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Genomic regions of wheat yellow mosaic virus involved in the pathotypes against wheat cultivars

Takehiro Ohki: Hokkaido Agricultural Research Ctr, NARO

<div><em>Wheat yellow mosaic virus</em> (WYMV) belonging to the genus <em>Bymovirus</em>,<em> Potyviridae</em> has two, positive-sense, and single-strand genomic RNAs. RNA1 is ca. 7.7 kb long, and encodes a polyprotein consisted of coat protein and seven putative nonstructural proteins. RNA2 is ca. 3.7 kb long, and encodes two proteins that constitute a single polyprotein. WYMV is divided into pathotypes I and II by the reaction of wheat differential cultivars “Fukuhokomugi” and “Shiranekomugi”; pathtype I shows systemic infection with both cultivars but pthotype II doesn’t infect “Fukuhokomugi”. In this study, we investigated the viral genomic regions involved in the pathotypes using infectious clones of pathotypes I and II of WYMV. When the two wheat cultivars were inoculated with reassort viruses which exchanged either RNA1 or RNA2 from the other pathotypes, the reassort virus with RNA1 from pathotype I infected systemically both cultivars as did pathotype I, indicating the involvement of RNA1 in the pathotypes. Infectious clones of the chimeric and point mutated viruses revealed that the replacement of three amino acids in cylindrical inclusion body protein (CI) of pathotype II with those of pathotype I resulted in the same pathogenicity pattern of pathotype I. Both pathotypes I and II showed different host reaction against two cultivars, but successfully multiplied within protoplasts of the two cultivars. These results suggest that pathotypes of WYMV is associated with amino acid changes in CI and ascribes to the inhibition in cell-to-cell and/or long distance movement of pathotype II within wheat host tissues.</div>