Stacked genetically modified soybean harboring herbicide resistance and insecticide rCry1Ac shows strong defense and redox homeostasis disturbance after glyphosate-based herbicide application

Abstract

Background: World agricultural production of genetically modified (GM) products, in particular, the combination of different traits/genes in the same plant has been a trend over the last decade. There has been concerns raised over stacking multiple herbicide and insect-resistant transgenes that could result in fitness costs depending on the type and strength of selection pressures exerted by the environment. Here, we report the results of transcriptomic analysis comparing the effect of glyphosate-based herbicide (GBH) in the single-transgene versus stacked, herbicide resistant soybeans varieties on various biological processes, metabolic pathways, and main shikimic enzymes.Results: Gene expression data were grouped according to the 'herbicide treatment factor'. Defense metabolism and redox homeostasis were equally modulated in single-transgene and stacked variety samples. Carbon accumulation and energy metabolisms were distinct between the varieties and photosynthesis metabolism was found negatively affected in the single-transgene variety only. In the stacked variety, the shikimate pathway was modulated by the accumulation of transcripts from phenylalanine gene and other cascade genes. As expected, the RT-PCR results confirmed that the expression of native EPSPS was upregulated in both varieties when herbicide was applied. On the other hand, transgenic EPSPS expression was down regulated in both GM varieties upon herbicide application which cannot be explained. Conclusion: Glyphosate-based herbicides toxicity suggests its effects on carbon central metabolism and flux, redox metabolism, photosynthesis, and to the plant’s hormone and defense response. The observed unintended effects in GM herbicide-tolerant varieties unravels the deleterious effects previously observed on GM tolerant varieties growth and production. The impact of GBH on shikimate and cascade pathways was observed in terms of both native and transgenic insensitive EPSPS modulation, alteration of jasmonic acid and lignin metabolism in both single-transgene and stacked variety. Whereas the energy metabolism and carbon flux were differently affected in these varieties. Oxidative stress, more specifically glutathione metabolism, induced by GBH, was observed in this study. The stacked variety showed a more pronounced stress response (activation of specific stress defense proteins, Rboh, WRKY) and secondary compounds (β-glucosidase, isoflavone 7-O-methyltransferase). Omics profiling techniques, such as transcriptomic, can be considered tools to support risk assessment based on detecting unintended effects due to the GBH application.

The genetic architecture and genomic context of glyphosate resistance in Amaranthus tuberculatus

“…Relatedly, our genes were enriched for function in multicellular organismal processes and development, with roles in dormancy, germination, photomorphogenesis and flowering time, several of which also being enriched in response to herbicides in the single-transgene soybean variety (Zanatta et al, 2020). Together, our results suggest a key role of pleiotropic constraints, in the form of trade-offs with growth and reproduction, mediating the frequency of alleles contributing to the polygenic bases of glyphosate resistance.…”

“…In particular, a recent analysis of the transcriptomic response to glyphosate in genetically modified soybean with one or multiple stacked TSR mechanisms (Zanatta, Benevenuto, Nodari, & Agapito-Tenfen, 2020) provides an interesting case study, as the genetic architecture of NTSR we identify is predominantly on the background of two large-effect TSR mechanisms, akin to their genetically modified stacked-TSR backgrounds. The KEGG pathways in soybean with the largest number of genes involved in response to glyphosate were metabolic pathways and biosynthesis of secondary metabolites (Zanatta et al, 2020). In comparison, of our 6 GO categories that were significant even after conservative Bonferroni correction, 4 were related to metabolism or biosynthesis.…”