Characterization of resistance to tombusvirus in nicotiana species

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract, appears in the public.pdf file.Title from PDF of title page (University ofMissouri--Columbia, viewed on January 25, 2011).Thesis advisor: Dr. James E. Schoelz.Vita.Includes bibliographical references.Ph. D. University of Missouri--Columbia 2009.Dissertations, Academic -- University of Missouri--Columbia -- Plant pathology.Our lab studies resistance to tombusviruses such as Tomato bushy stunt virus (TBSV), Cymbidium ringspot virus (CymRSV), and Cucumber necrosis virus (CNV) in Nicotiana species, according to the ''gene for gene'' model, which requires the recognition between a plant resistance (R) gene and a viral avirulence (Avr) gene, resistance that is commonly associated with a hypersensitive response (HR). Previously, we introgressed a dominant resistance from N. glutinosa into N. clevelandii, and showed that the R gene against tombusviruses could be a member of the N family of R genes, but distinct from it. In this study, I found 15 groups of N gene homologs in these Nicotiana species, and hypothesized that one of these is the tombusvirus R gene. A screen of 22 Nicotiana species that belong to 10 out of 14 sections of the Nicotiana genus showed that 18 species were resistant, 13 of them with HR. The tombusvirus P22 proteins triggered HR in N. glutinosa, N. edwardsonii, and N. forgetiana TW50, whereas the P19 protein elicited HR in N. tabacum, N. sylvestris, and N. bonariensis. To identify other tombusvirus genes that might act as Avr genes, I tested the TBSV replicase p33 and p92 genes and the coat protein p41 gene. The coat protein gene elicited HR in most species within the Alatae section. I suggested there are at least five R genes against tombusviruses, and showed that agroinfiltration is a powerful technique to screen not only a diversity of plant species as sources for R genes to study their evolution, but also to express viral genes as possible Avr determinants