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Zhao T, Goedhart CM, Sam PN, Sabouny R, Lingrell S, Cornish AJ, Lamont RE, Bernier FP, Sinasac D, Parboosingh JS, Vance JE, Claypool SM, Innes AM, Shutt TE. PISD is a mitochondrial disease gene causing skeletal dysplasia, cataracts, and white matter changes. Life Sci Alliance 2019; 2:2/2/e201900353. [PMID: 30858161 PMCID: PMC6412922 DOI: 10.26508/lsa.201900353] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Revised: 02/25/2019] [Accepted: 02/26/2019] [Indexed: 12/18/2022] Open
Abstract
This work demonstrates that pathogenic variants in PISD cause mitochondrial disease and suggests a novel mechanistic link whereby impaired lipid content in the inner mitochondrial membrane alters the activity of inner mitochondrial membrane proteases. Exome sequencing of two sisters with congenital cataracts, short stature, and white matter changes identified compound heterozygous variants in the PISD gene, encoding the phosphatidylserine decarboxylase enzyme that converts phosphatidylserine to phosphatidylethanolamine (PE) in the inner mitochondrial membrane (IMM). Decreased conversion of phosphatidylserine to PE in patient fibroblasts is consistent with impaired phosphatidylserine decarboxylase (PISD) enzyme activity. Meanwhile, as evidence for mitochondrial dysfunction, patient fibroblasts exhibited more fragmented mitochondrial networks, enlarged lysosomes, decreased maximal oxygen consumption rates, and increased sensitivity to 2-deoxyglucose. Moreover, treatment with lyso-PE, which can replenish the mitochondrial pool of PE, and genetic complementation restored mitochondrial and lysosome morphology in patient fibroblasts. Functional characterization of the PISD variants demonstrates that the maternal variant causes an alternative splice product. Meanwhile, the paternal variant impairs autocatalytic self-processing of the PISD protein required for its activity. Finally, evidence for impaired activity of mitochondrial IMM proteases suggests an explanation as to why the phenotypes of these PISD patients resemble recently described “mitochondrial chaperonopathies.” Collectively, these findings demonstrate that PISD is a novel mitochondrial disease gene.
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Affiliation(s)
- Tian Zhao
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Biochemistry and Molecular Biology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Caitlin M Goedhart
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Pingdewinde N Sam
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Rasha Sabouny
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Biochemistry and Molecular Biology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Susanne Lingrell
- Department of Medicine and Group on Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada
| | - Adam J Cornish
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Ryan E Lamont
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Francois P Bernier
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Pediatrics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - David Sinasac
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Jillian S Parboosingh
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | | | - Jean E Vance
- Department of Medicine and Group on Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada
| | - Steven M Claypool
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - A Micheil Innes
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada .,Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Pediatrics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Timothy E Shutt
- Alberta Children's Hospital Research Institute, Department of Medical Genetics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada .,Department of Biochemistry and Molecular Biology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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Vieler A, Wu G, Tsai CH, Bullard B, Cornish AJ, Harvey C, Reca IB, Thornburg C, Achawanantakun R, Buehl CJ, Campbell MS, Cavalier D, Childs KL, Clark TJ, Deshpande R, Erickson E, Armenia Ferguson A, Handee W, Kong Q, Li X, Liu B, Lundback S, Peng C, Roston RL, Simpson JP, TerBush A, Warakanont J, Zäuner S, Farre EM, Hegg EL, Jiang N, Kuo MH, Lu Y, Niyogi KK, Ohlrogge J, Osteryoung KW, Shachar-Hill Y, Sears BB, Sun Y, Takahashi H, Yandell M, Shiu SH, Benning C. Correction: Genome, Functional Gene Annotation, and Nuclear Transformation of the Heterokont Oleaginous Alga Nannochloropsis oceanica CCMP1779. PLoS Genet 2017; 13:e1006802. [PMID: 28542203 PMCID: PMC5441573 DOI: 10.1371/journal.pgen.1006802] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
[This corrects the article DOI: 10.1371/journal.pgen.1003064.].
