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Biochemistry Cell
Biology Computational
Biology Developmental
Biology Ecology Evolution Genetics Microbiology Molecular
Biology Plant
Biology Science
Education Structural
Biology |
Professional Interests - Publications - Contact Information - Lab Personnel Professional Interests of Valerie Oke
Bacteria exist in communities, interacting with cells of the same species, microbes of other species, and eukaryotes. During these interactions, the bacterial cells exhibit complex behavior and can differentiate into multiple cell types. We study a bacterium, called Sinorhizobium meliloti, that is interesting because it interacts symbiotically with plants of the legume family in a process called nodulation. The bacteria induce formation of a new organ on the roots of host plants called a nodule. The bacterial cells take up residence in the nodule and differentiate into a distinct cell-type called a bacteroid, which is capable of fixing atmospheric nitrogen into ammonia. This nitrogen, now in usable form, is provided to the plant. We are interested in understanding how the bacteria adapt and differentiate within the root nodule.
The Rhizobium-legume interaction is a mutually beneficial symbiosis because the bacteria provide nitrogen in a usable form to the plant, and the plant provides nutrients to the bacteria. Ecologically, the symbiosis is important because it allows the plants to live in nitrogen-poor soil. Agriculturally, the symbiosis is important for increasing the nitrogen content of soil without the addition of fertilizer. For example, the bacterium that we study, S. meliloti, nodulates the crop plants alfalfa and several sweet clovers. Although the symbiosis is mutually beneficial, the nodule may still be a stressful environment for the bacterial cells. We study two families of genes that are used for stress response: rpoH and groEL. In E. coli, rpoH encodes a transcription factor that directs transcription of genes, such as groEL, that encode chaperones involved in protein folding and other genes that encode proteases. rpoH in E. coli is expressed at low levels during growth under normal conditions and is upregulated in response to stress. S. meliloti contains two copies of rpoH and five copies of groEL. We have shown that the absence of RpoH1 prevents nitrogen fixation, and the absence of both RpoH1 and RpoH2 prevents nodulation. In addition, we have demonstrated that one of the groEL genes, groEL1, is necessary and sufficient for successful symbiosis. However, in S. meliloti groEL1 is not controlled by RpoH1 and RpoH2. Therefore, the requirement during symbiosis for RpoH1 and RpoH2 is not due to the requirement for GroEL. Currently we are determining what genes are under the control of RpoH1 and RpoH2 in order to understand how these transcription factors are used in S. meliloti, especially during symbiosis. In addition, we are studying the five groEL genes to determine if they are differentially regulated or if they encode chaperones with different substrate specificities. Publication
Archive Recent Publications of Valerie Oke
Bittner, A.N., A. Foltz, and V. Oke (2007) Only one of five groEL genes is required for viability and successful symbiosis in Sinorhizobium meliloti. J. Bacteriol. 189:1884-1889
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