Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2017
Publication Date: 9/8/2017
Citation: Veetil, T., McCoppin, N.K., Domier, L.L. 2017. Strain-specific association of soybean dwarf virus small subgenomic RNA with virus particles. Virus Research. 242:100-105.
Interpretive Summary: Soybean dwarf virus (SbDV) infects soybean plants and causes significant yield losses in soybean in Japan. In the Midwestern United States, SbDV is present at low levels in soybean fields each year. SbDV is dependent upon aphids for its movement from infected to healthy plants. In Japan, fox glove aphids transmit SbDV from red clover to soybean seedlings early in the growing season. The virus particles transmitted by aphids are composed of a protein shell, which encases and protects the genetic material (RNA) of the virus. The assembly of virus particles involves the specific association of virus proteins with virus RNA. If the factors involved in these specific interactions could be identified, it may be possible to interfere with the assembly of SbDV particles and thus prevent its transmission by aphids and reduce the incidence of SbDV infections. In this study, we examined the RNA composition of SbDV particles and showed that there are at least two independent regions in the SbDV genome that cause SbDV RNAs to be incorporated into virus particles. This information will be useful to scientists interested in studying the assembly of RNAs into virus particles.
Technical Abstract: Encapsidation of viral RNAs by structural proteins is a highly specific process that is an essential step in the virus life cycle. Soybean dwarf virus (SbDV), like other members of the Luteoviridae, produces a large subgenomic RNA (LsgRNA) for expression of structural and movement proteins and a small subgenomic RNA (SsgRNA) that is not known to encode a protein. In most luteovirids, only the genomic RNA is detected in virus particles. The packaging of SbDV RNAs was analyzed using one soybean (W4) and two red clover (ClAgt2 and ClIL2) isolates of the dwarfing strain of SbDV. Sucrose gradient-purified SbDV virions from soybean plants systemically infected with ClAgt2 and Nicotiana benthamiana leaves agroinfiltrated with ClIL2 encapsidated both genomic RNA (gRNA) and SsgRNA while, N. benthamiana leaves agroinfiltrated with isolate W4 packaged only gRNA. The LsgRNA was protected from RNase degradation, but not packaged into virions as indicated by its presence primarily in ELISA-negative fractions near the tops of sucrose gradients even in mutants that did not express coat protein. Domain swapping and site-directed mutagenesis showed that nucleotide differences in the SsgRNA region between isolates conferred differential encapsidation of this RNA. Our study found that packaging of SbDV SsgRNA is isolate specific and the packaging signal for SsgRNA is distinct from the signal recognized for packaging of SbDV gRNA.