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Resistance to Potato Late Blight
Potato is the fourth most important food crop in the world, next only to rice, wheat, and corn.  We are investigating how potatoes have developed genetic resistance to late blight, a devastating disease caused by the oomycete pathogen Phytophthora infestans.  The first shock of devastation caused by P. infestans was the well-known “Irish Potato Famine”, which led to the death of approximately one million people through starvation and disease, with another million thought to have emigrated as a result of the famine.  Potatoes contain many resistance genes (R genes) against late blight and some of these genes have been investigated since 1950s.  Several of these R genes have been cloned recently.  However, most of these genes have been overcome by the pathogen at some point, and therefore no longer protect potatoes from the disease.  Our lab has cloned an R gene, termed RB (Song et al., 2003, PNAS), and noticed it behaves somewhat differently than other R genes.  Usually, if the pathogen has the corresponding avirulence gene to the potato R gene, the plant host cells will rapidly die, inhibiting the spread of the pathogen.  When late blight attacks a potato plant with the RB gene the pathogen is slowed down, but not completely eliminated.  We are interested in determining the function of the RB gene and how it regulates the potato defense to late blight.  The RB gene is particularly interesting because transgenic potatoes containing this gene have shown high levels of “broad-spectrum” resistance against all tested strains of P. infestans.  Our long-term goal is to understand the molecular mechanisms responsible for such a broad-spectrum resistance.  We are also using both transgenic and non-transgenic approaches to deploy the RB gene in potato cultivars.

Structure and Evolution of Plant Centromeres
The centromere is a cytologically defined entity with highly conserved functions: it is responsible for sister chromatid cohesion and is the site for the assembly of the kinetochore, a proteinaceous structure to which spindle fibers attach during cell division.  Although the functions of centromeres are conserved in all eukaryotes, the primary DNA sequence that underlies centromeres has no discernable conservation among model eukaryotes, which has been one of the most intriguing enigmas in biology.  We are interested in studying the structure, function, and evolution of plant centromeres.  One of our long-term goals is to develop plant artificial chromosomes consisting of cloned plant centromeric DNA by using maize and rice as models.  Our research work on maize centromeres is performed in collaboration with Dr. Kelly Dawe and Dr. Wayne Parrot at the University of Georgia, Dr. Jim Birchler at the University of Missouri, and Dr. Gernot Presting at the University of Hawaii, and is supported by a Plant Genome award from the National Science Foundation (http://www.plantcentromeres.org/).  Our research work on rice centromeres has been focused on the centromere of chromosome 8 (Cen8).  Centromeres from most multicellular eukaryotes are typically located in megabase-sized arrays of satellite repeats, making their precise mapping difficult.  In contrast, rice Cen8 contains a high percentage of single copy sequences, which has allowed its DNA sequence to be completely determined (Nagaki et al. 2004, Nat. Genet.).  We are currently studying the Cen8 from several wild rice species to understand the evolution of such a large and unique chromosomal domain (http://www.hort.wisc.edu/EGRC/).