Office: 560 Hutchison Hall
Office Phone: 530-752-3502
Lab Phone: 530-752-1050
FAX: 530-752-5809
E-Mail: vmwilliamson@ucdavis.edu
Appointment: 1987
B.A., 1971, Biology. Northeastern University, Boston, MA
Ph.D., 1978, Biochemistry, University of California, Davis
Teaches:
Molecular Biology Laboratory Techniques (ANG111); Agricultural Biotechnology (PLP140)
Research:
Root-knot nematodes are obligate endoparasites that induce roots to form morphologically distinct galls and "giant" cells. These specialized host cells act as feeding sites to support nematode development. This group of plant parasitic nematodes causes billions of dollars in damage and infects thousands of plant species. Our laboratory is using molecular and genetic tools to study the interactions between host and parasite.
Host resistance to root-knot nematodes
Many commercial tomato lines contain a gene, Mi-1, that confers resistance against root-knot nematodes. Mi-1 has been isolated in our lab and shown to encode a member of the large NBS-LRR family of pathogen resistance proteins in plants. By analysis of transgenic plants, we showed that this same gene confers resistance against the potato aphid. We have been investigating the mechanisms by which Mi-1 recognizes the presence of the nematode and triggers a signal transduction pathway leading to resistance. Using in vitro mutagenesis followed by examination of phenotypes in transformed roots or after transient expression in leaves, we have found that intramolecular interactions are important for regulation of induction of the defense response. We have also used our mutants in Mi-1 to identify components of the signal transduction pathway leading to resistance.
Another line of research has been to identify additional resistance genes that can confer resistance to Mi-1-virulent nematodes. We have mapped one such gene, Mi-3, in the wild tomato species Lycopersicon peruvianum. Using a combination of classical genetics and molecular techniques, we have localized Mi-3 to a DNA clone of <50 kb. Transformation studies to identify the resistance gene are in progress.
Root-knot nematode pathogenicity
Although the Mi-1 gene has been effective for controlling root-knot nematodes on tomato for many years, some nematode isolates have the ability to reproduce on plants with this gene. Using DNA markers and RNAi, we have identified a candidate gene that may be required for the nematode to be recognized by plants with Mi-1.
Our group is interested in understanding host recognition and pathogenicity of root-knot nematodes. We have identified strains of the root-knot nematode species Meloidogyne hapla that differ in attraction to specific plant hosts, and also in ability to reproduce on resistant plants. We have developed attraction assays and identified volatile compounds that may be important for host recognition. We have established a genetic system for M. hapla and have successfully carried out crosses between inbred strains that differ in virulence, host attraction, and molecular markers. Analysis of segregation of phenotypes in progeny should lead to identification of traits involved in host recognition and pathogenicity of this complex and fascinating parasite. Several research groups are now focusing on M. hapla as the canonical species for exploring the interactions of endoparasitic nematodes with their plant hosts. A large number of ESTs are available, BAC libraries have been made, and a project has been initiated to sequence the genome of this organism. These resources will expedite our efforts to understand factors important for host recognition and pathogenicity in root-knot nematodes.
Nematode identification
Nematodes are numerous and ubiquitous in most environments. Identification of plant parasitic nematode species in field samples can often be quite difficult. We have developed molecular assays for identification of several plant parasitic nematodes of agricultural importance in California and Africa.
Lab members:
Kevin Fort Graduate Student, Genetics Graduate Group
Chin-Feng Hwang Assistant Specialist
Ann Liu Undergraduate Assistant
Qingli Liu Graduate Student, Plant Pathology Graduate Group
Steven Lower Post Doctoral Scientist
Waclawa Pudlo Lab Assistant
Adam Telleen Graduate Student, Plant Biology Graduate Group
Yong Wen Lab Assistant
Jafar Yaghoobi Research Scientist
Selected Publications:
Williamson, V.M., Caswell-Chen, E., Westerdahl, B., Wu, F.F., and Carle, G. 1997. A PCR assay identify and distinguish single juveniles of M. hapla and M. incognita. J. Nematol. 29:9-15.
Al-Banna, L., Williamson, V.M., and Gardner, S.L. 1997. Phylogenetic analysis of nematodes of the genus Pratylenchus using nuclear 26S rDNA. Molecular Phylogenetics and Evolution 7:94-102.
Kaloshian, I., Yaghoobi, J., Liharska, T., Hontelez, J., Hanson, D., Hogan, P., Jesse, T., Wijbrandi, J., Simons, G., Vos, P., Zabel, P., and Williamson, V.M. 1998. Genetic and physical localization of the root-knot nematode resistance locus Mi in tomato. Mol. Gen. Genet 257: 376-385.
Milligan, S.B., Bodeau, J., Yaghoobi, J., Kaloshian, I., Zabel, P., and Williamson, V.M. 1998. The root knot nematode resistance gene Mi from tomato is a member of the leucine zipper, nucleotide binding, leucine-rich repeat family of plant genes. The Plant Cell 10:1307-1320.
Rossi, M., Goggin, F.L., Milligan, S.B., Kaloshian, I., Ullman, D.E., and Williamson, V.M. 1998. The nematode resistance gene Mi of tomato confers resistance against the potato aphid. Proc. Natl. Acad. Sci. USA 95:9750-9754..
Williamson, V.M. 1998. Root-knot nematode resistance genes in tomato and their potential for future use. Ann. Rev. Phytopathol. 36:277-93.
Brenner, E.D., Lambert, K.N., Kaloshian, I., and Williamson, V.M. 1998. Characterization of LeMir, a root-knot nematode induced gene in tomato whose encoded product is secreted from the root. Plant Physiology 118:237-247.
Williamson, V.M. 1999. Plant nematode resistance genes. Current Opinion in Plant Biology 2:327-331.
Zhong, X.-B., Bodeau, J., Fransz, P.F., Williamson, V.M., van Kammen, A., de Jong, H., and Zabel, P. 1999. FISH to meiotic pachytene chromosomes of tomato reveals the root-knot nematode resistance gene Mi-1 and the acid phosphatase gene Aps-1 to be located near the junction of euchromatin and pericentromeric heterochromatin of chromosome arms 6S and 6L, respectively. Theor. Appl. Genet. 98:365-370.
Hwang, C.F., Bhakta, A.V., Truesdell, G.M., Pudlo, W.M., and Williamson, V.M. 2000. Evidence for a role of the N terminus and leucine-rich repeat region of the Mi gene product in regulation of localized cell death. The Plant Cell 12:1319-1329.
Williamson, V.M., and C. A. Gleason. 2003. Plant - nematode interactions. Current Opinion in Plant Biology 6: 327-333.
Hwang, C.-F., and Williamson, V. M. 2003. Leucine-rich repeat-mediated intramolecular interactions in nematode recognition and cell death signaling by the tomato resistance protein Mi. The Plant Journal 34:585-593.
Branch, C., Hwang, C.F., Navarre, D.A., and Williamson, V.M. 2004. Salicylic acid is part of the Mi-1-mediated defense response to root-knot nematode in tomato. Mol. Plant
Microbe Int., 17:351-356.
Seah, S.K., Yaghoobi, J., Rossi, M., Gleason, C.A., and Williamson, V.M. 2004. Suppressed recombination at Mi-1, the root-knot nematode and aphid resistance gene locus in tomato, is associated with an inverted chromosomal segment. Theor. Appl. Genetics, 108:1635-1642.
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