Molecular mechanisms of T-DNA transfer from Agrobacterium to plant cells during formations of crown gas tumor.

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We have demonstrated that when Agrobacterium infects dicotyledonous plants, the T-DNA region of Ti plasmid is circularized in bacterial cells. This reaction is induced by the diffusible plant factor(s) secreted from plant cells. We also have shown that monocotyledonous plants which have been thought to be resistant to agrobacterial infection contain inducing substance(s), yet it differs from that of dicotyledonous plants. We try to purify the plant factor from wheat bran and determine its molesular structures. During purification, inducing activity was split into two fractions, one was hydrophilic and the other hydrophobic, both of which were required for induction of T-DNA circularization. In addition, we have revealed that the virD locus of Ti plasmid is involved in the circularization event. The virD1 and D2 genes in this locus are together necessary. Products encoded by these genes seem to have activity of endonuclease or recombinase specific for the T-DNA border sequences. RMA polymerase of Agrobacterium was shown to be a negative regulator for T-DNA circularization which competes with products of virD1 and D2. We try to purify both virD proteins as well as other virD proteins (D3 and D4), and elucidate enzymatic properties of these proteins.