NICOTIANA BENTHAMIANA PLANTS TRANSFORMED WITH THE COMPLETE PREREADTHROUGH DOMAIN OR THE NPROXIMAL REGION OF THE REPLICASE GENE FROM CYMBIDIUM RINGSPOT VIRUS RNA ARE RESISTANT TO VIRUS INFECTION
M. Russo, R. Lupo, P. Ciuffreda, L. Rubino
Nicotiana benthamiana plants were transformed with sequences derived from the 5’-terminal open reading frames (ORF 1 and 2) of the cymbidium ringspot tombusvirus (CymRSV). These sequences included the pre-readthrough region of the replicase or its N-terminal region, the readthrough domain, and the full-length replicase gene in which the stop codon of ORF 1 was abolished. Some lines transformed with the first two sequences showed complete resistance when challenged with CymRSV. Experiments using protoplasts from resistant lines showed that the resistance operates at the single cell level by abolishing viral replication. Lines resistant to CymRSV were susceptible to two other tombusviruses, artichoke mottled crinkle and carnation Italian ringspot. These data and the lack of correlation between transgene expression and resistance would suggest this to be a form of RNA-mediated resistance. Since resistant lines were only found among those transformed with sequences involved in the build-up of the virus replication complex, it is suggested that resistance may be due to the interference of these sequences with those of the infecting virus.