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Resistance to Bean pod mottle virus in Transgenic Soybean Lines Expressing the Capsid Polyprotein

Transgenic fertile soybean plants were generated from somatic embryos of soybean (Glycine max) cv. Jack transformed via particle bombardment with the capsid polyprotein (pCP) gene of Bean pod mottle virus(BPMV). The plant transformation vector (pHIG/BPMV-pCP) utilized in these experiments contained the BPMV-pCP coding sequence, an intron-containing GUS gene, and the hygromycin phosphotransferase gene. Southern blot hybridization analysis showed that 19 transgenic soybean plants selected for resistance to hygromycin contained the genes for GUS and BPMV-pCP. The progeny of five of these transgenic soybean plants (plants 137, 139, 157, 183, and 186) were characterized in detail. An additional transgenic plant (plant 200) contained the intron-GUS and hygromycin resistance genes, but lacked the BPMV-pCP gene and was used as a negative control. Southern blot hybridization analysis of the five transgenic plants showed the presence of three copies of the T-DNA in a similar banding pattern suggesting that they were derived from a single transformation event. Western and northern blot analyses showed that the expression levels of BPMV-pCP and pCP transcript were high in these five pCP plants. Infectivity assays with detached leaves demonstrated that all five pCP plants exhibited resistance to virus infection because they accumulated lower levels of BPMV compared with plant 200 and nontransformed controls. Unlike the T₂ progeny of line 183-1 that segregated with respect to the pCP gene and, consequently, to BPMV resistance, the T₂ progeny of the homozygous line 183-2 showed little or no symptoms in response to rub-inoculation with virions of a severe strain of BPMV. Although BPMV accumulation was evident in leaves on which viruliferous beetles were allowed a 72-h inoculation access period, the upper noninoculated leaves of the T₂ progeny of line 183-2 plants were symptomless and accumulated little or no virus. Because the progeny of this homozygous transgenic line exhibited systemic resistance, they could potentially be useful in generating commercial cultivars resistant to BPMV.