Caitilyn Allen

Plant Pathology
Ph.D.: Virginia Polytechnic Institute and State University in Plant Pathology
NRI July 2007 Meeting Talks
Recent Publications

Research Program

My research group focuses on the interactions between the plant pathogenic bacterium Ralstonia solanacearum and its plant hosts. R. solanacearum causes bacterial wilt, a soilborne disease found in tropical and warm temperate regions all over the world. Because of its very broad host range of wide geographical distribution, it is arguably the world's single most harmful bacterial plant pathogen. This fascinating and destructive bacterium presents many intriguing questions. How can R. solanacearum infect so many different host plants? How does the bacterium regulate its diverse and complex set of virulence genes?

Genetics of bacterial wilt virulence.
Genome sequences of two R. solanacearum strains have created great opportunities for sweeping and fast-moving genetic analyses of this pathogen. As a result, we can now use powerful genomic tools to understand one of the most damaging pathogens in the developing tropics. We use a combination of focused and open-ended molecular genetic approaches to identify traits that R. solanacearum needs to cause wilt disease and form latent infections in the unique nutrient-poor and microaerophilic environment of the plant xylem. We also focus on plant responses to infection with R. solanacearum, and on the regulatory genes that control bacterial virulence factor expression. These studies help illuminate R. solanacearum's rich and complicated regulartory network, which responds to such diverse signals as bacterial density, contact with the plant or root exudates, and oxidative stress. Because R. solanacearum is a plant pathogen, not a laboratory model organism, we do our experiments in planta under biologically realistic conditions and we work with economically important natural hosts such as tomato, potato, tobacco, and geranium.

Identifying R. solanacearum genes expressed during growth in the plant. In vivo expression technology (IVET) has allowed us to open-endedly seek R. solanacearum genes likely required for bacterial growth in the unique nutrient-poor and microaerophilic environment of the plant xylem, as well as genes that encode novel or specific virulence factors. This project is yielding exciting molecular-level insights into the secret life of a vascular pathogen. Some of the in planta-expressed genes are familiar virulence factors of animal pathogens, while others are completely novel.

Breeding for wilt resistance/International plant pathology. Bacterial wilt has a disproportionately high impact on subsistence and small-scale growers in the developing world. Disease-resistant plants are the best option for control of this disease. We collaborate with researchers at the University of San Carlos in Guatemala to breed tomatoes that are resistant to bacterial wilt and adapted to Guatemalan climate and market demands.

R. solanacearum bact

R. solanacearum, geraniums, and bioterrorism. A subgroup of R. solanacearum, Race 3 Biovar 2 (R3Bv2), is listed as a potential bioterrorism agent (Select Agent) in the United States. This group, which causes serious losses on potatoes in the highland tropics, is now subject to the strictest quanantine and biosecurity regulations. Although Although R3Bv2 is not established in North America, it has been introduced several times on imported geranium cuttings. Recent introductions of this pathogen on geranium cuttings have cost the ornamental industry millions of dollars. Our lab studies the interaction between R3Bv2 and geranium plants to help develop regulatory policy that corresponds to the true biological risk posed by this pathogen. We are also surveying the native populations of R. solanacearum in Guatemala to better understand, predict, and diagnose this pathogen. Additionally, I'm leading a multi- institutional integrated project to develop rapid, sensitive diagnogtic tools, effective outreach materials, and an improved understanding of the biology and behavior of R3Bv2.

Allen Lap 2007

Allen lab group photo, Summer 2007

Recent Publications:

J. M. Young, C. Allen, T. Coutinho, T. Denny, J. Elphinstone, M. Fegan, M. Gillings, T. R. Gottwald, J. H. Graham, J. D. Janse, M. M. Lopez, C. Morris, N. Parkinson, J. Rodrigues Neto, M. Scortichini, and Y. Takikawa. Plant pathogenic bacteria as bioterror weapons: A real threat? In revision forPhytopathology.

