Agrobacterium Regulation of Plant Responses

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Genetic transformation of plants by Agrobacterium tumefaciens is the only documented case of gene transfer to eukaryotes in nature. As such, this system has attracted a great deal of attention from a broad scientific audience concerned with its biology, its use in unraveling complex problems in plant genetics and its biotechnological applications in creating transgenic plants. Recent findings have broadened the possible applications of Agrobacterium as a vector for the transfer of DNA to fungi, oomycetes and animals. Using cDNA-AFLP analysis, our laboratory demonstrated that Agrobacterium and E.coli alter the expression of plant defense and stress response genes of Ageratum conyzoides cells in culture. However, Agrobacterium also induced a gene encoding a nodulin-like protein which was not altered by E.coli suggesting that Agrobacterium can induce specific host genes. The project expands on these observations and will study global expression in cell cultures of the model plant Arabidopsis thaliana using high density microarray technology. Cell cultures of Arabidopsis will be cocultivated for 24 hours with E.coli as well as transfer proficient Agrobacterium and mutants blocked at different major steps in the infection process. Comparing the genes expressed using microarrays will reveal these genes that are specifically altered by Agrobacterium. Comparing the alterations in gene expression induced by the transfer proficient strain with the mutants will begin to identify genetic factors responsible for these alterations. The effects observed using the first set of mutants will be further refined by using additional mutants blocked at single steps in the infection process. The results of these experiments should provide insight into the unique genetic factors of the near symbiont Agrobacterium which provides its ability to overcome host defenses and ultimately lead to the transfer of DNA to a remarkably wide range of plants and other eukaryotic cells.