The relationship of Resistance (R) gene-mediated defense to other forms of resistance in plants is considered, and the natures of the products of dominant and recessive R genes are reviewed. Various factors involved in expressing R gene-mediated resistance are described. These include phytohormones and plant effector molecules: the former regulating different pathways for disease resistance and the latter having direct effects on viral genomes or encoded proteins. Finally, the status of our knowledge concerning the cell-death hypersensitive response and its relationship to the actual resistance response involved in inhibiting virus infection is examined.
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