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Yang C, Li J, Huang Z, Zhang X, Gao X, Zhu C, Morris PF, Zhang X. Structural and catalytic analysis of two diverse uridine phosphorylases in Phytophthora capsici. Sci Rep 2020; 10:9051. [PMID: 32493959 PMCID: PMC7271239 DOI: 10.1038/s41598-020-65935-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [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: 12/09/2019] [Accepted: 05/08/2020] [Indexed: 11/09/2022] Open
Abstract
Uridine phosphorylase (UP) is a key enzyme of pyrimidine salvage pathways that enables the recycling of endogenous or exogenous-supplied pyrimidines and plays an important intracellular metabolic role. Here, we biochemically and structurally characterized two evolutionarily divergent uridine phosphorylases, PcUP1 and PcUP2 from the oomycete pathogen Phytophthora capsici. Our analysis of other oomycete genomes revealed that both uridine phosphorylases are present in Phytophthora and Pythium genomes, but only UP2 is seen in Saprolegnia spp. which are basal members of the oomycetes. Moreover, uridine phosphorylases are not found in obligate oomycete pathogens such as Hyaloperonospora arabidopsidis and Albugo spp. PcUP1 and PcUP2 are upregulated 300 and 500 fold respectively, within 90 min after infection of pepper leaves. The crystal structures of PcUP1 in ligand-free and in complex with uracil/ribose-1-phosphate, 2'-deoxyuridine/phosphate and thymidine/phosphate were analyzed. Crystal structure of this uridine phosphorylase showed strict conservation of key residues in the binding pocket. Structure analysis of PcUP1 with bound ligands, and site-directed mutagenesis of key residues provide additional support for the "push-pull" model of catalysis. Our study highlights the importance of pyrimidine salvage during the earliest stages of infection.
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Affiliation(s)
- Cancan Yang
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271000, China
| | - Jing Li
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271000, China
| | - Zhenling Huang
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271000, China
| | - Xuefa Zhang
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271000, China
| | - Xiaolei Gao
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271000, China
| | - Chunyuang Zhu
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271000, China
| | - Paul F Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, 43403, USA
| | - XiuGuo Zhang
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271000, China.
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Lou YR, Ahmed S, Yan J, Adio AM, Powell HM, Morris PF, Jander G. Arabidopsis ADC1 functions as an N δ -acetylornithine decarboxylase. J Integr Plant Biol 2020; 62:601-613. [PMID: 31081586 DOI: 10.1111/jipb.12821] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2019] [Accepted: 04/28/2019] [Indexed: 06/09/2023]
Abstract
Polyamines are small aliphatic amines found in almost all organisms, ranging from bacteria to plants and animals. In most plants, putrescine, the metabolic precursor for longer polyamines, such as spermidine and spermine, is produced from arginine, with either agmatine or ornithine as intermediates. Here we show that Arabidopsis thaliana (Arabidopsis) arginine decarboxylase 1 (ADC1), one of the two known arginine decarboxylases in Arabidopsis, not only synthesizes agmatine from arginine, but also converts Nδ -acetylornithine to N-acetylputrescine. Phylogenetic analyses indicate that duplication and neofunctionalization of ADC1 and NATA1, the enzymes that synthesize Nδ -acetylornithine in Arabidopsis, co-occur in a small number of related species in the Brassicaceae. Unlike ADC2, which is localized in the chloroplasts, ADC1 is in the endoplasmic reticulum together with NATA1, an indication that these two enzymes have access to the same substrate pool. Together, these results are consistent with a model whereby NATA1 and ADC1 together provide a pathway for the synthesis of N-acetylputrescine in Arabidopsis.
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Affiliation(s)
- Yann-Ru Lou
- Boyce Thompson Institute for Plant Research, Ithaca, NY, 14853, USA
| | - Sheaza Ahmed
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, 43403, USA
| | - Jian Yan
- Key Laboratory of Agro-Environment in the Tropics, Ministry of Agriculture and Rural Affairs, South China Agricultural University, Guangzhou, 510642, China
| | - Adewale M Adio
- Boyce Thompson Institute for Plant Research, Ithaca, NY, 14853, USA
| | - Hannah M Powell
- Boyce Thompson Institute for Plant Research, Ithaca, NY, 14853, USA
| | - Paul F Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, 43403, USA
| | - Georg Jander
- Boyce Thompson Institute for Plant Research, Ithaca, NY, 14853, USA
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Li J, Ai C, Yang C, Jiang W, Sheng H, Morris PF, Zhang X. Phytophthora capsici PcFtsZ2 Is Required for Asexual Development and Plant Infection. Mol Plant Microbe Interact 2020; 33:727-741. [PMID: 32096689 DOI: 10.1094/mpmi-01-20-0002-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
In bacteria, FtsZ proteins form a Z ring that is the initial step preceding septal fission. FtsZ proteins enable the division of mitochondria in early eukaryotes and are present in some kingdoms but have been lost in animals, fungi, and plants. Here, we have identified two Phytophthora capsici ortholog genes of Escherichia coli FtsZs, designated PcFtsZ1 and PcFtsZ2. Overexpression of PcFtsZ2 in E. coli fully complemented the overexpression phenotype of EcFtsZ. In contrast, overexpression of PcFtsZ1 in E. coli had minimal impact on cell division and separation. Thus, we focused on evaluating the impact of altered expression of PcFtsZ2 in P. capsici, as it exhibited the strongest phenotype. PcFtsZ2 was expressed at the highest levels in mycelia, sporangia, and germinating cysts, as well as in late infection. PcFtsZ2 mis-expression lines showed aberrant asexual growth and development of P. capsici. Alterations in the expression of PcFtsZ2 changed the distribution of mitochondria in hyphae and sporangia and, also, affected the number, size, and shape of actin plaques. Silencing of PcFtsZ2 restrained growth and development of invasive structures, especially cysts and sporangia, substantially inhibiting the ability of transformants to cause blight lesions. In overexpressed transformant lines, cyst and sporangial germination rates were only half that of controls, but hyphal growth from direct germination of sporangia was more rapid than controls. These transformant lines were only slightly impaired in virulence relative to controls. This study emphasizes the essential role of the evolutionarily conserved FtsZ2 proteins in affecting cytoskeleton dynamics.
