Evidence that badnavirus infection in Musa can originate from integrated pararetroviral sequences

When some virus- and disease-free Musa spp. (banana and plantain) are propa gated by tissue culture, the resulting plants develop infections with banan a streak badnavirus (BSV), a pararetrovirus. In sharp contrast to the virio n DNA recovered from natural infections, the Virion DNA from tissue culture -associated infections of different Musa spp. was highly similar if not ide ntical. Although BSV does not employ integration during the infection cycle , BSV DNA was found to be integrated Into the Musa genome. While one integr ation consisted of a partial BSV genome, a second contained more than one c omplete genome that was almost identical to BSV recovered from tissue cultu re-derived plants. The arrangement of this integrated BSV DNA suggests that it can yield an infectious episomal genome via homologous recombination. T his report documents the first instance of integrated DNA of a nonintegrati ng virus giving rise to an episomal viral Infection and identifies tissue c ulture as a possible trigger for the infection, raising the question of whe ther similar activatable viral sequences exist in the genomes of other plan ts and animals. (C) 1999 Academic Press.