Characterization of the Sinorhizobium meliloti exoR protein
Item
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Title
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Characterization of the Sinorhizobium meliloti exoR protein
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Identifier
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d_2009_2013:7119baaca417:10402
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identifier
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10449
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Creator
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Lu, Hai-Yang,
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Contributor
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Hai-Ping Cheng
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Date
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2009
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Language
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English
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Publisher
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City University of New York.
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Subject
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Microbiology | Molecular biology | exoR | exoS | flagella | rhizobium | succinoglycan | symbiosis
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Abstract
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The soil bacterium Sinorhizobium meliloti is capable of establishing a symbiotic relationship with its leguminous plant host alfalfa by forming nitrogen-fixing root nodules through a series of signal exchanges and structural changes. The presence of a potential bacterial signal molecule, succinoglycan, is required for the invasion step of this symbiosis. The production of succinoglycan, which is inversely coupled with the production of flagella, is tightly regulated by the S. meliloti ExoR protein and the ExoS/ChvI two-component regulatory system. To better understand the regulatory function of ExoR and its relationship with the ExoS/ChvI system, I have carried out extensive genetic and biochemical analyses of ExoR and ExoS proteins. I found that ExoR is a periplasmic protein and it functions only in the periplasm. Interestingly, the C-terminal 20 amino acids appear not to be essential for the regulatory function of ExoR. Most importantly, the ExoR protein is digested in the periplasm, which appears to be the molecular mechanism regulating the amount of functional ExoR protein in the periplasm. The genetic analysis of my collection of exoR, exoS, and chvI mutants suggests that ExoR functions upstream of the ExoS/ChvI two-component signal transduction pathway. This conclusion was further supported by the analysis of the exoR expression in different genetic backgrounds, which suggests the ExoR-ExoS-ChvI pathway is feedback regulated by ExoR. The combination of biochemical and genetic analyses suggest that ExoR functions in the periplasm through interaction with the ExoS sensing domain to keep ExoS in the off state. The proteolysis of ExoR would reduce the amount of functional ExoR and lead to the activation of ExoS and the expression of the genes regulated by the pathway. With the continuous discovery of ExoR/ExoS/ChvI homologous systems in a wide range of bacteria, my findings will contribute to a better understanding of the S. meliloti-alfalfa symbiosis and the pathogenicity of some bacterial plant and animal pathogens.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Biology
