Inheritance Analysis of Herbicide-Resistant Transgenic Soybean Lines

Four transgenic soybean lines generated via Agrobacterium-mediated transformation were used to analyze inheritance of the transgenes. Seed chip GUS assay and herbicide leaf painting and spraying assays were applied to test the gus reporter gene and the herbicide resistant bar selectable marker gene, respectively. Three of the four transgenic soybean lines were stably inherited in a Mendelian fashion with co-segregation of both transgenes in a 3:1 segregation ratio in the T₁ progeny, indicating that both transgenes were integrated into the same locus of the soybean genome. Homozygous transgenic progeny plants were obtained in the T₂ generation of these lines, and the transgenes were inherited in five successive generations. However, in one transgenic line, all the T₁ progeny plants showed GUS negative and herbicide sensitive. Southern blotting analysis confirmed that the transgenes were passed into the T₁ progeny, indicating that the transgenes were both silenced. To test if the transgene silencing was due to transcriptional or post-transcriptional level, Soybean mosaic virus (SMV) was inoculated on leaf tissues of the T₁ plants to test possible reverse effects on transgene silencing. Infection with SMV did not suppress transgene silencing, suggesting that transgene silencing in this transgenic line may not be due to post-transcriptional gene silencing.