ORIGINAL ABSTRACT

Transgene flow from genetically engineered (GE) crops to their wild relatives has aroused worldwide biosafety concerns. Environmental impact caused by transgene flow from GE glyphosate herbicide-tolerant rice overexpressing the endogenous EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) transgene to its wild relatives has become a great concern. This is due to the significantly increased fitness conferred by the transgene in crop-wild hybrids. Whether the increased fitness is maintained consistently in the advanced generations of the hybrid progenies is unclear and needs science-based evaluation. Such evaluation plays an essential role in understanding the potential environmental impact caused, particularly by the EPSPS transgene. We therefore examined the relative expression quantities (REQs) of the EPSPS (trans)gene and fitness-related traits in advanced F3-F5 hybrid lineages derived from crosses between GE EPSPS rice (Oryza sativa) and two wild rice (Oryza rufipogon) populations in common garden experiments. Our results showed that the crop-wild rice hybrid lineages containing the transgene have significantly higher REQs of the EPSPS (trans)gene and increased values of the fitness-related traits, including the number of tillers, panicles, and seeds per plant. In addition, the fitness benefit, conferred by overexpressing the EPSPS transgene, presented consistently in GE F3-F5 hybrid lineages. Consequently, the overexpression of the rice endogenous EPSPS transgene may consistently increase the fitness of crop-wild rice hybrid progenies in advanced generations, which may promote the persistence and spread of the transgene in wild rice populations. Thus, assessing the long-term environmental impact caused by the outflow of the glyphosate-tolerant EPSPS transgene from GE rice should be seriously considered.