Schrammeijer B, Hemelaar J, Hooykaas P J
Institute of Molecular Plant Sciences, Clusius Laboratory, Leiden University, The Netherlands.
Mol Plant Microbe Interact. 1998 May;11(5):429-33. doi: 10.1094/MPMI.1998.11.5.429.
Octopine and nopaline strains of Agrobacterium tumefaciens differ in their ability to induce tumors on Nicotiana glauca. The presence of a virF locus on the octopine Ti plasmid makes N. glauca a host plant for these strains, indicating that the VirF protein is a host-range determinant. Here we show the presence of a virF locus not only on the Agrobacterium vitis octopine/cucumopine plasmids pTiAg57 and pTiTm4, but also on the nopaline Ti plasmids pTiAT1, pTiAT66a, and pTiAT66b. On the octopine Ti plasmids from A. tumefaciens the virF gene is located between the virE locus and the left border of the T-region. In contrast, the virF gene on Ti plasmids of A. vitis is located at the very left end of the vir-region near the virA locus. The virF gene of pTiAg57 has been sequenced and codes for a protein of 202 amino acids with a molecular mass of 22,280 Da. Comparison showed that the virF gene from A. vitis strain Ag57 is almost identical to that from A. tumefaciens octopine strains. The transcription of the pTiAg57 virF is inducible by the plant phenolic compound acetosyringone through the presence of a vir-box consensus sequence in its promoter region. The VirF protein from pTiAg57 can complement octopine A. tumefaciens strains deleted for virF as shown by tumor formation on N. glauca.
根癌土壤杆菌的章鱼碱型和胭脂碱型菌株在诱导烟草产生肿瘤的能力上存在差异。章鱼碱型Ti质粒上virF位点的存在使烟草成为这些菌株的宿主植物，这表明VirF蛋白是宿主范围决定因素。在这里，我们发现不仅根癌土壤杆菌葡萄亚种的章鱼碱型/黄瓜碱型质粒pTiAg57和pTiTm4上存在virF位点，而且胭脂碱型Ti质粒pTiAT1、pTiAT66a和pTiAT66b上也存在该位点。在根癌土壤杆菌的章鱼碱型Ti质粒上，virF基因位于virE位点和T区域左边界之间。相比之下，葡萄亚种Ti质粒上的virF基因位于vir区域的最左端，靠近virA位点。pTiAg57的virF基因已被测序，编码一个由202个氨基酸组成、分子量为22280 Da的蛋白质。比较表明，葡萄亚种菌株Ag57的virF基因与根癌土壤杆菌章鱼碱型菌株的virF基因几乎相同。pTiAg57 virF的转录可被植物酚类化合物乙酰丁香酮诱导，这是通过其启动子区域存在一个vir-box共有序列实现的。如在烟草上形成肿瘤所示，来自pTiAg57的VirF蛋白可以互补缺失virF的章鱼碱型根癌土壤杆菌菌株。
