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? What traits allow it to live at high cell densities in some plants without causing symptoms? How does the bacterium regulate its diverse and complex set of virulence genes?

Genetics of bacterial wilt virulence.

Genome sequences of several 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 molecular genetic approaches to identify traits that R. solanacearum needs to cause wilt disease and form latent infections in the unique nutrient-poor and microaerobic environment of the plant xylem. We also study 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 regulatory 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 functions needed during growth in the plant.

Transcriptomic tools like microarrays are helping us find R. solanacearum genes required for bacterial growth in 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 Central American climate and market demands.

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. R3bv2, which causes serious losses on potatoes in the highland tropics, is now subject to the strictest quanantine and biosecurity regulations. 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. 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. (http://plantpath.ifas.ufl.edu/rsol/index.html)


Allen Lab group photo, Fall 2008

Selected Recent Publications

Toukam, G., G. Cellier, E. Wicker, C. Guilbaud, R. Kahane, C. Allen, and P. Prior. 2009. Broad diversity of Ralstonia solanacearum strains in Cameroon.  Plant Disease: in press.

Allen, C., A. F. Bent, and A. O. Charkowski. 2009. Underexplored niches in research on plant pathogenic bacteria. Plant Physiology 150:1631-37.

Flores-Cruz, Z. and C. Allen. 2009. Ralstonia solanacearum encounters an oxidative environment during tomato infection. Molecular Plant-Microbe Interactions: 22:773-782.

Milling, A., F. Meng, T. P. Denny, and C. Allen. 2009. Interactions with hosts at cool temperatures, not cold tolerance, explain the unique epidemiology of Ralstonia solanacearum Race 3 biovar 2. Phytopathology 99:1127-1134.

Champoiseau, P., J. Jones, and C. Allen. 2009.  Ralstonia solanacearum Race 3 biovar 2 causes tropical losses and temperate anxieties. Plant Health Progress doi:10.1094/PHP-2009-0313-01-RV.

Nakaho, K. and C. Allen. 2009. A pectinase-deficient Ralstonia solanacearum strain induces reduced and delayed structural defenses in tomato xylem. Journal of Phytopathology157: 228-34.

Hong, J.C., T. Momol, J. Jones, P. Ji, S. Olson, C. Allen, A. Sanchez-Perez, P. Pradhanang, K. Guven. 2008. Detection of Ralstonia solanacearum in irrigation ponds and aquatic weeds associated with ponds in North Florida. Plant Disease: 92:1674-82.

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. 2008. Plant pathogenic bacteria as bioterror weapons: A real threat? Phytopathology 98:1060-1065.

Sanchez-Perez, A., L. Mejia, M. Fegan, and C. Allen.  2008.  Diversity and distribution of Ralstonia solanacearum strains in Guatemala and rare occurance of tomato fruit infection. Plant Pathology 57:320-331.

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

 González, E.T. D.G. Brown, J.K. Swanson, and C. Allen. 2007. Using the Ralstonia 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 of Ralstonia solanacearum Race 3 biovar 2 in geraniums. Plant Disease 91:828-834.

Brown, D.G., J. Swanson, and C. Allen.  2007. Two host-induced Ralstonia solanacearum multidrug efflux pumps, AcrAB and DinF, contribute to bacterial wilt virulence. Applied and Environmental Microbiology73:2777-2786.

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

Ji, P., C. Allen, A. Sanchez-Perez, J. Yao, J G. Elphinstone, J. Jones, and T. Momol. 2007. New diversity and diagnostic challenges associated with Ralstonia 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.

Yao, J. and C. Allen. 2006.  Chemotaxis is required for virulence and competitive fitness in the bacterial wilt pathogen Ralstonia solanacearum.  Journal of 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. González , 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 of Ralstonia solanacearum race 3 biovar 2 during latent and active infection of geranium. Phytopathology 95:136-143.

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)

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 in Ralstonia solanacearum cells or extracts applied to Arabidopsis thaliana. Molecular Plant-Microbe Interactions 17:696-706.

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

González, E. T., and C. Allen. 2003. Characterization of a Ralstonia solanacearum operon required for polygalacturonate degradation and uptake of galacturonic acid. Molecular 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

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.

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

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

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

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

Laferriere, L., J. P. Helgeson, and C. Allen. 1999. Fertile Solanum tuberosum + S. commersonii somatic hybrids as sources of resistance to bacterial wilt caused by Ralstonia solanacearum Race 3.  Theor. Appl. 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. Appl. Environ. Microbiology 64: 4918-4923.

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

 Huang, Q. and C. Allen. 1997. An exo-poly-alpha-D-galacturonosidase, PehB, is required for wildtype virulence of Ralstonia solanacearum. Journal of Bacteriology 179: 7369-78.