Agrobacterium -Mediated Plant Transformation: the Biology behind the “Gene-Jockeying” Tool

Abstract

SUMMARY Agrobacterium tumefaciens and related Agrobacterium species have been known as plant pathogens since the beginning of the 20th century. However, only in the past two decades has the ability of Agrobacterium to transfer DNA to plant cells been harnessed for the purposes of plant genetic engineering. Since the initial reports in the early 1980s using Agrobacterium to generate transgenic plants, scientists have attempted to improve this “natural genetic engineer” for biotechnology purposes. Some of these modifications have resulted in extending the host range of the bacterium to economically important crop species. However, in most instances, major improvements involved alterations in plant tissue culture transformation and regeneration conditions rather than manipulation of bacterial or host genes. Agrobacterium-mediated plant transformation is a highly complex and evolved process involving genetic determinants of both the bacterium and the host plant cell. In this article, I review some of the basic biology concerned with Agrobacterium-mediated genetic transformation. Knowledge of fundamental biological principles embracing both the host and the pathogen have been and will continue to be key to extending the utility of Agrobacterium for genetic engineering purposes.

The versatile bacterial type IV secretion systems

“…In fact, A. tumefaciens shows enhanced virulence following infection of an Arabidopsis strain bearing a PP2C gene (abi1) mutation, and so it is proposed that PP2C acts to suppress virulence by dephosphorylation of VirD2 (REF. 80). VirD2 also interacts with a member of the Arabidopsis KARYOPHERIN-α family, AtKAPα; these proteins mediate the nuclear import of NLS-containing proteins, indicating their involvement in nuclear import of VirD2 and, hence, the T-DNA 81 .…”

“…Similarly, the Ran GTPase is implicated in T-complex targeting to the nucleus 81 . Mutational studies of Arabidopsis, as well as a surrogate yeast host, are uncovering many additional cellular factors that contribute to successful T-strand delivery and integration into the plant genome [80][81][82][83] . Given the large numbers of cellular factors identified so far, it is likely that the T-DNA and the reported effector proteins represent only a subset of the molecules translocated by the VirB/D4 T4S system during infection.…”

Divide and conquer: development and cell cycle genes in plant transformation

“…For most plant species, however, the process is still unfeasible or highly inefficient [2], making it unavailable, for practical purposes, as a routine plant-breeding tool. Furthermore, the rate of publications on transgenic technology development in plants has lagged in recent years, threatening to undermine progress in both the science and the application [3].…”

“…The processes of plant transformation and regeneration from a transgenic cell can stall at several key points, including: (1) the acquisition of a stem-cell-like state in cells as they re-enter the cell cycle [7]; (2) progression between the G1 and S phases of the cycle [8,9] (Box 1); and (3) the differentiation of the transformed cell into a new embryo or meristem [10][11][12][13]. In this manuscript, we consider transformation to be the recovery of cells expressing a foreign gene for use as a selectable marker, and regeneration to be the organogenesis or embryogenesis from the genetically transformed cells.…”

Effect of orientation of transcription of a gene in an inverted transferred DNA repeat on transcriptional gene silencing in rice transgenics—a case study

“…Agrobacterium tumefaciens-mediated plant transformation offers the advantage of defining the transferred DNA (T-DNA) between the right (RB) and left (LB) T-DNA borders (Gelvin 2003). The formation of inverted T-DNA repeats (IRs) upon A. tumefaciens-mediated plant transformation was first reported in tobacco calli (Kwok et al 1985).…”