplasts, and quantitated Mg-chelatase activity in membranes isolated from these chloroplasts. We also monitored GUN4 levels in the soluble and membrane-containing fractions derived from chloroplasts fed with various porphyrins. Our results indicate that 5-aminolevulinic acid feeding stimulates Mg-chelatase activity in chloroplast membranes and that the porphyrin-bound forms of GUN4 and possibly ChlH associate most stably with chloroplast membranes. These findings are consistent with GUN4 stimulating chlorophyll biosynthesis not only by activating Mg-chelatase but also by promoting interactions between ChlH and chloroplast membranes.
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Affiliation(s)
- Neil D. Adhikari
- From the Department of Energy Plant Research Laboratory
- Genetics Program, and
| | - Robert Orler
- From the Department of Energy Plant Research Laboratory
| | - Joanne Chory
- the Howard Hughes Medical Institute and Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037
| | | | - Robert M. Larkin
- From the Department of Energy Plant Research Laboratory
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824 and
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