Probing of plant transcriptomes reveals the hidden genetic diversity of the family Secoviridae.

Secoviruses are single-stranded RNA viruses that infect plants. In the present study, we identified 61 putative novel secoviral genomes in various plant species by mining publicly available plant transcriptome data. These viral sequences represent the genomes of 13 monopartite and 48 bipartite secovirids. The genome sequences of 52 secovirids were coding-complete, and nine were partial. Except for small open reading frames (ORFs) determined in waikaviral genomes and RNA2 of torradoviruses, all of the recovered genomes/genome segments contained a large ORF encoding a polyprotein. Based on genome organization and phylogeny, all but three of the novel secoviruses were assigned to different genera. The genome organization of two identified waika-like viruses resembled that of the recently identified waika-like virus Triticum aestivum secovirus. Phylogenetic analysis revealed a pattern of host-virus co-evolution in a few waika- and waika-like viruses and increased phylogenetic diversity of nepoviruses. The study provides a basis for further investigation of the biological properties of these novel secoviruses.