JIA-2018-09

2039 PAN Yuan et al. Journal of Integrative Agriculture 2018, 17(9): 2031–2041 it is possible that ER tubules are used directly by P6 IBs as a conduit for both intracellular and intercellular transports. Viruses cause a large array of different disease symptoms in susceptible plants, and the plant evolves special mechanisms to resist virus invasion. RNA silencing is one of the main adaptive defense mechanisms against virus. However, viruses encode special proteins called viral silencing suppressors that interfere with many steps of host gene silencing pathways. These include the 2b protein encoded by cucumber mosaic virus (CMV), which interacts with argonaute 1 (AGO1) to prevent the assembly of the RNA-induced silencing complex (RISC) (Zhang et al . 2006). The tombusvirus P19 protein exerts a different mechanism of activity by competing with AGO1 for virus- induced siRNA binding to prevent RISC targeting of viral RNA and cleavage of exogenous genes (Haas et al . 2008). Considering the function of CaMV P6, we postulated that SVBV P6 is a silencing suppressor protein that functions to interfere with the RISC pathway, and we demonstrated that the protein could enhance the ectopic GFP expression. We also showed that the function of SVBV P6 was completely destroyed by deleting the C-terminal 25 aa residues. We raise the hypothesis that the 25 aa is indispensable for SVBV infection, and this hypothesis is consistent with the studies showing that a CaMV mutant lacking the 25 aa C-terminal region fails to form inclusion bodies or infect turnips (Lutz et al . 2015). 5. Conclusion SVBV ORF VI was expressed ectopically in N . benthamiana . P6 protein accumulated in the nuclei and formed amorphous, cytoplasmic IBs with different sizes. P6 IBs aligned with microtubules and the endoplasmic reticulum, and trafficked along microfilaments for co-localization with the P1 protein at periphery of cells, suggesting that P6 IBs might transport virons to P1 in the plasmodesmata via the cytoskeleton and host secretory pathways. In addition, P6 protein deleted NLS region did not localize in the nucleus, did not form IBs, and was unable to facilitate exogenous green fluorescent protein expression. Acknowledgements We gratefully acknowledge Prof. Tao Xiaorong (Nanjing Agricultural University, China) for providing the microtubules marker protein (mCherry-MAP65-1) and ER marker protein (mCherry-HDEL). This work was supported by the Fund of State Key Laboratory for Biology of Plant Diseases and Insect Pests (SKLOF201710), the National Natural Science Foundation of China (31671999, 31371915) and the Zhejiang Natural Science Foundation of China (LY17C140001). Appendices associated with this paper can be available on http://www.ChinaAgriSci.com/V2/En/appendix.htm References Angel C A, Lutz L, Yang X H, Rodriguez A, Adair A, Zhang Y, Leisner S M, Nelson R S, Schoelz J E. 2013. The P6 protein of Cauliflower mosaic virus interacts with CHUP1, a plant protein which moves chloroplasts on actin microfilaments. Virology , 443 , 363–374. Baker R, Bragard C, Candresse T, Gilioli G, Gregoire J C, Jeger M H, Karadjov O E. 2014. Scientific opinion on the pest categorisation of Strawberry vein banding virus . Efsa Journal , 12 , 3772. Baughman G A, Jacobs J D, Howell S H. 1988. Cauliflower mosaic virus gene VI produces a symptomatic phenotype in transgenic tobacco plants. Proceedings of the National Academy of Sciences of the United States of America , 85 , 733–737. Bouchery Y, Givord L, Monestiez P. 1990. Comparison of short- and long-feed transmission of the cauliflower mosaic virus Cabb-S strain and S delta II hybrid by two species of aphid: Myzus persicae (Sulzer) and Brevicoryne brassicae (L.). Research in Virology , 141 , 677–683. Carluccio A V, Zicca S, Stavolone L. 2014. Hitching a ride on vesicles: cauliflower mosaic virus movement protein trafficking in the endomembrane system. Plant Physiology , 164 , 1261–1270. Chen J, Doyle C, Qi X Y, Zheng H Q. 2012. The endoplasmic reticulum: A social network in plant cells. Journal of Integrative Plant Biology , 54 , 840–850. Christopher N, Katy M, Elizabeth B, Thomas W. 2007. A guide to viral inclusions, membrane rearrangements, factories, and viroplasm produced during virus replication. In: Advances in Virus Research . Academic Press, New York. pp. 101–182. Grangeon R, Agbeci M, Chen J, Grondin G, Zheng H, Laliberte J F. 2012. Impact on the endoplasmic reticulum and Golgi apparatus of turnip mosaic virus infection. Journal of Virology , 86 , 9255–9265. Haas G, Azevedo J, Moissiard G, Geldreich A, Himber C, Bureau M, Fukuhara T, Keller M, Voinnet O. 2008. Nuclear import of CaMV P6 is required for infection and suppression of the RNA silencing factor DRB4. Embo Journal , 27 , 2102–2112. Haas M, Bureau M, Geldreich A, Yot P, Keller M. 2002. Cauliflower mosaic virus : Still in the news. Molecular Plant Pathology , 3 , 419–429. Haas M, Geldreich A, Bureau M, Dupuis L, Leh W, Vetter G, Kobayashi K, Hohn T, Ryabova L, Yot P, Keller M. 2005. The open reading frame VI product of Cauliflower mosaic virus is a nucleocytoplasmic protein: Its N terminus mediates its nuclear export and formation of electron-dense viroplasms.