Replicase-derived resistance against Pea early browning virus in Nicotianabenthamiana is an unstable resistance based upon posttranscriptional gene silencing

Virus resistance in Nicotiana benthamiana plants containing a translatable Pea early browning virus (PEBV) 54K sequence from the 201K replicase gene h as been reported previously. Resistant plants contain multiple transgene co pies divided between two loci. Analysis of a genetic series containing the two loci in separate homozygous or heterozygous condition suggest that only one of the loci is necessary to induce the resistance. The resistance obse rved in R2 and R3 generations of lines containing both transgene loci in ho mozygous condition became less consistent in R4 and R5 generations. This in versely correlated with steady-state transgene transcript levels of the seg regating populations. The use of recombinant Potato virus X vectors carryin g PEBV 54K sequences showed that the resistance is based upon posttranscrip tional gene silencing, is non-strand specific, and recognizes 3' located se quences within the PEBV 54K sequence.