Reassortment between genetically distinct Japanese and US strains of Soil-borne wheat mosaic virus: RNA1 from a Japanese strain and RNA2 from a US strain make a pseudorecombinant virus

Abstract

Soil-borne wheat mosaic virus (SBWMV), the type species of the genus Furovirus, has a plus-sense bipartite RNA genome. Japanese and US strains of SBWMV are genetically distantly related, despite their biologically identical properties. Here we report formation of a pseudorecombinant virus consisting of RNA1 from a Japanese strain and RNA2 from a US strain, using infectious in vitro transcripts for both strains. Full-length infectious cDNA clones for a Japanese strain were previously constructed (Yamamiya and Shirako [38]). For RNA1 of a US strain, due to instability of full-length cDNA clones in Escherichia coli cells, it was necessary to prepare a full-length template DNA for in vitro transcription by combining overlapping 5'-terminal and 3'-terminal cDNAs individually cloned in two plasmids, whereas for RNA2 a full-length cDNA clone was the template. For infectivity assays, Chenopodium quinoa, a local lesion host, and wheat, a systemic host, were used. A mixture of Japanese RNA1 transcripts and US RNA2 transcripts caused formation of local lesions on C. quinoa leaves and systemic infection to wheat plants. The nucleotide sequence of the progeny viral RNA2 was identical to that of the US RNA2. The reciprocal combination was not infectious to either host. These results confirm that the Japanese and US SBWMV are genetically distantly related strains belonging to a single species.

Biological and genetic diversity of plasmodiophorid-transmitted viruses and their vectors

“…In fact, SBWMV was recently found in Germany (Kühne 2009) and in Hokkaido (Shirako et al 2012), and an isolate (SBWMV-Mar) from France is very closely related to Japanese SBWMV-JT (Hariri and Meyer 2007) (Table 1). Furthermore, the fact that recombinant viruses can be formed between some of these viruses (Miyanishi et al 2002) suggests that they could be regarded as strains of SBWMV. Thus, the classification of species of wheat-infecting furoviruses remains as a matter of debate (Hao et al 2012;Kühne 2009).…”

Plant viruses and viroids in Japan

“…Spontaneous deletion of the readthrough domain, downstream of the capsid protein (CP) coding domain, of JSBWMV RNA2 results in more severe symptom induction relative to the wild-type virus. As interspecies reassortment of RNA1 and RNA2 was observed between JSBWMV and SBWMV in the laboratory experiment (Miyanishi et al 2002), mixed infections of wheat by these furoviruses may allow for the emergence of new strains (Tamada and Kondo 2013). Of members of the genus Tobamovirus, 15 viruses have been reported from Japan (Table 1 and Supplementary Table S1), among which the following tobamoviruses were first found and characterized in Japan.…”

“…In Japan, SBWMV and CWMV have been isolated from Hokkaido and Tochigi Prefecture, respectively. JSBWMV has been molecularly and biologically well-characterized (Miyanishi et al 2002;Ohsato et al 2003;Yamamiya et al 2005). Spontaneous deletion of the readthrough domain, downstream of the capsid protein (CP) coding domain, of JSBWMV RNA2 results in more severe symptom induction relative to the wild-type virus.…”