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Kleetz J, Mizza AS, Shevyreva I, Welter L, Brocks C, Hemschemeier A, Aktas M, Narberhaus F. Three separate pathways in Rhizobium leguminosarum maintain phosphatidylcholine biosynthesis, which is required for symbiotic nitrogen fixation with clover. Appl Environ Microbiol 2024; 90:e0059024. [PMID: 39120150 PMCID: PMC11409717 DOI: 10.1128/aem.00590-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2024] [Accepted: 06/24/2024] [Indexed: 08/10/2024] Open
Abstract
Phosphatidylcholine (PC) is critical for the nitrogen-fixing symbiosis between rhizobia and legumes. We characterized three PC biosynthesis pathways in Rhizobium leguminosarum and evaluated their impact on nitrogen fixation in clover nodules. In the presence of choline, a PC synthase catalyzes the condensation of cytidine diphosphate-diacylglycerol with choline to produce PC. In the presence of lyso-PC, acyltransferases acylate this mono-acylated phospholipid to PC. The third pathway relies on phospholipid N-methyltransferases (Pmts), which sequentially methylate phosphatidylethanolamine (PE) through three rounds of methylation, yielding PC via the intermediates monomethyl-PE and dimethyl-PE. In R. leguminosarum, at least three Pmts participate in this methylation cascade. To elucidate the functions of these enzymes, we recombinantly produced and biochemically characterized them. We moved on to determine the phospholipid profiles of R. leguminosarum mutant strains harboring single and combinatorial deletions of PC biosynthesis genes. The cumulative results show that PC production occurs through the combined action of multiple enzymes, each with distinct substrate and product specificities. The methylation pathway emerges as the dominant PC biosynthesis route, and we pinpoint PmtS2, which catalyzes all three methylation steps, as the enzyme responsible for providing adequate PC amounts for a functional nitrogen-fixing symbiosis with clover. IMPORTANCE Understanding the molecular mechanisms of symbiotic nitrogen fixation has important implications for sustainable agriculture. The presence of the phospholipid phosphatidylcholine (PC) in the membrane of rhizobia is critical for the establishment of productive nitrogen-fixing root nodules on legume plants. The reasons for the PC requirement are unknown. Here, we employed Rhizobium leguminosarum and clover as model system for a beneficial plant-microbe interaction. We found that R. leguminosarum produces PC by three distinct pathways. The relative contribution of these pathways to PC formation was determined in an array of single, double, and triple mutant strains. Several of the PC biosynthesis enzymes were purified and biochemically characterized. Most importantly, we demonstrated the essential role of PC formation by R. leguminosarum in nitrogen fixation and pinpointed a specific enzyme indispensable for plant-microbe interaction. Our study offers profound insights into bacterial PC biosynthesis and its pivotal role in biological nitrogen fixation.
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Affiliation(s)
- Julia Kleetz
- Microbial Biology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Ann-Sophie Mizza
- Microbial Biology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Irina Shevyreva
- Microbial Biology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Leon Welter
- Microbial Biology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Claudia Brocks
- Photobiotechnology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Anja Hemschemeier
- Photobiotechnology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Meriyem Aktas
- Microbial Biology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Franz Narberhaus
- Microbial Biology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
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Ben Gaied R, Sbissi I, Tarhouni M, Brígido C. Bacterial Endophytes from Legumes Native to Arid Environments Are Promising Tools to Improve Mesorhizobium-Chickpea Symbiosis under Salinity. BIOLOGY 2024; 13:96. [PMID: 38392314 PMCID: PMC10886315 DOI: 10.3390/biology13020096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 01/26/2024] [Accepted: 02/01/2024] [Indexed: 02/24/2024]
Abstract
Symbiotic nitrogen fixation is a major contributor of N in agricultural ecosystems, but the establishment of legume-rhizobium symbiosis is highly affected by soil salinity. Our interest is focused on the use of non-rhizobial endophytes to assist the symbiosis between chickpea and its microsymbiont under salinity to avoid loss of production and fertility. Our aims were (1) to investigate the impact of salinity on both symbiotic partners; including on early events of the Mesorhizobium-chickpea symbiosis, and (2) to evaluate the potential of four non-rhizobial endophytes isolated from legumes native to arid regions (Phyllobacterium salinisoli, P. ifriqiyense, Xanthomonas translucens, and Cupriavidus respiraculi) to promote chickpea growth and nodulation under salinity. Our results show a significant reduction in chickpea seed germination rate and in the microsymbiont Mesorhizobium ciceri LMS-1 growth under different levels of salinity. The composition of phenolic compounds in chickpea root exudates significantly changed when the plants were subjected to salinity, which in turn affected the nod genes expression in LMS-1. Furthermore, the LMS-1 response to root exudate stimuli was suppressed by the presence of salinity (250 mM NaCl). On the contrary, a significant upregulation of exoY and otsA genes, which are involved in exopolysaccharide and trehalose biosynthesis, respectively, was registered in salt-stressed LMS-1 cells. In addition, chickpea co-inoculation with LMS-1 along with the consortium containing two non-rhizobial bacterial endophytes, P. salinisoli and X. translucens, resulted in significant improvement of the chickpea growth and the symbiotic performance of LMS-1 under salinity. These results indicate that this non-rhizobial endophytic consortium may be an appropriate ecological and safe tool to improve chickpea growth and its adaptation to salt-degraded soils.
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Affiliation(s)
- Roukaya Ben Gaied
- Laboratory of Pastoral Ecosystems and Promotion of Spontaneous Plants and Associated Micro-Organisms, Institute of Arid Lands, University of Gabes, Medenine 4119, Tunisia
- MED-Mediterranean Institute for Agriculture, Environment and Development, Universidade de Évora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal
| | - Imed Sbissi
- Laboratory of Pastoral Ecosystems and Promotion of Spontaneous Plants and Associated Micro-Organisms, Institute of Arid Lands, University of Gabes, Medenine 4119, Tunisia
| | - Mohamed Tarhouni
- Laboratory of Pastoral Ecosystems and Promotion of Spontaneous Plants and Associated Micro-Organisms, Institute of Arid Lands, University of Gabes, Medenine 4119, Tunisia
| | - Clarisse Brígido
- MED-Mediterranean Institute for Agriculture, Environment and Development & CHANGE-Global Change and Sustainability Institute, Institute for Advanced Studies and Research, Universidade de Évora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal
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Li X, Li Z. What determines symbiotic nitrogen fixation efficiency in rhizobium: recent insights into Rhizobium leguminosarum. Arch Microbiol 2023; 205:300. [PMID: 37542687 DOI: 10.1007/s00203-023-03640-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 07/21/2023] [Accepted: 07/24/2023] [Indexed: 08/07/2023]
Abstract
Symbiotic nitrogen fixation (SNF) by rhizobium, a Gram-negative soil bacterium, is an essential component in the nitrogen cycle and is a sustainable green way to maintain soil fertility without chemical energy consumption. SNF, which results from the processes of nodulation, rhizobial infection, bacteroid differentiation and nitrogen-fixing reaction, requires the expression of various genes from both symbionts with adaptation to the changing environment. To achieve successful nitrogen fixation, rhizobia and their hosts cooperate closely for precise regulation of symbiotic genes, metabolic processes and internal environment homeostasis. Many researches have progressed to reveal the ample information about regulatory aspects of SNF during recent decades, but the major bottlenecks regarding improvement of nitrogen-fixing efficiency has proven to be complex. In this mini-review, we summarize recent advances that have contributed to understanding the rhizobial regulatory aspects that determine SNF efficiency, focusing on the coordinated regulatory mechanism of symbiotic genes, oxygen, carbon metabolism, amino acid metabolism, combined nitrogen, non-coding RNAs and internal environment homeostasis. Unraveling regulatory determinants of SNF in the nitrogen-fixing protagonist rhizobium is expected to promote an improvement of nitrogen-fixing efficiency in crop production.
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Affiliation(s)
- Xiaofang Li
- Institute of Biopharmaceuticals, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China.
- School of Pharmaceutical Sciences, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China.
| | - Zhangqun Li
- School of Pharmaceutical Sciences, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China
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4
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Shang JY, Zhang P, Jia YW, Lu YN, Wu Y, Ji S, Chen L, Wang ET, Chen WX, Sui XH. Coordinated regulation of symbiotic adaptation by NodD proteins and NolA in the type I peanut bradyrhizobial strain Bradyrhizobium zhanjiangense CCBAU51778. Microbiol Res 2022; 265:127188. [PMID: 36152611 DOI: 10.1016/j.micres.2022.127188] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 08/27/2022] [Accepted: 09/06/2022] [Indexed: 10/14/2022]
Abstract
Type I peanut bradyrhizobial strains can establish efficient symbiosis in contrast to symbiotic incompatibility induced by type II strains with mung bean. The notable distinction in the two kinds of key symbiosis-related regulators nolA and nodD close to the nodABCSUIJ operon region between these two types of peanut bradyrhizobia was found. Therefore, we determined whether NolA and NodD proteins regulate the symbiotic adaptations of type I strains to different hosts. We found that NodD1-NolA synergistically regulated the symbiosis between the type I strain Bradyrhizobium zhanjiangense CCBAU51778 and mung bean, and NodD1-NodD2 jointly regulated nodulation ability. In contrast, NodD1-NolA coordinately regulated nodulation ability in the CCBAU51778-peanut symbiosis. Meanwhile, NodD1 and NolA collectively contributes to competitive nodule colonization of CCBAU51778 on both hosts. The Fucosylated Nod factors and intact type 3 secretion system (T3SS), rather than extra nodD2 and full-length nolA, were critical for effective symbiosis with mung bean. Unexpectedly, T3SS-related genes were activated by NodD2 but not NodD1. Compared to NodD1 and NodD2, NolA predominantly inhibits exopolysaccharide production by promoting exoR expression. Importantly, this is the first report that NolA regulates rhizobial T3SS-related genes. The coordinated regulation and integration of different gene networks to fine-tune the expression of symbiosis-related genes and other accessory genes by NodD1-NolA might be required for CCBAU51778 to efficiently nodulate peanut. This study shed new light on our understanding of the regulatory roles of NolA and NodD proteins in symbiotic adaptation, highlighting the sophisticated gene networks dominated by NodD1-NolA.
