Homologous Recombination and Gene Silencing in Plants

pp 25-38

Recombination of a Plant Pararetrovirus: Cauliflower Mosaic Virus

  • Thomas Hohn

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Although pararetroviruses have originally been classified as DNA viruses, they are closely related to retroviruses with respect to their genome organisation and their mode of replication. A pregenomic, terminally redundant RNA is reverse transcribed to yield ds DNA. A peculiarity of pararetroviruses is that open circular DNA is stored within mature virions and supercoiled DNA accumulates as mini-chromosomes in the nucleus (reviews: Bonneville et al. 1988; Covey 1991; Fütterer & Hohn 1991; Bonneville & Hohn 1993). Pararetroviruses are known from animals (hepadnaviruses) and from plants (isosahedral caulimoviruses and bacilliform badnaviruses). The best studied of the plant pararetroviruses is cauliflower mosaic virus (CaMV), the type member of caulimoviruses. Recombination of animal pararetroviruses (hepadnaviruses) has been observed only between integrated and non-integrated copies (Sprengel et al. 1987; Hino et al. 1991; Georgi-Geissberger et al. 1992).