RNA silencing supressors (RSSs) are very important factors for virus biology.
Virus encodes RSS irrespective of their genome size, for example the geminivus genome with only 2.7kb genome size encodes three suppressors (AL2/AC2, AC4 and possibly ?C1) where as CTV with large genome size of 40kb encodes three RSS. Therefore the size of the genome is not an indicator of number RSS.
Through their evolution plants and pathogens have adapted and evolved a wide variety of sophisticated strategies to attack, defend, and counterattack. Plants have acquired abilities to sense and defend against invading pathogens by utilizing pre-existing and/or induced barriers to stop infection. In parallel, plant pathogens have evolved diverse ways to counter or overcome host disease resistance. One of the common pathogen strategies involves the production of plant defense suppressors. Co-evolution must therefore be a common phenomenon since the intimate ecological relationships among the many species probably derive from co-evolutionary events in which adaptive changes in one species are followed by adaptive changes in others. There obviously has been and still is a great deal of interdependence among many life forms and theses cannot be fully understood except in an evolutionary frame work.
The plant has a resistance defensive mechanism as RNAi silencing, a mechanism that targets viral genomes and transcripts to degradation, several recent studies have revealed viral suppressors that target plant proteins and the possible actions that viruses take during their interference with the defense systems of the host: many unanswered questions remain. For example, the type of proteolysis machinery used by P0 to degrade its plant interactor AGO1 is a matter of debate and the mechanism by which V2 disrupts the RNAi- silencing system of the plant is unknown. The more we dig into the on-going battle between viruses and their hosts, the more we discover about the intriguing defense and counter defense that enable plants and viruses to coexist. To conclude it can be stated that the interactions between antiviral RNA silencing and the countermeasures viruses have evolved to frustrate such process. On one hand a very important topic in virology and on the other hand a strong starting point for breakthroughs in other fields of research such as functional genomics and development. In an application environment, RNA silencing has allowed us to develop efficient and broad virus resistance in plants.
RNAi suppression holds the potential of unearthing many unexpected surprises and this promising field is the object of intense investigation.