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Affiliation(s)
- Jiao Ying Shang
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Pan Zhang
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China; CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
| | - Yu Wen Jia
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Yi Ning Lu
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Yue Wu
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Shuang Ji
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - La Chen
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - En Tao Wang
- Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México, D. F. 11340, Mexico
| | - Wen Xin Chen
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Xin Hua Sui
- State Key Laboratory of Agrobiotechnology, MOA Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing 100193, China.
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Rodríguez-Esperón MC, Eastman G, Sandes L, Garabato F, Eastman I, Iriarte A, Fabiano E, Sotelo-Silveira JR, Platero R. Genomics and transcriptomics insights into luteolin effects on the beta-rhizobial strain Cupriavidus necator UYPR2.512. Environ Microbiol 2021; 24:240-264. [PMID: 34811861 DOI: 10.1111/1462-2920.15845] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 11/04/2021] [Accepted: 11/08/2021] [Indexed: 11/28/2022]
Abstract
Cupriavidus necator UYPR2.512 is a rhizobial strain that belongs to the Beta-subclass of proteobacteria, able to establish successful symbiosis with Mimosoid legumes. The initial steps of rhizobium-legumes symbioses involve the reciprocal recognition by chemical signals, being luteolin one of the molecules involved. However, there is a lack of information on the effect of luteolin in beta-rhizobia. In this work, we used long-read sequencing to complete the genome of UYPR2.512 providing evidence for the existence of four closed circular replicons. We used an RNA-Seq approach to analyse the response of UYPR2.512 to luteolin. One hundred and forty-five genes were differentially expressed, with similar numbers of downregulated and upregulated genes. Most repressed genes were mapped to the main chromosome, while the upregulated genes were overrepresented among pCne512e, containing the symbiotic genes. Induced genes included the nod operon and genes implicated in exopolysaccharides and flagellar biosynthesis. We identified many genes involved in iron, copper and other heavy metals metabolism. Among repressed genes, we identified genes involved in basal carbon and nitrogen metabolism. Our results suggest that in response to luteolin, C. necator strain UYPR2.512 reshapes its metabolism in order to be prepared for the forthcoming symbiotic interaction.
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Affiliation(s)
- M C Rodríguez-Esperón
- Laboratorio de Microbiología Ambiental, Departamento de Bioquímica y Genómica Microbianas, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay
| | - G Eastman
- Departamento de Genómica, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay
| | - L Sandes
- Laboratorio de Microbiología Ambiental, Departamento de Bioquímica y Genómica Microbianas, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay
| | - F Garabato
- Laboratorio de Microbiología Ambiental, Departamento de Bioquímica y Genómica Microbianas, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay
| | - I Eastman
- Laboratorio de Microbiología Ambiental, Departamento de Bioquímica y Genómica Microbianas, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay
| | - A Iriarte
- Laboratorio de Biología Computacional, Departamento de Desarrollo Biotecnológico, Facultad de Medicina, Instituto de Higiene, Montevideo, Uruguay
| | - E Fabiano
- Departamento de Bioquímica y Genómica Microbianas, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay
| | - J R Sotelo-Silveira
- Departamento de Genómica, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay
| | - R Platero
- Laboratorio de Microbiología Ambiental, Departamento de Bioquímica y Genómica Microbianas, Instituto de Investigaciones Biológicas Clemente Estable, Montevideo, Uruguay
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Huo H, Wang X, Liu Y, Chen J, Wei G. A Nod factor- and type III secretion system-dependent manner for Robinia pseudoacacia to establish symbiosis with Mesorhizobium amorphae CCNWGS0123. TREE PHYSIOLOGY 2021; 41:817-835. [PMID: 33219377 DOI: 10.1093/treephys/tpaa160] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 11/15/2020] [Indexed: 06/11/2023]
Abstract
Under nitrogen-limiting conditions, symbiotic nodulation promotes the growth of legume plants via the fixation of atmospheric nitrogen to ammonia by rhizobia in root nodules. The rhizobial Nod factor (NF) and type III secretion system (T3SS) are two key signaling pathways for establishing the legume-rhizobium symbiosis. However, whether NF signaling is involved in the nodulation of Robinia pseudoacacia and Mesorhizobium amorphae CCNWGS0123, and its symbiotic differences compared with T3SS signaling remain unclear. Therefore, to elucidate the function of NF signaling in nodulation, we mutated nodC in M. amorphae CCNWGS0123, which aborted NF synthesis. Compared with the plants inoculated with the wild type strain, the plants inoculated with the NF-deficient strain exhibited shorter shoots with etiolated leaves. These phenotypic characteristics were similar to those of the plants inoculated with the T3SS-deficient strain, which served as a Nod- (non-effective nodulation) control. The plants inoculated with both the NF- and T3SS-deficient strains formed massive root hair swellings, but no normal infection threads were detected. Sections of the nodules showed that inoculation with the NF- and T3SS-deficient strains induced small, white bumps without any rhizobia inside. Analyzing the accumulation of 6 plant hormones and the expression of 10 plant genes indicated that the NF- and T3SS-deficient strains activated plant defense reactions while suppressing plant symbiotic signaling during the perception and nodulation processes. The requirement for NF signaling appeared to be conserved in two other leguminous trees that can establish symbiosis with M. amorphae CCNWGS0123. In contrast, the function of the T3SS might differ among species, even within the same subfamily (Faboideae). Overall, this work demonstrated that nodulation of R. pseudoacacia and M. amorphae CCNWGS0123 was both NF and T3SS dependent.
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Affiliation(s)
- Haibo Huo
- State Key Laboratory of Crop Stress Biology for Arid Areas, Shaanxi Key Laboratory of Agricultural and Environmental Microbiology, College of Life Science, Northwest A&F University, 3 Taicheng Road, Yangling 712100, Shaanxi, People's Republic of China
| | - Xinye Wang
- State Key Laboratory of Crop Stress Biology for Arid Areas, Shaanxi Key Laboratory of Agricultural and Environmental Microbiology, College of Life Science, Northwest A&F University, 3 Taicheng Road, Yangling 712100, Shaanxi, People's Republic of China
| | - Yao Liu
- State Key Laboratory of Crop Stress Biology for Arid Areas, Shaanxi Key Laboratory of Agricultural and Environmental Microbiology, College of Life Science, Northwest A&F University, 3 Taicheng Road, Yangling 712100, Shaanxi, People's Republic of China
| | - Juan Chen
- State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water conservation, Northwest A&F University, 26 Xinong Road, Yangling 712100, Shaanxi, People's Republic of China
| | - Gehong Wei
- State Key Laboratory of Crop Stress Biology for Arid Areas, Shaanxi Key Laboratory of Agricultural and Environmental Microbiology, College of Life Science, Northwest A&F University, 3 Taicheng Road, Yangling 712100, Shaanxi, People's Republic of China
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Assessment of Genetic Diversity and Symbiotic Efficiency of Selected Rhizobia Strains Nodulating Lentil ( Lens culinaris Medik.). PLANTS 2020; 10:plants10010015. [PMID: 33374129 PMCID: PMC7823456 DOI: 10.3390/plants10010015] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 12/13/2020] [Accepted: 12/14/2020] [Indexed: 11/30/2022]
Abstract
A total of 14 Rhizobium strains were isolated from lentil accessions grown at the ICARDA experimental research station at Marchouch in Morocco and used for molecular characterization and symbiotic efficiency assessment. Individual phylogenetic analysis using the 16S rRNA gene, house-keeping genes rpoB, recA, and gyrB, and symbiotic genes nodD and nodA along with Multilocus Sequence Analysis (MLSA) of the concatenated genes (16S rRNA-rpoB-recA-gyrB) was carried out for the identification and clustering of the isolates. The symbiotic efficiency of the strains was assessed on three Moroccan lentil cultivars (Bakria, Chakkouf, and Zaria) based on the number of nodules, plant height, plant dry weight, and total nitrogen content in leaves. The results showed that the individual phylogenetic analysis clustered all the strains into Rhizobium laguerreae and Rhizobium leguminosarum with sequence similarity ranging from 94 to 100%, except one strain which clustered with Mesorhizobium huakuii with sequence similarity of 100%. The MLSA of the concatenated genes and the related percentages of similarity clustered these strains into two groups of Rhizobium species, with one strain as a new genospecies when applying the threshold of 96%. For symbiotic efficiency, the Bakria variety showed the best association with 10 strains compared to its non-inoculated control (p-value ≤ 0.05), followed by Chakkouf and Zaria. The present study concluded that the genetic diversity and the symbiotic efficiency of Rhizobium strains appeared to be mainly under the control of the lentil genotypes.
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Walker L, Lagunas B, Gifford ML. Determinants of Host Range Specificity in Legume-Rhizobia Symbiosis. Front Microbiol 2020; 11:585749. [PMID: 33329456 PMCID: PMC7728800 DOI: 10.3389/fmicb.2020.585749] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Accepted: 11/06/2020] [Indexed: 01/24/2023] Open
Abstract
Leguminous plants possess the almost unique ability to enter symbiosis with soil-resident, nitrogen fixing bacteria called rhizobia. During this symbiosis, the bacteria physically colonize specialized organs on the roots of the host plant called nodules, where they reduce atmospheric nitrogen into forms that can be assimilated by the host plant and receive photosynthates in return. In order for nodule development to occur, there is extensive chemical cross-talk between both parties during the formative stages of the symbiosis. The vast majority of the legume family are capable of forming root nodules and typically rhizobia are only able to fix nitrogen within the context of this symbiotic association. However, many legume species only enter productive symbiosis with a few, or even single rhizobial species or strains, and vice-versa. Permitting symbiosis with only rhizobial strains that will be able to fix nitrogen with high efficiency is a crucial strategy for the host plant to prevent cheating by rhizobia. This selectivity is enforced at all stages of the symbiosis, with partner choice beginning during the initial communication between the plant and rhizobia. However, it can also be influenced even once nitrogen-fixing nodules have developed on the root. This review sets out current knowledge about the molecular mechanisms employed by both parties to influence host range during legume-rhizobia symbiosis.
