Piecing Together the Agrobacterium Type IV Secretion System Involved In DNA Transfer to Plants

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Agrobacterium is a soil bacterium with the natural ability to transfer DNA from the bacterium into the plant cell where it integrates into the plant's genome. Scientists co-opt this ability, allowing the genetic engineering of plants, with DNA of interest. While many steps in the transformation pathway have been elucidated, a major question remains. How is DNA transported out of the bacterium and into the plant? The Agrobacterium DNA transporter belongs to a growing class of evolutionarily conserved transporters, called type IV secretion systems (T4SS). T4SS are involved in i) bacterial mating, and ii) protein toxin export when pathogenic bacteria infect plant and animal hosts. The Agrobacterium T4SS contains 12 proteins; the long-term goal is to understand how these 12 proteins establish T4SS architecture and function. The research will first determine which proteins interact with each other, and thus are in close contact. This approach defines which pairs of proteins reside at the entrance, versus the exterior or interior of the channel, and leads to models for the assembly of theT4SS apparatus. Second, genetic strategies will confirm these predicted models. Finally, the research will determine the 3D structure of individual T4SS proteins using crystallography and bioinformatics. Thus, these studies will provide an exact structure for the T4SS. This basic research will impact society in medicine and agriculture. Structural information on the T4SS is essential to allow the development of disease treatment therapies that disrupt transporter function in bacteria that transfer toxins to susceptible hosts. Moreover, an understanding of T4SS may allow modification of the transporter in Agrobacterium to increase its effectiveness for plant transformation.