CP4-EPSPS protein expression levels
To facilitate the biosafety assessment of transgene escape to
populations of wild relative species, it is important to conduct
scientific research to properly estimate the expression levels of
transgenes in wild individuals as well as the inheritance of the
transgenes in wild populations (Zhu et al. 2004; Lu and Snow 2005; Lu
2008). In the present study, ELISA was used to detect CP4-EPSPS protein
expression levels at different soybean growth stages, while EPSPS
protein was detectable in F1-, F2- and
F3-resistant plants. This observation was consistent
with the findings of Kubo et al. (2013), who also showed that the gene
was stably expressed and produced functional protein. Our study and the
studies mentioned previously (Kubo et al. 2013) suggest that the
transgene will be able to confer tolerance to glyphosate in the new host
wild population. In addition, it is worth noting that a significant
decline in the total protein content in both hybrids was observed
compared to that in GM soybean. Since tolerance to glyphosate is very
dependent on EPSPS protein expression levels in plant tissues, a
reduction in the amount of endotoxin proteins in hybrids may contribute
to the variability in tolerance. Consistent with our results, a similar
conclusion was reported by Zhu et al. (2004), who also reported a
decrease in Bt protein content in transgenic Brassica rapa and
crop-weed hybrids. This difference may be associated with a weedy
genetic background, positional effects, and the number of transgenes
inserted per event (Moon et al. 2007).
Our study confirmed that the CP4-EPSPS protein was stably expressed in
the hybrid soybean line, endowing these hybrid soybeans with herbicide
tolerance, and the RR, RS and SS of F2 or
F3 populations had similar seed germination, aboveground
biomass, pod and seed number per plant and 100-seed weight, which
indicated that the presence and absence of EPSPS or the copy
number of the EPSPS gene were not significantly correlated with
vegetative growth and fecundity. In contrast, heterosis between GM and
wild soybean raises new competitive advantages for hybrids, allowing
hybrids to obtain some similar growth characteristics as female wild
soybean, such as seed dormancy, a higher stable grain weight, and
greater pod and seed numbers per plant; these growth characteristics
could increase the possibility of
dispersal of transgenes through seed systems and may adversely affect
genetic and species diversity of wild soybean. Thus, it is critical to
build effective risk management and control measures for the gene flow
of transgenes from GM soybean to wild soybean before commercial planting
of GM soybean in China.