Mechanisms of resistance to viruses

Resistance associated with a hypersensitive response (HR) and subsequent development of necrotic lesions (cell death) at the sites of virus infection can restrict virus movement in plants. Genes for HR are dominant and act on a gene-for-gene basis. Many viral proteins triggering HR have been identified. Also, several genes for HR-based virus resistance, or virus-induced cell death without resistance, have been isolated and characterized in plants, which provides novel insights to the mechanisms of virus resistance. Another international, major research frontier has formed more recently around RNA silencing, a universal RNA surveillance system and inducible virus defence mechanism in multicellular organisms. Many viral proteins interfere with different phases of RNA silencing. The data provide novel insights to break-down of resistance in mixed virus infections (viral synergism), resistance to virus movement, and recovery of plants from virus infection.