Citovsky Pict.

Vitaly H. Citovsky

Assistant Professor
Dept. Biochemistry and Cell Biology

Ph.D., Hebrew University, Jerusalem
Postdoctoral research, University of California, Berkeley



NUCLEAR TRANSPORT AND INTERCELLULAR COMMUNICATION IN PLANTS

My laboratory uses plant systems to study two basic biological processes: (i) nuclear transport and (ii) intercellular communication.

I. Plant Nuclear Import

Drosophila Cells Pict.To study plant nuclear transport, we utilize import of Agrobacterium T-DNA into the host cell nucleus. Using this experimental system, we have identified two Agrobacterium proteins, VirD2 and VirE2, which form a complex with the transported T-DNA and target it to and through the nuclear pore. Our results indicate that nuclear import of VirD2 and VirE2 occurs by a specific pathway which is developmentally controlled. We also show that nuclear import of VirE2 is plant-specific and does not occur in animal cells; in contrast, VirD2 is imported into plant and animal nuclei with equal efficiency.  We are using VirD2 and VirE2 as molecular probes to characterize plant cell nuclear import, identify and purify its protein machinery, and distinguish its regulatory mechanisms.

Figure Nuclear import in heterologous systems (microinjected Drosophila embryos and Xenopus oocytes) and in isolated plant and animal cell nuclei are being used as experimental systems to assay plant proteins potentially involved in VirD2 and VirE2 nuclear transport.











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II. Plant Intercellular Communication

Communication between plant cells largely occurs via intercellular connections, the plasmodesmata. As an experimental system to study plasmodesmal transport and regulation, we are using a unique class of biological molecules known to specifically and dramatically alter plasmodesmal function: cell-to-cell movement proteins of plant viruses. Movement proteins interact with plasmodesmata to increase their size exclusion limit. We have shown that these proteins also cooperatively bind viral genomic nucleic acids and shape them into unfolded cell-to-cell transport complexes which can be translocated through the enlarged plasmodesmal channels. We are using plant virus movement proteins as tools to identify cellular proteins involved in plasmodesmal transport. We also are developing genetic assays to screen for Arabidopsis mutants with altered plasmodesmal permeability and/or defects in cell-to-cell movement of plant viruses. Ultimately, we plan to elucidate the molecular pathways for intercellular communication through plasmodesmata.

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Selected Publications:

Citovsky, V., De Vos, G., and Zambryski, P. (1988) Single-stranded DNA binding protein encoded by the virE locus of Agrobacterium tumefaciens. Science 240, 501-504.

Citovsky, V., Wong, M. L., and Zambryski, P. (1989) Cooperative interaction of Agrobacterium VirE2 protein with single stranded DNA: implications for the T-DNA transfer process. Proc. Natl. Acad. Sci. USA 86, 1193-1197.

Citovsky, V., Knorr, D., Schuster, G., and Zambryski, P. (1990) The P30 movement protein of tobacco mosaic virus is a single strand nucleic acid binding protein. Cell 60, 637-647.

Citovsky, V., Knorr, D., and Zambryski, P. (1991) Gene I, a potential movement locus of CaMV, encodes an RNA binding protein. Proc. Natl. Acad. Sci. USA 88, 2476-2480.

Citovsky, V., Wong, M.L, Shaw, A., Prasad, B.V.V., and Zambryski, P. (1992) Visualization and characterization of tobacco mosaic virus movement protein binding to single-stranded nucleic acids. Plant Cell 4, 397-411.

Citovsky, V., Zupan, J., Warnick, D., and Zambryski, P. (1992) Nuclear localization of Agrobacterium VirE2 protein in plant cells. Science 256, 1802-1805.

Citovsky, V., McLean, B.G., Zupan, J., and Zambryski, P. (1993) Phosphorylation of TMV cell-to-cell movement protein by a developmentally regulated protein kinase associated with the plant cell wall. Genes & Dev. 7, 904-910.

Citovsky, V. and Zambryski, P. (1993) Transport of nucleic acids through membrane channels: snaking through small holes. Annu. Rev. Microbiol. 47, 167-197.

Citovsky, V. (1993) Probing plasmodesmal transport with plant viruses. Plant Physiol. 102, 1071-1076.

Citovsky V., Warnick, D., and Zambryski, P. (1994) Nuclear import of Agrobacterium VirD2 and VirE2 proteins in maize and tobacco. Proc. Natl. Acad. Sci. USA 91, 3210-3214.

Guralnick, B. and Citovsky, V. (1995) Nuclear localization of Agrobacterium VirD2 and VirE2 proteins in Drosophila embryos. submitted.

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