Interfering with viral infection. Plants Do it too

Viruses can be classified into taxa according to any number of criteria: whether the viral genome consists of DNA or RNA, and whether it is singleor double-stranded; the existence and nature of RNA intermediates that are required for viral replication; the variety of proteins that house or otherwise associate with the virion genome and whether the protein coat is in turn surrounded by membrane; virion size; and host range. Clearly, these characteristics can be interrelated. Indeed, they all reflect the basic viral strategy of invading the host cell so as to exploit the macromolecular and enzymatic machinery that is unique to the intracellular milieu of the living organism. Because viral infections are generally deleterious to invaded cells, host organisms have evolved a variety of mechanisms that combat viruses. The vertebrate immune system generates, in addition to specialized cells that directly attack viruses and infected cells, a battery of secreted immunoglobulin molecules that is sufficiently diverse to neutralize a broad spectrum of viral antigens. In contrast to animal systems, a general barrier to viral infection is afforded by the cell walls of plants and bacteria. Correspondingly, viruses have evolved a variety of elegant strategies to exploit, for their own purposes, the very molecular defenses that the host may use to ward off viral entry into cells. (The human immunodeficiency virus, utilizing the CD4 membrane protein to specifically bind to and infect leukocytes, exemplifies viral abilities to directly usurp host proteins.) And once it has circumvented obstacles to entering the host cell, the virus pursues an intracellular agenda that involves uncoating, the synthesis of proteins and nucleic acids necessary for genome replication and intercellular moveInterfering with Viral Infection: Plants Do It Too