Replication of Cowpea Mosaic Virus RNA1 or RNA2 Is Specifically Blocked in Transgenic Nicotiana benthamiana Plants Expressing the Full-Length Replicase or Movement Protein Genes. Titia Sijen. Department of Molecular Biology, Wageningen Agricultural University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands. Joan Wellink, Jeanine Hendriks, Jan Verver, and Ab van Kammen. Department of Molecular Biology, Wageningen Agricultural University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands. MPMI 8: 340-347. Accepted 20 January 1995. Copyright 1995 The American Phytopathological Society.

Nicotiana benthamiana plants were transformed with either the cowpea mosaic virus (CPMV) RNA2-derived movement protein gene or the RNA1-originating replicase gene. For both types of genes, half of the R2-generation lines showed complete resistance when challenged with CPMV. Experiments using protoplasts revealed that the resistance operates at the single cell level by specifically preventing replication of the RNA segment, from which the transgene was derived. In both cases, the resistance acts against wild-type strain CPMV-Sb and the very homologous CPMV-S1 and CPMV-S8 strains, but not to other comovirus species including cowpea severe mosaic virus (CPSMV). These data and the inability to detect transgene-encoded proteins, suggest an RNA-mediated nature of the resistance.