Lazareva Ekaterina A, Lezzhov Alexander A, Golyshev Sergey A, Morozov Sergey Y, Heinlein Manfred, Solovyev Andrey G
Department of Virology, Biological Faculty, Moscow State University, Moscow, Russia.
A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.
J Gen Virol. 2017 Sep;98(9):2379-2391. doi: 10.1099/jgv.0.000914. Epub 2017 Sep 4.
The cell-to-cell transport of many plant viruses through plasmodesmata requires viral movement proteins (MPs) encoded by a 'triple gene block' (TGB) and termed TGB1, TGB2 and TGB3. TGB3 is a small integral membrane protein that contains subcellular targeting signals and directs both TGB2 and the helicase domain-containing TGB1 protein to plasmodesmata-associated structures. Recently, we described a 'binary movement block' (BMB) coding for two MPs, BMB1 and BMB2. The BMB2 protein associates with endoplasmic reticulum (ER) membranes, accumulates at plasmodesmata-associated membrane bodies and directs the BMB1 helicase to these structures. TGB3 transport to cell peripheral bodies was previously shown to bypass the secretory pathway and involve a non-conventional mechanism. Here, we provide evidence that the intracellular transport of both poa semilatent virus TGB3 and hibiscus green spot virus BMB2 to plasmodesmata-associated sites can occur via lateral translocation along the ER membranes. Agrobacterium-mediated transient co-expression in Nicotiana benthamiana leaves revealed that green fluorescent protein (GFP)-fused actin-binding domains of Arabidopsis fimbrin (ABD2-GFP) and mouse talin (TAL-GFP) inhibited the subcellular targeting of TGB3 and BMB2 to plasmodesmata-associated bodies, which resulted in TGB3 and BMB2 accumulation in the cytoplasm in association with aberrant ER structures. Inhibition of COPII budding complex formation by the expression of a dominant-negative mutant of the small GTPase Sar1 had no detectable effect on BMB2 subcellular targeting, which therefore could occur without exit from the ER in COPII transport vesicles. Collectively, the presented data support the current view that plant viral MPs exploit the ER:actin network for their intracellular transport.
许多植物病毒通过胞间连丝进行细胞间运输需要由“三基因块”（TGB）编码的病毒运动蛋白（MP），分别称为TGB1、TGB2和TGB3。TGB3是一种小的整合膜蛋白，含有亚细胞靶向信号，并将TGB2和含解旋酶结构域的TGB1蛋白导向与胞间连丝相关的结构。最近，我们描述了一个编码两种MP（BMB1和BMB2）的“二元运动块”（BMB）。BMB2蛋白与内质网（ER）膜结合，在与胞间连丝相关的膜体中积累，并将BMB1解旋酶导向这些结构。先前已表明，TGB3向细胞周边体的运输绕过分泌途径，涉及一种非常规机制。在这里，我们提供证据表明，早熟禾半潜病毒TGB3和木槿绿斑病毒BMB2向与胞间连丝相关位点的细胞内运输都可以通过沿ER膜的侧向易位发生。在本氏烟草叶片中通过农杆菌介导的瞬时共表达表明，拟南芥丝状肌动蛋白（ABD2-GFP）和小鼠踝蛋白（TAL-GFP）的绿色荧光蛋白（GFP）融合肌动蛋白结合结构域抑制了TGB3和BMB2向与胞间连丝相关体的亚细胞靶向，这导致TGB3和BMB2在细胞质中与异常的ER结构相关联地积累。通过表达小GTP酶Sar1的显性负突变体抑制COPII出芽复合体的形成对BMB2的亚细胞靶向没有可检测到的影响，因此BMB2的亚细胞靶向可能在不从ER通过COPII运输小泡排出的情况下发生。总体而言，所呈现的数据支持当前的观点，即植物病毒MP利用ER：肌动蛋白网络进行细胞内运输。
