Agrobacterium: From Biology to Biotechnology

The common use of Agrobacterium as a gene vector for plants has somewhat ob-scured the fact that this bacterium remains an important plant pathogen. Pathogenic strainsof the genus Agrobacterium cause unorganized tissue growth called crown gall or profuseabnormal root development called hairy root. Agrobacterium tumefaciens induces galls onroots and crowns of several fruit and forest trees and ornamental plants. A. vitis is responsi-ble for the crown gall disease of grapevine, while A. rhizogenes induces abnormal rootingon its hosts. Plants tissues that become diseased undergo physiological changes resulting inweak growth, low yields or even death of the entire plant. Tumors originate from dividingplant cells, e. g. from cambium. Thus the cambial region becomes unable to differentiateinto efficient phloem and xylem elements leading to deficient nutrient transport. Symptomsmay appear on roots, crowns and aerial parts of attacked plants (Figure 1-1). Tumors areusually comprised of unorganized tissue, but sometimes they differentiate into roots orshoots. This depends on the host plant, the position on the infected plant or the inducingbacterium (Figure 1-2). As indicated by several reviews, crown gall has been a worldwideproblem in agriculture for over hundred years (Moore and Cooksey, 1981; Burr et al., 1998;Burr and Otten, 1999; Escobar and Dandekar, 2003). 2 Léon Otten, Thomas Burr and Ernö Szegedi