47 THE MECHANISM INFECTION OF AGROBACTERIUM TUMEFACIENS The Mechanism Infection of Agrobacterium tumefaciens (original) (raw)

Genetic Manipulation of Agrobacterium

Current Protocols in Microbiology, 2005

Agrobacterium species are plant-associated relatives of the rhizobia. Several species cause plant diseases such as crown gall and hairy root, although there are also avirulent species. A. tumefaciens is the most intensively studied species and causes crown gall, a neoplastic disease that occurs on a variety of plants. Virulence is specified by large plasmids, and in the case of A. tumefaciens this is called the Ti (tumor-inducing) plasmid. During pathogenesis virulent agrobacteria copy a segment of the Ti plasmid and transfer it to the plant, where it subsequently integrates into the plant genome, and expresses genes that result in the disease symptoms. A. tumefaciens has been used extensively as a plant genetic engineering tool and is also a model microorganism that has been well studied for host-microbe associations, horizontal gene transfer, cell-cell communication, and biofilm formation. This unit describes standard protocols for genetic manipulation of A. tumefaciens.

Agrobacterium tumefaciens as an agent of disease

Trends in Plant Science, 2003

Twenty-six years ago it was found that the common soil bacterium Agrobacterium tumefaciens is capable of extraordinary feats of interkingdom genetic transfer. Since this discovery, A. tumefaciens has served as a model system for the study of type IV bacterial secretory systems, horizontal gene transfer and bacterial-plant signal exchange. It has also been modified for controlled genetic transformation of plants, a core technology of plant molecular biology. These areas have often overshadowed its role as a serious, widespread phytopathogen-the primary driver of the first 80 years of Agrobacterium research. Now, the diverse areas of A. tumefaciens research are again converging because new discoveries in transformation biology and the use of A. tumefaciens vectors are allowing the development of novel, effective biotechnology-based strategies for the control of crown gall disease.

Agrobacterium-Mediated Transformation

Genetic Transformation in Crops, 2020

Agrobacterium-mediated transformation (AMT) heavily relies on the capability of bacterial pathogen Agrobacterium tumefaciens in transferring foreign genes into a wide variety of host plants. Currently, AMT is the most commonly used method for generating transgenic plants. On the other hand, A. tumefaciens was very useful for plant breeding. It also accelerated the technology of plant breeding to obtain specific characters. Gene transfer from bacteria to plants is a complex mechanism that involves several functional steps. This chapter will give brief information related to AMT mechanism, including the history of crown gall disease, the natural pathogenesis of A. tumefaciens, and the general protocol of AMT.

Transfection and transformation of Agrobacterium tumefaciens

MGG Molecular & General Genetics, 1978

The freeze thaw transfection procedure of was adapted for the transfection and transformation of A. tumefaciens. Transfection of the strains B6S3 and B6-6 with DNA of the temperate phage PS8cc186 yielded a maximum frequency of 2 10-7 transfectants per total recipient population. In transformation of the strain GV3100 with the P type plasmid RP4 a maximum frequency of 3.5 10-7 transformants per total recipient population was obtained. Agrobacterium Ti-plasmids were introduced in the strain GV3100 with a maximal efficiency of 4.5 10-8. These experiments provide further evidence that the Ti-plasmid is responsible for the oncogenic properties of A tumefaciens and for its capacity to induce "opine" synthesis in Crown-gall plant cells.

Mechanisms of crown gall formation: T-DNA transfer fromAgrobacterium tumefaciens to plant cells

The Botanical Magazine Tokyo, 1989

Agrobacterium tumefaciens harbouring the Ti plasmid incites crown gall tumor on dicotyledonous species. Upon infection of these plants, T-DNA in the Ti plasmid is transferred by unknown mechanisms to plant cells to be integrated into nuclear DNA. When Agrobacterium is incubated with protoplasts or seedlings of dicotyledonous plants, circularization of T-DNA and expression of vir (virulence) genes on the Ti plasmid are induced. The circularization event is efficiently induced by mesophyll protoplasts of tobacco which are highly competent for transformation by the T-DNA, and is also induced by diffusible phenolic compounds excreted from the protoplasts. The circularization and formation of crown gall both require the expression of the v/rD locus, one of the inducible vir genes. These results suggest that the circularization of T-DNA reflects one of steps of the T-DNA transfer during formation of crown gall. In contrast to dicotyledonous plants, monocotyledonous plants are thought to be unresponsive to infection by Agrobacterium. We showed that monocotyledonous plants do not excrete diffusible inducers for the expression of v/r genes, while the); contain a novel type of a signal substance(s). This inducer is not detected in the exudates of seedlings of monocotyledonous plants, but is found in the extracts from the seedlings, and also those from the seeds, bran and germ of wheat and oats. This finding suggests that T-DNA processing, and possibly its transfer, should take place when Agrobacterium invades seedlings and seeds of monocotyledonous plants.

