Examination of host genetic determinants of the hypersensitive response in Nicotiana edwardsonii to CaMV and TMV

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The hypersensitive response (HR) is an indicator of genetic resistance when screening for disease resistance to viral pathogens. Genetic resistance has been described as having two characteristics: rapid cell death at the site of inoculation and localization of the pathogen to that site. I examined a resistant Nicotiana hybrid, which does not respond with HR-mediated cell death, yet maintains resistance to Cauliflower mosaic virus (CaMV) strain W260. Another host gene, CCD1, blocks both HR-mediated and systemic cell death induced specifically by P6 of CaMV strain W260. Interfering double stranded RNA (RNAi) technology has proven to be a very effective way to silence a single gene in plants. With the design and construction of gene silencing hairpins homologous with known conserved sequences of identified R genes, it is possible to silence large families of R genes. Examination of the HR in these silenced plants can identify putative resistance genes. With these silencing hairpins, I showed that the endogenous N gene can be silenced with both constructs. Additionally, resistance to another virus, Tomato bushy stunt virus (TBSV), breaks down in the silenced plants. This is evidence that not only the N gene can be silenced, but also that resistance genes that differ from the N gene by as much as 10% can also be silenced when homologous sequences are used.