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Affiliation(s)
- Liam Walker
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
| | - Beatriz Lagunas
- School of Life Sciences, University of Warwick, Coventry, United Kingdom
| | - Miriam L Gifford
- School of Life Sciences, University of Warwick, Coventry, United Kingdom.,Warwick Integrative Synthetic Biology Centre, University of Warwick, Coventry, United Kingdom
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Rhizobium leguminosarum bv. trifolii NodD2 Enhances Competitive Nodule Colonization in the Clover-Rhizobium Symbiosis. Appl Environ Microbiol 2020; 86:AEM.01268-20. [PMID: 32651206 DOI: 10.1128/aem.01268-20] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 07/02/2020] [Indexed: 01/01/2023] Open
Abstract
Establishment of the symbiotic relationship that develops between rhizobia and their legume hosts is contingent upon an interkingdom signal exchange. In response to host legume flavonoids, NodD proteins from compatible rhizobia activate expression of nodulation genes that produce lipochitin oligosaccharide signaling molecules known as Nod factors. Root nodule formation commences upon legume recognition of compatible Nod factor. Rhizobium leguminosarum was previously considered to contain one copy of nodD; here, we show that some strains of the Trifolium (clover) microsymbiont R. leguminosarum bv. trifolii contain a second copy designated nodD2. nodD2 genes were present in 8 out of 13 strains of R. leguminosarum bv. trifolii, but were absent from the genomes of 16 R. leguminosarum bv. viciae strains. Analysis of single and double nodD1 and nodD2 mutants in R. leguminosarum bv. trifolii strain TA1 revealed that NodD2 was functional and enhanced nodule colonization competitiveness. However, NodD1 showed significantly greater capacity to induce nod gene expression and infection thread formation. Clover species are either annual or perennial and this phenological distinction is rarely crossed by individual R. leguminosarum bv. trifolii microsymbionts for effective symbiosis. Of 13 strains with genome sequences available, 7 of the 8 effective microsymbionts of perennial hosts contained nodD2, whereas the 3 microsymbionts of annual hosts did not. We hypothesize that NodD2 inducer recognition differs from NodD1, and NodD2 functions to enhance competition and effective symbiosis, which may discriminate in favor of perennial hosts.IMPORTANCE Establishment of the rhizobium-legume symbiosis requires a highly specific and complex signal exchange between both participants. Rhizobia perceive legume flavonoid compounds through LysR-type NodD regulators. Often, rhizobia encode multiple copies of nodD, which is one determinant of host specificity. In some species of rhizobia, the presence of multiple copies of NodD extends their symbiotic host-range. Here, we identified and characterized a second copy of nodD present in some strains of the clover microsymbiont Rhizobium leguminosarum bv. trifolii. The second nodD gene contributed to the competitive ability of the strain on white clover, an important forage legume. A screen for strains containing nodD2 could be utilized as one criterion to select strains with enhanced competitive ability for use as inoculants for pasture production.
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De Paepe B, Maertens J, Vanholme B, De Mey M. Chimeric LysR-Type Transcriptional Biosensors for Customizing Ligand Specificity Profiles toward Flavonoids. ACS Synth Biol 2019; 8:318-331. [PMID: 30563319 DOI: 10.1021/acssynbio.8b00326] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Transcriptional biosensors enable key applications in both metabolic engineering and synthetic biology. Due to nature's immense variety of metabolites, these applications require biosensors with a ligand specificity profile customized to the researcher's needs. In this work, chimeric biosensors were created by introducing parts of a donor regulatory circuit from Sinorhizobium meliloti, delivering the desired luteolin-specific response, into a nonspecific biosensor chassis from Herbaspirillum seropedicae. Two strategies were evaluated for the development of chimeric LysR-type biosensors with customized ligand specificity profiles toward three closely related flavonoids, naringenin, apigenin, and luteolin. In the first strategy, chimeric promoter regions were constructed at the biosensor effector module, while in the second strategy, chimeric transcription factors were created at the biosensor detector module. Via both strategies, the biosensor repertoire was expanded with luteolin-specific chimeric biosensors demonstrating a variety of response curves and ligand specificity profiles. Starting from the nonspecific biosensor chassis, a shift from 27.5% to 95.3% luteolin specificity was achieved with the created chimeric biosensors. Both strategies provide a compelling, faster, and more accessible route for the customization of biosensor ligand specificity, compared to de novo design and construction of each biosensor circuit for every desired ligand specificity.
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Affiliation(s)
- Brecht De Paepe
- Centre for Synthetic Biology, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium
| | - Jo Maertens
- Centre for Synthetic Biology, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium
| | - Bartel Vanholme
- Department of Plant Biotechnology and Bioinformatics, Ghent University − VIB Center for Plant Systems Biology, Technologiepark 927, 9052 Ghent, Belgium
| | - Marjan De Mey
- Centre for Synthetic Biology, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium
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11
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Bustamante-Brito R, Vera-Ponce de León A, Rosenblueth M, Martínez-Romero JC, Martínez-Romero E. Metatranscriptomic Analysis of the Bacterial Symbiont Dactylopiibacterium carminicum from the Carmine Cochineal Dactylopius coccus (Hemiptera: Coccoidea: Dactylopiidae). Life (Basel) 2019; 9:life9010004. [PMID: 30609847 PMCID: PMC6463064 DOI: 10.3390/life9010004] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Revised: 12/14/2018] [Accepted: 12/25/2018] [Indexed: 11/16/2022] Open
Abstract
The scale insect Dactylopius coccus produces high amounts of carminic acid, which has historically been used as a pigment by pre-Hispanic American cultures. Nowadays carmine is found in food, cosmetics, and textiles. Metagenomic approaches revealed that Dactylopius spp. cochineals contain two Wolbachia strains, a betaproteobacterium named Candidatus Dactylopiibacterium carminicum and Spiroplasma, in addition to different fungi. We describe here a transcriptomic analysis indicating that Dactylopiibacterium is metabolically active inside the insect host, and estimate that there are over twice as many Dactylopiibacterium cells in the hemolymph than in the gut, with even fewer in the ovary. Albeit scarce, the transcripts in the ovaries support the presence of Dactylopiibacterium in this tissue and a vertical mode of transmission. In the cochineal, Dactylopiibacterium may catabolize plant polysaccharides, and be active in carbon and nitrogen provisioning through its degradative activity and by fixing nitrogen. In most insects, nitrogen-fixing bacteria are found in the gut, but in this study they are shown to occur in the hemolymph, probably delivering essential amino acids and riboflavin to the host from nitrogen substrates derived from nitrogen fixation.
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Affiliation(s)
- Rafael Bustamante-Brito
- Center for Genomic Sciences, Universidad Nacional Autónoma de México, UNAM, Cuernavaca, Morelos C.P. 62210, Mexico.
| | - Arturo Vera-Ponce de León
- Center for Genomic Sciences, Universidad Nacional Autónoma de México, UNAM, Cuernavaca, Morelos C.P. 62210, Mexico.
- Department of Ecology, Evolution and Organismal Biology, The Ohio State University, Columbus, OH 43210, USA.
| | - Mónica Rosenblueth
- Center for Genomic Sciences, Universidad Nacional Autónoma de México, UNAM, Cuernavaca, Morelos C.P. 62210, Mexico.
| | - Julio César Martínez-Romero
- Center for Genomic Sciences, Universidad Nacional Autónoma de México, UNAM, Cuernavaca, Morelos C.P. 62210, Mexico.
| | - Esperanza Martínez-Romero
- Center for Genomic Sciences, Universidad Nacional Autónoma de México, UNAM, Cuernavaca, Morelos C.P. 62210, Mexico.
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12
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Wassem R, Marin AM, Daddaoua A, Monteiro RA, Chubatsu LS, Ramos J, Deakin WJ, Broughton WJ, Pedrosa FO, Souza EM. A NodD-like protein activates transcription of genes involved with naringenin degradation in a flavonoid-dependent manner inHerbaspirillum seropedicae. Environ Microbiol 2017; 19:1030-1040. [DOI: 10.1111/1462-2920.13604] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 11/16/2016] [Indexed: 11/29/2022]
Affiliation(s)
- R. Wassem
- Departamento de Genética; Universidade Federal do Paraná; Curitiba PR Brazil
| | - A. M. Marin
- Departamento de Bioquímica; Universidade Federal do Paraná; Curitiba PR Brazil
| | - A. Daddaoua
- Department of Environmental Protection; Estación Experimental del Zaídin CSIC; Granada Spain
| | - R. A. Monteiro
- Departamento de Bioquímica; Universidade Federal do Paraná; Curitiba PR Brazil
| | - L. S. Chubatsu
- Departamento de Bioquímica; Universidade Federal do Paraná; Curitiba PR Brazil
| | - J.L. Ramos
- Department of Environmental Protection; Estación Experimental del Zaídin CSIC; Granada Spain
| | - W. J. Deakin
- Laboratoire de Biologie Moléculaire des Plantes Supérieures (LBMPS), Département de Biologie végétale; Sciences III, 30 Quai Ernest-Ansermet, Université de Genève; Genève 4 CH-1211 Switzerland
| | - W. J. Broughton
- Laboratoire de Biologie Moléculaire des Plantes Supérieures (LBMPS), Département de Biologie végétale; Sciences III, 30 Quai Ernest-Ansermet, Université de Genève; Genève 4 CH-1211 Switzerland
| | - F. O. Pedrosa
- Departamento de Bioquímica; Universidade Federal do Paraná; Curitiba PR Brazil
| | - E. M. Souza
- Departamento de Bioquímica; Universidade Federal do Paraná; Curitiba PR Brazil
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The Pathway-Specific Regulator ClaR of Streptomyces clavuligerus Has a Global Effect on the Expression of Genes for Secondary Metabolism and Differentiation. Appl Environ Microbiol 2015; 81:6637-48. [PMID: 26187955 DOI: 10.1128/aem.00916-15] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2015] [Accepted: 07/08/2015] [Indexed: 12/11/2022] Open
Abstract
Streptomyces clavuligerus claR::aph is a claR-defective mutant, but in addition to its claR defect it also carries fewer copies of the resident linear plasmids pSCL2 and pSCL4 (on the order of 4 × 10(5)-fold lower than the wild-type strain), as shown by qPCR. To determine the function of ClaR without potential interference due to plasmid copy number, a new strain, S. clavuligerus ΔclaR::aac, with claR deleted and carrying the wild-type level of plasmids, was constructed. Transcriptomic analyses were performed in S. clavuligerus ΔclaR::aac and S. clavuligerus ATCC 27064 as the control strain. The new ΔclaR mutant did not produce clavulanic acid (CA) and showed a partial expression of genes for the early steps of the CA biosynthesis pathway and a very poor expression (1 to 8%) of the genes for the late steps of the CA pathway. Genes for cephamycin C biosynthesis were weakly upregulated (1.7-fold at 22.5 h of culture) in the ΔclaR mutant, but genes for holomycin biosynthesis were expressed at levels from 3- to 572-fold higher than in the wild-type strain, supporting the observed overproduction of holomycin by S. clavuligerus ΔclaR::aac. Interestingly, three secondary metabolites produced by gene clusters SMCp20, SMCp22, and SMCp24, encoding still-cryptic compounds, had partially or totally downregulated their genes in the mutant, suggesting a regulatory role for ClaR wider than previously reported. In addition, the amfR gene was downregulated, and consequently, the mutant did not produce aerial mycelium. Expression levels of about 100 genes in the genome were partially up- or downregulated in the ΔclaR mutant, many of them related to the upregulation of the sigma factor-encoding rpoE gene.
