SGS3 Cooperates with RDR6 in Triggering Geminivirus-Induced Gene Silencing and in Suppressing Geminivirus Infection in Nicotiana Benthamiana

Abstract

RNA silencing has an important role in defending against virus infection in plants. Plants with the deficiency of RNA silencing components often show enhanced susceptibility to viral infections. RNA-dependent RNA polymerase (RDRs) mediated-antiviral defense has a pivotal role in resistance to many plant viruses. In RDR6-mediated defense against viral infection, a plant-specific RNA binding protein, Suppressor of Gene Silencing 3 (SGS3), was also found to fight against some viruses in Arabidopsis. In this study, we showed that SGS3 from Nicotiana benthamiana (NbSGS3) is required for sense-RNA induced post-transcriptional gene silencing (S-PTGS) and initiating sense-RNA-triggered systemic silencing. Further, the deficiency of NbSGS3 inhibited geminivirus-induced endogenous gene silencing (GIEGS) and promoted geminivirus infection. During TRV-mediated NbSGS3 or N. benthamiana RDR6 (NbRDR6) silencing process, we found that their expression can be effectively fine-tuned. Plants with the knock-down of both NbSGS3 and NbRDR6 almost totally blocked GIEGS, and were more susceptible to geminivirus infection. These data suggest that NbSGS3 cooperates with NbRDR6 against GIEGS and geminivirus infection in N. benthamiana, which provides valuable information for breeding geminivirus-resistant plants.

Regulator of Gene Silencing-Calmodulin associates with mRNA granules and the autophagy protein ATG8

“…Since its discovery as a target for potyviral HC-Pro, additional studies show that rgsCaM-like proteins interact with multiple viral suppressor proteins from a wide array of plant viruses (Nakahara et al, 2012; Li et al, 2014; Yong Chung et al, 2014; Li et al, 2017). By using surface plasmon resonance analysis, (Nakahara et al, 2012) demonstrated the interaction of tobacco rgsCaM with the bromoviral suppressor of silencing 2b protein as well as other viral suppressors.…”

“…A strong connection of rgsCaM to autophagy has been discovered by Li et al (2017), who demonstrated that the SGS3 protein encoded by SUPPRESSOR OF GENE SILENCING 3 is a direct interaction target for rgsCaM (Li et al, 2017). SGS3 is an RNA-binding homodimeric protein that forms a stable complex with RNA-dependent RNA polymerase 6 (RDR6).…”

“…SGS3 is an RNA-binding homodimeric protein that forms a stable complex with RNA-dependent RNA polymerase 6 (RDR6). SGS3 is an essential chaperone protein for RDR6-catalyzed synthesis of dsRNA templates required for secondary siRNA production in viral and transgene PTGS pathways (Mourrain et al, 2000; Fukunaga and Doudna, 2009; Li et al, 2017). SGS3 and RDR6 accumulate within cytosolic foci termed siRNA bodies that are proposed to be involved in transacting siRNA biosynthesis (Elmayan et al, 2009; Kumakura et al, 2009; Jouannet et al, 2012).…”

“…SGS3 and RDR6 accumulate within cytosolic foci termed siRNA bodies that are proposed to be involved in transacting siRNA biosynthesis (Elmayan et al, 2009; Kumakura et al, 2009; Jouannet et al, 2012). Overexpression of rgsCaM lowered the levels of SGS3 protein as well as the number of siRNA bodies (Li et al, 2017). This effect of rgsCaM overexpression was suppressed by autophagy inhibitors and RNA i reduction of the expression of key autophagy genes (Li et al, 2017).…”

“…Overexpression of rgsCaM lowered the levels of SGS3 protein as well as the number of siRNA bodies (Li et al, 2017). This effect of rgsCaM overexpression was suppressed by autophagy inhibitors and RNA i reduction of the expression of key autophagy genes (Li et al, 2017). From these observations, the suppression of PTGS activity by rgsCaM was attributed to the autophagic turnover of SGS3/RDR6, which would reduce the ability of the cell to produce dsRNA for the production of secondary siRNAs.…”