|June Bowman Nasrallah
B McClintock Professor
Department of Plant Biology
260 Emerson Hall
Ithaca, NY 14853-2703
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
- 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.
- 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.
- Nasrallah, M.E., P. Liu, and Nasrallah,
J.B. 2002. Generation of self-incompatible
Arabidopsis thaliana by transfer of two S
locus genes from A. lyrata. Science 297: 247-249.
- Kachroo, A., Schopfer, C.R., Nasrallah,
M.E., and Nasrallah, J.B. 2001. Allele-specific
receptor-ligand interactions in Brassica
self-incompatibility. Science 293: 1824-1826.
- Schopfer, C.R., Nasrallah, M.E., and
Nasrallah, J.B. 1999. The male determinant
of self-incompatibility in Brassica. Science
- Stein, J.C., Howlett, B., Boyes, D.C.,
Nasrallah, M.E. and Nasrallah, J.B.
1991. Molecular cloning of a putative
receptor protein kinase gene encoded
at the self-incompatibility locus of
Brassica oleracea. Proc. Natl. Acad.
Sci. USA 88: 8816-8820.