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14
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Arrigoni G, Tolin S, Moscatiello R, Masi A, Navazio L, Squartini A. Calcium-dependent regulation of genes for plant nodulation in Rhizobium leguminosarum detected by iTRAQ quantitative proteomic analysis. J Proteome Res 2013; 12:5323-30. [PMID: 24041410 DOI: 10.1021/pr400656g] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rhizobia, the nitrogen-fixing bacterial symbionts of legumes, represent an agricultural application of primary relevance and a model of plant-microbe molecular dialogues. We recently described rhizobium proteome alterations induced by plant flavonoids using iTRAQ. Herein, we further extend that experimentation, proving that the transient elevation in cytosolic calcium is a key signaling event necessary for the expression of the nodulation (nod) genes. Ca(2+) involvement in nodulation is a novel issue that we recently flagged with genetic and physiological approaches and that hereby we demonstrate also by proteomics. Exploiting the multiple combinations of 4-plex iTRAQ, we analyzed Rhizobium leguminosarum cultures grown with or without the nod gene-inducing plant flavonoid naringenin and in the presence or absence of the extracellular Ca(2+) chelator EGTA. We quantified over a thousand proteins, 189 of which significantly altered upon naringenin and/or EGTA stimulation. The expression of NodA, highly induced by naringenin, is strongly reduced when calcium availability is limited by EGTA. This confirms, from a proteomic perspective, that a Ca(2+) influx is a necessary early step in flavonoid-mediated legume nodulation by rhizobia. We also observed other proteins affected by the different treatments, whose identities and roles in nodulation and rhizobium physiology are likewise discussed.
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Affiliation(s)
- Giorgio Arrigoni
- Proteomics Center of Padova University , Via G. Orus 2b, 35129 Padova, Italy
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15
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Reen FJ, Barret M, Fargier E, O’Muinneacháin M, O’Gara F. Molecular evolution of LysR-type transcriptional regulation in Pseudomonas aeruginosa. Mol Phylogenet Evol 2013; 66:1041-9. [DOI: 10.1016/j.ympev.2012.12.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Revised: 12/13/2012] [Accepted: 12/17/2012] [Indexed: 11/25/2022]
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16
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Phylogenetic classification of diverse LysR-type transcriptional regulators of a model prokaryote Geobacter sulfurreducens. J Mol Evol 2012; 74:187-205. [PMID: 22526031 DOI: 10.1007/s00239-012-9498-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Accepted: 03/28/2012] [Indexed: 10/28/2022]
Abstract
The protein family of LysR-type transcriptional regulators (LTTRs) is highly abundant among prokaryotes. We analyzed 10,145 non-redundant microbial sequences with homology to eight LysR family regulators of a model prokaryote, Geobacter sulfurreducens, and employed phylogenetic tree inference for LTTR classification. We also analyzed the arrangement of genome clusters containing G. sulfurreducens LTTR genes and searched for LTTR regulatory motifs, suggesting likely regulatory targets of G. sulfurreducens LTTRs. This is the first study to date providing a detailed classification of LTTRs in the deltaproteobacterial family Geobacteraceae.
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Lee HI, Lee JH, Park KH, Sangurdekar D, Chang WS. Effect of soybean coumestrol on Bradyrhizobium japonicum nodulation ability, biofilm formation, and transcriptional profile. Appl Environ Microbiol 2012; 78:2896-903. [PMID: 22307307 PMCID: PMC3318843 DOI: 10.1128/aem.07336-11] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Accepted: 01/27/2012] [Indexed: 11/20/2022] Open
Abstract
Flavonoids, secondary plant metabolites which mainly have a polyphenolic structure, play an important role in plant-microbe communications for nitrogen-fixing symbiosis. Among 10 polyphenolic compounds isolated from soybean roots in our previous study, coumestrol showed the highest antioxidant activity. In this study, its effect on the soybean nodulation was tested. The soybean symbiont Bradyrhizobium japonicum USDA110 pretreated with 20 μM coumestrol enhanced soybean nodulation by increasing the number of nodules 1.7-fold compared to the control. We also tested the effect of coumestrol on B. japonicum biofilm formation. At a concentration of 2 μM, coumestrol caused a higher degree of biofilm formation than two major soybean isoflavonoids, genistein and daidzein, although no biofilm formation was observed at a concentration of 20 μM each compound. A genome-wide transcriptional analysis was performed to obtain a comprehensive snapshot of the B. japonicum response to coumestrol. When the bacterium was incubated in 20 μM coumestrol for 24 h, a total of 371 genes (139 upregulated and 232 downregulated) were differentially expressed at a 2-fold cutoff with a q value of less than 5%. No common nod gene induction was found in the microarray data. However, quantitative reverse transcription-PCR (qRT-PCR) data showed that incubation for 12 h resulted in a moderate induction (ca. 2-fold) of nodD1 and nodABC, indicating that soybean coumestrol is a weak inducer of common nod genes. In addition, disruption of nfeD (bll4952) affected the soybean nodulation by an approximate 30% reduction in the average number of nodules.
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Affiliation(s)
- Hae-In Lee
- Department of Biology, University of Texas, Arlington, Texas, USA
| | - Jin-Hwan Lee
- Division of Monitoring and Analysis, Nakdong River Basin Environmental Office, Ministry of Environment, Changwon, Republic of Korea
- Division of Applied Life Science, Department of Agricultural Chemistry, Institute of Agricultural and Life Science, Gyeongsang National University, Jinju, Republic of Korea
| | - Ki-Hun Park
- Division of Applied Life Science, Department of Agricultural Chemistry, Institute of Agricultural and Life Science, Gyeongsang National University, Jinju, Republic of Korea
| | - Dipen Sangurdekar
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, USA
| | - Woo-Suk Chang
- Department of Biology, University of Texas, Arlington, Texas, USA
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18
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Khan F, Agarwal S, Mishra BN. GENOME WIDE IDENTIFICATION OF DNA BINDING MOTIFS OF NodD-FACTOR IN SINORHIZOBIUM MELILOTI AND MESORHIZOBIUM LOTI. J Bioinform Comput Biol 2011; 3:773-801. [PMID: 16078361 DOI: 10.1142/s0219720005001338] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2003] [Revised: 01/08/2005] [Accepted: 02/23/2005] [Indexed: 11/18/2022]
Abstract
NodD transcription factor is a regulatory protein of nitrogen fixing bacteria, which activates expression of nod genes participating in nodulation during interaction with its symbiont legumes. It's DNA binding motifs have been characterized and reported in Sinorhizobium meliloti and this pattern information has been used in our theoretical analyses to detect its novel regulated genes in genomes of S. meliloti and Mesorhizobium loti. M. loti, a symbiont to model legume plant Lotus japonicus, showed presence of these regulatory motifs in upstream sequences of nod and other functionally related genes. The methodology involved comparative potential weight matrix construction through GIBBS SAMPLER (RSAT) and MEME tools, using information of conserved upstream sequences of nine genes including nod and neighboring genes of both genomes possessing nod-box like motif. The resultant DNA consensus sequence had highly conserved nod-box like 17 bp long motif consensus sequence pattern for binding of detected NodD transcription factors as analyzed by homologous clustering method and therefore the genome wide predictions were considered highly accurate since confirmed by operon delineation method and the described methodology can be used in other nitrogen fixing bacteria to pursue the study in detail.
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Affiliation(s)
- Feroz Khan
- Department of Biotechnology, Institute of Engineering & Technology, UP Technical University, Lucknow, UP, India.
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19
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Müller A, Schlicker C, Fehringer M, Masepohl B, Hofmann E. Expression, purification, crystallization and preliminary X-ray analysis of the DNA-binding domain of Rhodobacter capsulatus MopB. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011; 67:377-9. [PMID: 21393847 DOI: 10.1107/s1744309110054710] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2010] [Accepted: 12/30/2010] [Indexed: 11/10/2022]
Abstract
The LysR-type regulator MopB represses transcription of several target genes (including the nitrogen-fixation gene anfA) in Rhodobacter capsulatus at high molybdenum concentrations. In this study, the isolated DNA-binding domain of MopB (MopBHTH) was overexpressed in Escherichia coli. Purified MopBHTH bound the anfA promoter as shown by DNA mobility-shift assays, demonstrating the function of the isolated regulator domain. MopBHTH was crystallized using the sitting-drop vapour-diffusion method in the presence of 0.2 M lithium sulfate, 0.1 M phosphate/citrate pH 4.2, 20%(w/v) PEG 1000 at 291 K. The crystal belonged to space group P3(1)21 or P3(2)21, with unit-cell parameters a=b=61.84, c=139.64 Å, α=β=90, γ=120°, and diffracted to 3.3 Å resolution at a synchrotron source.
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Affiliation(s)
- Alexandra Müller
- Lehrstuhl für Biologie der Mikroorganismen, Fakultät für Biologie und Biotechnologie, Ruhr-Universität Bochum, 44780 Bochum, Germany
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20
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Moscatiello R, Squartini A, Mariani P, Navazio L. Flavonoid-induced calcium signalling in Rhizobium leguminosarum bv. viciae. THE NEW PHYTOLOGIST 2010; 188:814-823. [PMID: 20738787 DOI: 10.1111/j.1469-8137.2010.03411.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
• Legume-rhizobium symbiosis requires a complex dialogue based on the exchange of diffusible signals between the partners. Compatible rhizobia express key nodulation (nod) genes in response to plant signals - flavonoids - before infection. Host plants sense counterpart rhizobial signalling molecules - Nod factors - through transient changes in intracellular free-calcium. Here we investigate the potential involvement of Ca(2+) in the symbiotic signalling pathway activated by flavonoids in Rhizobium leguminosarum bv. viciae. • By using aequorin-expressing rhizobial strains, we monitored intracellular Ca(2+) dynamics and the Ca(2+) dependence of nod gene transcriptional activation. • Flavonoid inducers triggered, in R. leguminosarum, transient increases in the concentration of intracellular Ca(2+) that were essential for the induction of nod genes. Signalling molecules not specifically related to rhizobia, such as strigolactones, were not perceived by rhizobia through Ca(2+) variations. A Rhizobium strain cured of the symbiotic plasmid responded to inducers with an unchanged Ca(2+) signature, showing that the transcriptional regulator NodD is not directly involved in this stage of flavonoid perception and plays its role downstream of the Ca(2+) signalling event. • These findings demonstrate a key role played by Ca(2+) in sensing and transducing plant-specific flavonoid signals in rhizobia and open up a new perspective in the flavonoid-NodD paradigm of nod gene regulation.