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Affiliation(s)
- Jing Li
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271018, China
| | - CongCong Ai
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271018, China
| | - CanCan Yang
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271018, China
| | - WeiLin Jiang
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271018, China
| | - Hui Sheng
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271018, China
| | - Paul F Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, U.S.A
| | - XiuGuo Zhang
- Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect Pests, College of Plant Protection, Shandong Agricultural University, Tai'an, 271018, China
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Ariyaratne M, Ge L, Morris PF. Characterization of Membrane Transporters by Heterologous Expression in E. coli and Production of Membrane Vesicles. J Vis Exp 2019. [PMID: 31957746 DOI: 10.3791/60009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Several methods have been developed to functionally characterize novel membrane transporters. Polyamines are ubiquitous in all organisms, but polyamine exchangers in plants have not been identified. Here, we outline a method to characterize polyamine antiporters using membrane vesicles generated from the lysis of Escherichia coli cells heterologously expressing a plant antiporter. First, we heterologously expressed AtBAT1 in an E. coli strain deficient in polyamine and arginine exchange transporters. Vesicles were produced using a French press, purified by ultracentrifugation and utilized in a membrane filtration assay of labeled substrates to demonstrate the substrate specificity of the transporter. These assays demonstrated that AtBAT1 is a proton-mediated transporter of arginine, γ-aminobutyric acid (GABA), putrescine and spermidine. The mutant strain that was developed for the assay of AtBAT1 may be useful for the functional analysis of other families of plant and animal polyamine exchangers. We also hypothesize that this approach can be used to characterize many other types of antiporters, as long as these proteins can be expressed in the bacterial cell membrane. E. coli is a good system for the characterization of novel transporters, since there are multiple methods that can be employed to mutagenize native transporters.
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Affiliation(s)
| | - Lingxiao Ge
- Department of Biological Sciences, Bowling Green State University
| | - Paul F Morris
- Department of Biological Sciences, Bowling Green State University;
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Song W, Yang C, Zhu C, Morris PF, Zhang X. Crystal structure and expression patterns of prolyl 4-hydroxylases from Phytophthora capsici. Biochem Biophys Res Commun 2018; 508:1011-1017. [PMID: 30551874 DOI: 10.1016/j.bbrc.2018.12.022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 12/04/2018] [Indexed: 11/19/2022]
Abstract
Prolyl 4-hydroxylases (P4Hs) are members of the Fe2+ and 2-oxoglutarate- dependent oxygenases family, which play central roles in the collagen stabilization, hypoxia sensing, and translational regulation in eukaryotes. Thus far, nothing is known about the role of P4Hs in development and pathogenesis in oomycetes. Here we show that the Phytophthora capsici genome contains five putative prolyl 4-hydroxylases. In mycelia, all P4Hs were downregulated in response to hypoxia, but the expression of PcP4H1 was most affected. Strikingly, Pc4H1 was upregulated more than 110 fold at the onset of infection, and Pc4H5 was upregulated seven fold, while the expression of other P4H's were unchanged. Similar to well-characterized P4H proteins, the crystallographic structure of PcP4H1 contains a highly conserved double-stranded β-helix core fold and catalytic residues. However, the binding affinity of 2-oxoglutarate to PcP4H1 is very low. The extended C-terminal α-helix bundle and longer β2-β3 disordered substrate binding loop may help in confirming the peptide target of this enzyme.
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Affiliation(s)
- Weiwei Song
- College of Plant Protection, Shandong Agricultural University, Taian, 271018, China
| | - Cancan Yang
- College of Plant Protection, Shandong Agricultural University, Taian, 271018, China
| | - Chunyuan Zhu
- College of Life Sciences, Shandong Agricultural University, Taian, 271018, China
| | - Paul F Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, 43403, USA
| | - Xiuguo Zhang
- College of Plant Protection, Shandong Agricultural University, Taian, 271018, China.
