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

我们已经证明，当农杆菌感染双子叶植物时，Ti质粒的T-DNA区域在细菌细胞中被环化。该反应由植物细胞分泌的可扩散植物因子诱导。我们还表明，被认为对农杆菌感染具有抗性的单子叶植物含有诱导物质，但它不同于双子叶植物。本文试图从麦麸中分离纯化植物因子，并对其分子结构进行测定。在纯化过程中，诱导活性被分成两个部分，一个是亲水性的，另一个是疏水性的，这两者都是诱导T-DNA环化所必需的。此外，我们还发现Ti质粒的virD位点参与了环化事件。该基因座中的virD 1和D2基因一起是必需的。由这些基因编码的产物似乎具有特异于T-DNA边界序列的内切酶或重组酶活性。农杆菌的RMA聚合酶被证明是T-DNA环化的负调控因子，其与virD 1和D2的产物竞争。我们试图纯化这两个virD蛋白以及其他virD蛋白（D3和D4），并阐明这些蛋白质的酶学性质。

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.