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21
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Kamboj DV, Bhatia R, Pathak DV, Sharma PK. Role of nodD gene product and flavonoid interactions in induction of nodulation genes in Mesorhizobium ciceri. PHYSIOLOGY AND MOLECULAR BIOLOGY OF PLANTS : AN INTERNATIONAL JOURNAL OF FUNCTIONAL PLANT BIOLOGY 2010; 16:69-77. [PMID: 23572956 PMCID: PMC3550621 DOI: 10.1007/s12298-010-0009-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Mesorhizobium ciceri is a host specific bacterium which nodulates the genus, Cicer. Host specificity is regulated at first step by induction of nodulation (nod) genes in the presence of NodD protein and inducers (flavonoids) of plant origin. The inducer specificity of M. ciceri nodD gene was studied in NodD-mutant strain HN-9 carrying heterologous nodD genes and nodAlacZ fusion. The induction profile of nod promoter in M. ciceri revealed that nodD gene product of M. ciceri is specifically activated by chickpea root exudates only. M. ciceri HN-9 (nodA-lacZ) containing heterologous nodD genes from Rhizobium leguminosarum bv. viciae, R. leguminosarum bv. trifolii and Sinorhizobium meliloti was induced in presence of a number of flavonoids. On the other hand, induction profile of nod promoter showed that heterologous nodD gene products were activated to different levels in NodD(-) mutant of M. ciceri in presence of root exudates from homologous as well as heterologous legume hosts. The transfer of FITA (Flavonoid independent transcription activation) nodD gene in NodD(-) mutant, M. ciceri HN-9, was able to break the inducer specificity barrier and nod promoter was induced to maximum level irrespective of the presence or absence of inducer. It is concluded from the results that host specificity in M. ciceri - chickpea (Cicer arietinum) symbiosis is regulated at first step by the host specific interaction of nodD gene product of M. ciceri and inducers present in the root exudates of chickpea.
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Affiliation(s)
- D. V. Kamboj
- />Division of Biotechnology, Defense Research and Development Establishment (DRDE), Gwalior, 474 002 India
| | - Ranjana Bhatia
- />MTCC, Institute of Microbial Technology, Sec. 39A, Chandigarh, 160 036 India
| | - D. V. Pathak
- />Department of Microbiology, Chaudhary Charan Singh Haryana Agricultural University, Hisar, 125 004 India
| | - P. K. Sharma
- />Department of Microbiology, Chaudhary Charan Singh Haryana Agricultural University, Hisar, 125 004 India
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22
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Müller MG, Forsberg LS, Keating DH. The rkp-1 cluster is required for secretion of Kdo homopolymeric capsular polysaccharide in Sinorhizobium meliloti strain Rm1021. J Bacteriol 2009; 191:6988-7000. [PMID: 19734304 PMCID: PMC2772494 DOI: 10.1128/jb.00466-09] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2009] [Accepted: 08/31/2009] [Indexed: 11/20/2022] Open
Abstract
Under conditions of nitrogen stress, leguminous plants form symbioses with soil bacteria called rhizobia. This partnership results in the development of structures called root nodules, in which differentiated endosymbiotic bacteria reduce molecular dinitrogen for the host. The establishment of rhizobium-legume symbioses requires the bacterial synthesis of oligosaccharides, exopolysaccharides, and capsular polysaccharides. Previous studies suggested that the 3-deoxy-D-manno-oct-2-ulopyranosonic acid (Kdo) homopolymeric capsular polysaccharide produced by strain Sinorhizobium meliloti Rm1021 contributes to symbiosis with Medicago sativa under some conditions. However, a conclusive symbiotic role for this polysaccharide could not be determined due to a lack of mutants affecting its synthesis. In this study, we have further characterized the synthesis, secretion, and symbiotic function of the Kdo homopolymeric capsule. We showed that mutants lacking the enigmatic rkp-1 gene cluster fail to display the Kdo capsule on the cell surface but accumulate an intracellular polysaccharide of unusually high M(r). In addition, we have demonstrated that mutations in kdsB2, smb20804, and smb20805 affect the polymerization of the Kdo homopolymeric capsule. Our studies also suggest a role for the capsular polysaccharide in symbiosis. Previous reports have shown that the overexpression of rkpZ from strain Rm41 allows for the symbiosis of exoY mutants of Rm1021 that are unable to produce the exopolysaccharide succinoglycan. Our results demonstrate that mutations in the rkp-1 cluster prevent this phenotypic suppression of exoY mutants, although mutations in kdsB2, smb20804, and smb20805 have no effect.
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Affiliation(s)
- Maike G. Müller
- Department of Microbiology and Immunology, Loyola University Chicago, Maywood, Illinois 60153, Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602
| | - Lennart S. Forsberg
- Department of Microbiology and Immunology, Loyola University Chicago, Maywood, Illinois 60153, Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602
| | - David H. Keating
- Department of Microbiology and Immunology, Loyola University Chicago, Maywood, Illinois 60153, Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602
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Moscatiello R, Alberghini S, Squartini A, Mariani P, Navazio L. Evidence for calcium-mediated perception of plant symbiotic signals in aequorin-expressing Mesorhizobium loti. BMC Microbiol 2009; 9:206. [PMID: 19775463 PMCID: PMC2759959 DOI: 10.1186/1471-2180-9-206] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Accepted: 09/23/2009] [Indexed: 11/22/2022] Open
Abstract
Background During the interaction between rhizobia and leguminous plants the two partners engage in a molecular conversation that leads to reciprocal recognition and ensures the beginning of a successful symbiotic integration. In host plants, intracellular Ca2+ changes are an integral part of the signalling mechanism. In rhizobia it is not yet known whether Ca2+ can act as a transducer of symbiotic signals. Results A plasmid encoding the bioluminescent Ca2+ probe aequorin was introduced into Mesorhizobium loti USDA 3147T strain to investigate whether a Ca2+ response is activated in rhizobia upon perception of plant root exudates. We find that M. loti cells respond to environmental and symbiotic cues through transient elevations in intracellular free Ca2+ concentration. Only root exudates from the homologous host Lotus japonicus induce Ca2+ signalling and downstream activation of nodulation genes. The extracellular Ca2+ chelator EGTA inhibits both transient intracellular Ca2+ increase and inducible nod gene expression, while not affecting the expression of other genes, either constitutively expressed or inducible. Conclusion These findings indicate a newly described early event in the molecular dialogue between plants and rhizobia and highlight the use of aequorin-expressing bacterial strains as a promising novel approach for research in legume symbiosis.
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Affiliation(s)
- Roberto Moscatiello
- Dipartimento di Biologia, Università di Padova, Via U, Bassi 58/B, 35131 Padova, Italy.
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24
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Maddocks SE, Oyston PCF. Structure and function of the LysR-type transcriptional regulator (LTTR) family proteins. MICROBIOLOGY-SGM 2009; 154:3609-3623. [PMID: 19047729 DOI: 10.1099/mic.0.2008/022772-0] [Citation(s) in RCA: 630] [Impact Index Per Article: 42.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The LysR family of transcriptional regulators represents the most abundant type of transcriptional regulator in the prokaryotic kingdom. Members of this family have a conserved structure with an N-terminal DNA-binding helix-turn-helix motif and a C-terminal co-inducer-binding domain. Despite considerable conservation both structurally and functionally, LysR-type transcriptional regulators (LTTRs) regulate a diverse set of genes, including those involved in virulence, metabolism, quorum sensing and motility. Numerous structural and transcriptional studies of members of the LTTR family are helping to unravel a compelling paradigm that has evolved from the original observations and conclusions that were made about this family of transcriptional regulators.
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Affiliation(s)
- Sarah E Maddocks
- Department of Oral and Dental Science, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, UK
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25
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Somers E, Vanderleyden J, Srinivasan M. Rhizosphere Bacterial Signalling: A Love Parade Beneath Our Feet. Crit Rev Microbiol 2008; 30:205-40. [PMID: 15646398 DOI: 10.1080/10408410490468786] [Citation(s) in RCA: 165] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Plant roots support the growth and activities of a wide variety of microorganisms that may have a profound effect on the growth and/or health of plants. Among these microorganisms, a high diversity of bacteria have been identified and categorized as deleterious, beneficial, or neutral with respect to the plant. The beneficial bacteria, termed plant growth-promoting rhizobacteria (PGPR), are widely studied by microbiologists and agronomists because of their potential in plant production. Azospirillum, a genus of versatile PGPR, is able to enhance the plant growth and yield of a wide range of economically important crops in different soils and climatic regions. Plant beneficial effects of Azospirillum have mainly been attributed to the production of phytohormones, nitrate reduction, and nitrogen fixation, which have been subject of extensive research throughout the years. These elaborate studies made Azospirillum one of the best-characterized genera of PGPR. However, the genetic and molecular determinants involved in the initial interaction between Azospirillum and plant roots are not yet fully understood. This review will mainly highlight the current knowledge on Azospirillum plant root interactions, in the context of preceding and ongoing research on the association between plants and plant growth-promoting rhizobacteria.
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Affiliation(s)
- E Somers
- Centre of Microbial and Plant Genetics, K U Leuven, Heverlee, Belgium.