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Affiliation(s)
- Chang Xu
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, 43403-0212
| | - Paul F. Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, 43403-0212
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Wagner A, Norris S, Chatterjee P, Morris PF, Wildschutte H. Aquatic Pseudomonads Inhibit Oomycete Plant Pathogens of Glycine max. Front Microbiol 2018; 9:1007. [PMID: 29896163 PMCID: PMC5986895 DOI: 10.3389/fmicb.2018.01007] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Accepted: 04/30/2018] [Indexed: 11/17/2022] Open
Abstract
Seedling root rot of soybeans caused by the host-specific pathogen Phytophthora sojae, and a large number of Pythium species, is an economically important disease across the Midwest United States that negatively impacts soybean yields. Research on biocontrol strategies for crop pathogens has focused on compounds produced by microbes from soil, however, recent studies suggest that aquatic bacteria express distinct compounds that efficiently inhibit a wide range of pathogens. Based on these observations, we hypothesized that freshwater strains of pseudomonads might be producing novel antagonistic compounds that inhibit the growth of oomycetes. To test this prediction, we utilized a collection of 330 Pseudomonas strains isolated from soil and freshwater habitats, and determined their activity against a panel of five oomycetes: Phytophthora sojae, Pythium heterothalicum, Pythium irregulare, Pythium sylvaticum, and Pythium ultimum, all of which are pathogenic on soybeans. Among the bacterial strains, 118 exhibited antagonistic activity against at least one oomycete species, and 16 strains were inhibitory to all pathogens. Antagonistic activity toward oomycetes was significantly more common for aquatic isolates than for soil isolates. One water-derived strain, 06C 126, was predicted to express a siderophore and exhibited diverse antagonistic profiles when tested on nutrient rich and iron depleted media suggesting that more than one compound was produced that effectively inhibited oomycetes. These results support the concept that aquatic strains are an efficient source of compounds that inhibit pathogens. We outline a strategy to identify other strains that express unique compounds that may be useful biocontrol agents.
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Affiliation(s)
| | | | | | - Paul F. Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, United States
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Patel J, Ariyaratne M, Ahmed S, Ge L, Phuntumart V, Kalinoski A, Morris PF. Dual functioning of plant arginases provides a third route for putrescine synthesis. Plant Sci 2017; 262:62-73. [PMID: 28716421 DOI: 10.1016/j.plantsci.2017.05.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 05/04/2017] [Accepted: 05/25/2017] [Indexed: 05/19/2023]
Abstract
Two biosynthetic routes are known for putrescine, an essential plant metabolite. Ornithine decarboxylase (ODC) converts ornithine directly to putrescine, while a second route for putrescine biosynthesis utilizes arginine decarboxylase (ADC) to convert arginine to agmatine, and two additional enzymes, agmatine iminohydrolase (AIH) and N-carbamoyl putrescine aminohydrolase (NLP1) to complete this pathway. Here we show that plants can use ADC and arginase/agmatinase (ARGAH) as a third route for putrescine synthesis. Transformation of Arabidopsis thaliana ADC2, and any of the arginases from A. thaliana (ARGAH1, or ARGHA2) or the soybean gene Glyma.03g028000 (GmARGAH) into a yeast strain deficient in ODC, fully complemented the mutant phenotype. In vitro assays using purified recombinant enzymes of AtADC1 and AtARGAH2 were used to show that these enzymes can function in concert to convert arginine to agmatine and putrescine. Transient expression analysis of the soybean genes (Glyma.06g007500, ADC; Glyma.03g028000 GmARGAH) and the A. thaliana ADC2 and ARGAH genes in leaves of Nicotiana benthamiana, showed that these proteins are localized to the chloroplast. Experimental support for this pathway also comes from the fact that expression of AtARGAH, but not AtAIH or AtNLP1, is co-regulated with AtADC2 in response to drought, oxidative stress, wounding, and methyl jasmonate treatments. Based on the high affinity of ARGAH2 for agmatine, its co-localization with ADC2, and typically low arginine levels in many plant tissues, we propose that these two enzymes can be major contributors to putrescine synthesis in many A. thaliana stress responses.
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Affiliation(s)
- Jigar Patel
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, United States
| | - Menaka Ariyaratne
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, United States
| | - Sheaza Ahmed
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, United States
| | - Lingxiao Ge
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, United States
| | - Vipaporn Phuntumart
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, United States
| | - Andrea Kalinoski
- Department of Surgery, University of Toledo, 3000 Arlington Ave, Toledo, OH 43614, United States
| | - Paul F Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, United States.
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Ahmed S, Ariyaratne M, Patel J, Howard AE, Kalinoski A, Phuntumart V, Morris PF. Altered expression of polyamine transporters reveals a role for spermidine in the timing of flowering and other developmental response pathways. Plant Sci 2017; 258:146-155. [PMID: 28330558 DOI: 10.1016/j.plantsci.2016.12.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Revised: 12/01/2016] [Accepted: 12/08/2016] [Indexed: 05/25/2023]
Abstract
Changes in the levels of polyamines are correlated with the activation or repression of developmental response pathways, but the role of polyamine transporters in the regulation of polyamine homeostasis and thus indirectly gene expression, has not been previously addressed. Here we show that the A. thaliana and rice transporters AtPUT5 and OsPUT1 were localized to the ER, while the AtPUT2, AtPUT3, and OsPUT3 were localized to the chloroplast by transient expression in N. benthamiana. A. thaliana plants that were transformed with OsPUT1 under the control the PUT5 promoter were delayed in flowering by 16days. In contrast, put5 mutants flowered four days earlier than WT plants. The delay of flowering was associated with significantly higher levels of spermidine and spermidine conjugates in the leaves prior to flowering. A similar delay in flowering was also noted in transgenic lines with constitutive expression of either OsPUT1 or OsPUT3. All three transgenic lines had larger rosette leaves, thicker flowering stems, and produced more siliques than wild type plants. In contrast, put5 plants had smaller leaves, thinner flowering stems, and produced fewer siliques. Constitutive expression of PUTs was also associated with an extreme delay in both plant senescence and maturation rate of siliques. These experiments provide the first genetic evidence of polyamine transport in the timing of flowering, and indicate the importance of polyamine transporters in the regulation of flowering and senescence pathways.
