Stachel S E, Nester E W
EMBO J. 1986 Jul;5(7):1445-54. doi: 10.1002/j.1460-2075.1986.tb04381.x.
The genetic transformation of plant cells by Agrobacterium tumefaciens is mediated by the genes of the Ti plasmid vir region. To determine the genetic and transcriptional organization of the vir region of pTiA6, vir plasmid clones were saturated with insertion mutations of a Tn3-lacZ transposon. This element is both an insertion mutagen and a reporter for the expression of the sequences into which it has inserted. One hundred and twenty-four vir::Tn3-lac insertions were analyzed for their mutagenic effect on Agrobacterium virulence, and for their expression of beta-galactosidase activity, the lacZ gene product, in vegetative bacteria and in bacteria cocultivated with plant cells. These data in conjunction with genetic complementation results show that the pTiA6 vir region contains six distinct vir complementation groups: virA, virB, virC, virD, virE and virG. Mutations in these loci eliminate (virA, virB, virD and virG) or significantly restrict (virC and virE) the ability of Agrobacterium to transform plant cells. Each of the vir loci corresponds to a single vir transcription unit: virA is constitutively expressed and non-inducible; virB, virC, virD and virE are expressed only upon activation by plant cells; and virG is both constitutively expressed and plant-inducible. The two largest vir operons, virB and virD, are probably polycistronic. The pTiA6 vir region also contains plant-inducible loci (pin) which are non-essential for virulence.
根癌土壤杆菌对植物细胞的遗传转化是由Ti质粒毒力区的基因介导的。为了确定pTiA6毒力区的遗传和转录组织，用Tn3 - lacZ转座子的插入突变使毒性质粒克隆饱和。该元件既是一种插入诱变剂，也是其插入序列表达的报告基因。分析了124个vir::Tn3 - lac插入对土壤杆菌毒力的诱变作用，以及它们在营养细菌和与植物细胞共培养的细菌中β - 半乳糖苷酶活性（lacZ基因产物）的表达。这些数据与遗传互补结果表明，pTiA6毒力区包含六个不同的毒力互补组：virA、virB、virC、virD、virE和virG。这些位点的突变消除（virA、virB、virD和virG）或显著限制（virC和virE）土壤杆菌转化植物细胞的能力。每个毒力位点对应一个单一的毒力转录单元：virA组成型表达且不可诱导；virB、virC、virD和virE仅在植物细胞激活后表达；virG既是组成型表达又是植物诱导型表达。两个最大的毒力操纵子virB和virD可能是多顺反子的。pTiA6毒力区还包含对毒力非必需的植物诱导位点（pin）。
