 Many plant viruses have developed mechanisms that counter the plants PTGS-systems by evolving proteins, such as p19 and NSs, that interfere with the PTGS-pathway at different levels.Although it is not clear exactly how p19 works to suppress RNA silencing, studies have shown that transiently expressed proteins in "Nicotiana benthamiana" leaves have an up to 50-fold higher yield when coinfiltrated with TBSV p19.TSWV and other tospovirus NSs proteins have been shown to be effective as suppressors of both local and systemic silencing, and may be a useful alternative to p19 where the latter has been shown not to be effective.