Virus resistance in transgenic sweetpotato [Ipomoea batatas L. (Lam)] expressing the coat protein gene of sweet potato feathery mottle virus

One of the most-serious diseases of sweet potato [Ipomoea batatas (L.) Lam] is russet crack disease caused by sweet potato feathery mottle virus (SPFMV). We constructed an expression vector carrying the coat protein (CP) and hygromycin phosphotransferase (hpt) genes driven by cauliflower mosaic virus 35 S promoters. Accordingly, we introduced the expression vector into sweet potato variety Chikei 682-11 by the electroporation method. Among 449 calli obtained after antibiotic selection, 19 plants from seven independent calli grew to form adventitious shoots. Three transgenic lines were obtained from independent calli, based on analysis of the CP and hpt genes. The transcription and translation of the CP gene were shown in these transgenic lines by Northern- and Western-blot analyses. To assay the virus resistance of the transgenic lines, each line was vegetatively propagated and then grafted with morning glory (Ipomoea nil) that had been infected with SPFMV-S. A PAS-ELISA assay with polyclonal and serum of the CP demonstrated that virus accumulation 3 months after grafting with the infected morning glory was suppressed in the transgenic lines as compared with non-transgenic ones. These transgenic lines were shown to be highly resistant not only to primary but also to secondary infection by SPFMV-S. Thus we concluded that the three transgenic lines with the CP gene of SPFMV-S can be used for coat protein-mediated resistance to the virus.