南方水稻黑条矮缩病毒S6编码一个沉默抑制子

 【目的】分析南方水稻黑条矮缩病毒（SRBSDV）基因组S6编码的SP6蛋白的抑制子活性，明确SRBSDV是否编码RNA沉默抑制子来干扰植物的沉默。【方法】将分别含有SP6与GFP质粒的农杆菌共浸润转GFP基因的16c本氏烟纯合系，观察SP6对局部沉默和系统沉默的抑制作用；将含有SP6，GFP和dsGFP质粒的农杆菌三者共浸润，观察SP6对由dsRNA引起的沉默的抑制作用；在同一植株不同部位接种GFP和SP6，观察SP6对RNA沉默信号传导的影响；通过马铃薯X病毒（Potato virus X，PVX）在本氏烟上表达SP6，观察SP6是否能增强PVX的致病性。【结果】SP6能抑制由GFP正义RNA介导的沉默，但其抑制作用较弱，仅能延缓局部沉默和系统沉默的产生。SP6能灭活RNA沉默信号，阻止沉默信号的长距离传导，回复GFP的沉默，但不能抑制由dsRNA引起的沉默。利用PVX在本氏烟上表达SP6能增强PVX的致病性。【结论】SP6是病毒编码的RNA沉默抑制子，在RNA沉默的起始和信号传导阶段起作用。

Identification of an RNA Silencing Suppressor Encoded by Southern rice black-streaked dwarf virus S6

【Objective】The objective of this study is to analyze the RNA silencing suppressor activity of SP6 protein encoded by SRBSDV segment 6 (S6) and to clear whether SRBSDV encodes RNA silencing suppressor to interfere with RNA silencing pathway. 【Method】To investigate the suppress activity of SP6 on local and systemic silencing induced by sense RNA, SP6 was coinfiltrated with the reporter green fluorescent protein (GFP) in transgenic Nicotiana benthamiana line 16c carrying GFP. SP6 was also coinfiltrated with GFP and dsGFP to determine whether it interfered with local and systemic silencing induced by dsRNA. GFP and SP6 were infiltrated in different parts of leaves in a same plant, respectively, to characterize whether SP6 can block the spread of RNA silencing signal. SP6 was over-expressed in the PVX heterogenous system to find out whether it was a pathogenicity determinant. 【Result】The local and systemic silencing can be delayed, but not inhibited, in N. benthamiana leaves agroinfiltrated with SP6 and GFP. SP6 can block the spread of the silencing signal and reverse the GFP silencing, but can not inhibit the silence induced by dsRNA. Expression of SP6 enhanced Potato virus X pathogenicity in N. benthamiana. 【Conclusion】SP6 is an RNA silencing suppressor encoded by Southern rice black-streaked dwarf virus. It may target the initiate step and prevent the spread of RNA silencing signal in the RNA silencing pathway.