ARS | Publication request: Triticum Mosaic Virus: Genetic evidence for recent population expansion and balancing selection

Submitted to: American Phytopathological Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: May 30, 2012
Publication Date: June 1, 2012
Citation: French, R.C., Siefers, D.L., Wegulo, S.N., Tatineni, S. 2012. Triticum Mosaic Virus: Genetic evidence for recent population expansion and balancing selection. American Phytopathological Society Abstracts. 112:S4.42.

Technical Abstract: Triticum Mosaic Virus (TriMV), a mite-transmitted pathogen of wheat, was first discovered in Kansas in 2006, and is a novel species in the family Potyviridae. The P1 and coat protein (CP) coding regions of 14 isolates from Colorado and 18 isolates from Nebraska were amplified by RT-PCR and sequenced. Average pairwise sequence diversity was 0.4% for P1 and 0.2% for CP. The ratio of non-synonymous to synonymous substitutions was 0.19 for P1 and 0.12 for CP coding regions indicating that both cistrons are subject to strong purifying selection. Comparison of sequence diversity within and between the CO and NE samples revealed little population subdivision between geographical regions (Fst = 4.0%). Mismatch analyses of both coding regions provided evidence for population expansion. Temporal analysis using the BEAST software package suggests that this population expansion began circa 1997. Almost all polymorphic sites occurred at low frequencies, however, one site at amino acid residue 17 of the CP cistron occurred at an intermediate frequency. Half of the isolates had a threonine at this position while the other half had an alanine. Polymorphisms that are maintained at intermediate frequencies are generally believed to be a genetic signature of balancing selection. Potential selective forces acting on TriMV CP may be maintenance of virus in different alternative hosts or virus transmission by different mite biotypes.