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Cornish AJ, Ginovska B, Thelen A, da Silva JCS, Soares TA, Raugei S, Dupuis M, Shaw WJ, Hegg EL. Single-Amino Acid Modifications Reveal Additional Controls on the Proton Pathway of [FeFe]-Hydrogenase. Biochemistry 2016; 55:3165-73. [PMID: 27186945 DOI: 10.1021/acs.biochem.5b01044] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The proton pathway of [FeFe]-hydrogenase is essential for enzymatic H2 production and oxidation and is composed of four residues and a water molecule. A computational analysis of this pathway in the [FeFe]-hydrogenase from Clostridium pasteurianum revealed that the solvent-exposed residue of the pathway (Glu282) forms hydrogen bonds to two residues outside of the pathway (Arg286 and Ser320), implying that these residues could function in regulating proton transfer. In this study, we show that substituting Arg286 with leucine eliminates hydrogen bonding with Glu282 and results in an ∼3-fold enhancement of H2 production activity when methyl viologen is used as an electron donor, suggesting that Arg286 may help control the rate of proton delivery. In contrast, substitution of Ser320 with alanine reduces the rate ∼5-fold, implying that it either acts as a member of the pathway or influences Glu282 to permit proton transfer. Interestingly, quantum mechanics/molecular mechanics and molecular dynamics calculations indicate that Ser320 does not play a structural role or indirectly influence the barrier for proton movement at the entrance of the channel. Rather, it may act as an additional proton acceptor for the pathway or serve in a regulatory role. While further studies are needed to elucidate the role of Ser320, collectively these data provide insights into the complex proton transport process.
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Affiliation(s)
- Adam J Cornish
- Department of Biochemistry & Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States.,Great Lakes Bioenergy Research Center, Michigan State University , East Lansing, Michigan 48824, United States
| | - Bojana Ginovska
- Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Adam Thelen
- Department of Biochemistry & Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States
| | - Julio C S da Silva
- Department of Fundamental Chemistry, Federal University of Pernambuco , Cidade Universitária,50740-560 Recife, PE, Brazil
| | - Thereza A Soares
- Department of Fundamental Chemistry, Federal University of Pernambuco , Cidade Universitária,50740-560 Recife, PE, Brazil
| | - Simone Raugei
- Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Michel Dupuis
- Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Wendy J Shaw
- Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Eric L Hegg
- Department of Biochemistry & Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States.,Great Lakes Bioenergy Research Center, Michigan State University , East Lansing, Michigan 48824, United States
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Yang H, Gandhi H, Cornish AJ, Moran JJ, Kreuzer HW, Ostrom NE, Hegg EL. Isotopic fractionation associated with [NiFe]- and [FeFe]-hydrogenases. Rapid Commun Mass Spectrom 2016; 30:285-292. [PMID: 27071219 DOI: 10.1002/rcm.7432] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
RATIONALE Hydrogenases catalyze the reversible formation of H2 from electrons and protons with high efficiency. Understanding the relationships between H2 production, H2 uptake, and H2-H2O exchange can provide insight into the metabolism of microbial communities in which H2 is an essential component in energy cycling. METHODS We used stable H isotopes (1H and 2H) to probe the isotope effects associated with three [FeFe]-hydrogenases and three [NiFe]-hydrogenases. RESULTS All six hydrogenases displayed fractionation factors for H2 formation that were significantly less than 1, producing H2 that was severely depleted in 2H relative to the substrate, water. Consistent with differences in their active site structure, the fractionation factors for each class appear to cluster, with the three [NiFe]-hydrogenases (α = 0.27–0.40) generally having smaller values than the three [FeFe]-hydrogenases (α = 0.41–0.55). We also obtained isotopic fractionation factors associated with H2 uptake and H2-H2O exchange under conditions similar to those utilized for H2 production, providing a more complete picture of the reactions catalyzed by hydrogenases. CONCLUSIONS The fractionation factors determined in our studies can be used as signatures for different hydrogenases to probe their activity under different growth conditions and to ascertain which hydrogenases are most responsible for H2 production and/or uptake in complex microbial communities.
