Daphne Preuss

The University of Chicago

My research is aimed at identifying cellular components that mediate inheritance in plants, from the gene products that control reproduction to those that regulate DNA transmission. We are currently pursuing two distinct research programs: 1) characterizing the DNA signals that regulate centromere structure and function; and 2) identifying species-specific signals that control cell-cell interactions during pollination.
Centromere morphology has been characterized in many higher plants, and proteins that localize to distinct centromere domains have been identified, but far less is known of the mechanisms that regulate the assembly of those proteins onto precise sites on the DNA. Recently, we used the unique genetics available in Arabidopsis (see Preuss et al., Science 264:1458-1460) to map the regions that function as centromeres on all five chromosomes (Copenhaver, Browne and Preuss, 1998, PNAS 95: 247-252). Using genetic markers as anchors, we assembled physical maps covering the unique DNA within each centromere, (Copenhaver et al., Science 286:2468-2474). The efforts of sequencing teams at TIGR, Cold Spring Harbor, and Washington University yielded DNA sequences that nearly span two centromeric intervals. Within the next year, extensive sequence characterization of all five Arabidopsis centromeres will be obtained. Our work is serving as a model for the genome projects of other higher eukaryotes, which have now begun to consider large-scale sequencing of centromeric regions. Consequently, the field can begin to address a long standing question in centromere biology: Why do centromeric sequences appear to evolve rapidly, despite the conserved nature of centromere functions? To address this question, we have begun exploring the diversity and evolution of centromeric sequences. We are forming collaborations, such as this one, with others interested in plant phylogenetics, with the goal of determining whether syntenic regions, common to higher centromeres, can be identified. In addition, we have begun exploring sequence divergence of centromeres, first among twenty different varieties of Arabidopsis, and subsequently, among other closely related species. Importantly, by analyzing the secondary structure of Arabidopsis centromeres, we have defined signatures that allow us to purify and sequence centromere DNA from other species, avoiding the arduous genetic mapping that was necessary in Arabidopsis. Through these efforts, we plan to determine which centromeric regions are responsible for high-fidelity inheritance.

Over the past several years, my laboratory has also identified many genes that control species-specific communication between plant reproductive cells. We recently demonstrated that pollen adhesion depends on a species-specific lipophilic adhesive that generates a remarkably strong binding force between pollen grains and female cells (Zinkl et al., Development, 126: 5431-5440). We have also investigated pollen recognition, and have identified pollen surface proteins that play role in mate selection (Mayfield and Preuss, Nature Cell Biology 2:128-130). Interestingly, these proteins diverge rapidly through evolution; such diversity may hold the key to understanding a potential mechanism for plant speciation.

As the sequence of the Arabidopsis genome unfolds, the community is shifting from gene-discovery to determining gene functions. In anticipation of the availability of a complete genome sequence my laboratory has begun conducting large-scale screens to identify genes required for species-specific interactions during reproduction. We will use these technological advances to significantly accelerate the pace of our research, enabling us to rapidly identify genes required for this unique signaling pathway. Ultimately, we expect to not only unravel the code that identifies each pollen grain as belonging to a particular species, but also to understand the diverse signaling events that facilitate plant reproduction.