Plants transformed with a region of the 201-kilodalton replicase gene from pea early browning virus RNA1 are resistant to virus infection.

The 3' proximal portion of the gene encoding the 201-kDa putative replicase protein from the Tobravirus pea early browning virus (PEBV) can potentially be expressed separately as a 54-kDa protein. Nicotiana benthamiana plants transformed with the open reading frame (ORF) encoding the 54-kDa protein, designated 54K ORF, were resistant to infection by purified PEBV at inoculum doses of up to 1 mg/ml, the highest concentration tested. However, resistance was abolished by the introduction into the 54K ORF of mutations that would cause premature termination of translation. This suggests that the resistance mechanism requires the involvement of an intact 54-kDa protein. The 54K ORF-transformed plants were also resistant to infection by broad bean yellow band virus and an uncharacterized isolate of British PEBV (PGRO R) but were not resistant to infection by two other tobraviruses, pepper ringspot virus and the I6 isolate of tobacco rattle virus. Additionally, two variants of PEBV which overcame 54K ORF-mediated resistance have been isolated, the analysis of which might provide important information about both the resistance mechanism itself and the process of normal virus replication.