Oral Technical Session: Virology

106-O

Evolutionary trends and inferences for viruses of the Secoviridae: Evidence of an ancient modular evolution.
J. R. THOMPSON (1), K. L. Perry (1), N. Kamath (1)
(1) Cornell University, Ithaca, NY, U.S.A.

The Secoviridae family of viruses is a member of the Picornavirales order, an important group of non-enveloped viruses that infect vertebrates, arthropods, plants and algae. The plant infecting Secoviridae are vectored by a range of arthropods, including nematodes, beetles and aphids. In this work we set out to gain an understanding of secovirid evolution by analyzing full-length and partial genome sequences using a variety of computational approaches to reconstruct time-measured and co-evolutionary phylogenies, determine rates of nucleotide substitution and find evidence for interspecies recombination. The selection pressures (d_N/d_S) and phylogenies of the six principal genes 1N(ProCo), RdRp, HEL, Pro, 2N(MP) and CP were highly variable and implied contrasting evolutionary scenarios. Position-Specific Scoring Matrices generated from representatives of the principal monophyletic groups and analyzed by position-specific iterative basic alignment search tool (PSI-BLAST) found a distant though significant homology between the CP and Pro genes and those of animal infecting members of the Picornavirales, while other genes had strikingly alternative affinities both within and outside the Secoviridae. From these findings we propose a general model for secovirid evolution that aims at explaining both the modular composition of the genome and the process of genome segmentation.