Abstract
Genetically engineered (GE) rice endogenous epsps (5-enolpyruvoylshikimate-3-phosphate synthase) gene overexpressing EPSPS can increase glyphosate herbicide-resistance of cultivated rice. This type of epsps transgene can enhance the fecundity of rice crop-weed hybrid offspring in the absence of glyphosate, stimulating great concerns over undesired environmental impacts of transgene flow to populations of wild relatives. Here, we report the substantial alteration of phenology and fitness traits in F1-F3 crop-wild hybrid descendants derived from crosses between an epsps GE rice line and two endangered wild rice (Oryza rufipogon) populations, based on the common-garden field experiments. Under the glyphosate-free condition, transgenic hybrid lineages showed significantly earlier tillering and flowering, as well as increased fecundity and overwintering survival/regeneration abilities. In addition, a negative correlation was observed between the contents of endogenous EPSPS of wild, weedy, and cultivated rice parents and fitness differences caused by the incorporation of the epsps transgene. Namely, a lower level of endogenous EPSPS in the transgene-recipient populations displayed a more pronounced enhancement in fitness. The altered phenology and enhanced fitness of crop-wild hybrid offspring by the epsps transgene may cause unwanted environmental consequences when this type of glyphosate-resistance transgene introgressed into wild rice populations through gene flow.
Highlights
Engineered (GE) rice endogenous epsps (5-enolpyruvoylshikimate-3-phosphate synthase) gene overexpressing EPSPS can increase glyphosate herbicide-resistance of cultivated rice
(1) Does the over-expressing epsps transgene change the life-cycle traits of crop-wild hybrid descendants in the glyphosate-free environment? (2) Does the epsps transgene increase the fecundity and over-winter survival of crop-wild hybrid descendants? (3) Does the genetic background of transgene recipients affect the fitness of the epsps transgene in different types of rice parents, including Wild parent (WR), WDR, and cultivated rice? The answer of these questions will help us to appropriately estimate the potential environmental/ecological consequences caused by introgression of the overexpressing epsps herbicide-resistance transgene into WR populations, likely to predict the potential consequences for other crop-wild transgene introgressions
We found altered phenological characteristics, increased fecundity, and enhanced ability of overwinter survival for stocks/tillers in the crop-wild rice hybrid lineages containing an epsps glyphosate-resistance transgene, based on our three-year common-garden experiments
Summary
Engineered (GE) rice endogenous epsps (5-enolpyruvoylshikimate-3-phosphate synthase) gene overexpressing EPSPS can increase glyphosate herbicide-resistance of cultivated rice This type of epsps transgene can enhance the fecundity of rice crop-weed hybrid offspring in the absence of glyphosate, stimulating great concerns over undesired environmental impacts of transgene flow to populations of wild relatives. The introgression of herbicide-resistance transgenes from GE rice into WDR populations through spontaneous gene flow and its social/environmental impact by increased weed problems becomes a great biosafety concern[3]. A recent study reported significantly increased fecundity and ratios of tryptophan concentration and photosynthesis in crop-weed hybrid lineages containing an herbicide-resistance transgene, at the absence of herbicide[16] This transgene is an engineered rice endogenous epsps (5-enolpyruvoylshikimate-3-phosphate synthase) gene that overexpresses EPSPS. Will the epsps herbicide-resistance transgene introgressed into any of the wild rice species produce the same fitness effect to their populations?
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