Susceptibility to recombination rearrangements of a chimeric plum pox potyvirus genome after insertion of a foreign gene

Infectious RNA transcripts were generated from a chimeric cDNA clone of the plum pox potyvirus (PPV) genome containing the bacterial beta-glucuronidase (GUS) gene inserted between the sequences coding for the pi and HC proteins. An artificial cleavage site specific for the NIa viral proteinase was engineered between the GUS and HC sequences to produce free GUS and HC proteins. The resulting virus PPVGus down arrow was stably maintained during the first round of infection, although plants remained symptomless and virus accumulation was delayed with respect to wild-type infection. PPVGus down arrow deleted variants, missing between 645 and 1779 nt, were detected in a subsequent plant passage. PPVGus down arrow deletions were confined inside the GUS gene, never affecting the pi and HC coding regions, in contrast with previous reports of deletions in other potyvirus-based vector, in which deletions frequently reached the HC gene. These results suggest that the N-terminus of the PPV HC protein may be essential for virus viability. Analysis of the deletion endpoints showed short stretches of similarity in donor and acceptor RNAs, as well as oligo A tracts conserved in most junction sites, suggesting that deletions in PPVGus down arrow might take place by similarity-assisted recombination events. (C) 1998 Elsevier Science B.V. All rights reserved.