A. tumefaciens attaching itself to a carrot cell
Smith & Townsend, 1907
Bacterium tumefaciens Smith and Townsend 1907
Agrobacterium tumefaciens is the causal agent of Crown Gall disease (the formation of tumours) in over 140 species of dicot. See also Cancer A tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells (termed neoplastic Dicotyledons, or "dicots", is a name for a group of Flowering plants whose Seed typically has two embryonic leaves or Cotyledons There It is a rod shaped, Gram negative soil bacterium (Smith et al. Gram-negative bacteria are those Bacteria that do not retain Crystal violet dye in the Gram staining protocol The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have , 1907). Symptoms are caused by the insertion of a small segment of DNA (known as the T-DNA, for 'transfer DNA') into the plant cell, which is incorporated at a semi-random location into the plant genome. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known T-DNA is the transferred DNA of the tumor-inducing (Ti plasmid of some species of bacteria such as Agrobacterium tumefaciens and In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby
Agrobacterium tumefaciens (or A. tumefaciens) is an alphaproteobacterium of the family Rhizobiaceae, which includes the nitrogen fixing legume symbionts. The Proteobacteria are a major group ( Phylum) of Bacteria. They include a wide variety of Pathogens such as Escherichia, The Rhizobiaceae are a family of Proteobacteria, including many (but not all species of Rhizobia as well as plant parasites like Agrobacterium Nitrogen fixation is the process by which Nitrogen is taken from its natural relatively inert molecular form (N2 in the atmosphere and converted into A legume is a Plant in the family Fabaceae (or Leguminosae or a Fruit of these specific plants This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek Unlike the nitrogen fixing symbionts, tumor producing Agrobacterium are parasitic and do not benefit the plant. Parasitism is a type of symbiotic relationship between Organisms of different Species. The wide variety of plants affected by Agrobacterium makes it of great concern to the agriculture industry (Moore et al. , 1997).
Economically, A. tumefaciens is a serious pathogen of grape vines, stone fruits, nut trees, sugar beets, horse radish and rhubarb. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious Vitis is a genus of about 60 species of vining plants in the Flowering plant family Vitaceae. In Botany, a drupe is a Fruit in which an outer fleshy part ( Exocarp, or skin and Mesocarp, or flesh surrounds a shell (the pit Sugar beet ( Beta vulgaris L a member of the Chenopodiaceae family is a plant whose root contains a high concentration of Sucrose. Horseradish ( Armoracia rusticana, syn Cochlearia armoracia) is a Perennial plant of the Brassicaceae family which also includes mustard Rheum is a genus of Perennial plants that grows from thick short Rhizomes The genus is in the family Polygonaceae, and includes the vegetable
In order to be virulent, the bacterium must contain a tumour-inducing plasmid (Ti plasmid or pTi), of 180 kb, which encodes the T-DNA and all the genes necessary to transfer it to the plant cell. Virulence (also called pestiferousness) refers to the degree of Pathogenicity of a Microbe, or in other words the relative ability of a Microbe Ti plasmid is a circular Plasmid that often but not always is a part of the genetic equipment that Agrobacterium tumefaciens and Agrobacterium In Molecular biology, two Nucleotides on opposite complementary DNA or RNA strands that are connected via Hydrogen bonds are called History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Many strains of A. tumefaciens do not contain a pTi.
Since the Ti plasmid is essential to cause disease, pre-penetration events in the rhizosphere occur to promote bacterial conjugation - exchange of plasmids amongst bacteria. Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact In the presence of opines, A. Opines are low molecular weight compounds found in plant crown gall tumors produced by the parasitic bacterium Agrobacterium. tumefaciens produces a diffusible conjugation signal called 30C8HSL or the Agrobacterium autoinducer. This activates the transcription factor TraR, positively regulating the transcription of genes required for conjugation. In the field of Molecular biology, a transcription factor (sometimes called a sequence-specific DNA binding factor is a Protein that binds to specific sequences Transcription is the synthesis of RNA under the direction of DNA
The Agrobacterium tumefecian infects the plant through its Ti plasmid. The Ti plasmid integrates a segment of its DNA, known as T DNA, into the chromosomal DNA of its host plant cells.
A. tumefaciens have flagella that allow them to swim through the soil towards photoassimilates that accumulate in the rhizosphere around roots. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel In Botany, a photoassimilate is one of a number of biological compounds formed by assimilation using Light-dependent reactions This term is most commonly Some strains may chemotactically move towards chemicals that indicate a wounded plant cell, such as acetosyringone. In biology strain is a low-level Taxonomic rank used in three related ways Chemotaxis, a kind of Taxis, is the phenomenon in which bodily cells bacteria, and other single-cell or Multicellular organisms direct their movements
Attachment is a two step process. Following an initial weak and reversible attachment, the bacteria synthesize cellulose fibrils that anchor them to the wounded plant cell. Cellulose is an Organic compound with the formula, a Polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4 Fibril is a fine Fiber approximately 1 nm in diameter Cytoplasmic fibrils are observed on the protoplasmic cylinders found in most Spirochetal Four main genes are involved in this process: chvA, chvB, pscA and att. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance It appears that the products of the first three genes are involved in the actual synthesis of the cellulose fibrils. These fibrils also anchor the bacteria to each other, helping to form a microcolony.
