My research focuses on molecular plant-virus interactions. Areas of interests include gene expression and replication and RNA and DNA viruses, mechanisms of plant resistance to viral infections and resistance-breaking by RNA viruses, recombination, and evolution of RNA viruses.

Replication of RNA viruses depends on an RNA-dependent RNA polymerase consisting of virus- and host-encoded protein subunits. The replicase of red clover necrotic mosaic virus (RCNMV) has been purified in my laboratory. And the virus-encoded replicase subunits are being expressed in bacterial and baculovirus expression systems. Our long term goal is to identify novel molecules (such as peptides) that can either disrupt the assembly or block the function of viral RNA replicases.

Recombination between RNA viruses and viral sequences expressed in transgenic plants is being addressed by another research project. We continue to investigate the recombination between transgenically expressed RCNMV RNA-2 lacking a functional 5' terminus and an infecting RNA-1.

A virus unique to the Sonoran Desert, saguaro cactus virus (SCV), has been intensively studied. The complete sequence of the small RNA viral genome has been determined. The gene expression of SCV is being characterized by in vitro translation studies of viral subgenomic RNAs and in vitro RNA transcripts. With the infectious cDNA clones that have recently been developed, SCV has become an excellent model system to study viral gene expression and replication.

Currently, we are also investigating the molecular mechanisms of plant resistance and the breakdown of the resistance by viral mutations, using potato virus Y (PVY) as a model system. Mutants of PVY generated from a single passage through a host plant have been shown to overcome a previously resistant host.

Weng, Z., and Xiong, Z. 1995. A method for accurate determination of terminal sequences of viral genomic RNA. Genome Res. 5, 202-207

Xiong, Z., and Lommel, S. A. 1993. The role of the red clover necrotic mosaic virus capsid and cell-to-cell movement proteins in viral infection. Virology 192, 27-32.

Xiong, Z., Kim, K., and Lommel, S. A. 1993. Synthesis of the putative red clover necrotic mosaic viurs RNA polymerase by ribosomal frameshifting in vitro. Virology 193, 213- 221.

Xiong, Z., and Lommel, S. A. 1991. Red clover necrotic mosaic virus infectious transcripts synthesized in vitro. Virology 182, 388-392.

Sudarsono, Woloshuk, S. L., Lommel, S. A., Xiong, Z., Hellmann, G. M., Wernsman, E. A., and Weissinger, A. K. 1993. Nucleotide-sequence of the capsid protein cistrons from 6 potato virus-y (pvy) isolates infecting tobacco. Archives of Virology 132, 161- 170.

Lommel, S. A., Kendall, T. L., Xiong, Z., and Nutter, R. C. 1991. Identification of the maize chlorotic mottle virus capsid protein cistron and characterization of its subgenomic messenger RNA. Virology 181, 382-385.

Xiong, Z., and Lommel, S. A. 1989. The complete nucleotide sequence and genome organization of red clover necrotic mosaic virus RNA-1. Virology 171, 543-554.

Xiong, Z., Hiebert, E., and Purcifull, D. E. 1988. Characterization of the peanut mottle virus genome by in vitro translation. Phytopathology 78, 1128-1134.