PhOBF1, a petunia ocs element binding factor, plays an important role in antiviral RNA silencing.

Daoyang Sun,Shaohua Li,Cai-Zhong Jiang,Michael S Reid,Yanlong Zhang,Lixin Niu

doi:10.1093/jxb/erw490

Abstract

Virus-induced gene silencing (VIGS) is a common reverse genetics strategy for characterizing the function of genes in plants. The detailed mechanism governing RNA silencing efficiency triggered by viruses is largely unclear. Here, we reveal that a petunia (Petunia hybrida) ocs element binding factor, PhOBF1, one of the basic leucine zipper (bZIP) transcription factors, was up-regulated by Tobacco rattle virus (TRV) infection. Simultaneous silencing of PhOBF1 and a reporter gene, phytoene desaturase (PDS) or chalcone synthase (CHS), by TRV-based VIGS led to a failure of the development of leaf photobleaching or the white-corollas phenotype. PhOBF1 silencing caused down-regulation of RNA silencing-related genes, including RNA-dependent RNA polymerases (RDRs), Dicer-like RNase III enzymes (DCLs), and Argonautes (AGOs). After inoculation with the TRV-PhPDS, PhOBF1-RNAi lines exhibited a substantially impaired PDS silencing efficiency, whereas overexpression of PhOBF1 resulted in a recovery of the silencing phenotype (photobleaching) in systemic leaves. A compromised resistance to TRV and Tobacco mosaic virus was found in PhOBF1-RNAi lines, while PhOBF1-overexpressing lines displayed an enhanced resistance to their infections. Compared with wild-type plants, PhOBF1-silenced plants accumulated lower levels of free salicylic acid (SA), salicylic acid glucoside, and phenylalanine, contrarily to higher levels of those in plants overexpressing PhOBF1. Furthermore, transcripts of a number of genes associated with the shikimate and phenylpropanoid pathways were decreased or increased in PhOBF1-RNAi or PhOBF1-overexpressing lines, respectively. Taken together, the data suggest that PhOBF1 regulates TRV-induced RNA silencing efficiency through modulation of RDRs, DCLs, and AGOs mediated by the SA biosynthesis pathway.

Highlights

Virus-induced gene silencing (VIGS), related to post-tran- (Reid et al, 2009; Jiang et al, 2011)
We have recently reported an ethylene-responsive element binding factor, PhERF2, which plays a critical role in Tobacco rattle virus (TRV)-induced RNA silencing and antiviral defense via transcriptional modulation of RDR2, RDR6, DCL2, and AGO2 in petunia (Sun et al, 2016)
We found that transcript abundances of genes such as 3-deoxy-d-arabino-heptulosonate-7-phosphate synthase (DAHPS), shikimate kinase (SK1), 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS), chorismate synthase (CS), chorismate mutase 1 (CM1), Fig. 7

Summary

Introduction

Virus-induced gene silencing (VIGS), related to post-tran- (Reid et al, 2009; Jiang et al, 2011). This RNA silencing scriptional gene silencing, is an attractively fast approach machinery employs a number of core components, includfor degradation of homologous RNA molecules in plants ing RNA-dependent RNA polymerases (RDRs), Dicer-like 916 | Sun et al. RNase III enzymes (DCLs), and Argonautes (AGOs), to implement small interfering RNA (siRNA)-mediated gene knockdown in a sequence-specific manner (Schwach et al, 2005; Jaubert et al, 2011). How these RNA silencing components are transcriptionally regulated remains largely unknown

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