Sanchez-Perez, A., L. Mejia, M. Fegan, and C. Allen. 2008. Diversity and distribution ofRalstonia solanacearum strains in Guatemala and rare occurance of tomato fruit infection.Plant Pathology: 57: e-print before publication doi: 10.1111/j.1365-3059.2007.01769.x

Yao, J. and C. Allen. 2007. The plant pathogenRalstonia solanacearum needs aerotaxis for normal biofilm formation and interactions with its tomato host.Journal of Bacteriology 189:6415-6424.

Brown, D.G., J. Swanson, and C. Allen. 2007. Two host-inducedRalstonia solanacearum multidrug efflux pumps, AcrAB and DinF, contribute to bacterial wilt virulence.Applied and Environmental Microbiology:73:2777-2786

González, E.T. D.G. Brown, J.K. Swanson, and C. Allen. 2007. Using theR. solanacearum Tat secretome to identify additional bacterial wilt virulence factors. Applied and Environmental Microbiology: 73:3779-3786

Swanson, J. K., L. Montes, L. Mejia and C. Allen. 2007. Detection of latent infections ofRalstonia solanacearum Race 3 biovar 2 in
geranium.Plant Disease: 91:828-834

Ji, P., C. Allen, A. Sanchez-Perez,, J. Yao, J G. Elphinstone, J. Jones, and T. Momol. 2007. New diversity and diagnostic challenges
associated withRalstonia solanacearum strains in Florida.Plant Disease 91:195-203

Allen, C. 2007. Bacteria, Bioterrorism, and the Geranium Ladies of Guatemala. pp.169-177 in:Wages of Empire: Neoliberal policies,
repression, and women's poverty. (A. L. Cabezas, E. Reese, and M. Waller, editors) Paradigm Press, Boulder, Colorado.

Allen, C. 2007. It's a Boy! Gender expectations intrude on the study of sex determination.DNA and Cell Biology. 26(10): 699-705.

Yao, J. and C. Allen.2006. Chemotaxis is required for virulence and competitive fitness in the bacterial wilt pathogenRalstonia
solanacearum.J. Bacteriology 188:3697-3708.

Gabriel, D. W., C. Allen, M. Schell, T. Denny, J. T. Greenberg, Q. Huang, Y.-P. Duan, Z. Flores, J. Clifford, G. Presting, E. T. Gonzalez ,
J. Reddy, J. Elphinstone, J. Swanson, J. Yao, V. Mulholand, L. Liu, W. Farmerie, M. Patnaikuni, B. Balogh, D. J. Norman, A. Alvarez, J. A.
Castillo, J. B. Jones, G. S. Saddler, T. Walunas, A. Zhukov, and N. Mikhailova. 2006. Identification of Open Reading Frames unique to a
Select Agent:Ralstonia solanacearum race 3 biovar 2.Molecular Plant-Microbe Interactions 19:69-79.

Swanson, J. J. Yao, J. Tans-Kersten, and C. Allen. 2005. Behavior ofRalstonia solanacearum race 3 biovar 2 during latent and active
infection of geranium.Phytopathology 95:136-143.

Allen, C., P. Prior, and A.C. Hayward, editors. 2005.Bacterial Wilt: The Disease and the Ralstonia solanacearum Species Complex. APS Press, St. Paul, 508 pages. (an APS Press bestseller for 2005)

Brown, D.G., and C. Allen. 2004.Ralstonia solanacearum genes induced during growth in tomato: an inside view of bacterial wilt.Molecular Microbiology 53:1641-1660.

Pfund, C., J. Tans-Kersten, M. Dunning, C. Allen, and A. Bent. 2004. Flagellin is not a major defense elicitor inRalstonia solanacearum cells or extracts applied toArabidopsis thaliana.Mol. Plant-Microbe Interactions 17:696-706.

Tans-Kersten, J., D. Brown, and C. Allen. 2004. Swimming motility, a virulence factor ofRalstonia solanacearum, is regulated by FlhDC and by the plant host environment.Mol. Plant-Microbe Interactions. 17:686-695.

González, E. T., and C. Allen. 2003. Characterization of aRalstonia solanacearum operon required for polygalacturonate degradation and uptake of galacturonic acid.Mol. Plant-Microbe Interactions 16:536-544.

