Abstract
It is essential to assess environmental impact of transgene flow from genetically engineered crops to their wild or weedy relatives before commercialization. Measuring comparative trials of fitness in the transgene-flow-resulted hybrids plays the key role in the assessment, where the segregated isogenic hybrid lineages/subpopulations with or without a transgene of the same genomic background are involved. Here, we report substantial genomic differentiation between transgene-present and -absent lineages (F2-F3) divided by a glyphosate-resistance transgene from a crop-wild/weed hybrid population in rice. We further confirmed that such differentiation is attributed to increased frequencies of crop-parent alleles in transgenic hybrid lineages at multiple loci across the genome, as estimated by SSR (simple sequence repeat) markers. Such preferential transmission of parental alleles was also found in equally divided crop-wild/weed hybrid lineages with or without a particular neutral SSR identifier. We conclude that selecting either a transgene or neutral marker as an identifier to create hybrid lineages will result in different genomic background of the lineages due to non-random transmission of parental alleles. Non-random allele transmission may misrepresent the outcomes of fitness effects. We therefore propose seeking other means to evaluate fitness effects of transgenes for assessing environmental impact caused by crop-to-wild/weed gene flow.
Highlights
The undesired environmental impact caused by transgene flow from genetically engineered (GE) crops to their wild and weedy relatives has stimulated great biosafety concerns worldwide[1,2,3,4,5,6]
The Fst values between the corresponding ideal groups were all less than 0.001 for both crop-wild/weed hybrid populations (Table 1), suggesting extremely low genomic differentiation. These results indicated that the division of transgenic and non-transgenic hybrid lineages using the transgene as an identifier would result in differences in their genomic background, probably due to the non-random transmission of parental alleles
The neutrality test confirmed the significant deviation of parental alleles from the theoretical values at most of these loci for both crop-wild and crop-weed hybrid lineages (Supplementary Tables 3, 4)
Summary
The undesired environmental impact caused by transgene flow from genetically engineered (GE) crops to their wild and weedy relatives has stimulated great biosafety concerns worldwide[1,2,3,4,5,6]. The common practice to assess such impact includes two key components: determining frequencies of (trans)gene flow and estimating fitness effects of a transgene acquired by wild/weedy relative populations[5,6,7]. Transgenic fitness is estimated in a common-garden experiment, where artificially produced ISOGENIC hybrid lineages (or subpopulations) with or without a transgene from a crop-wild/weed hybrid population (F2 or BC1) are included for comparison[10, 17,18,19,20,21,22]. In our common garden experiment aimed to estimate fitness of an epsps (5-enolpyruvoylshikimate-3phosphate synthase) transgene, we observed phenotypic differences between F3 transgenic and non-transgenic seedlings derived from the same crop-wild F1 hybrids (Fig. 2). Can the artificial selection for a specific gene (identifier) distort a part of the Hybrid population F2-W F3-W
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