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Affiliation(s)
- Sheaza Ahmed
- Department of Biological Sciences, Bowling Green State University, Bowling Green Oh, 43403, United States
| | - Menaka Ariyaratne
- Department of Biological Sciences, Bowling Green State University, Bowling Green Oh, 43403, United States
| | - Jigar Patel
- Department of Biological Sciences, Bowling Green State University, Bowling Green Oh, 43403, United States
| | - Alexander E Howard
- Department of Biological Sciences, Bowling Green State University, Bowling Green Oh, 43403, United States
| | - Andrea Kalinoski
- Department of Surgery, University of Toledo, 3000 Arlington Ave. Toledo, OH 43614, United States
| | - Vipaporn Phuntumart
- Department of Biological Sciences, Bowling Green State University, Bowling Green Oh, 43403, United States
| | - Paul F Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green Oh, 43403, United States.
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Fu L, Zhu C, Ding X, Yang X, Morris PF, Tyler BM, Zhang X. Characterization of Cell-Death-Inducing Members of the Pectate Lyase Gene Family in Phytophthora capsici and Their Contributions to Infection of Pepper. Mol Plant Microbe Interact 2015; 28:766-75. [PMID: 25775270 DOI: 10.1094/mpmi-11-14-0352-r] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Pectate lyases (PL) play a critical role in pectin degradation. PL have been extensively studied in major bacterial and fungal pathogens of a wide range of plant species. However, the contribution of PL to infection by oomycete pathogens remains largely unknown. Here, we cloned 22 full-length pectate lyase (PcPL) genes from a highly aggressive strain of Phytophthora capsici SD33. Of these, PVX agroinfiltration revealed that 12 PcPL genes were found to be highly induced during infection of pepper by SD33 but the induction level was twofold less in a mildly aggressive strain, YN07. The four genes with the highest transcript levels as measured by by quantitative reverse-transcription polymerase chain reaction (PcPL1, PcPL15, PcPL16, and PcPL20) also produced a severe cell death response following transient expression in pepper leaves but the other eight PcPL genes did not. Overexpression of these four genes increased the virulence of SD33 on pepper slightly, and increased it more substantially during infection of tobacco. Overexpression of the genes in YN07 restored its aggressiveness to near that of SD33. Gene silencing experiments with the 12 PcPL genes produced diverse patterns of silencing of PcPL genes, from which it could be inferred from regression analysis that PcPL1, PcPL16, and PcPL20 could account for nearly all of the contributions of the PcPL genes to virulence.
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Affiliation(s)
- Li Fu
- 1 Department of Plant Pathology, Shandong Agricultural University, No. 61, Daizong Street, Taian, Shandong, 271018, China
| | - Chunyuan Zhu
- 1 Department of Plant Pathology, Shandong Agricultural University, No. 61, Daizong Street, Taian, Shandong, 271018, China
| | - Xiaomeng Ding
- 1 Department of Plant Pathology, Shandong Agricultural University, No. 61, Daizong Street, Taian, Shandong, 271018, China
| | - Xiaoyan Yang
- 1 Department of Plant Pathology, Shandong Agricultural University, No. 61, Daizong Street, Taian, Shandong, 271018, China
| | - Paul F Morris
- 2 Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403 U.S.A
| | - Brett M Tyler
- 3 Center for Genome Research and Biocomputing, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, 97331, U.S.A
| | - Xiuguo Zhang
- 1 Department of Plant Pathology, Shandong Agricultural University, No. 61, Daizong Street, Taian, Shandong, 271018, China
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Morris PF, Szabo CP. Meanings of thinness and dysfunctional eating in black South African females: a qualitative study. ACTA ACUST UNITED AC 2013; 16:338-42. [PMID: 24051666 DOI: 10.4314/ajpsy.v16i5.45] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2011] [Accepted: 11/09/2012] [Indexed: 11/17/2022]
Abstract
OBJECTIVE This study qualitatively explored local meanings of thinness and dysfunctional eating in black adolescent females in the rapidly westernizing socio-cultural context of post-apartheid South Africa. METHODS Four (n=4) urban state highschools in KwaZulu-Natal were selected from which 40 subjects were sampled from Grades 9-12. Focus groups were conducted following a semi-structured interview and analysed using Constant Comparative Analysis. RESULTS Subjects reported a wide range of different meanings for thinness, which included traditional idioms of distress and typically western pressures towards thinness, which was particularly evident in the multicultural schools. Subjects also reported a wide range of dysfunctional eating practices (such as purging) which were underscored by a wide range of motivations, including traditional practices and western body image concern; and which did not tend to follow patterns of 'dieting' that are typical in affluent, western societies. CONCLUSION Western pressures towards thinness may be blending with traditional idioms of distress and culturally sanctioned rituals of remedial purging and social over-eating, thereby placing this group at particular risk for a range of dysfunctional eating patterns that may not follow typically western paradigms or diagnostic systems.