Brower, AM, Chris M. Golde, and C. Allen. 2003. Residential learning communities positively affect college binge drinking",NASPA Journal 40: No. 3, Article 9. http://publications.naspa.org/naspajournal/vol40/iss3/art9.pdf

Williamson, L., C. Allen, K. Nakaho, and B. Hudelson. 2002.Ralstonia solanacearum race 3, biovar 2 strains isolated from geranium are
pathogenic on potato.Plant Disease 86 :987-991.

Allen, C. 2002. Teaching courses in molecular plant-microbe interactions. In: Biology of Plant-Microbe Interactions, Vol. 3, S.A.
Leong, C. Allen, E. Triplett, eds. APS Press, St. Paul.

Leong, S.A., C. Allen, E. Tripplett, editors. 2002.Biology of Plant-Microbe Interactions, Vol. 3. APS Press, St. Paul, 360 p.

Tans-Kersten, J., H. Huang, and C. Allen 2001.Ralstonia solanacearum needs motility for invasive virulence on tomato.J. Bacteriology
183:3597-3605.

Allen, C., A. Kelman, and E.R. French. 2001. Bacterial Wilt Diseasein: APS Revised Compendium of Potato Diseases, W. R. Stevenson and R. Loria, eds. APS Press, St Paul.

Allen, C. 2001. What do you do over there, anyway? Tales of an academic dual citizen. p. 22-29 in:Feminist Science Studies (M. Mayberry, B. Subraminium, L. Weasel, eds). Routledge Publishers, New York.

Allen, C. 2001. Shades of Gray: Changing the content of science courses to include and encourage the underrepresented. p.68-75In:
Flickering Clusters: Women, Science, and Collaborative Transformations (C. Ney, J. Ross, and L. Stempel, editors). University of Wisconsin Press, Madison.

Tans-Kersten, J., J. Gay, and C. Allen. 2000.Ralstonia solanacearum AmpD is required for wild-type bacterial wilt virulence.Mol. Plant
Pathology 1:179-185.

Huang, Q., and C. Allen. 2000. Polygalacturonases contribute to colonization ability and virulence ofRalstonia solanacearum on tomato
plants.Physiol. Mol. Plant Pathology 57:77-83.

Laferriere, L., J. P. Helgeson, and C. Allen. 1999. FertileSolanum tuberosum +S. commersonii somatic hybrids as sources of resistance to bacterial wilt caused byRalstonia solanacearum Race 3. Theoretical and Applied Genetics 98: 1272-1278.

Allen, C. 1999. Supporting female undergraduate science and engineering majors with a residential program. Journal of Women and Minorities in Science & Engineering: 5:265-278.

Tans-Kersten, J., Y. Guan, and C. Allen. 1998.Ralstonia solanacearum pectin methylesterase is required for growth on methylated pectin, but not for bacterial wilt virulence.Applied and Environmental Microbiology 64: 4918-4923.

Allen, C., J. Gay, and L. Simon-Buela. 1997. A regulatory locus,pehSR, controls polygalacturonase production and other virulence functions inRalstonia solanacearum.Molecular Plant-Microbe Interactions 10: 1054-1064.

Huang, Q. and C. Allen. 1997. Anexo-poly-alpha-D-galacturonosidase, PehB, is required for wildtype virulence ofRalstonia solanacearum.J. Bacteriology 179: 7369-78.

Edited Books
Allen, C., P. Prior, and A.C. Hayward. 2005. Bacterial Wilt: The Disease and the Ralstonia solanacearum Species Complex. APS Press, St. Paul. 508 pages. (APS Press bestseller for 2005)
Leong, S.A., C. Allen, E. Tripplett, editors. 2002. Biology of Plant-Microbe Interactions, Vol. 3. APS Press, St. Paul, 360 p.
Prior, P., C. Allen, and J. Elphinstone, editors. 1998. Bacterial Wilt Disease: Molecular and Ecological Aspects. Springer Verlag, Berlin.