Molecular bases of initial processes for formation of crown gall tumor

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(1)Mechanisms of plant signal perception by Agrobacterium We have demonstrated that the periplasmic domain and TM2 of a VirA sensor protein are involved in recognition of sugar signal, but not in that of phenolic signal. We have isolated chvE mutations which restore enhancement of vir induction by sugars in the vir A mutant which shows a sugar-non-responsive phenotype. This result indicates that the ChvE protein physically interacts with the VirA protein in the signal pathway mediated by these proteins. (2)vir genes responsible for movement of T-DNA from Agrobacterium to plant cells We have that products of virB and virD4 genes are strictly required for transfer of T-DNA from Agrobacterium to plant cells and that a product of virE2 markedly potentiates this process, but is not essential. (3)Integration of T-DNA into plant nuclear DNA We have shown that in each case of two T-DNA-transformed tobacco tumors, significant sequence homology is present between the region adjacent to the integration target site and both external regions of the T-DNA breakpoints. These findings suggest that sequence homology between the incoming T-DNA and plant chromosomal DNA has an important function in T-DNA integration. We also found that members of a new family of SINE (short interspersed DNA element), which is designated as the TS family, were present in DNA region adjacent to T-DNA integration targets of tobacco chromosomes. A relationship between integration events of T-DNA and the Ts family remains to be proved.