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Affiliation(s)
- P F Morris
- Division of Psychiatry, Department of Neurosciences, Faculty of Health Sciences, University of the Witwatersrand. South Africa
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Shtarkman YM, Koçer ZA, Edgar R, Veerapaneni RS, D’Elia T, Morris PF, Rogers SO. Subglacial Lake Vostok (Antarctica) accretion ice contains a diverse set of sequences from aquatic, marine and sediment-inhabiting bacteria and eukarya. PLoS One 2013; 8:e67221. [PMID: 23843994 PMCID: PMC3700977 DOI: 10.1371/journal.pone.0067221] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [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: 09/17/2012] [Accepted: 05/20/2013] [Indexed: 11/21/2022] Open
Abstract
Lake Vostok, the 7th largest (by volume) and 4th deepest lake on Earth, is covered by more than 3,700 m of ice, making it the largest subglacial lake known. The combination of cold, heat (from possible hydrothermal activity), pressure (from the overriding glacier), limited nutrients and complete darkness presents extreme challenges to life. Here, we report metagenomic/metatranscriptomic sequence analyses from four accretion ice sections from the Vostok 5G ice core. Two sections accreted in the vicinity of an embayment on the southwestern end of the lake, and the other two represented part of the southern main basin. We obtained 3,507 unique gene sequences from concentrates of 500 ml of 0.22 µm-filtered accretion ice meltwater. Taxonomic classifications (to genus and/or species) were possible for 1,623 of the sequences. Species determinations in combination with mRNA gene sequence results allowed deduction of the metabolic pathways represented in the accretion ice and, by extension, in the lake. Approximately 94% of the sequences were from Bacteria and 6% were from Eukarya. Only two sequences were from Archaea. In general, the taxa were similar to organisms previously described from lakes, brackish water, marine environments, soil, glaciers, ice, lake sediments, deep-sea sediments, deep-sea thermal vents, animals and plants. Sequences from aerobic, anaerobic, psychrophilic, thermophilic, halophilic, alkaliphilic, acidophilic, desiccation-resistant, autotrophic and heterotrophic organisms were present, including a number from multicellular eukaryotes.
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Affiliation(s)
- Yury M. Shtarkman
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America
| | - Zeynep A. Koçer
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America
| | - Robyn Edgar
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America
| | - Ram S. Veerapaneni
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America
| | - Tom D’Elia
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America
| | - Paul F. Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America
| | - Scott O. Rogers
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, United States of America
- * E-mail:
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Mulangi V, Chibucos MC, Phuntumart V, Morris PF. Kinetic and phylogenetic analysis of plant polyamine uptake transporters. Planta 2012. [PMID: 22711282 DOI: 10.1007/s00425-012-1668-1660] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The rice gene Polyamine Uptake Transporter1 (PUT1) was originally identified based on its homology to the polyamine uptake transporters LmPOT1 and TcPAT12 in Leishmania major and Trypanosoma cruzi, respectively. Here we show that five additional transporters from rice and Arabidopsis that cluster in the same clade as PUT1 all function as high affinity spermidine uptake transporters. Yeast expression assays of these genes confirmed that uptake of spermidine was minimally affected by 166 fold or greater concentrations of amino acids. Characterized polyamine transporters from both Arabidopsis thaliana and Oryza sativa along with the two polyamine transporters from L. major and T. cruzi were aligned and used to generate a hidden Markov model. This model was used to identify significant matches to proteins in other angiosperms, bryophytes, chlorophyta, discicristates, excavates, stramenopiles and amoebozoa. No significant matches were identified in fungal or metazoan genomes. Phylogenic analysis showed that some sequences from the haptophyte, Emiliania huxleyi, as well as sequences from oomycetes and diatoms clustered closer to sequences from plant genomes than from a homologous sequence in the red algal genome Galdieria sulphuraria, consistent with the hypothesis that these polyamine transporters were acquired by horizontal transfer from green algae. Leishmania and Trypansosoma formed a separate cluster with genes from other Discicristates and two Entamoeba species. We surmise that the genes in Entamoeba species were acquired by phagotrophy of Discicristates. In summary, phylogenetic and functional analysis has identified two clades of genes that are predictive of polyamine transport activity.
