Nbrgs-CaM是一个本氏烟内源抑制子，它不仅能抑制正义单链GFP诱导的转录后基因沉默与双生病毒诱导的内源基因沉默，还能增强双生病毒在本氏烟上的侵染，但其抑制RNA沉默与增强双生病毒致病性的机理尚不清楚。我们前期研究发现Nbrgs-CaM与本氏烟基因沉默抑制子SGS3互作，本项目拟通过转基因过表达与沉默NbSGS3，明确它在RNA沉默与植物抗病毒中的作用；分析Nbrgs-CaM与NbSGS3互作结构域，明确互作结构域与其抑制RNA沉默的相关性；分析Nbrgs-CaM竞争NbRDR6结合NbSGS3的能力及它对NbSGS3结合‘dsRNA’活性的影响；利用Nbrgs-CaM转基因植株，分析Nbrgs-CaM对NbSGS3亚细胞定位及与NbRDR6互作的影响。本项目的开展有望解析Nbrgs-CaM抑制RNA沉默在双生病毒致病性中的机理、丰富植物RNA沉默与内源RNA沉默抑制子的网络。

Nbrgs-CaM is an endogenous RNA silencing suppressor in Nicotiana benthamiana, which could suppress sense single-stranded GFP induced post-transcriptional gene silencing (PTGS) and geminivirus-induced endogenous gene Sulphur desaturase silencing, and could promote geminivirus infections in N. benthamiana. However, the underlying mechanism of Nbrgs-CaM suppressing RNA silencing and enhancing geminivirus infections has not been elucidated. Our preliminary research confirmed that Nbrgs-CaM interacted with NbSGS3. In the present proposal, we attempt to obtain the following results : 1) Identify the functions of NbSGS3 in inducing RNA silencing and conferring the resistance to plant viruses in the overexpression and down-regulation of NbSGS3 transegenenic plants; 2) Elucidate the molecular mechanism underlying Nbrgs-CaM PTGS suppression through analyzing the key domains of Nbrgs-CaM in interacting with NbSGS3 and suppressing PTGS; 3) Determine the effects of Nbrgs-CaM on NbSGS3 interacting with NbRDR6 and binding 5’ overhang double stranded RNA; 3) Determine the effects of Nbrgs-CaM on the subcellular localization structure in siRNA-bodies of NbSGS3 and the interaction between NbSGS3 and NbRDR6 by bimolecular fluorescence complementation assay. The objective of carrying out this project is expected to unveil the mechanism of Nbrgs-CaM PTGS suppression in promoting geminivirus infections, which will also contribute to our better understanding of the network of the plant RNA silencing and the endogenous RNA silencing suppressors.