Factors Influencing Induction of Agrobacterium tumefaciens Virulence Genes

Agrobacterium species are routinely employed for plant genetic modification due to the relatively simple procedures, cost-competitiveness, low copy number, independence to vector DNAs, and targeted integration into transcriptionally active regions of plant chromosomes with defined T-DNA. However, to date, there are still a great number of plant species reluctant to Agrobacterium-mediated transformation. Evidence suggests that the infection capability of Agrobacterium is determined by virulence (vir) genes of Ti plasmid outside of A. tumefaciens chromosome. Among all vir genes, virA and virG are constitutively expressed, while the expression of other vir genes is induced by phenolic compounds. In addition, carbohydrates can enhance vir induction mediated by phenolic compounds, while low phosphate and acidic pH conditions may also enhance the induction of vir genes. To improve Agrobacterium-mediated transformation efficiency for potential applications in research and industry, molecular mechanisms of vir induction by factors such as phenolic compounds, carbohydrates, low phosphate, acidic pH and incubation temperature are discussed in this review.