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Affiliation(s)
- Vaishali Mulangi
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, USA
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Mulangi V, Chibucos MC, Phuntumart V, Morris PF. Kinetic and phylogenetic analysis of plant polyamine uptake transporters. Planta 2012; 236:1261-1273. [PMID: 22711282 DOI: 10.1007/s00425-012-1668-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Accepted: 05/18/2012] [Indexed: 06/01/2023]
Abstract
The rice gene Polyamine Uptake Transporter1 (PUT1) was originally identified based on its homology to the polyamine uptake transporters LmPOT1 and TcPAT12 in Leishmania major and Trypanosoma cruzi, respectively. Here we show that five additional transporters from rice and Arabidopsis that cluster in the same clade as PUT1 all function as high affinity spermidine uptake transporters. Yeast expression assays of these genes confirmed that uptake of spermidine was minimally affected by 166 fold or greater concentrations of amino acids. Characterized polyamine transporters from both Arabidopsis thaliana and Oryza sativa along with the two polyamine transporters from L. major and T. cruzi were aligned and used to generate a hidden Markov model. This model was used to identify significant matches to proteins in other angiosperms, bryophytes, chlorophyta, discicristates, excavates, stramenopiles and amoebozoa. No significant matches were identified in fungal or metazoan genomes. Phylogenic analysis showed that some sequences from the haptophyte, Emiliania huxleyi, as well as sequences from oomycetes and diatoms clustered closer to sequences from plant genomes than from a homologous sequence in the red algal genome Galdieria sulphuraria, consistent with the hypothesis that these polyamine transporters were acquired by horizontal transfer from green algae. Leishmania and Trypansosoma formed a separate cluster with genes from other Discicristates and two Entamoeba species. We surmise that the genes in Entamoeba species were acquired by phagotrophy of Discicristates. In summary, phylogenetic and functional analysis has identified two clades of genes that are predictive of polyamine transport activity.
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Affiliation(s)
- Vaishali Mulangi
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, USA
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Conti EA, Morris PF, Hunkins JA. The North Carolina Department of Transportation's vision for healthy communities through sustainable transportation. N C Med J 2012; 73:274-277. [PMID: 23033713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The North Carolina Department of Transportation increasingly includes the health of North Carolinians in its transportation decision-making. With an expanded mission that now includes health, the agency is integrating public health considerations into its initiatives, plans, and policies, as well as exploring the use of health impact assessments.
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Affiliation(s)
- Eugene A Conti
- North Carolina Department of Transportation, Raleigh, NC 27601, USA
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Tyler BM, Wu M, Wang J, Cheung W, Morris PF. Chemotactic Preferences and Strain Variation in the Response of Phytophthora sojae Zoospores to Host Isoflavones. Appl Environ Microbiol 2010; 62:2811-7. [PMID: 16535375 PMCID: PMC1388913 DOI: 10.1128/aem.62.8.2811-2817.1996] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The zoospores of Phytophthora sojae are chemotactically attracted to the isoflavones genistein and daidzein that are released by soybean roots. In this study we have examined the response of P. sojae zoospores to a wide range of compounds having some structural similarity to genistein and daidzein, including isoflavones, flavones, chalcones, stilbenes, benzoins, benzoates, benzophenones, acetophenones, and coumarins. Of 59 compounds examined, 43 elicited some response. A comparison of the chemotactic responses elicited by the various compounds revealed a primary role for the phenolic 4(prm1)- and 7-hydroxyl groups on the isoflavone structure. A few compounds acted as repellents, notably methylated flavones with a hydrophobic B ring. The chemotactic response to many of the analogs was markedly different among different strains of P. sojae.
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Morris PF, Phuntumart V. Inventory and Comparative Evolution of the ABC Superfamily in the Genomes of Phytophthora ramorum and Phytophthora sojae. J Mol Evol 2009; 68:563-75. [DOI: 10.1007/s00239-009-9231-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 04/02/2009] [Accepted: 04/03/2009] [Indexed: 12/27/2022]
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Tyler BM, Tripathy S, Zhang X, Dehal P, Jiang RHY, Aerts A, Arredondo FD, Baxter L, Bensasson D, Beynon JL, Chapman J, Damasceno CMB, Dorrance AE, Dou D, Dickerman AW, Dubchak IL, Garbelotto M, Gijzen M, Gordon SG, Govers F, Grunwald NJ, Huang W, Ivors KL, Jones RW, Kamoun S, Krampis K, Lamour KH, Lee MK, McDonald WH, Medina M, Meijer HJG, Nordberg EK, Maclean DJ, Ospina-Giraldo MD, Morris PF, Phuntumart V, Putnam NH, Rash S, Rose JKC, Sakihama Y, Salamov AA, Savidor A, Scheuring CF, Smith BM, Sobral BWS, Terry A, Torto-Alalibo TA, Win J, Xu Z, Zhang H, Grigoriev IV, Rokhsar DS, Boore JL. Phytophthora genome sequences uncover evolutionary origins and mechanisms of pathogenesis. Science 2006; 313:1261-6. [PMID: 16946064 DOI: 10.1126/science.1128796] [Citation(s) in RCA: 719] [Impact Index Per Article: 39.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Draft genome sequences have been determined for the soybean pathogen Phytophthora sojae and the sudden oak death pathogen Phytophthora ramorum. Oömycetes such as these Phytophthora species share the kingdom Stramenopila with photosynthetic algae such as diatoms, and the presence of many Phytophthora genes of probable phototroph origin supports a photosynthetic ancestry for the stramenopiles. Comparison of the two species' genomes reveals a rapid expansion and diversification of many protein families associated with plant infection such as hydrolases, ABC transporters, protein toxins, proteinase inhibitors, and, in particular, a superfamily of 700 proteins with similarity to known oömycete avirulence genes.
