1. Agrobacterium tumefaciens

2. Bacteria multiply primarily in soil, not in tumors
Able saprophyte
Attracted to wounds
Infects and transfers T-DNA from Ti plasmid to plant cells, resulting in synthesis of plant growth regulators (hormones) for undifferentiated growth (tumors), and biosynthesis of opines (nutrient source for bacteria)
Bacteria multiply primarily in soil, not in tumors
Very broad host range most dicots and a few monocots
Ti plasmid can be manipulated to customize transferred DNA and make use of A. t. as genetic engineering tool
Ti plasmid is the virulence determining factor and can be transferred from one strain to another strain, making the recipient virulent and able to infect.

3. Agrobacterium tumefaciens
Crown gall of tomato
Agrobacterium tumefaciens
Rose
Tobacco

4. Infection process
(a) Chemical recognition of host and activation of virulence gene expression,
(b) physical recognition and interaction between bacterium and host,
(c) production of transferred substrates and transfer machinery,
(d ) transfer of substrates out of the bacterium and into the host cell,
(e) movement of substrates into nucleus,
(f) integration of T-DNA into host genome,
(g) expression of T-DNA.

5. Signals that induce vir gene expression
Low pH Low PO4
Acetosyringone
VirAG two component system receptor and kinase dimers two trans membrane domains kinase self inhibition and with the phenols phosphorylation on virG; chvE responding to sugar low pH making the phenol signaling easier.
Wound conditions
Necessary structural elements decide the specificity
Diverse inducing signals decide the broad host range
McCullen and Binns (2006) Annu. Rev. Cell Dev. Biol. 22:

7. Type IV secretion system (T4SS)
VirD2-T-strand,
VirE2,
VirE3,
VirF,
VirD5
Recruiter for D4 and the ATPase providing the energy to translocate the macromolecules
Physical interaction evidences
Polar location
McCullen and Binns (2006) Annu. Rev. Cell Dev. Biol. 22:

8. McCullen and Binns (2006) Annu. Rev. Cell Dev. Biol. 22:101-127
Physical attachment surface beta-1,2-glucan. Transferred macromolecules structure
McCullen and Binns (2006) Annu. Rev. Cell Dev. Biol. 22:

9. Type IV secretion is conserved
Function could be diverse but the cluster structure and the protein sequences are conserved among different strains

10. Decreased expression or overexpression of more than 100 plant genes can alter susceptibility
rat (recalcitrant to Agrobacterium transformation) genes (attachment, transfer, integration)
importins
PP2C (virD2) overexpression -> decreased nuclear targeting. Mutation - >higher susceptibility to Agro infection
VIP1(b-zip) - (virE2)overexpression ->increased susceptibility. Piggybacks virE2 into nucleus?
skp1 - (virF) cell cycle setting, targeting for proteosome?
hat (hypersusceptible to Agrobacterium transformation) genes (e.g., MTF, WRKY – plant defense)

12. Agrobacterium exploits a defense response
Dafny-Yelin et al. (2008) Trends Plant Sci. 13:

13. Dimerization of VirD2 Binding Protein Is Essential for
Agrobacterium Induced Tumor Formation in Plants
Padavannil et al. (2014) PLoS Pathog 10: e

14. A. tumefaciens responses to plant-derived signaling molecules
Phenolic compound can increase the Ti plasmid copies. Opine can activate the opine metabolism genes, as well as quorum sensing system to induce the Ti conjugation. QS also increase the Ti copy numbers. SA GABA activate the quorum quenching, downregulate the QS; SA IAA EA downregulate Vir gene
Subramoni et al (2014) Front Plant Sci. 5: 322.

15. Remaining questions Mechanism of T-DNA transfer and integration
A. t. chromosomal genes involved in pathogenesis and host range determination (transformation efficiency)
Plant genes involved in all aspects, especially:
Host specificity
Integration (primary limiting factor)
(Can alteration of req’d plant genes confer resistance to crown gall?)
(Can alteration of req’d plant genes improve transformation?)
Coevolution