Genetic RNA-RNA Recombination in Positive-Stranded RNA Viruses of Plants

Abstract

Plus-stranded (+) RNA viruses replicate without generating DNA intermediates. Nevertheless, like DNA-based organisms, they undergo evolution and adaptation to a new environment. The mechanisms involved in generating the diversity among (+) RNA viruses include such processes as high-frequency point mutagenesis, homologous and nonhomologous recombination between related RNA viruses, reassortment among multipartite RNA genomes, or crossings with cellular RNAs (King 1988; Strauss & Strauss 1988; Goldbach 1990; Lai 1992; Dolja & Carrington 1992). The nucleotide sequences of more than 100 viral (+) RNA genomes are available. This, surprisingly, revealed the modular nature of the assembly of their genome, among such sequence moduls as core RNA replicase genes, accessory genes, movement and capsid genes as well as cis-acting elements (Gibbs 1987; Zimmern 1988; Goldbach et al. 1991; Dolja & Carrington 1992). This supported the role of genetic recombination in virus evolution and maintenance. Both nonhomologous and homologous recombination events have been described for a limited number of animal and plant RNA viruses. In this chapter we review recombination studies in (+) RNA viruses with the emphasis put on plant RNA viruses.