Andrew O Jackson

Professor
Ph.D.  University of Manitoba , 1970
  

381 Koshland Hall
Berkeley, California 94720
andyoj@berkeley.edu
office: 510-642-3906   lab: 510-642-8042   fax:  510-642-4995

     Recent publications      People

Our research goals are to understand how viruses elicit plant diseases and to devise mechanisms for disease control in transgenic plants. Two viruses with distinct strategies of replication are currently being emphasized in these studies. These include a negative strand plant rhabdovirus, sonchus yellow net virus (SYNV) that replicates in the nucleus, and a tripartite plus sense RNA virus, barley stripe mosaic virus (BSMV) that replicates in the cytoplasm.

Genetic and biochemical analyses are being used to investigate the replication and movement of these viruses and to determine virus-host interactions culminating in disease. Each of the viruses engages in unique host associations during infection, and each virus gene has multiple roles in pathogenesis and mediates different host responses. Molecular genetic approaches and cytological studies used to follow infection processes are providing new information about the mechanisms of interactions with host cellular components during infection.

We have a major effort focused on studies of the plant rhabdoviruses. SYNV, the model system used for these studies, has a number of characteristics similar to those of rhabdoviruses that cause diseases of invertebrates and vertebrates. The rhabdoviruses have bacilliform or bullet-shaped particles consisting of an envelope surrounding an internal nucleocapsid core that contains the negative sense genomic RNA. The animal rhabdoviruses replicate in the cytoplasm and the best studied example, vesicular stomatitis virus (VSV) encodes five proteins. However, SYNV differs from VSV by replicating in the nucleus and by encoding a sixth gene that is required for cell-to-cell movement of nucleocapsids. Three of the common proteins (designated N, P, and L) form the nucleocapsid core, which has an RNA-dependent-RNA-polymerase (RdRp) activity that functions in transcription of mRNAs and replication of the viral genomic and antigenomic RNAs. Virus particles also contain a matrix protein that coils the nucleocapsid and a surface glycoprotein that spans the viral envelope to associate with the matrix protein and the nucleocapsid core.



We have shown that large subnuclear inclusions are formed during SYNV infection of plants and that these inclusions are the sites of viral replication. We have isolated an RdRp complex from the nuclei of infected plants, and have shown that the complex contains the N, P and L proteins plus the genomic RNA. Plant and yeast cells have been used to characterize this complex by investigating the interactions of the virus and host proteins required for establishment of the subnuclear replication site. Our studies show that homologous and heterologous interactions of the N and P proteins are required for formation of the subnuclear viroplasms, and that nuclear localization of the N and P proteins requires interactions with different nuclear import proteins.



We are also attempting to construct biologically active derivatives that can be used for genetic analyses of replication and pathogenesis. This is a challenging task because the nucleocapsid is the minimal unit of infectivity and must be assembled in cells in order to jumpstart replication.

A second, long-term effort of the lab focuses on the study of the biological properties of the hordeiviruses, exemplified by BSMV. Hordeivirus genomes consist of three positive sense RNAs designated ?, ?, and ?. Using biologically active clones for genetic analyses, we have shown that each of the seven genes encoded by the virus contribute to pathogenesis, and that the regulation of these genes and differences in their structure have profound effects on the disease phenotype in barley and other cereals, as well as Nicotiana benthamiana, and Chenopodium species.

Two distinct gene products encoded by RNAs α and γ are required for formation of the RdRp that associates with chloroplast outer membrane vesicles to form sites of viral replication. BSMV is distinct from many other viruses in that the coat protein is dispensable for the cell-to-cell and vascular movement functions. These functions require each of three proteins encoded in a triple gene block (TGB) on RNAβ Our studies have shown that the relative abundance of the TGB proteins is important for cell-to-cell movement and that the levels of the proteins are coordinated by transcription of two subgenomic messenger RNAs and unusual translational mechanisms.

Ectopic expression of various combinations of the TGB proteins is being used to probe their subcellular localization and to provide models for cell to cell movement of a nucleoprotein complex that can be recovered from infected plants. Pathogenicity functions of the hordeiviruses are mediated by a seventh protein, γb that is translated from a subgenomic mRNA derived from RNAγ. The γb protein has N-terminal zinc finger and C-terminal coiled coil motifs whose mutations result in several distinctive disease phenotypes. RNA binding activities mediated by the zinc finger motif and protein-protein associations of γb are also critical for functions of γb that result in suppression of host silencing defenses.

Jackson AO, Dietzgen RG, Goodin MM, Bragg JN, Deng M. Biology of plant rhabdoviruses. Annu Rev Phytopathol. 2005;43:623-60.

Bragg JN, Lawrence DM, Jackson AO. The N-terminal 85 amino acids of the barley stripe mosaic virus gammab pathogenesis protein contain three zinc-binding motifs. J Virol. 2004 Jul;78(14):7379-91.

Johnson JA, Bragg JN, Lawrence DM, Jackson AO. Sequence elements controlling expression of Barley stripe mosaic virus subgenomic RNAs in vivo. Virology. 2003 Aug 15;313(1):66-80.

Goodin MM, Dietzgen RG, Schichnes D, Ruzin S, Jackson AO. pGD vectors: versatile tools for the expression of green and red fluorescent protein fusions in agroinfiltrated plant leaves. Plant J. 2002 Aug;31(3):375-83.

Qiu, W.P., Park, J.-W., Jackson, A.O., and Scholthof, H.B. (2001) Retention of a small replicase gene segment in Tomato bushy stunt virus defective RNAs inhibits their trans-replication by the helper virus. Virology 281; 51-60.

Lawrence, D. M. and Jackson, A. O. (2001). Requirements for cell to cell movement of barley stripe mosaic virus in monocot and dicot hosts. Mol. Plant Path. 2: 65-75.

Lawrence, D. M. and Jackson, A. O. (2001). Interactions of the TGB1 protein during cell to cell movement of barley stripe mosaic virus. J.Virol. 75: 8712-8723.

Goodin, M. G. Austin, J., Tobias, R., Fujita, M., Morales, C. and Jackson, A. O. (2001). Interactions and nuclear import of the n and p proteins of sonchus yellow net virus, a plant nucleorhabdovirus. J. Virol. 75:9393-9406.