Nucleotide sequences and taxonomy of satsuma dwarf virus.
(1/2)
The nucleotide sequences of genomic RNA1 (6795 nt) and RNA2 (5345 nt) of satsuma dwarf virus (SDV), a tentative member of the genus Nepovirus, were determined. The deduced genome organization of SDV showed similarities to the organization in como-, faba- and nepoviruses. There is extensive amino acid sequence similarity in the N-terminal regions of the proteins encoded by RNA1 and RNA2, as reported previously only for tomato ringspot nepovirus. However, unlike definitive nepoviruses, which have a single coat protein, SDV has two coat proteins. SDV RNA2 does not contain the long (> 1300 nt) 3' non-coding region characteristic of some nepoviruses. Phylogenetic analysis of SDV RNA polymerase placed SDV apart from como-, faba- and nepoviruses. These unique features suggest that SDV is distinct from the Comovirus, Fabavirus and Nepovirus genera, and needs to be separated into a new genus, probably within the family Comoviridae. (+info)
Evidence for participation of RNA 1-encoded elicitor in Cowpea mosaic virus-mediated concurrent protection.
(2/2)
The cowpea (Vigna unguiculata) line Arlington, inoculated with Cowpea mosaic virus (CPMV), showed no symptoms, and no infectivity or accumulation of capsid antigen was detected at several days after inoculation. Coinoculation, but not sequential inoculation, of CPMV with similar concentrations of another Comovirus; Cowpea severe mosaic virus (CPSMV), resulted in reduced numbers of CPSMV-induced lesions. This apparent, CPMV-mediated reduction in number of CPSMV-induced infection centers was termed concurrent protection. We report results obtained by inoculating two nearly isogenic cowpea lines derived from a CPMV-susceptible cowpea crossed to Arlington, one line CPMV-susceptible and the other resistant. The CPMV virions B and M, encapsidating genomic RNAs 1 and 2, respectively, were extensively purified by gradient centrifugation. In the CPMV-resistant cowpea, either CPMV or CPMV B affected concurrent protection against CPSMV and against two distinct non-Comoviruses: Cherry leafroll virus and Southern bean mosaic virus. Adding CPMV M to the inoculum did not enhance CPMV-B-mediated protection. CPMV B was ineffective in protecting CPMV-susceptible cowpea. We postulate that CPMV-mediated concurrent protection is elicited in CPMV-resistant cowpea by a CPMV RNA-1-encoded factor and acts to reduce accumulation or spread of CPMV and certain coinoculated challenging viruses in or from the inoculated cell. Coinoculated CPMV did not protect CPMV-resistant cowpea against Tomato bushy stunt virus or Cucumber mosaic virus. (+info)