Wheat, oats, rice, and other cereal grains are key pillars of human societies worldwide. Along with other members of the grass family, these plants provide the majority of the calories humans eat, either directly as grains or indirectly as meat and milk produced by grazing animals. Unfortunately, these important grasses are plagued by several families of plant viruses, including the barley and cereal yellow dwarf viruses, which damage cereal grain production worldwide. These viruses also harm wild grasses and can advance the spread of invasive species in nature. How have influential viruses like these emerged and what factors have contributed to their spread and diversification? To find clues about virus history, the project team will recover and analyze genetic sequences of old viruses preserved within historical collections of dried plants around the world. Phylogenetic analysis of the viruses will reveal how these viruses have spread over time and permit estimates of dates of key events in their history. The research will also provide information on the influence of humans on the spread of plant viruses.
Human development of agriculture and global trade are two factors that have likely influenced the emergence and spread of potent viruses. This research will provide missing information about virus dynamics in the past and produce new insight into the ways by which human activities influence the development of virus threats. The project?s broader impact will include training of educators and students from underrepresented groups, contributions to microbial ecology outreach efforts through a science museum, and the addition of information about virus relationships to curated plant collections.
Many fear viruses because some, such as influenza virus have been known to mutate frequently to more infectious forms. Yet, there is also reason to believe that, despite these frequent mutations, viruses evolve slowly, at the same pace as their host organisms. Reconciling fast and slow rates of virus evolution, would be facilitated by availability of viruses of yesteryear. In this project, the investigators examined decades old grass specimens in herbaria and found that they contain evidence of the presence of viruses related to present-day luteoviruses. These viruses, besides infecting grain crops, alter the composition of grasses in our grasslands. That the virus sequences were indeed old was concluded from two observations. The old sequence had more changes from C residues to U residues in their virion RNA strands than are found when pairs of present day sequences are compared. C deamination to U is a known slow chemical instability of RNA genome nucleotides. The second observation rests on comparison of the old sequences with those of present-day related viruses. The old viruses studied were related to two viruses we know about. The genome of one current virus was similar to one half of the old virus with a second contemporary virus being most related to the other half. There are no extant examples of the hypothesized arrangement of the old viruses. This observation suggests that modern viruses arose by exchange between viruses that no longer exist today. In the process of conducting this research at Oklahoma State University, one female graduate student obtained training and mentoring which is leading to a PhD degree and continued involvement in virus evolution studies in 2015. In addition, numerous undergraduate students, mostly female obtained undergraduate research experiences working on the project.
