Virus-induced gene silencing in Nicotiana benthamiana triggered by heterologous gene sequences from Viola philippica

Virus-induced gene silencing (VIGS) is a particularly useful tool for functional genomics. In the present study, we attempted to utilize this technology to infer the function of genes from Viola philippica using a tobacco rattle virus (TRV) construct. Firstly, the phytoene desaturase gene from V. philippica (VpPDS) was silenced, and local leaf bleaching was observed but did not exhibit systemic effects, thereby limiting utilization of TRV-mediated gene silencing in the recipient plant. However, we observed systemic gene silencing in Nicotiana benthamiana when the VpPDS sequence was used as a trigger, thereby suggesting that heterologous gene sequences could elicit gene silencing. We then investigated the role of gene PISTILLATA from V. philippica (VpPI) of the B-class MADS-box gene family, which regulates the identity and development of stamens and petals. Using the coding region of VpPI as triggers, we determined the gene silencing efficiency of the corresponding GLOBOSA paralogs in N. benthamiana (NbGLO1 and NbGLO2), and we observed stamen-to-carpel transformation and distorted corollas in N. benthamiana suggesting that VpPI functioned as the NbGLO gene. However, the 3'-untranslated region (3'UTR) of VpPI and each 3'UTR of the NbGLO genes downregulated its own corresponding gene, hardly producing floral homeotic alterations. This work provides a better understanding of gene-specific probe design for gene silencing as well as shows that heterologous sequence-triggered VIGS is an efficient way to investigate functional conservation of orthologous genes.