Robert A. Owens
Dr. Robert A. Owens was born in Providence, Rhode Island. He obtained his B.Sc. degree in botany from the University of Rhode Island (1968) and a Ph.D. in biochemistry and biophysics from the University of California, Davis (1974). After post-doctoral studies at Columbia University, Dr. Owens joined the USDA’s Plant Virology Laboratory in Beltsville as a research chemist in 1975.
Building on experience obtained from studies of Dutch elm disease carried out under the direction of Drs. Frank Howard and Carl Beckman (University of Rhode Island), Dr. Owens began his research career as a graduate student at UC-Davis, where he demonstrated that the coat proteins of Cowpea mosaic virus are synthesized on cytoplasmic (and not chloroplast) ribosomes. These studies, carried out in the laboratory of George Bruening, highlighted the need to carry out in vitro translation studies with plant viral RNAs in cell-free extracts prepared from eukaryotic rather than prokaryotic cells. Post-doctoral studies in the Department of Biological Sciences at Columbia University focused on the synthesis of histone mRNAs in cell-free extracts of mammalian cells. Dr. Owens then joined the Viroid Investigation Program, headed by T. O. Diener, at the USDA’s Beltsville Agricultural Research Center. His early work focused on molecular mechanisms of viroid replication and resulted in the first cloning of cDNA molecules complementary to Potato spindle tuber viroid (PSTVd). These cDNAs were then used to create the first nucleic acid hybridization-based diagnostic test for viroids.
Dr. Owens is widely known for his pioneering studies on molecular detection of viroids. Soon after publication of the rapid and sensitive dot blot hybridization assay, he and colleagues began collaborations with the International Potato Center (CIP, Lima, Peru) and Agdia (Elkhardt, IN) aimed at integrating the assay into large-scale disease screening programs. In addition to eliminating PSTVd from the CIP breeding program, these longterm collaborations catalyzed the rapid adoption of dot blot and other nucleic acid-based diagnostic protocols worldwide. Results are now available in hours, rather than the days to months required for conventional bioassays or gel electrophoretic analysis, and offer greatly improved sensitivity. Later studies with Luis Salazar and colleagues at CIP have focused on a series of emerging disease problems threatening U.S. agriculture; accomplishments include identification of avocado as the first woody host for PSTVd, characterization of a whitefly-transmitted closterovirus (Potato yellow vein virus) as the causal agent of potato yellow vein disease, and screening U.S. potato varieties for resistance/tolerance to Potato mop top virus.
In 1983, Dr. Owens and colleagues reported that greater-thanunit-length cDNA copies of PSTVd were infectious, thereby opening the way for the application of reverse genetics to fundamental questions of viroid molecular biology. Subsequent mutational analyses, including the construction of novel viroid chimeras, have demonstrated the importance of different structural interactions for the ability of viroids to replicate and induce disease in vivo. Pathogenicity of PSTVd and related viroids was shown to be specified not by a single pathogenicity domain but by multiple genetic determinants distributed throughout the molecule. An early collaboration with colleagues at Calgene (Davis, CA) used infectious PSTVd cDNAs as reporter genes to monitor TDNA transfer from A. tumefaciens to susceptible plant hosts, thereby leading to various agroinfection strategies currently used to study gene expression and/or silencing.
As “obligate parasites of the cell’s transcriptional machinery,”Dr. Owens realized that viroids provide a rich source of molecular signals that could be used to redirect host gene expression. In the mid-1990s, a series of collaborative studies with Biao Ding (Ohio State University) as well as Rosemarie Hammond and Yan Zhao (Beltsville) used PSTVd replication to probe the pathways used by plant cells to transport RNA. This work capitalized on the absence of pathogen-encoded proteins, which makes viroids especially powerful tools to examine RNA import into the nucleus, movement from cell to cell via the plasmodesmata, and long-distance transport via the phloem. The studies showed that fusion with PSTVd sequences redirects RNA molecules to the nucleus and facilitates their movement through the plasmodesmata and that long-distance movement and viroid entry into uninfected host tissues is developmentally controlled. Similar studies led by Dr. Owens are currently underway to identify the signals used by other viroids to enter the chloroplast prior to replication, signals that could be used by plant biotechnologists to redirect mRNAs from the cytoplasm to the chloroplast and greatly increase the amount of protein synthesized.
Dr. Owens’ focus on fundamental viroid molecular biology has been accompanied by a consistent determination to apply the knowledge gained to urgent disease problems. In addition to his long-term collaborations with both CIP and the private sector, Dr. Owens’ expertise and impartiality proved essential to efforts to resolve a 1996 U.S.-Canada dispute that threatened the ability of Maine growers to export their seed potatoes to Canada. A letter from the commissioner of the Maine Department of Agriculture, Food, and Rural Resources documented his contributions to preserving the $30 million Maine seed potato industry. More recently, RT-PCR protocols developed by Dr. Owens have improved the ability of Florida’s Bureau of Citrus Budwood Registration to detect viroid infections, and field studies have been initiated to evaluate the potential of viroid-induced dwarfing to improve the competitive position of Florida citrus producers.
Dr. Owens’ achievements have established him as a national and international authority and leader in the field of plant pathology and viroid research. His laboratory has attracted a series of post-doctoral scientists, U.S. and foreign visiting scholars, and graduate students. An invited participant in numerous national and international meetings and coauthor of an undergraduate virology text, Dr. Owens has also served as international expert and member of NRI, NSF, BARD, and USAID grant review panels and has assisted young faculty members embarking upon careers in viroid research. A past member of the editorial board of Virology, he currently serves on the editorial board of Virus Genes and reviews manuscripts for several other virology journals, Phytopathology, and Plant Disease.
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