Crown Gall Disease

Causative agent, method of action, and treatment for Crown Gall Disease.

1. Case Study – Sugar Beets After helping your parents harvest sugar beets, you notice that many of the beets have odd-looking bumps. The beets that have these growths appear slightly stunted when compared to the beets without any visible growths. Erin Richards – BIOC 460

2. What disease do you suspect? Crown Gall Disease

3. What causative agent do you suspect? Agrobacterium tumefaciens

4. Agrobacterium tumefaciens Gram negative, obligate aerobic, bacilli Common soil bacteria Associates with the roots of many plants by chemotaxis Contains a Ti (tumor-inducing) plasmid

5. Ti Plasmid E xpressed when plant dimethoxyl phenolic compounds (released from wound sites) are detected by the bacteria virA encodes a histidine kinase ( VirA ) Inhibits motility and allows bacteria to adhere to plant roots Phosphorylates VirG , a response regulator VirG -P activates transcription of the remaining virulence genes Endonucleases cleave Ti plasmid to form T-DNA T-pilus formation for gene transfer

6. Transformation T-pilus enters through damage in cell wall Transfers T-DNA in a VirD2-VirE2 protein complex to protect from plant cell nucleases L ocalization sequence brings T-DNA protein complex to plant cell nucleus T-DNA integrated into chromosome by plant cell DNA repair enzymes, which are heavily expressed during damage events T-DNA expressed by plant-cell machinery

7. A Tumor-Inducing Infection Transcription and translation of T-DNA produces the primary oncogenes auxin and cytokinin and the secondary oncogene for opine-synthesis enzymes Auxin promotes cell elongation Cytokinin promotes cell division Leads to abnormal cell size and division Opines are utilized as carbon and nitrogen sources during metabolism in A. tumefaciens Opines taken up into cell by permeases encoded on Ti plasmid Also induces the transfer of more Ti plasmids, leading to an increase in gene product

8. Cause of Death Redistribution of plant cell resources leads to stunted growth Uncontrolled cell proliferation at infection site leads to tumors or galls Poor cell differentiation in root galls leads to decreased uptake of water and nutrients for the plant, eventually leading to plant death Galls may fall off after plant death, exposing surrounding plants to A. tumefaciens A. tumefaciens may also be transferred by biting insects or harvesting equipment

9. What treatments would you suggest? Plant A. tumefaciens resistant crops Use biochemical agents

10. Treatment Replant entire field with cereal crops for a long period of time Cereal crops are not in the host range of A. tumefaciens Lack of hosts significantly decreases A. tumefaciens population Spray antibiotics, such as agrocin , on entire field Agrocin structurally resembles the opine agrocinopine A, taken up by A. tumefaciens Agrocin inhibits nucleic acid and protein synthesis by obstructing intake of amino acid residues by pathogenic A. tumefaciens

11. References Martin, Giles S. “Sugar Beet Field.” 2010. JPEG . Neher , Oliver T. ”Crown Gall”. The Amalgamated Sugar Company, Bugwood.org , n.d. JPEG. Pacurar , Daniel I., et al. “ Agrobacterium tumefaciens : From Crown Gall to Genetic Transformation.” Physiological and Molecular Plant Pathology , 76, 2, 2011, pp. 76 – 81. Kado , Clarence I. “Crown Gall.” The American Phytopathological Society, http://www.apsnet.org/edcenter/ intropp /lessons/prokaryotes/Pages/ CrownGall.aspx . Accessed 19 Dec. 2016. “ Agrobacterium tumefaciens (Crown Gall Disease).” S-cool . http://www.s-cool.co.uk/a-level/biology /genetic-engineering/revise-it/vectors-and- pcr . Accessed 19 Dec. 2016. McCardell , Barbara A. and C. F. Pootjes . “Chemical Nature of Agrocin 84 and Its Effect on a Virulent Strain of Agrobacterium tumefaciens .” Antimicrobial Agents Chemotherapy , 10, 3, 1976, pp. 498 – 502. “Wheat Crops.” N.d. JPEG . “Agrocin-84.” Springer Scientific , n.d. JPEG .