After production of cellulose fibrils a Ca2+ dependent outer membrane protein called rhicadhesin is produced, which also aids in sticking the bacteria to the cell wall. Calcium (Ca2+ plays a vital role in the Anatomy, Physiology and Biochemistry of Organisms and of the cell, particularly Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Homologues of this protein can be found in other Rhizobia species.
Possible plant compounds, that initiate Agrobacterium to infect plant cells:
In order to transfer the T-DNA into the plant cell A. Pyrocatechol, more commonly known as catechol, is the Organic compound with the formula C6H4(OH2 Ferulic acid is an Organic compound that is an abundant Phenolic Phytochemical found in plant Cell walls It is a derivative of trans- Gallic acid is an Organic acid, also known as 345-trihydroxy Benzoic acid, found in Gallnuts Sumac, Witch hazel, Tea leaves Protocatechuic acid (PCA is an Polyphenol antioxidant found in roselle. Pyrogallol or benzene-123-triol is a white crystalline powder and a powerful reducing agent Sinapinic acid, or sinapic acid is a small naturally occurring Carboxylic acid. Vanillin, methyl vanillin, or 4-hydroxy-3-methoxybenzaldehyde, is an Organic compound with the molecular formula C8H8O3 Plant cells are eukaryotic cells that differ in several key respects from the cells of other eukaryotic Organisms Their distinctive features tumefaciens uses a Type IV secretion mechanism, involving the production of a T-pilus. A pilus ( Latin for 'hair' plural: pili) is a hairlike appendage found on the surface of many bacteria.
The VirA/VirG two component sensor system is able to detect phenolic signals released by wounded plant cells, in particular acetosyringone. This leads to a signal transduction event activating the expression of 11 genes within the VirB operon which are responsible for the formation of the T-pilus. In Biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another An operon is a functioning unit of key Nucleotide sequences including an operator, a common Promoter, and one or more structural Genes,
First, the VirB" pro-pilin is formed. This is a polypeptide of 121 amino acids which requires processing by the removal of 47 residues to form a T-pilus subunit. Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino The subunit is circularized by the formation of a peptide bond between the two ends of the polypeptide. A peptide bond is a Chemical bond formed between two Molecules when the Carboxyl group of one molecule reacts with the
Products of the other VirB genes are used to transfer the subunits across the plasma membrane. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer Yeast Two-hybrid studies provide evidence that VirB6, VirB7, VirB8, VirB9 and VirB10 may all encode components of the transporter. ENCODE (the ENC yclopedia O f D NA E lements is a public research consortium launched by the US National Human Genome Research Institute ( NHGRI An ATPase for the active transport of the subunits would also be required. ATPases are a class of Enzymes that catalyze the Decomposition of Adenosine triphosphate (ATP into Adenosine diphosphate (ADP and Active transport is the mediated process of moving particles across Biological membrane against the concentration gradient
The T-DNA must be cut out of the circular plasmid. A VirD1/D2 complex nicks the DNA at the left and right border sequences. The VirD2 protein is covalently attached to the 5' end. VirD2 contains a motif that leads to the nucleoprotein complex being targeted to the type IV secretion system (T4SS). In Genetics, a sequence motif is a Nucleotide or amino-acid Sequence pattern that is widespread and has or is conjectured to have a biological
In the cytoplasma of the recipient cell, the T-DNA complex becomes coated with VirE2 proteins, which are exported through the T4SS independently from the T-DNA complex. Nuclear localization signals, or NLS, located on the VirE2 and VirD2 are recognised by the importin alpha protein, which then associates with importin beta and the nuclear pore complex to transfer the T-DNA into the nucleus. A nuclear localizing sequence ( NLS) is an Amino acid sequence which acts like a 'tag' on the exposed surface of a Protein. Nuclear pores are large Protein complexes that cross the Nuclear envelope, which is the double membrane surrounding the eukaryotic In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed VIP1 also appears to be an important protein in the process, possibly acting as an adapter to bring the VirE2 to the importin. Once inside the nucleus, VIP2 may target the T-DNA to areas of chromatin that are being actively transcribed, so that the T-DNA can integrate into the host genome. Chromatin is the complex basis of DNA and protein that makes up Chromosomes It is found inside the nuclei of eukaryotic cells, and within the
In order to cause gall formation, the T-DNA encodes genes for the production of auxin or indole-3-acetic acid via the IAM pathway. Galls or plant galls are abnormal outgrowths of Plant tissues and can be caused by various Parasites from Fungi and bacteria, to Insects Auxins are a class of Plant growth substance (often called Phytohormone or Plant hormone) This biosynthetic pathway is not used in many plants for the production of auxin, so it means the plant has no molecular means of regulating it and auxin will be produced constitutively. Genes for the production of cytokinins are also expressed. Cytokinins (CK are a class of Plant growth substances ( Plant Hormones that promote Cell division. This stimulates cell proliferation and gall formation.
