Resistance to turnip crinkle virus in Arabidopsis is regulated by two hostgenes and is salicylic acid dependent but NPR1, ethylene, and jasmonate independent

Inoculation of turnip crinkle virus (TCV) on the resistant Arabidopsis ecot ype Dijon (Di-17) results in the development of a hypersensitive response ( HR) on the inoculated leaves. To assess the role of the recently cloned HRT gene in conferring resistance, we monitored both HR and resistance (lack o f viral spread to systemic tissues) in the progeny of a cross between resis tant Di-17 and susceptible Columbia plants. As expected, HR development seg regated as a dominant trait that corresponded with the presence of HRT. How ever, all of the F-1, plants and three-fourths of HR+ F-2 plants were susce ptible to the virus. These results suggest the presence of a second gene, t ermed RRT, that regulates resistance to TCV. The allele present in Di-17 ap pears to be recessive to the allele or alleles present in TCV-susceptible e cotypes. We also demonstrate that HR formation and TCV resistance are depen dent on salicylic acid but not on ethylene or jasmonic acid. Furthermore, t hese phenomena are unaffected by mutations in NPR1. Thus, TCV resistance re quires a yet undefined salicylic acid-dependent, NPR1-independent signaling pathway.