Exploitation of Agrobacterium tumefaciens

Abstract

During invasion of wounded plants, soil agrobacteria transfer a defined segment of their Ti and Ri plasmids into the plants. The transferred DNA, termed T-DNA, is integrated into the plant nuclear genome. Genes encoded by Ti and Ri plasmid T-DNAs are expressed in plants and confer the synthesis of plant growth factors as well as sugar and amino acid derivatives, called opines. Expression of T-DNA genes iaaM,iaaH, and ipt (see Hohn, Chap. 15, this Vol.) leads to production of phytohormones, auxin and cytokinin that induce proliferation of transformed cells to form undifferentiated tumors, crown galls. In contrast, cells transformed by rol A, B and C genes of Ri plasmid T-DNAs differentiate to hairy roots. While genetic analysis of the function and expression of these T-DNA genes provided a key for better understanding of various aspects of hormonal regulation and cell differentiation, studies of the T-DNA transfer and integration contributed directly to the development of T-DNA-based transformation vectors and transgenic plant technology. How T-DNA gene vectors are exploited to gain more insight to molecular biology of plants is the focus of this chapter.