Infectivity of Three Furoviruses to Japanese Wheat Cultivars and Involvement of Cysteine-Rich Protein

Furoviruses, which are members of the <i>Virgaviridae</i> family, are rod-shaped particles containing bipartite and positive-sense RNA genomes. Three furoviruses, Japanese soil-borne wheat mosaic virus (JSBWMV), Chinese wheat mosaic virus (CWMV), and soil-borne wheat mosaic virus (SBWMV), infect wheat in Japan; however, differences in their pathogenicity to wheat remain unclear. In this study, the infectivity of these three furoviruses in Japanese wheat cultivars was investigated using mechanical leaf inoculation. Of the 15 Japanese wheat cultivars inoculated with these furoviruses, 4 cultivars, such as Chikugoizumi, Fukusayaka, Shirogane komugi, and Yumekaori, were resistant to JSBWMV. In contrast, no cultivars with complete resistance to CWMV or SBWMV were noticed. Infectious cDNA clones of JSBWMV and CWMV were constructed to identify the viral factors involved in this resistance. Analysis of reassortment and chimeric viruses between JSBWMV and CWMV identified cysteine-rich protein (CRP) on RNA2 as the viral factor; a chimeric virus containing CWMV CRP infected all four cultivars, whereas that containing JSBWMV CRP was resisted. Furthermore, JSBWMV could multiply in the mesophyll protoplasts of the four JSBWMV-resistant cultivars, suggesting that the resistance mechanism did not block multiplication but affected local or systemic movement of the virus. Therefore, the identification of wheat genes involved in resistance to JSBWMV will contribute to the understanding of resistance mechanisms to furoviruses and interactions between furovirus CRPs and host factors.