2017 ASHS Annual Conference

Virus-induced gene silencing (VIGS) is a common strategy of reverse genetics for characterizing function of genes in plant. Molecular mechanisms governing silencing efficiency of VIGS are largely unknown. Here, we identified an ocs element binding factor, PhOBF1, one of basic-leucine zipper (bZIP) transcription factors that was up-regulated by Tobacco rattle virus (TRV) infection in petunia. Co-silencing of PhOBF1 with reporter genes, phytoene desaturase (PDS) or chalcone synthase (CHS), by TRV-based VIGS led to a failure of the development of leaf photobleaching and white phenotype in the purple corolla. PhOBF1 silencing caused down-regulation of key RNA silencing-related genes, including RNA-dependent RNA polymerases (RDRs), Dicer-like RNase III enzymes (DCLs) and Argonautes (AGOs). Overexpression of PhOBF1 resulted in a recovery of photobleaching phenotype in systemic leaves. A compromised resistance to TRV and Tobacco mosaic virus (TMV) was found in PhOBF1-RNAi plants, while PhOBF1-overexpressed plants displayed an enhanced resistance to their infections. Compared with wild-type plants, PhOBF1-suppressed transgenic plants accumulated lower levels of free salicylic acid (SA), salicylic acid glucoside (SAG) and phenylalanine, contrarily to higher levels of those in transgenic plants overexpressing PhOBF1. Furthermore, transcripts of a number of genes from the Shikimate and Phenylpropanoid pathways were decreased and increased in PhOBF1-RNAi and -overexpressed transgenic plants respectively. Taken together, our data demonstrate that PhOBF1 regulates TRV-induced gene silencing efficiency through SA-mediated modulation of RDRs, DCLs and AGOs.