Deletions in the 3' untranslated region of cowpea chlorotic mottle virus transgene reduce recovery of recombinant viruses in transgenic plants.

The 3' untranslated region (UTR) adjacent to the capsid gene is frequently included with the transgene in the construction of capsid protein mediated virus resistant transgenic plants. Since ribonucleotide sequences within the 3' UTR are involved in the initiation of viral replication, the presence of this sequence may encourage the participation of the transgene in RNA recombination. Experiments were designed to explore the involvement of the 3' UTR of cowpea chlorotic mottle virus (CCMV) in RNA recombination events between transgenes and challenging viruses. Nicotiana benthamiana was transformed with CCMV transgenes consisting of the 3' two-thirds of the capsid gene and fragments of the associated 3' UTR lacking the terminal 69, 83, or 214 nucleotides. Plants were inoculated with wild-type CCMV transcripts for RNAs 1 and 2 and a movement defective RNA 3 transcript lacking the 3' third of the capsid gene. While no recombinant virus was detected in plants expressing 3' deletion constructs, 3% of control transformants containing an identical segment of the capsid gene with the complete 3' UTR yielded viable recombinant virus. These results suggest that RNA recombination between transgenic RNA and viral RNA can be reduced significantly by omitting or disrupting the 3' UTR in the transgene.