Abstract
Upon Tobacco mosaic virus (TMV) infection, tobacco plants develop mosaic leaves that consist of two kinds of areas: the yellow green and dark green areas in which TMV accumulates to high levels and low levels, respectively. In this study, we examined whether and where RNA silencing is involved in the development of mosaic disease symptoms. In transgenic tobaccos in which an RNA silencing pathway was disturbed, dark green areas did not appear. This suggests that RNA silencing is required for the development of the dark green tissue. Other experiments revealed that RNA silencing is established in the cells located at the edges of the dark green areas, thereby restricting the expansion of virus-infected yellow green areas, and consequently defines the mosaic pattern. The development of mosaic symptoms is discussed in relation to the systemic spread of the virus and RNA silencing.
