SEQUENCE OF RNA-2 OF A NEMATODE-TRANSMISSIBLE ISOLATE OF TOBACCO RATTLE VIRUS

Tobacco rattle virus (TRV) isolate PPK20 is transmitted by Paratrichodorus pachydermus nematodes. The factor(s) determining vector transmissibility has been shown to be located on TRV RNA 2. Sequence determination revealed that PPK20 RNA 2 contains three open reading frames encoding the coat protein (cp) and proteins with molecular masses of 29.4 and 32.8 kDa. The 29.4 and 32.8 kDa protein-coding genes showed no significant sequence similarity to any other known tobravirus gene. A full-length cDNA of PPK20 RNA 2 cloned between the 35S promoter and nos terminator infected plants when co-inoculated with PPK20 RNA 1. Deletions in the reading frames of the 29.4 and 32.8 kDa proteins revealed that these sequences are dispensable for replication of PPK20 RNA 2 in plants. Subgenomic RNAs for translation of cp and the putative 29.4 and 32.8 kDa proteins were detected in infected leaves. The possible role of PPK20 RNA 2 nonstructural genes in TRV vector transmission is discussed.