Development of Beet necrotic yellow vein virus-based vectors for multiple-gene expression and guide RNA delivery in plant genome editing.

Many plant viruses with monopartite or bipartite genomes have been developed as efficient expression vectors of foreign recombinant proteins. Nonetheless， due to lack of multiple insertion sites in these plant viruses， it is still a big challenge to simultaneously express multiple foreign proteins in single cells. The genome of Beet necrotic yellow vein virus (BNYVV) offers an attractive system for expression of multiple foreign proteins owning to a multipartite genome composed of five positive-stranded RNAs. Here， we have established a BNYVV full-length infectious cDNA clone under the control of the Cauliflower mosaic virus 35S promoter. We further developed a set of BNYVV-based vectors that permit efficient expression of four recombinant proteins， including some large proteins with lengths up to 880 amino acids in the model plant Nicotiana benthamiana and native host sugar beet plants. These vectors can be used to investigate the subcellular co-localization of multiple proteins in leaf， root and stem tissues of systemically infected plants. Moreover， the BNYVV-based vectors were used to deliver NbPDS guide RNAs for genome editing in transgenic plants expressing Cas9， which induced a photobleached phenotype in systemically infected leaves. Collectively， the BNYVV-based vectors will facilitate genomic research and expression of multiple proteins， in sugar beet and related crop plants.