| Sinorhizobium meliloti requires a cobalamin-dependent ribonucleotide reductase for symbiosis with its plant host. | |
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MedLine Citation:
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PMID: 20698752 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Vitamin B(12) (cobalamin) is a critical cofactor for animals and protists, yet its biosynthesis is limited to prokaryotes. We previously showed that the symbiotic nitrogen-fixing alphaproteobacterium Sinorhizobium meliloti requires cobalamin to establish a symbiotic relationship with its plant host, Medicago sativa (alfalfa). Here, the specific requirement for cobalamin in the S. meliloti-alfalfa symbiosis was investigated. Of the three known cobalamin-dependent enzymes in S. meliloti, the methylmalonyl CoA mutase (BhbA) does not affect symbiosis, whereas disruption of the metH gene encoding the cobalamin-dependent methionine synthase causes a significant defect in symbiosis. Expression of the cobalamin-independent methionine synthase MetE alleviates this symbiotic defect, indicating that the requirement for methionine synthesis does not reflect a need for the cobalamin-dependent enzyme. To investigate the function of the cobalamin-dependent ribonucleotide reductase (RNR) encoded by nrdJ, S. meliloti was engineered to express an Escherichia coli cobalamin-independent (class Ia) RNR instead of nrdJ. This strain is severely defective in symbiosis. Electron micrographs show that these cells can penetrate alfalfa nodules but are unable to differentiate into nitrogen-fixing bacteroids and, instead, are lysed in the plant cytoplasm. Flow cytometry analysis indicates that these bacteria are largely unable to undergo endoreduplication. These phenotypes may be due either to the inactivation of the class Ia RNR by reactive oxygen species, inadequate oxygen availability in the nodule, or both. These results show that the critical role of the cobalamin-dependent RNR for survival of S. meliloti in its plant host can account for the considerable resources that S. meliloti dedicates to cobalamin biosynthesis. |
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Authors:
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Michiko E Taga; Graham C Walker |
Publication Detail:
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Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't |
Journal Detail:
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Title: Molecular plant-microbe interactions : MPMI Volume: 23 ISSN: 0894-0282 ISO Abbreviation: Mol. Plant Microbe Interact. Publication Date: 2010 Dec |
Date Detail:
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Created Date: 2010-11-02 Completed Date: 2011-01-11 Revised Date: 2011-12-21 |
Medline Journal Info:
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Nlm Unique ID: 9107902 Medline TA: Mol Plant Microbe Interact Country: United States |
Other Details:
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Languages: eng Pagination: 1643-54 Citation Subset: IM |
Affiliation:
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Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Bacterial Proteins
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genetics,
metabolism Gene Expression Regulation, Bacterial / physiology Medicago sativa / microbiology* Plant Root Nodulation / physiology Reactive Oxygen Species Ribonucleotide Reductases / genetics, metabolism* Sinorhizobium meliloti / genetics, metabolism* Symbiosis / physiology* Vitamin B 12 / metabolism* |
| Grant Support | |
ID/Acronym/Agency:
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GM31010/GM/NIGMS NIH HHS; K99 GM083343/GM/NIGMS NIH HHS; K99 GM083343-02/GM/NIGMS NIH HHS; R01 GM031030-30/GM/NIGMS NIH HHS |
| Chemical | |
Reg. No./Substance:
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0/Bacterial Proteins; 0/Reactive Oxygen Species; 68-19-9/Vitamin B 12; EC 1.17.4.-/Ribonucleotide Reductases |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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