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Cornish AJ, Green R, Gärtner K, Mason S, Hegg EL. Characterization of Hydrogen Metabolism in the Multicellular Green Alga Volvox carteri. PLoS One 2015; 10:e0125324. [PMID: 25927230 PMCID: PMC4416025 DOI: 10.1371/journal.pone.0125324] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 03/19/2015] [Indexed: 01/13/2023] Open
Abstract
Hydrogen gas functions as a key component in the metabolism of a wide variety of microorganisms, often acting as either a fermentative end-product or an energy source. The number of organisms reported to utilize hydrogen continues to grow, contributing to and expanding our knowledge of biological hydrogen processes. Here we demonstrate that Volvox carteri f. nagariensis, a multicellular green alga with differentiated cells, evolves H2 both when supplied with an abiotic electron donor and under physiological conditions. The genome of Volvox carteri contains two genes encoding putative [FeFe]-hydrogenases (HYDA1 and HYDA2), and the transcripts for these genes accumulate under anaerobic conditions. The HYDA1 and HYDA2 gene products were cloned, expressed, and purified, and both are functional [FeFe]-hydrogenases. Additionally, within the genome the HYDA1 and HYDA2 genes cluster with two putative genes which encode hydrogenase maturation proteins. This gene cluster resembles operon-like structures found within bacterial genomes and may provide further insight into evolutionary relationships between bacterial and algal [FeFe]-hydrogenase genes.
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Affiliation(s)
- Adam J. Cornish
- Great Lakes Bioenergy Research Center and the Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, Michigan, United States of America
| | - Robin Green
- Great Lakes Bioenergy Research Center and the Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, Michigan, United States of America
| | - Katrin Gärtner
- Great Lakes Bioenergy Research Center and the Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, Michigan, United States of America
| | - Saundra Mason
- Great Lakes Bioenergy Research Center and the Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, Michigan, United States of America
| | - Eric L. Hegg
- Great Lakes Bioenergy Research Center and the Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, Michigan, United States of America
- * E-mail:
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Cornish AJ, Gärtner K, Yang H, Peters JW, Hegg EL. Mechanism of proton transfer in [FeFe]-hydrogenase from Clostridium pasteurianum. J Biol Chem 2011; 286:38341-38347. [PMID: 21900241 DOI: 10.1074/jbc.m111.254664] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
[FeFe]-Hydrogenases are complex metalloproteins that catalyze the reversible reduction of protons to molecular hydrogen utilizing a unique diiron subcluster bridged to a [4Fe4S] subcluster. Extensive studies have concentrated on the nature and catalytic activity of the active site, yet relatively little information is available concerning the mechanism of proton transport that is required for this activity. Previously, structural characterization of [FeFe]-hydrogenase from Clostridium pasteurianum indicated a potential proton transport pathway involving four residues (Cys-299, Glu-279, Ser-319, and Glu-282) that connect the active site to the enzyme surface. Here, we demonstrate that substitution of any of these residues resulted in a drastic reduction in hydrogenase activity relative to the native enzyme, supporting the importance of these residues in catalysis. Inhibition studies of native and amino acid-substituted enzymes revealed that Zn(2+) specifically blocked proton transfer by binding to Glu-282, confirming the role of this residue in the identified pathway. In addition, all four of these residues are strictly conserved, suggesting that they may form a proton transport pathway that is common to all [FeFe]-hydrogenases.
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Affiliation(s)
- Adam J Cornish
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319
| | - Katrin Gärtner
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319
| | - Hui Yang
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319
| | - John W Peters
- Department of Chemistry and Biochemistry and Astrobiology Biogeocatalysis Research Center, Montana State University, Bozeman, Montana 59717
| | - Eric L Hegg
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319.
