Previous studies have shown that methionine from root exudates affects the rhizosphere bacterial population involved in soil nitrogen fixation. A transgenic line of Zigongdongdou soybean cultivar (ZD91) that expresses Arabidopsis cystathionine γ-synthase resulting in an increased methionine production was examined for its influence to the rhizosphere bacterial population. Using 16S rRNA gene-based pyrosequencing analysis of the V4 region and DNA extracted from bacterial consortia collected from the rhizosphere of soybean plants grown in an agricultural field at the pod-setting stage, we characterized the populational structure of the bacterial community involved. In total, 87,267 sequences (approximately 10,908 per sample) were analyzed. We found that Acidobacteria, Proteobacteria, Bacteroidetes, Actinobacteria, Chloroflexi, Planctomycetes, Gemmatimonadetes, Firmicutes, and Verrucomicrobia constitute the dominant taxonomic groups in either the ZD91 transgenic line or parental cultivar ZD, and that there was no statistically significant difference in the rhizosphere bacterial community structure between the two cultivars.

Transgenic plants may induce shifts in the microbial community composition that in turn alter microbially-mediated nutrient cycling in soil. Studies of how specific microbial groups respond to genetically modified (GM) planting help predict potential impacts upon processes performed by these groups. This study investigated the effect of transgenic high-methionine soybean cv. ZD91 on nitrogen-fixing and ammonia-oxidizing bacterial populations. A difference in nitrogen-fixing or ammonia-oxidizing bacteria community composition was not found, suggesting that cv. ZD91 does not alter the bacterial populations in rhizosphere soil. This study increases our understanding of the potential effect of transgenic soybean on microbial functional groups within soil by suggesting that nitrogen-transforming bacteria may be useful for future investigations on the GM crops impact in the soil ecosystem.

In the present study, a 3-year pot experiment was conducted to investigate the agronomic performance of different generation hybrids between genetically modified (GM) soybean and wild soybeans as well as inheritance of the CP4-EPSPS transgene and its effects on the seed germination rate, aboveground biomass, and fecundity in F1, F2 and F3 populations. Furthermore, the expression of transgenic proteins in various hybrids was also investigated. The results showed that the F1 hybrids had higher germination rates (weaker dormancy) and lower pod and seed numbers than the wild soybean. The F2 and F3 populations also had higher germination rates than wild soybean, but the F2 and F3 populations had nearly the same biomass, pod and seed yield as their maternal parents across the whole life cycle; while the seed germination rate, biomass, and fecundity were similar in EPSPS negative, homozygous and heterozygous plants of F2 and F3 populations. Furthermore, EPSPS proteins were detectable in F1, F2 and F3 progeny at different growth stages. While EPSPS genes had little effect on crop growth and reproduction, hybridization between GM soybean to wild soybean may have more impact on hybrid growth and fecundity, especially the seed germination rate and fecundity. F1, F2 and F3 had lower seed germination but higher pod and seed production than GM soybeans, and these parameters were close to those of wild soybean. Such characteristics acquired by gene flow have the potential to promote the adaptability of hybrids and may increase the possibility of dispersal of transgenes through seed systems.