Vector transmissibility is a biological characteristic of viruses, coded by the virus genome. Not only is this the case for insect-borne viruses but this also applies for nematode- and fungi-transmitted viruses. It is usually the virus coat protein that determines its transmissibility; however there are cases where in addition to the coat protein, the virus movement protein is also involved in this phenomenon. Notwithstanding, there are viruses like Tobacco mosaic virus, Tomato bushy stunt virus and Potato virus X that are structurally very stable and mechanically easily transmissible by infected plant sap but they are not vector-borne. Curiosity made us to look into possible manifestations of such a vector-independent manner of transmission at the genome level. When compared with vector-borne viruses such as Cucumber mosaic virus where a conserved stretch of eight amino acids is involved in the transmission by aphids, remains of such a motif turned out to be present in non-vectored viruses as well. This may suggest that the transmissibility and the conserved motif were not under selection pressure in non-vectored viruses simply because these viruses did not require transmission by vectors as they are easily transmitted through other means such as infected plant sap due to their stable particle structure. Therefore, lack of selection pressure for vector-transmission has exposed the motif to non-synonymous substitutions.
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