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Li F, Hou B, Hong G. Symbiotic plasmid is required for NolR to fully repress nodulation genes inRhizobium leguminosarumA34. Acta Biochim Biophys Sin (Shanghai) 2008. [DOI: 10.1111/j.1745-7270.2008.00467.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Chen L, Li FQ, Hou BH, Hong GF, Yao ZJ. Site-Specific Fluorescent Labeling Approaches for Naringenin, an Essential Flavonone in Plant Nitrogen-Fixation Signaling Pathways. J Org Chem 2008; 73:8279-85. [DOI: 10.1021/jo8014165] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Lei Chen
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China, and State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Feng-Qing Li
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China, and State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Bi-He Hou
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China, and State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Guo-Fan Hong
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China, and State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Zhu-Jun Yao
- State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China, and State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
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Li F, Hou B, Chen L, Yao Z, Hong G. In vitroobservation of the molecular interaction between NodD and its inducer naringenin as monitored by fluorescence resonance energy transfer. Acta Biochim Biophys Sin (Shanghai) 2008. [DOI: 10.1111/j.1745-7270.2008.00462.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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29
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Signal molecules in the peanut–bradyrhizobia interaction. Arch Microbiol 2007; 189:345-56. [DOI: 10.1007/s00203-007-0325-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2007] [Revised: 09/12/2007] [Accepted: 11/02/2007] [Indexed: 10/22/2022]
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Cheng GJ, Li YG, Zhou JC. Cloning and identification of opa22, a new gene involved in nodule formation by Mesorhizobium huakuii. FEMS Microbiol Lett 2006; 257:152-7. [PMID: 16553846 DOI: 10.1111/j.1574-6968.2006.00158.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Using Tn5-sacB insertion mutagenesis, 3000 mutants were obtained from Mesorhizobium huakuii 7653R. Eight nodulation-defective mutants were screened by plant nodulation experiments. The DNA sequences of the contiguous region from the Tn5 insertion site were determined by thermal asymmetric interlaced PCR. A new gene was cloned and designated opa22, as judged from its structural and functional homology. Sequence analysis indicated that opa22 was composed of 774 nucleotides and encoded a protein of 257 amino acids. RPS-BLAST analysis of the Opa22 protein showed a sequence similarity (88.9%) to the opacity protein and related to surface antigens of the bacterial outer membrane, which can mediate various pathogen-host cell interactions and promote invasion. Our results from root hair curling experiments suggested that expression of the opa22 gene might occur at the stage of infection thread formation and nodule development. The complement stain HK24 was able to restore the nodule forming ability of the mutant.
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Affiliation(s)
- Guo Jun Cheng
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, 430070, China
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31
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Lorio JC, Chronis D, Krishnan HB. Y4xP, an open reading frame located in a type III protein secretion system locus of Sinorhizobium fredii USDA257 and USDA191, encodes cysteine synthase. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2006; 19:635-43. [PMID: 16776297 DOI: 10.1094/mpmi-19-0635] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Sinorhizobium fredii USDA257, a soybean symbiont, exports several nodulation outer proteins (Nops) into the rhizosphere. These proteins, which are exported by a type III secretion system (TTSS), have a pivotal role in host-specific nodulation. The entire TTSS of S. fredii lies within a 31-kb region that includes conserved genes that code for secretion machinery proteins, Nops, and several open reading frames (ORF) of unknown function. Identifying the functions of these ORF is essential to understand fully the role of TTSS in nodulation. Here, we report the characterization of y4xP, an ORF of previously unknown function. Southern blot analysis revealed that USDA257 contains two copies of y4xP, while a sibling, USDA191, contains a single copy. The amino acid sequence of Y4XP is homologous to both eukaryotic and prokaryotic cysteine synthase, a key enzyme in sulfur assimilation. The coding region of USDA257 y4xP under control of T7 promoter was expressed in Escherichia coli, and the recombinant protein was purified by nickel-affinity chromatography. Antibodies generated against soybean cysteine synthase cross-reacted with the recombinant protein. A nonpolar mutant of y4xP of USDA191 showed a marked reduction in cysteine synthase activity. Enzyme activity was completely restored when the mutant was complemented with a plasmid containing the y4xP sequence. Cysteine synthase activity was confined to the cell cytosol. Extracellular protein fraction from genistein-induced USDA191 showed no cysteine synthase activity. This observation indicates that cysteine synthase, which is located in the TTSS locus, is not a type III secreted protein. A nonpolar cysteine synthase mutant was able to export all the Nops to the rhizosphere, albeit in reduced amounts compared with the wild-type USDA191. Interestingly, USDA191 cysteine synthase mutant was able to initiate nodules on 'McCall' soybean more efficiently than the wild-type. Our results demonstrate that y4xP encodes a cysteine synthase and inactivation of this gene enhances the ability of USDA191 to form nodules on 'McCall' soybean by regulating Nops production.
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Affiliation(s)
- Julio C Lorio
- Department of Plant Microbiology and Pathology, United States Department of Agriculture-Agricultural Research Service, University of Missouri, Columbia, MO 65211, USA
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32
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Parke D. Acquisition, reorganization, and merger of genes: novel management of the β-ketoadipate pathway in Agrobacterium tumefaciens. FEMS Microbiol Lett 2006. [DOI: 10.1111/j.1574-6968.1997.tb10164.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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33
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Haine V, Sinon A, Van Steen F, Rousseau S, Dozot M, Lestrate P, Lambert C, Letesson JJ, De Bolle X. Systematic targeted mutagenesis of Brucella melitensis 16M reveals a major role for GntR regulators in the control of virulence. Infect Immun 2005; 73:5578-86. [PMID: 16113274 PMCID: PMC1231144 DOI: 10.1128/iai.73.9.5578-5586.2005] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2004] [Revised: 03/07/2005] [Accepted: 05/10/2005] [Indexed: 11/20/2022] Open
Abstract
In order to identify transcriptional regulators involved in virulence gene control in Brucella melitensis, we generated a collection of 88 mutants in the AraC, ArsR, Crp, DeoR, GntR, IclR, LysR, MerR, RpiR, and TetR families of regulators. This collection was named LiMuR (library of mutants for regulators). We developed a method to test several mutants simultaneously in one animal in order to identify those unable to survive. This method, called the plasmid-tagged mutagenesis method, was used to test the residual virulence of mutants after 1 week in a mouse model of infection. Ten attenuated mutants, of which six and three belong to the GntR and LysR families, respectively, were identified and individually confirmed to replicate at lower rates in mice. Among these 10 mutants, only gntR10 and arsR6 are attenuated in cellular models. The LiMuR also allows simple screenings to identify regulators of a particular gene or operon. As a first example, we analyzed the expression of the virB operon in the LiMuR mutants. We carried out Western blottings of whole-cell extracts to analyze the production of VirB proteins using polyclonal antisera against VirB proteins. Four mutants produced small amounts of VirB proteins, and one mutant overexpressed VirB proteins compared to the wild-type strain. In these five mutants, reporter analysis using the virB promoter fused to lacZ showed that three mutants control virB at the transcriptional level. The LiMuR is a resource that will provide straightforward identification of regulators involved in the control of genes of interest.
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Affiliation(s)
- Valérie Haine
- Unité de Recherche en Biologie Moléculaire, Facultés Universitaires Notre Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, Belgium
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34
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Collavino M, Riccillo PM, Grasso DH, Crespi M, Aguilar M. GuaB activity is required in Rhizobium tropici during the early stages of nodulation of determinate nodules but is dispensable for the Sinorhizobium meliloti-alfalfa symbiotic interaction. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2005; 18:742-50. [PMID: 16042020 DOI: 10.1094/mpmi-18-0742] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The guaB mutant strain Rhizobium tropici CIAT8999-10T is defective in symbiosis with common bean, forming nodules that lack rhizobial content. In order to investigate the timing of the guaB requirement during the nodule formation on the host common bean by the strain CIAT899-10.T, we constructed gene fusions in which the guaB gene is expressed under the control of the symbiotic promoters nodA, bacA, and nifH. Our data indicated that the guaB is required from the early stages of nodulation because full recovery of the wild-type phenotype was accomplished by the nodA-guaB fusion. In addition, we have constructed a guaB mutant derived from Sinorhizobium meliloti 1021, and shown that, unlike R. tropici, the guaB S. meliloti mutant is auxotrophic for guanine and induces wild-type nodules on alfalfa and Medicago truncatula. The guaB R. tropici mutant also is defective in its symbiosis with Macroptilium atropurpureum and Vigna unguiculata but normal with Leucaena leucocephala. These results show that the requirement of the rhizobial guaB for symbiosis is found to be associated with host plants that form determinate type of nodules.
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Affiliation(s)
- Mónica Collavino
- Instituto de Bioquímica y Biología Molecular, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 1900-La Plata, Argentina
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35
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Li Q, Feng J, Hu HL, Chen XC, Li FQ, Hong GF. A HU-like gene mutation in Rhizobium leguminosarum bv. viciae affects the expression of nodulation genes. Mol Microbiol 2004; 51:861-71. [PMID: 14731285 DOI: 10.1046/j.1365-2958.2003.03873.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
NodD is the major regulator of nod genes expression in rhizobia. Previously, a HU-like protein in Rhizobium leguminosarum bv. viciae has been identified to bind specifically with nod promoters and be involved in in vitro nodD transcription, but its in vivo function remained unknown. In this work we have cloned and sequenced the R. leguminosarum bv. viciae gene, named hurL, for this HU-like protein. Using the E. coli-expressed HurL proteins, we proved that HurL had high affinity to several nod promoters and showed a stimulation effect on in vitro nodD transcription at appropriate concentration. The R. leguminosarum bv. viciae hurL gene was mutated by insertion of a kanamycin resistance cassette. The obtained hurL mutant strain M704 exhibited poor growth under free-living conditions and failed to induce nodules on Pisum sativum cv. Frisson and Vicia hirsuta. Further studies of NodD production and nod genes-lacZ fusions expression in the hurL mutant revealed that inactivation of hurL led to severe impairment in the nodD expression, repression in the inducible expression of nodA and nodF, and slight enhancement in the expression of px2, a gene identified earlier in this lab. These results suggested that hurL might be required for maintaining the normal expression of nod genes in R. leguminosarum bv. viciae.
