Soil-borne wheat mosaic virus (SBWMV), the type species of the genus Furovirus, contains a bipartite positive-stranded RNA genome (RNA1 and RNA2) encapsidated in separate rod-shaped particles. The vector that transmits this virus in soil is a plasmodiophoraceous protozoan, Polymyxa graminis. The optimum temperature for the propagation of this virus is 17°C, and systemically infected plants can recover from the virus if the temperature increases. The inoculation of infectious in vitro transcripts of RNA1 and RNA2 into barley mesophyll protoplasts showed that the CP most abundantly accumulated at 17°C, but was undetectable at 25°C (Ohsato et al., 2003), suggesting that replication of the virus is temperature sensitive. Here, the mutations occurred in the MP gene of the variants that could propagate under higher temperatures (25°C) were examined. It is suggested that these mutations are involved in changing of MP conformation/activity to make virus adapted to the new condition (higher temperature) for cell-to-cell and long-distance movement.