Various Defense Genes are Involved in Agrobacterium-Mediated Transformation

Root transformation assay is one of the most effective methods to study mechanism of Agrobacterium transformation. In this study, a tumorigenic strain, Agrobacterium tumefaciens A208 (three different concentrations; 10⁵, 10⁶ and 10⁷cfu/ml), was used to induce crown gall tumors in the roots of 264 Arabidopsis knock-out mutants for a root transformation screening. These mutants were selected based on 4 different categories: pathogenesis, coexpression with Agrobacterium related genes, and genes either induced or reduced after bacterium infection. Stable root transformation was conducted on the mutants using tumorigenic strain A208 then the numbers of tumors in each plant were counted after two weeks. Among 264 Arabidopsis  knock-out mutants tested, 33 mutants showed elevated levels of root transformation efficiency (over 1.5 fold increase) whereas 15 mutants displayed lower levels of root transformation efficiency (50% less than wild type). Specifically, mutant No. 34 and No. 34 interacting genes’ mutants (No. 22, 37, 155, 156 and 157) enhanced root transformation. These genes were related to defense response to bacterium and highly expressed after bacterium inoculation. However, these mutants did not display difference from wild-type control plant in transient transformation assay using GV3101 with pBISN1 (GUS). Based on these results, we speculate that mutant No.34, 22, 37, 155, 156 and 157 genes inhibit Agrobacterium-mediated T-DNA transformation process at host genome integration stage for plant self-defense. Further research will focus on testing these genes and their applications for improving soybean transformation.