Identification and characterization of Sinorhizobium meliloti genes involved in establishing symbiosis with its host plant alfalfa.
Item
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Title
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Identification and characterization of Sinorhizobium meliloti genes involved in establishing symbiosis with its host plant alfalfa.
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Identifier
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AAI3213144
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identifier
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3213144
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Creator
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Zhang, Xue-Song.
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Contributor
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Adviser: Hai-Ping Cheng
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Date
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2006
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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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Biology, Microbiology | Biology, Molecular | Biology, Ecology | Biology, Botany
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Abstract
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Soil bacterium Sinorhizobium meliloti establishes nitrogen-fixing symbiosis with its leguminous host plant, alfalfa, following a series of continuous signal exchanges. S. meliloti exopolysaccharide, succinoglycan, may be one such signal molecule that is essential for the symbiosis. Succinoglycan production is carried out by the products of exoY and other exo genes, and regulated by the ExoR protein, which has a putative glycosaminoglycan binding site. Site-directed mutagenesis analysis of this binding site carried out in this study suggests it may be important for the regulatory function of the ExoR protein. This is consistent with the finding that change of intracellular pool of glycosaminoglycan by mutagenizing the glmS gene or by supplying exogenous glucosamine could modulate the levels of succinoglycan production. All together, these findings raise the possibility that the regulatory function of the ExoR protein is modulated through its glycosaminoglycan binding site.;The complexity of alfalfa root structural changes during symbiosis and the amount of S. meliloti genes with unknown functions raised the possibility that more S. meliloti genes may function in the early stages of the symbiosis, which can not be easily identified using other methods. A positive functional screen of the entire S. meliloti genome for early symbiotic genes has been carried out using improved In Vivo Expression Technology (IVET). A group of 113 mostly previously unknown symbiotic genes or putative genes has been identified and 23 of them are inducible by alfalfa root exudates. Most of these genes have not been previously characterized and none of them belongs to the nodulation ( nod) gene family. The identification of this group of alfalfa root exudates inducible S. meliloti genes suggests that the interactions in the early stages of the S. meliloti and alfalfa symbiosis could be more complex and that further characterization of these genes will lead to better understanding of the start of this symbiosis.;Taken together, this study provides new insights into S. melloti -alfalfa interactions during the early stages of the symbiosis and lays the foundation for future studies of the symbiosis.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
