Huss B, Tinland B, Paulus F, Walter B, Otten L
Institut de Biologie Moléculaire des Plantes, Strasbourg, France.
Plant Mol Biol. 1990 Feb;14(2):173-86. doi: 10.1007/BF00018558.
The ubiquitous grapevine-associated octopine/cucumopine Ti plasmids of biotype III Agrobacterium tumefaciens strains carry two T regions, TA and TB, with a complex oncogene arrangement. Within the octopine/cucumopine group, two main strain types were identified: 'large TA' strains with a TA region resembling the TL region of the biotype I octopine strain Ach5 and 'small TA' strains with a similar T region organization as the 'large TA' strains but with a large internal TA deletion. Structural and functional studies of the representative 'large TA' strain Tm4 revealed six oncogenes. Each oncogene was inserted in a disarmed vector and tested for biological activity using the corresponding oncogenes of Ach5 as standards. Five Tm4 oncogenes, TA-iaaM, T-ipt, T-6b, TB-iaaH and TB-iaaM, were shown to be active, the IS-interrupted TA-iaaH gene was inactive. To study the role of each gene in the pTiTm4 context, several single and multiple pTiTm4 mutations were constructed. It was shown that whereas TA-iaaM and TB-iaaH are essential for tumour formation on grapevine, T-ipt, T-6b and TB-iaaM are not. The avirulence of the TA-iaaM- mutant was shown to be due to an inhibitory effect of the T-ipt gene, since a TA-iaaM-/T-ipt- double mutant was fully virulent. We conclude that the TA-iaaM gene of 'large TA' strains is specifically required to counteract the tumour growth inhibiting activity of the T-ipt gene. Both TA-iaaM and T-ipt are absent from the 'small TA' strains. A model on the roles and interactions of the different oncogenes in 'large TA' and 'small TA' strains is presented.
III型生物型根癌土壤杆菌菌株中普遍存在的与葡萄藤相关的章鱼碱/黄瓜碱Ti质粒携带两个T区域，TA和TB，其致癌基因排列复杂。在章鱼碱/黄瓜碱组中，鉴定出两种主要的菌株类型：“大TA”菌株，其TA区域类似于I型生物型章鱼碱菌株Ach5的TL区域；“小TA”菌株，其T区域组织与“大TA”菌株相似，但TA内部有大片段缺失。对代表性的“大TA”菌株Tm4进行的结构和功能研究揭示了六个致癌基因。每个致癌基因都被插入到一个解除武装的载体中，并以Ach5的相应致癌基因为标准测试其生物活性。结果表明，五个Tm4致癌基因TA-iaaM、T-ipt、T-6b、TB-iaaH和TB-iaaM具有活性，而IS中断的TA-iaaH基因无活性。为了研究每个基因在pTiTm4背景下的作用，构建了几个单突变和多突变的pTiTm4。结果表明，虽然TA-iaaM和TB-iaaH对葡萄藤上肿瘤的形成至关重要，但T-ipt、T-6b和TB-iaaM并非如此。TA-iaaM突变体的无毒力被证明是由于T-ipt基因的抑制作用，因为TA-iaaM-/T-ipt-双突变体具有完全的毒力。我们得出结论，“大TA”菌株的TA-iaaM基因是抵消T-ipt基因抑制肿瘤生长活性所特需的。“小TA”菌株中不存在TA-iaaM和T-ipt。本文提出了一个关于“大TA”和“小TA”菌株中不同致癌基因的作用和相互作用的模型。
