Jen G C, Chilton M D
Proc Natl Acad Sci U S A. 1986 Jun;83(11):3895-9. doi: 10.1073/pnas.83.11.3895.
Deletions of border regions of T-DNA on Agrobacterium Ti plasmid or mini-T plasmid have shown the right border region of pTiT37 T-DNA to be more active than the left border region in promoting T-DNA transformation. In this study we examine the possibility that the apparent difference in activity of left and right border regions may be due to position or orientation differences between the left and right borders with respect to the transferred onc genes. We have constructed eight similar single-border mini-T plasmids that contain a left border segment or a right border segment of pTiT37 T-DNA at various positions with either orientation with respect to the onc genes. We assayed the plant tumor-inducing activity of these mini-T plasmids in Agrobacterium tumefaciens LBA4404 containing the virulence helper plasmid pAL4404. Regardless of the position and orientation of the border-containing segment in the mini-T plasmid, mini-T plasmids with the right border segment were highly virulent, whereas those with the left border segment were only weakly so. These results indicate that the difference in transformational activity between the left and right border regions is intrinsic and not an effect of position or orientation with respect to the onc genes. The pattern of the mini-T plasmid sequences integrated into the plant genome suggests that T-DNA transformation involves the directional transfer of a linear intermediate bounded by the border repeats.
农杆菌Ti质粒或微型Ti质粒上T-DNA边界区域的缺失表明，pTiT37 T-DNA的右边界区域在促进T-DNA转化方面比左边界区域更具活性。在本研究中，我们探讨了左、右边界区域活性明显差异可能是由于左、右边界相对于转移的致癌基因在位置或方向上的差异所致的可能性。我们构建了八个相似的单边界微型Ti质粒，它们在相对于致癌基因的不同位置和方向上包含pTiT37 T-DNA的左边界片段或右边界片段。我们检测了这些微型Ti质粒在含有毒性辅助质粒pAL4404的根癌农杆菌LBA4404中的植物肿瘤诱导活性。无论微型Ti质粒中含边界片段的位置和方向如何，含有右边界片段的微型Ti质粒具有高毒性，而含有左边界片段的微型Ti质粒毒性较弱。这些结果表明，左、右边界区域之间转化活性的差异是内在的，而不是相对于致癌基因的位置或方向的影响。整合到植物基因组中的微型Ti质粒序列模式表明，T-DNA转化涉及由边界重复序列界定的线性中间体的定向转移。
