Development of resistant transgenic soybeans with inverted repeat-coat protein genes of soybean dwarf virus

In an attempt to generate soybean plants resistant to soybean dwarf virus (SbDV), we transformed a construct containing inverted repeat-SbDV coat protein (CP) genes spaced by β-glucuronidase (GUS) sequences into soybean somatic embryos via microprojectile bombardment. Three T₀ plants with an introduced CP gene were obtained, and one generated T₁ seeds. The presence of the transgene in T₁ plants was confirmed by PCR and Southern blot hybridization analysis, but expression of CP was not detected by northern blot hybridization analysis. Two months after inoculation of SbDV by aphid, T₂ plants contained little SbDV-specific RNA and remained symptomless. These plants contained SbDV-CP-specific siRNA. These results suggest that the T₂ plants achieved resistance to SbDV by an RNA-silencing-mediated process.     

<Emphasis Type="Italic">Soybean dwarf virus</Emphasis>-resistant transgenic soybeans with the sense coat protein gene

We transformed a construct containing the sense coat protein (CP) gene of Soybean dwarf virus (SbDV) into soybean somatic embryos via microprojectile bombardment to acquire SbDV-resistant soybean plants. Six independent T(0) plants were obtained. One of these transgenic lines was subjected to further extensive analysis. Three different insertion patterns of Southern blot hybridization analysis in T(1) plants suggested that these insertions introduced in T(0) plants were segregated from each other or co-inherited in T(1) progenies. These insertions were classified into two types, which overexpressed SbDV-CP mRNA and accumulated SbDV-CP-specific short interfering RNA (siRNA), or repressed accumulation of SbDV-CP mRNA and siRNA by RNA analysis prior to SbDV inoculation. After inoculation of SbDV by the aphids, most T(2) plants of this transgenic line remained symptomless, contained little SbDV-specific RNA by RNA dot-blot hybridization analysis and exhibited SbDV-CP-specific siRNA. We discuss here the possible mechanisms of the achieved resistance, including the RNA silencing.     

QTL analysis for resistance to Soybean dwarf virus in Indonesian soybean cultivar Wilis

Soybean dwarf virus (SbDV), a member of the Luteoviridae family, causes serious yield losses in soybean production in northern Japan. We previously found that an Indonesian soybean cv. Wilis had a high level of resistance to SbDV. Although Wilis is infected by SbDV, symptoms are always mild and develop considerably later compared with many susceptible cultivars. To identify the resistance gene(s) to SbDV in Wilis in a quantitative trait loci (QTL) analysis, we used 71 recombinant inbred lines derived from a cross between Wilis and the susceptible Japanese cv. Toyokomachi and a set of published simple sequence repeat (SSR) markers. The SbDV resistance in Wilis was mainly controlled by a single QTL located near the SSR marker Sat_271 on the linkage group A1. This QTL accounted for 79% of the phenotypic variance. A. Uchibori and J. Sasaki equally contributed to this work.