Valerie M. Williamson
Valerie M. Williamson -Professor of Plant Pathology
Phone: (530) 752-3502 Email: email@example.com
B.A., 1971, Biology. Northeastern University, Boston, MA
Ph.D., 1978, Biochemistry, University of California, Davis
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.
Genetics and genomics of root-knot nematodes: We have established a genetic system for Meloidogyne hapla and have successfully carried out crosses between inbred strains that differ in virulence, host attraction, and molecular markers. The genome of this species has been sequenced and annotated, and a set of F2 lines, which, due to the unusual reproductive mode, resemble recombinant inbred lines, has been produced and used to develop a sequence-anchored molecular map. These lines are maintained as cultures on tomato plants and have been used to assess behaviors including clumping and host attraction.
Nematode behavior and attraction to hosts: Root-knot nematodes are attracted to the root zone of elongation, but what attracts them to this region is unknown. We have developed an assay system using a gel of Pluronic F-127 and demonstrated infective juvenile attraction to the elongation zone as well as to volatile and soluble components of root tip exudates. Our goal is to analyze these extracts to identify chemicals responsible for modifying nematode behavior.
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 plant parasitic nematodes of agricultural importance in California and Africa.
Williamson, V.M., and Kumar, A. 2006. Nematode resistance genes in plants: the battle underground. Trends in Genetics 22:396-403.
Liu, Q.L., and Williamson, V.M. 2006. Host-specific pathogenicity and genome differences between inbred strains of Meloidoygne hapla. J. Nematol. 38:158-164.
Liu, Q.L., Thomas, V.P., and Williamson, V.M. 2007. Meiotic parthenogenesis in a root-knot nematode results in rapid genomic homozygosity. Genetics, 176: 1483-1490.
Gleason, C.A., Liu, Q.L., and Williamson, V.M. 2008. Silencing a candidate nematode effector gene corresponding to the tomato resistance gene Mi-1 leads to acquisition of virulence. Molecular Plant Microbe Int., 21:576-585.
Opperman, C.H., Bird, D.M., Williamson, V.M., Rokhsar, D.S., Burke, M., Cohn, J., Cromer, J., Diener, S., Gajan, J., Graham, S., Houfek, T.D., Liu, Q., Mitros, T., Schaff, J., Schaffer, R., Scholl, E.,Sosinski, B.R., Thomas, V.P., and Windham, E. 2008. Sequence and genetic map of Meloidogyne hapla: a compact nematode genome for plant parasitism. Proc. Nat. Acad. Sci. USA 105:14802-14807.
Wang, C., Lower, S., and Williamson, V.M. 2009. Application of pluronic gel to the study of root-knot nematode behaviour. Nematology 11:453-464.
Bird, D. McK., Williamson, V.M., Abad, P., McCarter, J., Danchin, E.G.J., Castagnone-Sereno, P., and Opperman, C.H. 2009. The Genomes of root-knot nematodes. Ann. Rev. Phytopathology 47:333-352.
Williamson, V.M., and Roberts, P.A. 2009. Mechanisms and genetics of resistance, In: Root-knot nematodes, R.N. Perry, M. Moens, and J. Starr, eds. CABI Publishing, UK., pp. 301-325
Wang, C., Bruening, G., and Williamson, V.M. 2009. Determination of preferred pH for root-knot nematode aggregation using pluronic F-127 gel. J. Chem. Ecol. 35:1242-1251.
Abad, P., and Williamson, V.M. 2010. Plant nematode interaction: a sophisticated dialogue. Advances in Botanical Research. 53: 147-292.
Wang, C.L., Lower S., Thomas V.P., Williamson V.M. 2010. Root-knot nematodes exhibit strain-specific clumping behavior that is inherited as a simple genetic trait. Plos One 5:e15148.
Gross, S.M., and Williamson, V.M. 2011. Tm1: A Mutator/Foldback transposable element family in root-knot nematodes. Plos One 6: e24534.
Thomas, V.P., Fudali, S.L., Schaff, J.E., Liu, Q., Scholl, E.H., Opperman, C.H., Bird, D. McK., and Williamson, V.M. 2012. A sequence-anchored linkage map of the plant-parasitic nematode Meloidogyne hapla reveals exceptionally high genome-wide recombination. G3: Genes| Genomes| Genetics, 2:815-824.
Fudali, S.L., Wang, C., and Williamson, V.M. 2013. Ethylene signaling modulates attractiveness of host roots to the root-knot nematode Meloidogyne hapla. Mol. Plant Microbe Int. 26:75-86.
Williamson, V.M., Thomas, V., Ferris, H., and Dubcovsky, J. 2013. A translocation from Aegilops ventricosa transferred to common wheat carries a resistance gene against root-knot nematodes. Crop Sci. 53:1412-1418.
Thomas, V. P., and Williamson, V.M. 2013. Segregation and mapping in the root-knot nematode Meloidogyne hapla of quantitatively inherited traits affecting parasitism. Phytopathology 103:935-940.
Chris Pagan - Staff Research Associate
Cinta Gimeno - Postdoctoral researcher
Sonchai Kwankuae - visiting scholar
AJ Ong - Lab assistant