The T-DNA contains genes for encoding enzymes that cause the plant to create specialized amino acids which the bacteria can metabolize, called opines (Zupan et al. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. , 2000). Opines are a class of chemicals that serve as a source of energy for A. Opines are low molecular weight compounds found in plant crown gall tumors produced by the parasitic bacterium Agrobacterium. tumefaciens, but not for most other organisms. The specific type of opine produced by A. tumefaciens C58 infected plants is nopaline (Escobar et al. , 2003).
Two nopaline type Ti plasmids, pTi-SAKURA and pTiC58, were fully sequenced. A. tumefaciens C58, the first fully sequenced pathovar, was first isolated from a cherry tree crown gall. A pathovar is a Bacterial strain or set of strains with the same or similar characteristics that is differentiated at infrasubspecific level from other strains of the same species The genome was simultaneously sequenced by Goodner et al. , 2001 and Wood et al. , 2001. The genome of A. tumefaciens C58 consists of a circular chromosome, two plasmids, and a linear chromosome. A plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA A chromosome is an organized structure of DNA and Protein that is found in cells. The presence of a covalently bonded circular chromosome is common to Bacteria, with few exceptions. However, the presence of both a single circular chromosome and single linear chromosome is unique to a group in this genus. The two plasmids are pTiC58, responsible for the processes involved in virulence, and pAtC58, coined the “cryptic” plasmid (Goodner et al. Virulence (also called pestiferousness) refers to the degree of Pathogenicity of a Microbe, or in other words the relative ability of a Microbe , 2001) (Wood et al. , 2001).
The pAtC58 plasmid has been shown to be involved in the metabolism of opines and to conjugate with other bacteria in the absence of the pTiC58 plasmid (Vaudequin-Dransart et al. , 1998). If the pTi plasmid is removed, the tumor growth that is the means of classifying this species of bacteria does not occur.
The DNA transmission capabilities of Agrobacterium have been extensively exploited in biotechnology as a means of inserting foreign genes into plants. Biotechnology is Technology based on Biology, especially when used in Agriculture, Food science, and Medicine. Marc Van Montagu and Jeff Schell, (University of Ghent and Plant Genetic Systems, Belgium) discovered the gene transfer mechanism between Agrobacterium and plants, which resulted in the development of methods to alter Agrobacterium into an efficient delivery system for gene engineering in plants (Schell J, Van Montagu M. Marc Van Montagu (born 10 November 1933 in Ghent) is a Belgian molecular biologist. Jozef Stefaan (Jeff Schell (20 July 1935 - 17 April 2003 was a Belgian molecular biologist. Ghent University (in Dutch Universiteit Gent, abbreviated UGent) is one of the three large Flemish universities. Plant Genetic Systems ( PGS) since 2002 part of Bayer CropScience, is a biotech company located in Ghent, Belgium. The Kingdom of Belgium is a Country in northwest Europe. It is a founding member of the European Union and hosts its headquarters as well as those , 1977). The plasmid T-DNA that is transferred to the plant is an ideal vehicle for genetic engineering (Zambryski, 1983). This is done by cloning a desired gene sequence into the T-DNA that will be inserted into the host DNA. This process has been performed using firefly luciferase gene to produce glowing plants. Luciferase is a generic name for Enzymes commonly used in nature for Bioluminescence. This luminescence has been a useful device in the study of plant chloroplast function and as a reporter gene (Root, 1988). Luminescence is also the title of an album by singer Anggun. Luminescence is Light not generated by high temperatures alone In Molecular biology, a reporter gene (often simply reporter) is a Gene that researchers attach to another gene of interest in Cell culture Under laboratory conditions the T-DNA has also been transferred to human cells, demonstrating the diversity of insertion application (Kunik et al. , 2001).
The mechanism by which Agrobacterium inserts materials into the host cell by a type IV secretion system, is very similar to mechanisms used by pathogens to insert materials (usually proteins) into human cells by type III secretion. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl It also employs a type of signaling conserved in many Gram-negative bacteria called quorum sensing. Quorum sensing is a type of decision-making process used by decentralized groups to coordinate behavior This makes Agrobacterium an important topic of medical research as well.