Li Fangfang, Zhang Changwei, Tang Ziwei, Zhang Lingrui, Dai Zhaoji, Lyu Shanwu, Li Yinzi, Hou Xilin, Bernards Mark, Wang Aiming
London Research and Development Centre, Agriculture and Agri-Food Canada, London, ON, N5V 4T3, Canada.
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
New Phytol. 2020 Oct;228(2):622-639. doi: 10.1111/nph.16716. Epub 2020 Jun 28.
Autophagy is an evolutionarily conserved pathway in eukaryotes that delivers unwanted cytoplasmic materials to the lysosome/vacuole for degradation/recycling. Stimulated autophagy emerges as an integral part of plant immunity against intracellular pathogens. In this study, we used turnip mosaic virus (TuMV) as a model to investigate the involvement of autophagy in plant RNA virus infection. The small integral membrane protein 6K2 of TuMV, known as a marker of the virus replication site and an elicitor of the unfolded protein response (UPR), upregulates the selective autophagy receptor gene NBR1 in a UPR-dependent manner. NBR1 interacts with TuMV NIb, the RNA-dependent RNA polymerase of the virus replication complex (VRC), and the autophagy cargo receptor/adaptor protein ATG8f. The NIb/NBR1/ATG8f interaction complexes colocalise with the 6K2-stained VRC. Overexpression of NBR1 or ATG8f enhances TuMV replication, and deficiency of NBR1 or ATG8f inhibits virus infection. In addition, ATG8f interacts with the tonoplast-specific protein TIP1 and the NBR1/ATG8f-containing VRC is enclosed by the TIP1-labelled tonoplast. In TuMV-infected cells, numerous membrane-bound viral particles are evident in the vacuole. Altogether these results suggest that TuMV activates and manipulates UPR-dependent NBR1-ATG8f autophagy to target the VRC to the tonoplast to promote viral replication and virion accumulation.
自噬是真核生物中一种进化上保守的途径，它将不需要的细胞质物质输送到溶酶体/液泡进行降解/回收。受刺激的自噬成为植物抵抗细胞内病原体免疫的一个组成部分。在本研究中，我们以芜菁花叶病毒（TuMV）为模型，研究自噬在植物RNA病毒感染中的作用。TuMV的小整合膜蛋白6K2，作为病毒复制位点的标志物和未折叠蛋白反应（UPR）的诱导剂，以UPR依赖的方式上调选择性自噬受体基因NBR1。NBR1与TuMV NIb相互作用，TuMV NIb是病毒复制复合体（VRC）的RNA依赖性RNA聚合酶，以及自噬货物受体/衔接蛋白ATG8f。NIb/NBR1/ATG8f相互作用复合体与6K2染色的VRC共定位。NBR1或ATG8f的过表达增强TuMV复制，而NBR1或ATG8f的缺失抑制病毒感染。此外，ATG8f与液泡膜特异性蛋白TIP1相互作用，含有NBR1/ATG8f的VRC被TIP1标记的液泡膜包围。在TuMV感染的细胞中，液泡中可见大量膜结合的病毒颗粒。总之，这些结果表明，TuMV激活并操纵UPR依赖的NBR1-ATG8f自噬，将VRC靶向液泡膜以促进病毒复制和病毒粒子积累。
