Continued overexpression of EPSPS transgene enhances fitness in multigeneration crop–wild rice hybrids and its long-term environmental impact

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 <i>EPSPS</i> (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 <i>EPSPS</i> transgene. We therefore examined the relative expression quantities (REQs) of the <i>EPSPS</i> (trans)gene and fitness-related traits in advanced F₃-F₅ hybrid lineages derived from crosses between GE <i>EPSPS</i> rice (<i>Oryza sativa</i>) and two wild rice (<i>Oryza rufipogon</i>) populations in common garden experiments. Our results showed that the crop-wild rice hybrid lineages containing the transgene have significantly higher REQs of the <i>EPSPS</i> (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 <i>EPSPS</i> transgene, presented consistently in GE F₃-F₅ hybrid lineages. Consequently, the overexpression of the rice endogenous <i>EPSPS</i> 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 <i>EPSPS</i> transgene from GE rice should be seriously considered.