VALERIE M. WILLIAMSON
Research:
Molecular studies on nematode and aphid resistance genes in tomato. Molecular characterization of root-knot nematodes.
Selected publications:
Kaloshian, I., Lange, W. H., and Williamson, V. M. 1995. An aphid-resistance locus is tightly linked to the nematode-resistance gene, Mi, in tomato. Proc. Natl. Acad. Sci. USA 92:622-625.
Yaghoobi, J., Kaloshian, I., Wen, Y., and Williamson, V.M. 1995. Mapping a new nematode resistance locus in Lycopersicon peruvianum. Theor. Appl. Genet. 91:457-464.
Williamson, V.M., and Hussey, R.S. 1996. Nematode pathogenesis and resistance in plants. The Plant Cell 8:1735-1745.
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.
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.
Research in Williamson laboratory
Root-knot nematodes are obligate endoparasites that induce plant roots to form morphologically distinct galls and specialized "giant" cells. These specialized host cells act as feeding sites to support nematode development. This group of plant parasitic nematodes causes billions of dollars of damage and infects thousands of plant species. Some tomato lines contain a gene, Mi1, that confers resistance to root-knot nematodes. Mi1 has recently been identified in my lab by positional cloning and complementation of function. By analysis of transgenic plants we have shown that this same gene confers resistance to the potato aphid. In vitro manipulations of the gene are in progress to investigate the protein domains responsible for recognition of the nematode and the aphid and for triggering the defense responses mediated by the gene. We have also identified, by differential screening, plant genes that are induced by nematodes in resistant plants. The developmental and spatial expression of specific genes and their possible roles in resistance are being analyzed.
Some root-knot nematodes have developed the ability to reproduce on plants with Mi. Another goal of the lab is to understand the genetic mechanisms by which virulence has developed in these asexual parasites. Does the nematode no longer produce the ligand recognized by the resistance gene or does it express factors that actively repress the host defenses? Another approach is to identify additional resistance genes that carry resistance to Mi1-virulent nematodes. We have mapped one such gene, Mi3, and are currently pursuing a map-based cloning approach to isolate a clone of this gene.
The research describe above is being carried out in the laboratory of Valerie Williamson, Department of Nematology, and at CEPRAP, an NSF Science and Technology Center in Davis.
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