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Affiliation(s)
- Brett M Tyler
- Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
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Chibucos MC, Morris PF. Levels of polyamines and kinetic characterization of their uptake in the soybean pathogen Phytophthora sojae. Appl Environ Microbiol 2006; 72:3350-6. [PMID: 16672477 PMCID: PMC1472313 DOI: 10.1128/aem.72.5.3350-3356.2006] [Citation(s) in RCA: 13] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2005] [Accepted: 03/02/2006] [Indexed: 11/20/2022] Open
Abstract
Polyamines are ubiquitous biologically active aliphatic cations that are at least transiently available in the soil from decaying organic matter. Our objectives in this study were to characterize polyamine uptake kinetics in Phytophthora sojae zoospores and to quantify endogenous polyamines in hyphae, zoospores, and soybean roots. Zoospores contained 10 times more free putrescine than spermidine, while hyphae contained only 4 times as much free putrescine as spermidine. Zoospores contained no conjugated putrescine, but conjugated spermidine was present. Hyphae contained both conjugated putrescine and spermidine at levels comparable to the hyphal free putrescine and spermidine levels. In soybean roots, cadaverine was the most abundant polyamine, but only putrescine efflux was detected. The selective efflux of putrescine suggests that the regulation of polyamine availability is part of the overall plant strategy to influence microbial growth in the rhizosphere. In zoospores, uptake experiments with [1,4-(14)C]putrescine and [1,4-(14)C]spermidine confirmed the existence of high-affinity polyamine transport for both polyamines. Putrescine uptake was reduced by high levels of exogenous spermidine, but spermidine uptake was not reduced by exogenous putrescine. These observations suggest that P. sojae zoospores express at least two high-affinity polyamine transporters, one that is spermidine specific and a second that is putrescine specific or putrescine preferential. Disruption of polyamine uptake or metabolism has major effects on a wide range of cellular activities in other organisms and has been proposed as a potential control strategy for Phytophthora. Inhibition of polyamine uptake may be a means of reducing the fitness of the zoospore along with subsequent developmental stages that precede infection.
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Affiliation(s)
- M Constantine Chibucos
- Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, USA
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Connolly MS, Sakihama Y, Phuntumart V, Jiang Y, Warren F, Mourant L, Morris PF. Heterologous expression of a pleiotropic drug resistance transporter from Phytophthora sojae in yeast transporter mutants. Curr Genet 2005; 48:356-65. [PMID: 16273370 DOI: 10.1007/s00294-005-0015-4] [Citation(s) in RCA: 14] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2005] [Revised: 07/24/2005] [Accepted: 07/28/2005] [Indexed: 11/28/2022]
Abstract
A system for the expression of an ATP binding cassette (ABC) transporter from the soybean pathogen Phytophthora sojae is described. Pdr1, an ABC transporter with homology to the pleiotropic drug resistance (PDR) family of transporters, was cloned by primer walking from a P. sojae genomic library. Reverse transcriptase PCR assays showed that the transcript disappeared after encystment of zoospores and was not detected in hyphal germlings in dilute salts, in hyphae growing in liquid V8 media, or in tissue extracts from infected hypocotyls. BLAST analysis of Pdr1 against the P. sojae EST database also revealed that this gene was present only in zoospore libraries. Comparison of the number of hits to Pdr1 with that of a set of housekeeping genes revealed that Pdr1 was expressed at rates two- to threefold higher than other transcripts. To test the hypothesis that Pdr1p functions as a broad substrate membrane transporter, Pdr1 was transformed into yeast mutants deficient in several drug resistance transporters. Yeast mutants transformed with Pdr1 possessed partial drug resistance against only 5 of 17 chemically distinct compounds. Thus, when expressed in yeast, this transporter has a significantly narrower substrate specificity in comparison to the yeast transporters, Pdr5p, Yorlp, and Snq2p.
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Abstract
Both the motile zoospores and the hyphal germ tubes of Phytophthora sojae respond chemotropically to the soybean isoflavones daidzein and genistein. The role of Ca(2+) in the cellular response to these host signals was investigated by using X-ray microanalysis of cells to monitor net changes in cellular levels of Ca(2+) and by quantifying the effects of exogenous Ca(2+) and daidzein on the developmental fate of encysted zoospores. Confirmation that isoflavones trigger a net influx of Ca(2+) into the cell was demonstrated by X-ray microanalysis of individual encysted zoospores. Zoospores exposed to 10 mM Ca(2+) and 1 microM daidzein at the time of encystment formed cysts that contained more Ca(2+) than zoospores exposed to Ca(2+) alone. The magnitude of internal Ca(2+) stores appears to be a determining factor affecting the developmental fate of P. sojae cysts.
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Affiliation(s)
- M S Connolly
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio, 43403, USA
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Morris PF, Bone E, Tyler BM. Chemotropic and contact responses of phytophthora sojae hyphae to soybean isoflavonoids and artificial substrates. Plant Physiol 1998; 117:1171-8. [PMID: 9701573 PMCID: PMC34881 DOI: 10.1104/pp.117.4.1171] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/1998] [Accepted: 05/12/1998] [Indexed: 05/18/2023]
Abstract
We have investigated the role of the isoflavones daidzein and genistein on the chemotropic behavior of germinating cysts of Phytophthora sojae. Hyphal germlings were shown to respond chemotropically to daidzein and genistein, suggesting that hyphal tips from zoospores that have encysted adjacent to the root may use specific host isoflavones to locate their host. Observations of the contact response of hyphal germlings were made on several different substrates in the presence and absence of isoflavones. Hyphal tips of germlings detected and penetrated pores in membranes and produced multiple appressoria on smooth, impenetrable surfaces. Hyphae that successfully penetrated the synthetic membrane were observed to grow away from the membrane surface. The presence of isoflavones in the medium surrounding the hyphal germlings did not appear to alter any of those habits. Daidzein and genistein did not inhibit germination or initial hyphal growth at concentrations up to 20 &mgr;M.
