Genome-Wide Variation Profile of the Genus Tobamovirus

The genus Tobamovirus belongs to the family Virgaviridae, and the genome consists of monopartite, positive, single-strand RNA. Most species contain four open reading frames encoding four essential proteins. Transmission occurs primarily through mechanical contact between plants, and in some cases, via seed dispersal. Tobamovirus fructirugosum (tomato brown rugose fruit virus, ToBRFV), the most recently described species in the genus, was first reported in 2015. It overcame genetic resistance that had been effective in tomato for sixty years, causing devastating losses in tomato production worldwide, and highlights the importance of understanding Tobamovirus genomic variation and evolution. In this study, we measured and characterized nucleotide variation for the entire genome and for all species in the genus Tobamovirus. Additionally, we measured the selection pressure acting on each open reading frame. Results showed that low nucleotide diversity and negative selection pressure are general features of tobamoviruses, with values that are approximately the same across open reading frames and without hypervariable areas. A comparison of nucleotide diversity between T. fructirugosum and its close relatives, T. tomatotessellati (tomato mosaic virus, ToMV) and T. tabaci (tobacco mosaic virus, TMV), showed low nucleotide diversity in the movement protein region harboring the resistance-breaking mutation. Furthermore, phylogenetic and diversity analyses showed that T. fructirugosum continues to evolve, and geographical distribution and host influence genomic diversity.