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Affiliation(s)
- Qiang Li
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai, 200031, China
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36
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Keating DH, Willits MG, Long SR. A Sinorhizobium meliloti lipopolysaccharide mutant altered in cell surface sulfation. J Bacteriol 2002. [PMID: 12426356 DOI: 10.1128/jb.184.23.6681] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/01/2023] Open
Abstract
The Rhizobium-legume symbiosis involves the formation of a novel plant organ, the nodule, in which intracellular bacteria reduce molecular dinitrogen in exchange for plant photosynthates. Nodule development requires a bacterial signal referred to as Nod factor, which in Sinorhizobium meliloti is a beta-(1,4)-linked tetramer of N-acetylglucosamine containing N-acyl and O-acetyl modifications at the nonreducing end and a critical 6-O-sulfate at the reducing end. This sulfate modification requires the action of three gene products: nodH, which catalyzes the sulfonyl transfer, and nodPQ, which produce the activated form of sulfate, 3'-phosphoadenosine-5'-phosphosulfate. It was previously reported that S. meliloti cell surface polysaccharides are also covalently modified by sulfate in a reaction dependent on NodPQ. We have further characterized this unique form of bacterial carbohydrate modification. Our studies have determined that one of the nodPQ mutant strains used in the initial study of sulfation of cell surface harbored a second unlinked mutation. We cloned the gene affected by this mutation (referred to as lps-212) and found it to be an allele of lpsL, a gene previously predicted to encode a UDP-glucuronic acid epimerase. We demonstrated that lpsL encoded a UDP-glucuronic acid epimerase activity that was reduced in the lps-212 mutant. The lps-212 mutation resulted in an altered lipopolysaccharide structure that was reduced in sulfate modification in vitro and in vivo. Finally, we determined that the lps-212 mutation resulted in a reduced ability to elicit the formation of plant nodules and by altered infection thread structures that aborted prematurely.
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Affiliation(s)
- David H Keating
- Howard Hughes Medical Institute. Department of Biology, Stanford University, Stanford, California 94305, USA
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37
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Keating DH, Willits MG, Long SR. A Sinorhizobium meliloti lipopolysaccharide mutant altered in cell surface sulfation. J Bacteriol 2002; 184:6681-9. [PMID: 12426356 PMCID: PMC135449 DOI: 10.1128/jb.184.23.6681-6689.2002] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2001] [Accepted: 08/09/2002] [Indexed: 11/20/2022] Open
Abstract
The Rhizobium-legume symbiosis involves the formation of a novel plant organ, the nodule, in which intracellular bacteria reduce molecular dinitrogen in exchange for plant photosynthates. Nodule development requires a bacterial signal referred to as Nod factor, which in Sinorhizobium meliloti is a beta-(1,4)-linked tetramer of N-acetylglucosamine containing N-acyl and O-acetyl modifications at the nonreducing end and a critical 6-O-sulfate at the reducing end. This sulfate modification requires the action of three gene products: nodH, which catalyzes the sulfonyl transfer, and nodPQ, which produce the activated form of sulfate, 3'-phosphoadenosine-5'-phosphosulfate. It was previously reported that S. meliloti cell surface polysaccharides are also covalently modified by sulfate in a reaction dependent on NodPQ. We have further characterized this unique form of bacterial carbohydrate modification. Our studies have determined that one of the nodPQ mutant strains used in the initial study of sulfation of cell surface harbored a second unlinked mutation. We cloned the gene affected by this mutation (referred to as lps-212) and found it to be an allele of lpsL, a gene previously predicted to encode a UDP-glucuronic acid epimerase. We demonstrated that lpsL encoded a UDP-glucuronic acid epimerase activity that was reduced in the lps-212 mutant. The lps-212 mutation resulted in an altered lipopolysaccharide structure that was reduced in sulfate modification in vitro and in vivo. Finally, we determined that the lps-212 mutation resulted in a reduced ability to elicit the formation of plant nodules and by altered infection thread structures that aborted prematurely.
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Affiliation(s)
- David H Keating
- Howard Hughes Medical Institute. Department of Biology, Stanford University, Stanford, California 94305, USA
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38
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Loh J, Lohar DP, Andersen B, Stacey G. A two-component regulator mediates population-density-dependent expression of the Bradyrhizobium japonicum nodulation genes. J Bacteriol 2002; 184:1759-66. [PMID: 11872728 PMCID: PMC134882 DOI: 10.1128/jb.184.6.1759-1766.2002] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bradyrhizobium japonicum nod gene expression was previously shown to be population density dependent. Induction of the nod genes is highest at low culture density and repressed at high population densities. This repression involves both NolA and NodD2 and is mediated by an extracellular factor found in B. japonicum conditioned medium. NolA and NodD2 expression is maximal at high population densities. We demonstrate here that a response regulator, encoded by nwsB, is required for the full expression of the B. japonicum nodYABC operon. In addition, NwsB is also required for the population-density-dependent expression of both nolA and nodD2. Expression of nolA and nodD2 in the nwsB mutant remained at a basal level, even at high culture densities. The nwsB defect could be complemented by overexpression of a second response regulator, NodW. Consistent with the fact that NolA and NodD2 repress nod gene expression, the expression of a nodY-lacZ fusion in the nwsB mutant was unaffected by culture density. In plant assays with GUS fusions, nodules infected with the wild type showed no nodY-GUS expression. In contrast, nodY-GUS expression was not repressed in nodules infected with the nwsB mutant. Nodule competition assays between the wild type and the nwsB mutant revealed that the addition of conditioned medium resulted in a competitive advantage for the nwsB mutant.
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Affiliation(s)
- John Loh
- Center for Legume Research and Department of Microbiology, The University of Tennessee, Knoxville, Tennessee 37996, USA
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39
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Krishnan HB. NolX of Sinorhizobium fredii USDA257, a type III-secreted protein involved in host range determination, Iis localized in the infection threads of cowpea (Vigna unguiculata [L.] Walp) and soybean (Glycine max [L.] Merr.) nodules. J Bacteriol 2002; 184:831-9. [PMID: 11790754 PMCID: PMC139521 DOI: 10.1128/jb.184.3.831-839.2002] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2001] [Accepted: 10/29/2001] [Indexed: 11/20/2022] Open
Abstract
Sinorhizobium fredii USDA257 forms nitrogen-fixing nodules on soybean (Glycine max [L.] Merr.) in a cultivar-specific manner. This strain forms nodules on primitive soybean cultivars but fails to nodulate agronomically improved North American cultivars. Soybean cultivar specificity is regulated by the nolXWBTUV locus, which encodes part of a type III secretion system (TTSS). NolX, a soybean cultivar specificity protein, is secreted by TTSS and shows homology to HrpF of the plant pathogen Xanthomonas campestris pv. vesicatoria. It is not known whether NolX functions at the bacterium-plant interface or acts inside the host cell. Antibodies raised against S. fredii USDA257 NolX were used in immunocytochemical studies to investigate the subcellular localization of this protein. Immunostaining of paraffin-embedded sections of developing soybean and cowpea (Vigna unguiculata [L.] Walp) nodules revealed localization of NolX in the infection threads. Protein A-gold immunocytochemical localization studies utilizing affinity-purified NolX antibodies revealed specific deposition of gold particles in the fibrillar material inside infection threads. Similar immunogold localization studies failed to detect NolX in thin sections of mature soybean and cowpea nodules. The results from this study indicate that NolX is expressed in planta only during the early stages of nodule development.
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Affiliation(s)
- Hari B Krishnan
- Plant Genetics Research Unit, USDA Agricultural Research Service, and Department of Agronomy, University of Missouri, Columbia, MO 65211, USA.
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40
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Affiliation(s)
- W J Broughton
- Laboratoire de Biologie Moléculaire des Plantes Supérieures, Université de Genève, 1292 Chambésy/Geneva, Switzerland.
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41
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Yang Y, Hu H, Hong G. px(2), the newly identified gene in Rhizobium leguminosarum, is characterized to enhance its adjacent nodF expression. Biochem Biophys Res Commun 2000; 275:91-6. [PMID: 10944447 DOI: 10.1006/bbrc.2000.3268] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
nodFEL operon is one of the NodD-dependent inducible nod operons that is clustered on the symbiosis plasmid of Rhizobium leguminosarum biovar viciae. A recent study on the upstream regulatory region of nodFEL operon had identified a new promoter, which was responsible for the transcription of a 0.72 Kb RNA molecule, called px(2), in the opposite direction to nodF. This new promoter was further characterized to overlap with that of nodF and its in vitro transcription was inhibited by another newly identified nod regulator, Px. In this paper we report that the sequence analysis of the px(2) transcript revealed only one open reading frame (ORF(66)), corresponding to a polypeptide of 66 amino acids. Moreover, the increase in px(2) copy numbers enhanced the in vivo inducible expression level of nodF, whereas the frame-shift mutation of ORF(66) eliminated such effect, providing evidence that px(2) is responsible for specifically upregulating nodF expression. This result also raises the big possibility that px(2) encodes this polypeptide. A model for coordinated expression of px(2) and nodF, transcribed divergently from each other, is proposed.
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Affiliation(s)
- Y Yang
- Shanghai Institute of Biochemistry, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai, 200031, China
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42
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Hu H, Liu S, Yang Y, Chang W, Hong G. In Rhizobium leguminosarum, NodD represses its own transcription by competing with RNA polymerase for binding sites. Nucleic Acids Res 2000; 28:2784-93. [PMID: 10908336 PMCID: PMC102654 DOI: 10.1093/nar/28.14.2784] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2000] [Revised: 05/26/2000] [Accepted: 05/26/2000] [Indexed: 11/15/2022] Open
Abstract
We isolated RNA polymerase (RNAP) from Rhizobium leguminosarum, the nitrogen-fixing symbiont of peas and VICIA: Its 91 kDa subunit, which is homologous to sigma(70) of Escherichia coli RNAP, is necessary for transcription of the regulatory nodD gene, which in the presence of certain flavonoids induces transcription of other nod genes that are needed for the early steps of infection. We also show that negative autoregulation of nodD was achieved through competition between RNAP and NodD for their respective binding sites, which largely overlap. Combined with the result that high concentrations of the flavonoid inducer naringenin relieved the binding affinity of NodD for its target DNA, the way in which the nod genes are activated is discussed.
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Affiliation(s)
- H Hu
- Shanghai Institute of Biochemistry, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
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43
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Abstract
Eukaryotes often form symbioses with microorganisms. Among these, associations between plants and nitrogen-fixing bacteria are responsible for the nitrogen input into various ecological niches. Plants of many different families have evolved the capacity to develop root or stem nodules with diverse genera of soil bacteria. Of these, symbioses between legumes and rhizobia (Azorhizobium, Bradyrhizobium, Mesorhizobium, and Rhizobium) are the most important from an agricultural perspective. Nitrogen-fixing nodules arise when symbiotic rhizobia penetrate their hosts in a strictly controlled and coordinated manner. Molecular codes are exchanged between the symbionts in the rhizosphere to select compatible rhizobia from pathogens. Entry into the plant is restricted to bacteria that have the "keys" to a succession of legume "doors". Some symbionts intimately associate with many different partners (and are thus promiscuous), while others are more selective and have a narrow host range. For historical reasons, narrow host range has been more intensively investigated than promiscuity. In our view, this has given a false impression of specificity in legume-Rhizobium associations. Rather, we suggest that restricted host ranges are limited to specific niches and represent specialization of widespread and more ancestral promiscuous symbioses. Here we analyze the molecular mechanisms governing symbiotic promiscuity in rhizobia and show that it is controlled by a number of molecular keys.
