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5′-Terminal stem-loop of carnation ringspot virus RNA1 is required for the efficient amplification of viral RNAs

Kaido, Masanori, Nagano, Hideaki, Omote, Kazunori, Takano, Yoshitaka, Mise, Kazuyuki, Okuno, Tetsuro
Virus research 2019 v.265 pp. 138-142
Carnation ringspot virus, Nicotiana, complementary DNA, leaves, messenger RNA, mutants, nucleotides, pathogenicity, prototypes, viruses
Carnation ringspot virus (CRSV) is the prototype virus of the genus Dianthovirus. Full-length cDNAs of CRSV strainsPV-0097 and PV-21 were constructed and the infectivity of in vitro transcripts was analyzed. Infectivity of PV-0097 and PV-21 to several plants was markedly higher than that of 1.30, a previously reported infectious CRSV clone. Overall RNA sequences of these viruses were similar, but PV-0097 and PV-21 contained additional nucleotides at the 5′ end of RNA1. Stem-loop structures were predicted in the 5′-terminal region of PV-0097 and PV-21 RNA1 but not in 1.30 RNA1. Mutant CRSV 1.30 RNA1 that contains the terminal 4 nucleotides of PV-0097, predicted to fold a 5′-terminal stem-loop structure, recovered higher level accumulation of viral RNAs in the inoculated protoplasts and leaves of Nicotiana benthamiana. These results suggest that the 5′-terminal stem-loop structure of CRSV RNA1 plays an important role in efficient amplification of the virus.