Plant Pathogens: RNA viruses

Abstract

Most viruses infecting higher plants have RNA genomes. These include viruses with genomes consisting of single-stranded positive-sense RNA, double-stranded RNA or negative-sense single-stranded RNA but, to date, no plant-infecting retroviruses have been discovered. Most plant viruses are transmitted by insects (predominantly probe-feeders such as aphids), whereas others are transmitted by nematodes and fungi. Plant viruses have evolved mechanisms to move around the host plant by exploiting the symplastic network of plasmodesmata (intercellular cytoplasmic bridges) and phloem (living vascular tissue). As with viruses infecting other eukaryotic hosts, plant-infecting RNA viruses have acquired adaptations to exploit the host cell’s protein synthesis machinery and membrane networks to express their proteins and replicate, respectively. Plant-infecting RNA viruses include important crop pathogens. Disease induction results from the interaction of specific viral proteins or nucleic acids with host targets, rather than from viral load per se. It is increasingly recognized that the disruption of RNA-silencing pathways in the host by virus-encoded counterdefense molecules is probably the most common mode of disease induction in virus-infected plants.