PLASMID VECTOR FOR CLONING INFECTIOUS CDNAS FROM PLANT RNA VIRUSES - HIGH INFECTIVITY OF CDNA CLONES OF TOMATO ASPERMY CUCUMOVIRUS

An improved version of the previously obtained cloning vector pCass wa s constructed by partially duplicating the 35S promoter used to drive the transient transcription of cloned viral cDNAs. Full-length cDNAs o f the three genomic RNAs of tomato aspermy cucumovirus (TAV) cloned in this improved pCass (designated pCass2) gave a 3-fold higher infectiv ity in two plant species tested than the same cDNAs cloned in pCass1 w ith only a single 35S promoter. Host range, symptoms, morphology of vi ral particles and viral progeny RNAs induced by these sets of infectio us cDNA clones analysed were identical to those induced by the wild-ty pe virus. A mutant of genomic TAV RNA 3 containing a 163 nt deletion i n the 3' untranslated region was stably maintained in the progeny RNAs , indicating that these cDNA clones may facilitate a study of virus fu nction. This is the first report of infectious cDNA clones of TAV as w ell as of infectious cDNA clones with a duplicated 35S promoter of CaM V.