Genomic Basis of Plant Immunity and Recovery from Viruses

Models of genome evolution predict that quantitative pathogen resistance is acquired slowly in geographies subjected to pathogen pressure but with punctuated epochs of gain, such as when a tetraploid is formed from two moderately resistant diploids. We aimed to characterize the genomic basis of virus resistance using plants from diverse geographic regions, ploidy levels, and in interspecific hybrids using the Nicotiana-nepovirus interaction as a model. To this end, we inoculated a panel of diverse Nicotiana species and interspecific hybrids with Grapevine fanleaf virus (GFLV) strains GHu and F13, and Tomato ringspot virus (ToRSV) strain AP. We tested inoculated and apical leaves for virus presence, and assessed systemic acquired resistance in a subset of recovered plants. Depending on the virus-host combination used, plants exhibited resistance profiles ranging from immunity to complete susceptibility, and four intermediate resistance phenotypes were defined. Based on an incompletely dominant resistance phenotype in F₁ interspecific hybrids and the manifestation of systemic acquired resistance in recovered plants, we conclude that Nicotianae resistance to nepoviruses is characterized by degrees of innate immunity and systemic acquired resistance additively inherited. While ploidy level was not a factor in nepovirus resistance, there was a relationship between resistance and geographical origin. We will discuss these findings in light of models of resistance evolution.