Research in my laboratory is centered on the initial interactions of the plant pathogenic bacterium, Agrobacterium tumefaciens, with potential host cells. A. tumefaciens is a soil bacterium. Infections of wound sites of plants with this bacterium result in the formation of crown gall tumors. We are particularly interested in the initial attachment of the bacteria to plant host cells. This initial loose binding is required for bacterial virulence and T-DNA transfer to plant cells. Bacterial mutants which are unable to carry out this attachment are avirulent. We are currently engaged in cloning and sequencing the genes required for this attachment. Their expression is regulated by signals from the wounded plant tissue. We are characterizing the compounds which are involved in this signaling and the genes which are regulated. Our results suggest that there is an initial exchange of signals between the bacterium and the plant before the bacteria bind irreversibly to the plant and the transfer of T-DNA can begin. We are also interested in the plant receptor to which the bacteria bind. We have identified mutants of the plant Arabidopsis which appear to be unable to bind the bacteria and are in the process of identifying the plant genes and proteins involved in bacterial binding.