Submitted to: Archives of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2009
Publication Date: 4/10/2009
Citation: Thekke, V.T., Hobbs, H.A., Domier, L.L. 2009. Sequence Diversity of Readthrough Proteins of Soybean Dwarf Virus Isolates from the Midwestern United States. Archives of Virology. 154(5):861-866. Interpretive Summary: Soybean dwarf virus (SbDV) infects soybean plants and causes significant yield losses in soybean in Japan where fox glove aphids transmit SbDV from red clover to soybean seedlings early in the growing season. Even though SbDV infects nearly 50% of red clover plants found growing next to soybean fields in the Midwestern United States, SbDV is only rarely detected in soybean fields, which has been attributed to the absence from North America of an aphid species that overwinters on red clover and colonizes soybean plants. The Asian soybean aphid, which colonizes both red clover and soybean was discovered in the Midwest in 2000. To determine whether changes in population structure had occurred since the introduction of the Asian soybean aphid, the genetic diversity of the regions of the genome of SbDV that produce proteins required for aphid transmission was assessed from virus isolates collected from clover and soybean. This analysis showed that clover and soybean populations of SbDV were closely related and could not be differentiated. This information will be useful to scientists interested in studying the population of viruses subsequent to the introduction of a new vector species.
Technical Abstract: Soybean dwarf virus (SbDV), a member of the family Luteoviridae, is phloem limited and persistently transmitted by colonizing aphids in a circulative and nonpropagative manner. The readthrough protein (RTP), a minor component of viral capsids, is composed of the coat protein (CP) with a C-terminal extension called the readthrough domain (RTD). The RTD is believed to have a significant role in specificity of aphid transmission of luteoviruses. The present study was conducted to analyze the amino acid sequence diversity of readthrough proteins. Clover and soybean leaf samples were collected Illinois and Wisconsin in 2003 through 2007. Samples positive for SbDV infection were reverse transcribed from total RNA extracts and the regions encoding RTP were amplified and sequenced. Analysis of predicted amino acids of 18 SbDV isolates revealed 36 amino acid changes in the 54 kDa RTD compared to only four in the 22 kDa CP. Among the isolates, the nucleotide sequence identity ranged from 95 to 99%. Phylogenetic analysis of both amino acid and nucleotide sequences showed two distinct clusters of SbDV isolates. Clover and soybean isolates were represented in both groups.