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Affiliation(s)
- X Perret
- Laboratoire de Biologie Moléculaire des Plantes Supérieures, Université de Genève, 1292 Chambésy/Geneva, Switzerland
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44
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Dusha I, Austin S, Dixon R. The upstream region of the nodD3 gene of Sinorhizobium meliloti carries enhancer sequences for the transcriptional activator NtrC. FEMS Microbiol Lett 1999; 179:491-9. [PMID: 10518756 DOI: 10.1111/j.1574-6968.1999.tb08768.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
In Sinorhizobium meliloti the expression of the nodulation genes nodABC is regulated in response to the level of fixed nitrogen (ammonia). Previous results suggested that the response to the nitrogen status is mediated by the two-component NtrB/NtrC system which controls transcription of the nodD3 gene, encoding a positive regulatory protein for the activation of nodABC transcription. Here we confirm by DNase I footprinting and gel shift assays that NtrC, when phosphorylated by NtrB, is able to interact with the enhancer sequences present upstream of nodD3. A model is proposed whereby NtrC functions to control the transcription from the two promoters in the upstream region of nodD3 in response to nitrogen status.
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Affiliation(s)
- I Dusha
- Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, P.O. Box 521, H-6701, Szeged, Hungary.
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Suominen L, Paulin L, Saano A, Saren AM, Tas E, Lindström K. Identification of nodulation promoter (nod-box) regions of Rhizobium galegae. FEMS Microbiol Lett 1999; 177:217-23. [PMID: 10474187 DOI: 10.1111/j.1574-6968.1999.tb13735.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
A hybridisation analysis of a genomic clone library of Rhizobium galegae HAMBI 1174 located four EcoRI fragments homologous to the nod-box promoter sequence of Sinorhizobium meliloti in two separate gene regions. Two of the five nod-boxes detected in the R. galegae genome were carried on a single cosmid clone, pRg30, upstream from the nodABCIJ and nodF genes, whereas the other three nod-boxes were carried on a different cosmid clone, pRg10. Hybridisations with various nod gene probes from S. meliloti and Rhizobium leguminosarum species detected a nodD homolog in pRg10. The sequence data obtained from regions adjacent to each nod-box in pRg10 confirmed the presence of a second nodD in the R. galegae genome and, in addition, revealed the presence of nodN, nodU, dctA nifH and nifQ-like genes in pRg10. Thus, by using a promoter-specific nod-box probe we could identify a new region carrying genes involved in nitrogen fixation and host specificity functions.
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Affiliation(s)
- L Suominen
- Department of Applied Chemistry and Microbiology, Helsinki University, Finland.
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Nowak-Thompson B, Chaney N, Wing JS, Gould SJ, Loper JE. Characterization of the pyoluteorin biosynthetic gene cluster of Pseudomonas fluorescens Pf-5. J Bacteriol 1999; 181:2166-74. [PMID: 10094695 PMCID: PMC93630 DOI: 10.1128/jb.181.7.2166-2174.1999] [Citation(s) in RCA: 171] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/1998] [Accepted: 01/19/1999] [Indexed: 11/20/2022] Open
Abstract
Ten genes (plt) required for the biosynthesis of pyoluteorin, an antifungal compound composed of a bichlorinated pyrrole linked to a resorcinol moiety, were identified within a 24-kb genomic region of Pseudomonas fluorescens Pf-5. The deduced amino acid sequences of eight plt genes were similar to the amino acid sequences of genes with known biosynthetic functions, including type I polyketide synthases (pltB, pltC), an acyl coenzyme A (acyl-CoA) dehydrogenase (pltE), an acyl-CoA synthetase (pltF), a thioesterase (pltG), and three halogenases (pltA, pltD, and pltM). Insertions of the transposon Tn5 or Tn3-nice or a kanamycin resistance gene in each of these genes abolished pyoluteorin production by Pf-5. The presumed functions of the eight plt products are consistent with biochemical transformations involved in pyoluteorin biosynthesis from proline and acetate precursors. Isotope labeling studies demonstrated that proline is the primary precursor to the dichloropyrrole moiety of pyoluteorin. The deduced amino acid sequence of the product of another plt gene, pltR, is similar to those of members of the LysR family of transcriptional activators. pltR and pltM are transcribed divergently from the pltLABCDEFG gene cluster, and a sequence with the characteristics of a LysR binding site was identified within the 486-bp intergenic region separating pltRM from pltLABCDEFG. Transcription of the pyoluteorin biosynthesis genes pltB, pltE, and pltF, assessed with transcriptional fusions to an ice nucleation reporter gene, was significantly greater in Pf-5 than in a pltR mutant of Pf-5. Therefore, PltR is proposed to be a transcriptional activator of linked pyoluteorin biosynthesis genes.
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Affiliation(s)
- B Nowak-Thompson
- Agricultural Research Service, U.S. Department of Agriculture, Corvallis, Oregon 97330, USA
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Downie JA, Brewin NJ. Plant-Microorganism Symbiosis. Development 1999. [DOI: 10.1007/978-3-642-59828-9_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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48
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Folch-Mallol JL, Manyani H, Marroquí S, Sousa C, Vargas C, Nava N, Colmenero-Flores JM, Quinto C, Megías M. Sulfation of nod factors via nodHPQ is nodD independent in Rhizobium tropici CIAT899. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 1998; 11:979-987. [PMID: 9768515 DOI: 10.1094/mpmi.1998.11.10.979] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
A cosmid from the Rhizobium tropici CIAT899 symbiotic plasmid, containing most of the nodulation genes described in this strain, has been isolated. Although this cosmid does not carry a nodD gene, it confers ability to heterologous Rhizobium spp. to nodulate R. tropici hosts (Phaseolus vulgaris, Macroptilium atropurpureum, and Leucaena leucocephala). The observed phenotype is due to constitutive expression of the nodABCSUIJ operon, which has lost its regulatory region and is expressed from a promoter present in the cloning vector. Thin-layer chromatography (TLC) analysis of the Nod factors produced by this construction shows that it is still capable of synthesizing sulfated compounds, suggesting that the nodHPQ genes are organized as an operon that is transcribed in a nodD-independent manner and is not regulated by flavonoids.
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Affiliation(s)
- J L Folch-Mallol
- Department of Microbiology and Parasitology, University of Seville, Spain
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Liu ST, Chang WZ, Cao HM, Hu HL, Chen ZH, Ni FD, Lu HF, Hong GF. A HU-like protein binds to specific sites within nod promoters of Rhizobium leguminosarum. J Biol Chem 1998; 273:20568-74. [PMID: 9685414 DOI: 10.1074/jbc.273.32.20568] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nodulation genes (nod) of rhizobia are essential for establishment of its symbiosis with specific legume hosts and are usually located on the Sym(biosis) megaplasmid. In this work we identified a new Sym plasmid independent protein in Rhizobium leguminosarum, Px, by its ability to bind to nod promoters and induce DNA bending. Depending upon its concentrations relative to DNA templates, Px could either stimulate or inhibit in vitro transcription of the major regulatory nodulation gene nodD. This may result from its property to bind to specific sites within nod promoters at lower concentration or in the presence of competitor calf thymus DNA but nonspecifically associate with DNA at higher levels or in the absence of competitors. Its binding sites within nodD and nodF promoters were determined by DNase I footprinting but showed no sequence consensus. N-terminal sequencing and Western blot revealed that Px belongs to the HU class of prokaryotic histone-like proteins. Its binding feature and functioning mechanism were discussed in the light of this discovery.
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Affiliation(s)
- S T Liu
- Shanghai Institute of Biochemistry, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
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50
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Lohrke SM, Day B, Kolli VS, Hancock R, Yuen JP, de Souza ML, Stacey G, Carlson R, Tong Z, Hur HG, Orf JH, Sadowsky MJ. The Bradyrhizobium japonicum noeD gene: a negatively acting, genotype-specific nodulation gene for soybean. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 1998; 11:476-88. [PMID: 9612946 DOI: 10.1094/mpmi.1998.11.6.476] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Bradyrhizobium japonicum strain USDA 110 is restricted for nodulation by soybean genotype PI 417566. We previously reported the identification of a USDA 110 Tn5 mutant, strain D4.2-5, that had the ability to overcome nodulation restriction conditioned by PI 417566 (S. M. Lohrke, J. H. Orf, E. Martínez-Romero, and M. J. Sadowsky, Appl. Environ. Microbiol. 61:2378-2383, 1995). In this study, we report the cloning and characterization of the negatively acting DNA region mutated in strain D4.2-5 that is involved in the genotype-specific nodulation of soybean. The Tn5 integration site was localized to a 5.2-kb EcoRI fragment isolated from wild-type USDA 110 genomic DNA. Saturation Tn5 mutagenesis of this 5.2-kb region and DNA homogenitization studies indicated that a 0.9-kb DNA region was involved in the genotype-specific nodulation of PI 417566. A single open reading frame (ORF) of 474 nucleotides, encoding a predicted protein of 158 amino acids, was identified within this region by DNA sequencing. This ORF was named noeD. Computer comparisons with available data bases revealed no significant similarities between the noeD DNA or predicted amino acid sequence and any known genes or their products. However, comparisons done with the region upstream of noeD revealed a high degree of similarity (about 76% similarity and 62% identity) to the N-terminal regions of the Rhizobium leguminosarum bv. viciae and R. meliloti nodM genes, which have been postulated to encode a glucosamine synthase. Southern hybridization analysis indicated that noeD is not closely linked to the main or auxiliary nodulation gene clusters in B. japonicum and that both nodulation-restricted and -unrestricted B. japonicum serogroup 110 strains contain a noeD homolog. High-performance liquid chromatography and fast atom bombardment-mass spectrometry analyses of the lipo-chitin oligosaccharide (LCO) nodulation signals produced by an noeD mutant showed a higher level of acetylation than that found with wild-type USDA 110. These results suggest that specific LCO signal molecules may be one of the factors influencing nodulation specificity in this symbiotic system.
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Affiliation(s)
- S M Lohrke
- Department of Soil, Water, and Climate, Biological Process Technology Institute, University of Minnesota, St. Paul 55108, USA
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