Our research focuses on three main projects: genetic transformation of plant cells by Agrobacterium, intercellular transport of plant viruses and plant cell proteins, and remodeling of plant chromatin by histone modifications.
The first two projects utilize plant pathogens—which pirate the host cellular pathways for their life cycles—as molecular tools to study fundamental questions in plant biology. The third project examines how plant genes are regulated by histone-modifying corepressor complexes.
Plant Genetic Transformation
In our studies of Agrobacterium, a unique bacterium capable of transfer of genetic material between prokaryotic and eukaryotic cells, we are identifying and characterizing the involvement of basic cellular systems—such as nuclear import machinery, targeted proteolysis machinery, targeting of multiprotein complexes to the cell chromatin, and DNA repair machinery—in the nuclear and intranuclear transport and integration of the invading T-DNA. Also, we are studying bacterial effectors that interact with these plant systems and may mimic some of their functions. We are especially interested in those effectors that are exported into the host cell and subvert its defense responses for the benefit of the invading pathogen. Consistent with the basic, evolutionarily-conserved nature of the host processes required for genetic transformation by Agrobacterium, we demonstrated that this plant pathogen can in fact genetically transform human cells.
Plant Intercellular Transport
In our studies of intercellular movement of plant viruses, we discovered that viral genomes most likely travel between cells as subviral complexes composed mainly of the viral genomic molecule and the viral cell-to-cell movement protein. We are identifying and characterizing cellular proteins that interact with the viral movement protein and likely regulate the process of the viral transport through plant intercellular connections, the plasmodesmata. Specifically, we focus on the viral and host control of the plasmodesmal callose sphincters that can constrict and relax these cell-to-cell channels.
We are also studying the structure, composition, and function of plant corepressor complexes involved in histone modification and chromatin remodeling. Histone modification represents a universal mechanism for regulation of eukaryotic gene expression that underlies such diverse biological processes as restriction of expression of neuronal genes to neurons in mammals and control of flowering in plants. In animal cells, these chromatin modifications are effected by well-defined multiprotein complexes containing specific histone-modifying activities. In plants, information about composition of chromatin-modifying corepressor complexes is just beginning to emerge. We are systematically identifying protein components of plant corepressor complexes, study their interactions in vivo, analyze their effects on histone methylation, acetylation, and ubiquitination, and employ reverse genetics to characterize the target genes of the corepressor complexes and their roles in plant development and morphogenesis.
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