Agrobacterium tumefaciens: From crown gall tumors to genetic transformation

Physiological and Molecular Plant Pathology, 2011

The phytopathogenic bacterium Agrobacterium tumefaciens is the causative agent of crown gall disease on a broad range of plant species. For more than a century this pathogen has fascinated biologists for various reasons. It has been believed that disclosing the mystery of the crown gall tumour disease in plants might help to understand the mechanisms of oncogenesis in general, and eventually use this knowledge to cure cancer in animals and humans. However, as the performer of the only known case of trans-kingdom DNA transfer, this natural genetic engineer is recognised by nowadays biologists particularly for this feature, and Agrobacterium-mediated genetic transformation has become the preferred method to generate transgenic plants. This review briefly highlights the key steps in DNA transfer during natural A. tumefaciens infection and the subsequent development of crown gall disease. It will focus on the adaptation and use of this proof of principle for the purpose of genetic transformation.

Agrobacterium tumefaciens Transformation of Monocotyledons

Crop Science, 1995

Agrobaclerium tumefaciens (Smitb and Townsend, 1907) bas been an extremely useful vector to transfer foreign genes into dicotyledonous plants. Monocotyledonous plants, particularly the cereals, have been considered outside the host range for A. tumefaciens, which has necessi tated the development of other transformation systems sucb as naked DNA delivery to protoplasts and, most recently, microprojectile bom bardment delivery of DNA to cells and tissues. Both systems have worked, but there are still many difficulties encountered in routine transrormation of any monocotyledon. Recently, there has been re newed interest in using the A. tumefacuns system to transform econom ically important grasses and other monocotyledons. This paper exam ines the literature and steps involved in transformation of monocotyledons by A. tumefaciens. The many recent advances in understanding the biology of the infection process (meristematic target cell, vir gene inducing compounds, and wide host range strains of A. tumefaciens), and availability or more monocotyledon gene promot ers and improved selectable markers greatly improve the opportunities of developing monocotyledon transformation systems with A. tume/a ciens.

New Approaches to Agrobacterium tumefaciens-Mediated Gene Transfer to Plants

Genetic Engineering - An Insight into the Strategies and Applications, 2016

Agrobacterium tumefaciens, a plant pathogen, is commonly used as a vector for the introduction of foreign genes into plants and consequent regeneration of transgenic plants. A. tumefaciens naturally infects the wound sites in dicotyledonous plants and induces diseases known as crown gall. The bacterium has a large plasmid that induces tumor induction, and for this reason, it was named tumor-inducing (Ti) plasmid. The expression of T-DNA genes of Ti-plasmid in plant cells causes the formation of tumors at the infection site. The molecular basis of Agrobacterium-mediated transformation is the stable integration of a DNA sequence (T-DNA) from Ti (tumor-inducing) plasmid of A. tumefaciens into the plant genome. A. tumefaciens-mediated transformation has some advantages compared with direct gene transfer methods such as integration of low copy number of T-DNA into plant genome, stable gene expression, and transformation of large size DNA segments. That is why manipulations of the plant, bacteria and physical conditions have been applied to increase the virulence of bacteria and to increase the transformation efficiency. Preculturing explants before inoculation, modification of temperature and medium pH, addition chemicals to inoculation medium such as acetosyringone, changing bacterial density, and cocultivation period, and vacuum infiltration have been reported to increase transformation. In this chapter, four new transformation protocols that can be used to increase the transformation efficiency via A. tumefaciens in most plant species are described.

Factor inducing Agrobacterium tumefaciens vir gene expression is present in monocotyledonous plants

Proceedings of the National Academy of Sciences, 1988

Agrobacterium tumefaciens harboring the tumor-inducing Ti plasmid incites crown gall tumor on dicotyledonous species. Upon infection of these plants, Ti plasmid DNA sequence is stably transferred (T-DNA) by unknown mechanisms to plant cells to be integrated into nuclear DNA. The T-DNA processing and transfer require the expression of vir (virulence) genes on the Ti plasmid, which are known to be induced by certain phenolic compounds released from cells at the wounded inoculation site. The results of the present study demonstrate that wheat and oats contain a substance(s) that induces vir gene expression, yet the inducing substance of wheat differs from the phenolic inducers in that it is hydrophilic and has a molecular weight of several thousand. The novel inducer was not detectable in the exudates of seedlings of these plants but was found in an extract from the transition region between shoot and root of the seedlings and also in extracts from the seeds, bran, and germ. This findi...