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Affiliation(s)
- PF Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403 (P.F.M., E.B.)
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Morris PF, Layzell DB, Canvin DT. Photorespiratory ammonia does not inhibit photosynthesis in glutamate synthase mutants of Arabidopsis. Plant Physiol 1989; 89:498-500. [PMID: 16666572 PMCID: PMC1055870 DOI: 10.1104/pp.89.2.498] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Exposure of ferredoxin-dependent glutamate synthase (EC 1.4.7.1) mutants of Arabidopsis thaliana to photorespiratory conditions resulted in the accumulation of NH(4) (+) and the inhibition of photosynthesis. However, upon transfer from 2% O(2), 350 microliters per liter CO(2), to 21% O(2), 350 microliters per liter CO(2), net photosynthesis declined at a slower rate in methionine sulfoximine treated leaf discs relative to controls. The recovery of photosynthesis was also more rapid in MSO-treated leaf discs although ammonia levels were more than threefold higher. Photosynthesis in leaf discs treated with azaserine was inhibited more than controls when transferred to 21% O(2) and recovered less than controls when returned to 2% O(2) although NH(4) (+) levels were not significantly different. The results obtained are consistent with the view that the rapid inhibition of photosynthesis in the glutamate synthase mutants in photorespiratory conditions is not due to the accumulation of NH(4) (+) but rather to the depletion of amino donors for glyoxylate and the consequent effects of glyoxylate on the lack of return of carbon to the chloroplast.
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Affiliation(s)
- P F Morris
- Department of Biology, Queen's University, Kingston, Ontario Canada, K7L 3N6
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Morris PF, Doong RL, Jensen RA. Evidence from Solanum tuberosum in Support of the Dual-Pathway Hypothesis of Aromatic Biosynthesis. Plant Physiol 1989; 89:10-4. [PMID: 16666497 PMCID: PMC1055790 DOI: 10.1104/pp.89.1.10] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Key branchpoint enzymes of aromatic amino acid biosynthesis, 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DS) and chorismate mutase (CM), have previously been shown to exist as separate compartmentalized isozymes in the chloroplasts and cytosol of tobacco, sorghum and spinach. Although additional examples of plants containing these isozyme pairs are accumulating, some studies in the literature report the presence of only the single plastidic DS or CM enzyme. Such apparent exceptions contradict the universality of pathway organization existing in higher plants that is implied by the dual-pathway hypothesis of aromatic biosynthesis. Since potato (Solanum tuberosum) exemplifies a case where only a single species of both DS and CM have been reported, we selected this system for further analysis. The DS-Mn and DS-Co isozyme pair, exhibiting all of the differential properties described in Nicotiana silvestris, have now been identified in S. tuberosum. Likewise, partial purification via DEAE-cellulose chromatography revealed two isozymes of CM in disks excised from tubers of S. tuberosum. The differential regulatory properties of these isozymes were comparable to the CM-1 and CM-2 isozymes of N. silvestris.
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Affiliation(s)
- P F Morris
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, 32611
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Morris PF, Layzell DB, Canvin DT. Ammonia Production and Assimilation in Glutamate Synthase Mutants of Arabidopsis thaliana. Plant Physiol 1988; 87:148-54. [PMID: 16666091 PMCID: PMC1054715 DOI: 10.1104/pp.87.1.148] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Ammonia production and assimilation(1) were examined in photorespiratory mutants of Arabidopsis thaliana L. lacking ferredoxin-dependent glutamate synthase (Fd-GluS) activity. Although photosynthesis was rapidly inhibited in these mutants in normal air, NH(4) (+) continued to accumulate. The accumulation of NH(4) (+) was also seen after an initial lag of 30 minutes in 2% O(2), 350 microliters per liter of CO(2) and after 90 minutes in 2% O(2), 900 microliters per liter of CO(2). The accumulation of NH(4) (+) in normal air and low O(2) was also associated with an increase in the total pool of amino acid-N and glutamine, and a decrease in the pools of glutamate, aspartate, alanine, and serine. Upon return to dark conditions, or to 21% O(2), 1% CO(2) in the light, the NH(4) (+) which had accumulated in the leaves was reassimilated into amino acids. The addition of methionine sulfoximine (MSO) resulted in higher accumulations of NH(4) (+) in glutamate synthase mutants and prevented the reassimilation of NH(4) (+) upon return to the dark. The addition of MSO also resulted in the accumulation of NH(4) (+) in glutamate synthase mutants in the light and in 21% O(2), 1% CO(2). These results indicate that glutamine synthetase is essential for the reassimilation of photorespiratory NH(4) (+) and for primary N assimilation in the leaves and strongly suggest that glutamate dehydrogenase plays only a minimal role in the assimilation of ammonia. Levels of NADH-dependent glutamate synthase (NADH-GluS) appear to be sufficient to account for the assimilation of NH(4) (+) by a GS/NADH-GluS cycle.
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Affiliation(s)
- P F Morris
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611
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