Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan.
Advanced Plant Biotechnology Center, National Chung Hsing University, Taichung, Taiwan.
J Exp Bot. 2019 Sep 24;70(18):4657-4670. doi: 10.1093/jxb/erz244.
Autophagy plays a critical role in plants under biotic stress, including the response to pathogen infection. We investigated whether autophagy-related genes (ATGs) are involved in infection with Bamboo mosaic virus (BaMV), a single-stranded positive-sense RNA virus. Initially, we observed that BaMV infection in Nicotiana benthamiana leaves upregulated the expression of ATGs but did not trigger cell death. The induction of ATGs, which possibly triggers autophagy, increased rather than diminished BaMV accumulation in the leaves, as revealed by gene knockdown and transient expression experiments. Furthermore, the inhibitor 3-methyladenine blocked autophagosome formation and the autophagy inducer rapamycin, which negatively and positively affected BaMV accumulation, respectively. Pull-down experiments with an antibody against orange fluorescent protein (OFP)-NbATG8f, an autophagosome marker protein, showed that both plus- and minus-sense BaMV RNAs could associate with NbATG8f. Confocal microscopy revealed that ATG8f-enriched vesicles possibly derived from chloroplasts contained both the BaMV viral RNA and its replicase. Thus, BaMV infection may induce the expression of ATGs possibly via autophagy to selectively engulf a portion of viral RNA-containing chloroplast. Virus-induced vesicles enriched with ATG8f could provide an alternative site for viral RNA replication or a shelter from the host silencing mechanism.
自噬在植物应对生物胁迫中起着关键作用，包括对病原体感染的反应。我们研究了自噬相关基因（ATGs）是否参与感染竹花叶病毒（BaMV），一种单链正链 RNA 病毒。最初，我们观察到，BaMV 在本氏烟叶片中的感染上调了 ATGs 的表达，但并未引发细胞死亡。可能引发自噬的 ATGs 的诱导，增加了而不是减少了叶片中 BaMV 的积累，这是通过基因敲低和瞬时表达实验揭示的。此外，自噬体形成抑制剂 3-甲基腺嘌呤（3-methyladenine）和自噬诱导剂雷帕霉素（rapamycin）分别负向和正向影响 BaMV 的积累。用针对橙色荧光蛋白（OFP）-NbATG8f 的抗体进行下拉实验，NbATG8f 是一种自噬体标记蛋白，表明正负义 BaMV RNA 都可以与 NbATG8f 结合。共聚焦显微镜显示，富含 ATG8f 的小泡可能来自叶绿体，包含 BaMV 病毒 RNA 及其复制酶。因此，BaMV 感染可能通过自噬诱导 ATGs 的表达，从而选择性地吞噬一部分含病毒 RNA 的叶绿体。富含 ATG8f 的病毒诱导小泡可能为病毒 RNA 复制提供替代场所，或逃避宿主沉默机制。
