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 have 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 soybean varieties on various biological processes, metabolic pathways, and key shikimic enzymes. Results Gene expression data showed that 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 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 hormone and defense response in plants. The observed unintended effects in GM herbicide-tolerant varieties unravel 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. The energy metabolism and carbon flux were differently affected in these varieties. Oxidative stress, more specifically glutathione metabolism, induced by GBH, was also 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 transcriptomics, can be considered tools to support risk assessment in detecting unintended effects due to the GBH application.

The genetic architecture and population genomic signatures of glyphosate resistance in Amaranthus tuberculatus

“…The synthesis of several natural products, including pigments and hormones, directly requires intermediates from the shikimate pathway (Maeda & Dudareva, 2012); similar to Zanatta et al, (2020), we find that genes functioning in response to chemicals are involved in diverse regulation of auxin, ethylene, abscisic acid, jasmonic acid and gibberellin. Since glyphosate accumulation occurs in active metabolic tissues (Cakmak et al, 2009), the primary location of plant hormone production, part of the toxicity induced by glyphosate is known to be the hormonal imbalance that influences both growth and development (Gomes et al, 2014).…”

“…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 six GO categories that were significant even after conservative Bonferroni correction, four were related to metabolism or biosynthesis.…”

“…Since glyphosate accumulation occurs in active metabolic tissues (Cakmak et al, 2009), the primary location of plant hormone production, part of the toxicity induced by glyphosate is known to be the hormonal imbalance that influences both growth and development (Gomes et al, 2014). 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 et al, 2020) provides an interesting comparison, 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.…”

Untargeted Proteomics-Based Approach to Investigate Unintended Changes in Genetically Modified Maize for Environmental Risk Assessment Purpose

“…Profiling techniques are broadly accepted as being capable of delivering sound descriptions of their target class of molecule in a range of diverse field from molecular medicine to food safety and plant physiology studies (Karahalil, 2016;Argueso et al, 2019;Mehta et al, 2019;Carrera et al, 2020). A number of molecular profiling studies have already indicated unintended effects of genetic modification (Coll et al, 2011;Wang et al, 2015Wang et al, , 2019Zanatta et al, 2020). These studies revealed inter alia that compared to an effect of the genetic modification in the GM plants, there is also effects on the plant's physiology arising from (i) the genetic background, (ii) environmental conditions during growth, (iii) sampling procedures and (iv) plant-to-plant variability.…”