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Hong G, Cornish AJ, Hegg EL, Pachter R. On understanding proton transfer to the biocatalytic [Fe-Fe](H) sub-cluster in [Fe-Fe]H(2)ases: QM/MM MD simulations. Biochim Biophys Acta 2011; 1807:510-7. [PMID: 21296047 DOI: 10.1016/j.bbabio.2011.01.011] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Revised: 01/26/2011] [Accepted: 01/31/2011] [Indexed: 11/19/2022]
Abstract
Proton transfer to the [Fe-Fe](H) sub-cluster in the Desulfovibrio desulfuricans (DdH) and Clostridium pasteurianum (CpI) [Fe-Fe] hydrogenases was investigated by a combination of first principles and empirical molecular dynamics simulations. Pathways that can be inferred from the X-ray crystal structures of DdH and CpI, i.e., (Glu159→Ser198→Glu156→water460→Cys178→DTMA([Fe-Fe](H)) and (Glu282→Ser319→Glu279→water612→Cys299), respectively, were considered. Proton transfer from Cys178 to DTMA in the [Fe-Fe](H) sub-cluster in DdH was readily observed in our results, specifically when [Fe-Fe](H) was in the reduced state ([Fe(I)-Fe(I)]) or in the mixed valence state for the protonated distal iron Fe(d) ([Fe(I)-Fe(II)-H(-)](H)). A concerted mechanism is proposed, where proton transfer in DdH from Glu159 to Glu156 via Ser198 and Glu156 to Cys178 via water460 readily occurred, as well as from Glu282 to Glu279 via Ser319 and Glu279 to Cys299 via water612 in CpI. The theoretical prediction of the proton transfer characteristics is consistent with the assumed biocatalytic mechanism of the [Fe-Fe] hydrogenases in which the proton binds at Fe(d), providing confirmation that has not been explored so far. The computational results were qualitatively validated by the agreement with experimental hydrogen production activity data for mutated CpI enzymes, relative to the wild-type protein. Finally, the insight provided by the simulations, combined, in part, with experimental validation, are important for establishing an approach in future exploration of proton transfer to the active site in this class of enzymes, and possibly also for biomimetic analogs.
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Affiliation(s)
- G Hong
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, OH 45433, USA
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Miller R, Wu G, Deshpande RR, Vieler A, Gärtner K, Li X, Moellering ER, Zäuner S, Cornish AJ, Liu B, Bullard B, Sears BB, Kuo MH, Hegg EL, Shachar-Hill Y, Shiu SH, Benning C. Changes in transcript abundance in Chlamydomonas reinhardtii following nitrogen deprivation predict diversion of metabolism. Plant Physiol 2010; 154:1737-52. [PMID: 20935180 PMCID: PMC2996024 DOI: 10.1104/pp.110.165159] [Citation(s) in RCA: 254] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Accepted: 10/07/2010] [Indexed: 05/17/2023]
Abstract
Like many microalgae, Chlamydomonas reinhardtii forms lipid droplets rich in triacylglycerols when nutrient deprived. To begin studying the mechanisms underlying this process, nitrogen (N) deprivation was used to induce triacylglycerol accumulation and changes in developmental programs such as gametogenesis. Comparative global analysis of transcripts under induced and noninduced conditions was applied as a first approach to studying molecular changes that promote or accompany triacylglycerol accumulation in cells encountering a new nutrient environment. Towards this goal, high-throughput sequencing technology was employed to generate large numbers of expressed sequence tags of eight biologically independent libraries, four for each condition, N replete and N deprived, allowing a statistically sound comparison of expression levels under the two tested conditions. As expected, N deprivation activated a subset of control genes involved in gametogenesis while down-regulating protein biosynthesis. Genes for components of photosynthesis were also down-regulated, with the exception of the PSBS gene. N deprivation led to a marked redirection of metabolism: the primary carbon source, acetate, was no longer converted to cell building blocks by the glyoxylate cycle and gluconeogenesis but funneled directly into fatty acid biosynthesis. Additional fatty acids may be produced by membrane remodeling, a process that is suggested by the changes observed in transcript abundance of putative lipase genes. Inferences on metabolism based on transcriptional analysis are indirect, but biochemical experiments supported some of these deductions. The data provided here represent a rich source for the exploration of the mechanism of oil accumulation in microalgae.
