State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest Agriculture & Forestry University, Yangling, P. R. China.
Plant Biol (Stuttg). 2021 Sep;23(5):843-849. doi: 10.1111/plb.13257. Epub 2021 May 31.
Plants possess an innate immune system for defence against pathogens. In turn, pathogens have various strategies to overcome complex plant defences. Among diverse pathogens, phytoplasmas are associated with serious diseases in a range of species. RNA silencing serves as an efficient defence system against pathogens in eukaryotes but can be interrupted by RNA silencing suppressors (RSSs) encoded by pathogens. Currently, many RSSs have been identified in viruses, bacteria, oomycetes and fungi. Phytoplasmas are pathogens in several hundred plant species. In this research, 37 candidate effectors of wheat blue dwarf (WBD) phytoplasma were screened for presence of RSS. Agro-infiltration assay, yeast expression system, floral-dip method for constructing transgenic A. thaliana, Western blotting and RT-qPCR were used for identification of RNA silencing suppressors. SWP16 encoded by WBD phytoplasma was found to be a secretory protein that inhibited accumulation of GFP siRNA and led to the accumulation of GPF mRNA in systemic N. benthamiana 16c. Furthermore, in A. thaliana SWP16 inhibited production of miRNAs, which are components of RNA silencing. SWP16 also promoted infection of potato virus X. We conclude that SWP16 encoded by WBD phytoplasma was an RSS, suppressing systemic RNA silencing. This is the first evidence that a phytoplasma encodes an RSS and provides a theoretical basis for research on the interaction mechanisms between pathogens and plants.
植物拥有先天免疫系统来抵御病原体。反过来，病原体也有各种策略来克服复杂的植物防御。在各种病原体中，植原体与多种物种的严重疾病有关。RNA 沉默是真核生物抵御病原体的有效防御系统，但可以被病原体编码的 RNA 沉默抑制子（RSSs）打断。目前，许多 RSSs 已在病毒、细菌、卵菌和真菌中被鉴定。植原体是几百种植物的病原体。在这项研究中，筛选了 37 种小麦蓝矮（WBD）植原体候选效应子，以检测 RSS 的存在。农杆菌浸润分析、酵母表达系统、构建转基因拟南芥的花浸法、Western blot 和 RT-qPCR 用于鉴定 RNA 沉默抑制子。发现 WBD 植原体编码的 SWP16 是一种分泌蛋白，它抑制 GFP siRNA 的积累，并导致系统 N. benthamiana 16c 中 GFP mRNA 的积累。此外，在拟南芥中，SWP16 抑制了 miRNA 的产生，miRNA 是 RNA 沉默的组成部分。SWP16 还促进了马铃薯病毒 X 的感染。我们得出结论，WBD 植原体编码的 SWP16 是一种 RSS，抑制了系统的 RNA 沉默。这是第一个证据表明植原体编码 RSS，并为研究病原体与植物之间的相互作用机制提供了理论依据。
