June B. Nasrallah
Professor
B McClintock Professorship

June B. Nasrallah

Phone

607-255-8189

Address

Department of Plant Biology
260 Emerson Hall
Cornell University
Ithaca, NY 14853-2703

Email

Web Sites

Lab Web Site
Department Profile

Background

Bachelor's Degree, American Univ Beirut (lebanon) 1970
Doctorate, Cornell University 1977

Member of the US National Academy of Sciences - 2003
American Society of Plant Biologists Martin Gibbs Medal - 2003

Research Description

Research in my laboratory is focused on the molecular genetic analysis of the early events of pollination in the crucifer family (Brassicaceae) and on understanding the genetic basis of outcrossing and self-fertilizing mating systems. In the crucifer family, as in many families, mating system and breeding structure are regulated through the operation of cell-to-cell communication and recognition events between the pistil on the one hand and the pollen grain or pollen tube on the other hand. Our analysis of early pollination events in two model systems, Brassica and Arabidopsis, allows us to investigate at the molecular level how the pistil acts as a selective barrier to fertilization. The long-term goal of our research is to elucidate the molecular mechanisms underlying the two possible fates followed by pollen grains once they are delivered to the stigma: 1) germination and growth of the pollen tube leading to fertilization and seed production; and 2) inhibition of germination and pollen tube development because of the operation of a genetic barrier to self-fertilization, termed self-incompatibility (SI), in which cells of the stigma epidermis inhibit the development of self-related, but not genetically unrelated, pollen. We determined that specificity in the SI response is determined by two highly polymorphic and co-adapted proteins, a receptor kinase displayed on the stigma surface and its pollen coat-localized peptide ligand. We transferred the SI trait into the highly self-fertile Arabidopsis thaliana by transformation with a receptor-ligand pair fderived rom its self-incompatible sister species, A. lyrata, and uncovered previously unsuspected natural variation for expression of SI in A. thaliana. Our current efforts are focused on exploiting this transgenic A. thaliana SI system and the many molecular genetic resources of this model plant to analyse this crypotic natural variation and to perform saturating mutagenesis of the SI response. This analysis is expected to elucidate the mechanism of SI and identify components of pollen-stigma signaling. It is also expected to explain how and when A. thaliana lost SI and became self-fertile, and more generally to elucidate the genetic basis of evolutionary switches from outcrossing to selfing in the crucifer family. more

Publications

Liu, P., Sherman-Broyles, S., Nasrallah, M.E., and Nasrallah J.B. 2007. A cryptic modifier causing transient self-incompatibility in Arabidopsis thaliana. Curr. Biol. 17: 734-740.

Sherman-Broyles, S., Boggs, N., Farkas, A., Liu, P., Vrebalov, J., Nasrallah, M.E. and Nasrallah, J.B. 2007. S locus genes and the evolution of self-fertility in Arabidopsis thaliana. Plant Cell 19, 94-106.

Tang, C., Toomajian, C., Sherman-Broyles, S., Plagnol, V., Guo, Y.L., Hu, T.T., Clark, R.M., Nasrallah, J.B., Weigel, D., and Nordborg, M. (2007). Evolution of Selfing in Arabidopsis thaliana. Science Jul 26; [Epub ahead of print]

Naithani, S., Chookajorn, T., Ripoll, D.R., and Nasrallah, J.B. (2007). Structural modules for receptor dimerization in the S-locus recepto kinase extracellular domain. Proc. Natl. Acad. Sci. USA 104: 12211-12216.

Nasrallah, J.B. 2005. Recognition and rejection of self in plant self-incompatibility: comparisons to animal histocompatibility. Trends Immunol. 26: 412-418.

Chookajorn, T., Kachroo, A., Ripoll, D.R., Clark, A.G., and Nasrallah, J.B. 2004. Specificity determinants and diversification of the Brassica self-incompatibility pollen ligand. Proc. Natl. Acad. Sci. USA 101: 911-917.

Click here for Dr. Nasrallah's PubMed listings.