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Xu C, Fan J, Cornish AJ, Benning C. Lipid trafficking between the endoplasmic reticulum and the plastid in Arabidopsis requires the extraplastidic TGD4 protein. Plant Cell 2008; 20:2190-204. [PMID: 18689504 PMCID: PMC2553622 DOI: 10.1105/tpc.108.061176] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 07/19/2008] [Accepted: 07/27/2008] [Indexed: 05/18/2023]
Abstract
The development of chloroplasts in Arabidopsis thaliana requires extensive lipid trafficking between the endoplasmic reticulum (ER) and the plastid. The biosynthetic enzymes for the final steps of chloroplast lipid assembly are associated with the plastid envelope membranes. For example, during biosynthesis of the galactoglycerolipids predominant in photosynthetic membranes, galactosyltransferases associated with these membranes transfer galactosyl residues from UDP-Gal to diacylglycerol. In Arabidopsis, diacylglycerol can be derived from the ER or the plastid. Here, we describe a mutant of Arabidopsis, trigalactosyldiacylglycerol4 (tgd4), in which ER-derived diacylglycerol is not available for galactoglycerolipid biosynthesis. This mutant accumulates diagnostic oligogalactoglycerolipids, hence its name, and triacylglycerol in its tissues. The TGD4 gene encodes a protein that appears to be associated with the ER membranes. Mutant ER microsomes show a decreased transfer of lipids to isolated plastids consistent with in vivo labeling data, indicating a disruption of ER-to-plastid lipid transfer. The complex lipid phenotype of the mutant is similar to that of the tgd1,2,3 mutants disrupted in components of a lipid transporter of the inner plastid envelope membrane. However, unlike the TGD1,2,3 complex, which is proposed to transfer phosphatidic acid through the inner envelope membrane, TGD4 appears to be part of the machinery mediating lipid transfer between the ER and the outer plastid envelope membrane. The extent of direct ER-to-plastid envelope contact sites is not altered in the tgd4 mutant. However, this does not preclude a possible function of TGD4 in those contact sites as a conduit for lipid transfer between the ER and the plastid.
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Affiliation(s)
- Changcheng Xu
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824, USA
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Xu C, Yu B, Cornish AJ, Froehlich JE, Benning C. Phosphatidylglycerol biosynthesis in chloroplasts of Arabidopsis mutants deficient in acyl-ACP glycerol-3- phosphate acyltransferase. Plant J 2006; 47:296-309. [PMID: 16774646 DOI: 10.1111/j.1365-313x.2006.02790.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The biosynthesis of phosphatidylglycerol represents a central pathway in lipid metabolism in all organisms. The enzyme catalyzing the first reaction of the pathway in the plastid, glycerol-3-phosphate acyl-acyl carrier protein acyltransferase, is thought to be encoded in Arabidopsis by the ATS1 locus. A number of genetic mutants deficient in this activity have been described. However, the corresponding mutant alleles have not yet been analyzed at the molecular level and a causal relationship between the mutant phenotypes and a deficiency at the ATS1 locus has not been established. The presence in all known ats1 mutants of near wild-type amounts of phosphatidylglycerol raised the question of whether an alternative pathway of phosphatidylglycerol assembly in the plastid exists. However, detailed analysis of several independent ats1 mutant alleles revealed that all are leaky. Reduction by RNAi of ats1-1 RNA levels in the ats1-1 mutant background led to a more severe growth phenotype (small green plants and reduced seed set), but did not decrease the relative amount of phosphatidylglycerol. In contrast, when the amount of ATS2 mRNA encoding the plastidic lysophosphatidic acid acyltransferase catalyzing the second reaction of the pathway was reduced by RNAi in the ats1-1 mutant background, phosphatidylglycerol amounts decreased, leading to a growth phenotype (small pale-yellow plants) that is reminiscent of the pgp1-1 mutant deficient in a late step of plastidic phosphatidylglycerol biosynthesis. These observations indicate coordinated regulation of plastid lipid metabolism and plant development.
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Affiliation(s)
- Changcheng Xu
- Department of Biochemistry, Michigan State University, East Lansing, MI 48824, USA
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