Submitted to: Archives of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2000
Publication Date: 2/1/2001
Citation: Choi, I., Hall, J.S., Henry, M., Zhang, L., Hein, G.L., French, R.C., Stenger, D.C. 2001. Sequence diversity among three strains of wheat streak mosaic tritimovirus. Archives Of Virology 146:619-628. Interpretive Summary: Complete nucleotide sequences of three Wheat streak mosaic virus (WSMV) strains were determined and compared. Strains of WSMV from the United States were closely related, whereas a strain of WSMV from Mexico was divergent. WSMV in Mexico appears to be genetically isolated from WSMV populations occurring in the Great Plains. An analysis of nucleotide sequence variation indicated that differences between the three strains of WSMV may be largely explained by neutral mutation and genetic drift, with the US and Mexican strains separated for a longer period of time compared to strains in the US. One region of the WSMV genome was devoid of nucleotide substitutions, implying strong selection for primary RNA sequence in the WSMV P3 gene. It is suggested that this region of intraspecies sequence conservation may result from the presence of a previously unrecognized RNA sequence element regulating some aspect of the WSMV life cycle.
Technical Abstract: The Type and Sidney 81 strains of Wheat streak mosaic virus (WSMV) from the American Great Plains were closely related, with sequence identities of 97.6% (nucleotide) and 98.7% (amino acid). In contrast, the El Batan 3 strain from central Mexico was divergent, and shared only 79.2-79.3% (nucleotide) and 90.3-90.5% (amino acid) sequence identity with Type and Sidney 81. All three WSMV strains were serologically related, but the El Batan 3 capsid protein (CP) had 15 fewer amino acid residues. Phylogenetic analysis of the WSMV CP gene indicated that Type, Sidney 81, and nine other American isolates of WSMV were closely related. The El Batan 3 sequence was distinct and may represent a geographically isolated WSMV population. Nucleotide substitutions among the WSMV strains were not randomly distributed across the genome; variation was greater than expected within P1, HC-Pro, and CP, and less than expected within P3. One 400 nucleotide region of the genome, corresponding to the 3'-end of P3, was strikingly deficient in silent substitutions, implying strong selection for nucleotide sequence conservation. Nonetheless, the ratio of synonymous to non- synonymous substitutions throughout the genome was essentially the same for all three WSMV strains. This suggests that neutral mutation and genetic drift contributed significantly to WSMV strain divergence.