Tobacco mosaic virus infection induces severe morphological changes of the endoplasmic reticulum

The tobacco mosaic virus (TMV) movement protein (MP) facilitates transport of virus infection between adjacent cells by modifying plasmodesmata. Previous studies suggested that the cytoskeleton and the endomembrane system are involved in this transport. We examined the effects of TMV infection on the endoplasmic reticulum (ER) in transgenic Nicotiana benthamiana that accumulate the green fluorescent protein (GFP) in the ER. Fluorescence microscopy was used to show that early in infection the ER undergoes dramatic morphological changes that include the conversion of tubular ER into large aggregates that revert to tubular ER in later stages of infection. These changes parallel MP accumulation and degradation. Furthermore, a fusion protein comprising MP fused to GFP accumulates in or on these large aggregates of ER. Expression of MP-GFP in the absence of virus infection led to the production of fluorescent aggregates of the same apparent form and size. Microsomes isolated from infected leaves contain MP. We show that the MP appears to behave as an integral ER membrane protein and is exposed on the cytosolic face of the ER. The importance of the association of MP with ER and its possible role in intracellular and intercellular spread of infection is discussed.

烟草花叶病毒（TMV）运动蛋白（MP）可通过修饰胞间连丝，促进病毒感染在相邻细胞间的传播。此前已有研究表明，细胞骨架与内膜系统参与了该转运过程。本研究针对内质网（ER）中积累绿色荧光蛋白（GFP）的转基因本氏烟草（Nicotiana benthamiana），探究了TMV感染对其内质网的影响。借助荧光显微镜观察发现，感染早期内质网会发生显著形态变化：管状内质网转化为大型聚集体，而在感染后期这些聚集体又会重新恢复为管状内质网结构。上述形态变化与MP的积累及降解过程同步发生。此外，由MP与GFP融合形成的融合蛋白会在这些大型内质网聚集体内部或表面积累。仅在无病毒感染的情况下表达MP-GFP融合蛋白，也可产生形态与尺寸一致的荧光聚集体。从感染叶片中分离得到的微粒体中可检测到MP。研究表明，MP可作为内质网整合膜蛋白，定位于内质网的胞质侧表面。本文最后讨论了MP与内质网结合的重要性，及其在病毒感染的细胞内与细胞间传播过程中可能发挥的作用。