Characterization of Cauliflower Mosaic Virus (CaMV) Resistance in Virus-Resistant Ecotypes of Arabidopsis. Anton CaIlaway. Boyce Thompson Institute, Tower Road, Cornell University, Ithaca, NY 14853, U.S.A. Wennuan Liu, Vyacheslav Andrianov, Laura Stenzler, Jianmin Zhao, Scott Wettlaufer, Prerana Jayakumar, and Stephen H. Howell. Boyce Thompson Institute, Tower Road, Cornell University, Ithaca, NY 14853, U.S.A. MPMI 9:810-818. Accepted 26 August 1996. Copyright 1996 The American Phytopathological Society.

Two Arabidopsis ecotypes are resistant to systemic infection by cauliflower mosaic virus (CaMV), a plant para-retrovirus. Arabidopsis ecotype Enkheim-2 (En-2) is highly resistant to CaMV infection while Bla-14 is more weakly resistant. CaMV resistance in En-2 can be largely attributed to the action of a single semidominant gene called cauliflower mosaic virus resistancel (CARI), located at a locus on chromosome 1. Resistance in Bla-14 is tightly linked to CAR1 and may be due to a weak allele at the same locus or another gene in a gene cluster. A quantitative polymerase chain reaction assay in conjunction with replication- and movement-incompetent viral mutants was used to determine whether virus replication or movement is affected in the resistant ecotypes. The pattern of accumulation of the wild-type virus in the resistant ecotype, En-2, was similar to that of a movement-incompetent CaMV mutant, suggesting that CAR1 interferes with or fails to support CaMV movement. CaMV-inocuIated En-2 plants do not show visible signs of a hypersensitive response. However, indicators of an induced defense response do appear in CaMV-infected En-2 plants, such as the activation of pathogenesis-related protein gene expression and the production of camalexin, an Arabidopsis1 phytoalexin. Defense responses induced chemically or by mutation in the susceptible ecotypes delayed and reduced the severity of a CaMV infection. These findings suggest that CAR1 acts either in the susceptible ecotype to support virus movement or in the resistant ecotype to signal a defense response.