Host gene-mediated virus resistance mechanisms and signaling in Arabidopsis

Plants resist viral infections either via an active mechanism, involving the participation of resistance (R) genes and subsequent signal transduction pathways, or in a passive manner, which entails the absence of essential host factors required for replication or movement of the virus. An active resistance response involves strain-specific recognition of a virus-encoded elicitor, through direct or indirect interaction with the corresponding R gene product. This in turn activates downstream signaling, which leads to prevention of viral spread and confers resistance against the pathogen. An R gene-mediated recognition of virus often turns on defense responses such as the accumulation of salicylic acid (SA), the expression of pathogenesisrelated (PR) genes, and the development of a hypersensitive response (HR) on the inoculated leaves. The HR is defined by necrotic lesion formation at the site of infection and is thought to help prevent multiplication and movement by confining the virus to the region immediately surrounding the necrotic lesions.