RNA silencing suppressor-influenced performance of a virus vector delivering both guide RNA and Cas9 for CRISPR gene editing

We report on further development of the agroinfiltratable Tobacco mosaic virus (TMV)-based overexpression (TRBO) vector to deliver CRISPR/Cas9 components into plants. First, production of a Cas9 (HcoCas9) protein from a binary plasmid increased when co-expressed in presence of suppressors of gene silencing, such as the TMV 126-kDa replicase or the Tomato bushy stunt virus P19 protein. Such suppressor-generated elevated levels of Cas9 expression translated to efficient gene editing mediated by TRBO-G-3'gGFP expressing GFP and also a single guide RNA targeting the mgfp5 gene in the Nicotiana benthamiana GFP-expressing line 16c. Furthermore, HcoCas9 encoding RNA, a large cargo insert of 4.2 kb, was expressed from TRBO-HcoCas9 to yield Cas9 protein again at higher levels upon co-expression with P19. Likewise, co-delivery of TRBO-HcoCas9 and TRBO-G-3'gGFP in the presence of P19 also resulted in elevated levels percentages of indels (insertions and deletions). These data also revealed an age-related phenomenon in plants whereby the RNA suppressor P19 had more of an effect in older plants. Lastly, we used a single TRBO vector to express both Cas9 and a sgRNA. Taken together, we suggest that viral RNA suppressors could be used for further optimization of single viral vector delivery of CRISPR gene editing parts.