Transgene behavior in Zea mays L. crosses across different genetic backgrounds: Segregation patterns, cry1Ab transgene expression, insecticidal protein concentration and bioactivity against insect pests

Abstract

Brazil and South Africa, countries with economies in transition, are characterized by a dual agrarian structure co-occurring, sometimes, alongside in the same region. Large-scale commercial farming produces crops for export to global markets on the one hand, and smallscale farming, on the other hand, provides for subsistence and local markets. In both systems, maize (Zea mays) is a key crop for these two countries. For the commercial system, maize is a commodity crop while for the small-scale system it is the prime staple crop. In commercial systems, farmers predominantly grow genetically modified (GM) hybrid maize. In small-scale systems, farmers rely on open pollinated varieties (OPVs) and/or landraces and are largely dependent on seed saving systems. The aim of this study was to understand the relationship between transgene expression rates, the resulting concentrations of the transgene product (Bt protein) and its bioactivity in insect pests following transgene flow from GM hybrid maize into non-genetically modified, non-GM near-isogenic maize hybrid (ISO) and OPVs. We modeled segregation patterns and measured cry1Ab transgene expression (mRNA quantification), Cry1Ab protein concentration and pest survival. Two groups of F1, F2 crosses and backcrosses with GM, ISO and OPV maize varieties from Brazil and South Africa were used. Bioassays with the larvae of two lepidopteran maize pest species, Helicoverpa armigera and Spodoptera littoralis, were carried out. Overall, the cry1Ab transgene outcrossed effectively into the genetic backgrounds tested. The cry1Ab transgene was stably expressed in both ISO and OPV genetic backgrounds. Transgene introgression led to consistent, though highly variable, concentrations of Cry1Ab toxins that were similar to those observed in GM parental maize. Most crosses, but not all, suggested the expected Mendelian segregation pattern. Transgene expression rates were significantly higher than expected from purely Mendelian segregation in the South African crosses. In South African materials, ISO and OPV crosses produced significantly lower Cry1Ab

Transgene behavior in genetically modified teosinte hybrid plants: transcriptome expression, insecticidal protein production and bioactivity against a target insect pest

“…Future research will benefit from a note of caution stemming from results presented here: we show here that there is poor or no correlation between the active presence of the cry1Ab transgene, the corresponding levels of mRNA or Bt toxin in leaves, and the insecticidal bioactivity of the toxin. These results are similar to earlier findings in crossing experiments with open-pollinated varieties of maize, instead of teosinte plants [39]. As in those complementary studies, we confirm here again that cry1Ab-derived mRNA is not a good predictor of Cry1Ab concentration or insect mortality.…”

“…Overall, as previously observed in experiments with non-GM maize plants (i.e., hybrids and open-pollinated maize varieties, Lohn et al [39]), the mRNA levels of the cry1Ab transgene in the crop-hybrid teosinte plants do not appear to determine directly, in any measurable way, the concentration of the produced Cry1Ab toxin. Based on other studies, the suggestion for such an apparently paradoxical behavior is that there are other plant regulatory processes influencing the final concentration levels of the Cry1Ab toxin, such as post-transcriptional, translational and protein degradation/synthesis regulation [40][41][42][43], or even promoter activity changes that could be influencing in the mRNA level changes [44].…”

Agronomic characteristics and genetic relationship of putative transgenic rice lines of cv. Fatmawati with the Glu-1Dx5 transgene

“…This is due to self-pollination that results in genotypic segregation, in which some plants contained the Glu-1Dx5 transgene, but some did not. This is because that transgene segregation may occur after consecutive self-pollination as reported by for UidA gene (GUS) and cry1Ab transgene Lohn et al 2020). This data confirms that the Glu-1Dx5 transgene has been integrated into the rice genome of cultivar Fatmawati.…”

Transgene Flow: Challenges to the On-Farm Conservation of Maize Landraces in the Brazilian Semi-Arid Region

“…Zenner-de-Polanía (2021) [ 37 ] reported that the greatest concern regarding maize transgene flow is a potential damage to the diversity of existing breeds and the accumulation of transgenic DNA. Lonh et al (2020) [ 38 ] observed degeneration of maize landraces in a study carried out in the state of Santa Catarina in the southern region of Brazil, where the transgenic protein Cry1AB was introduced in a landrace to monitor the evolution of gene expression and concentration as well as its effects on the mortality of insects Helicoverpa armigera and Spodoptera littoralis . It was concluded that unintentional crossing between landraces and transgenic varieties causes irreversible damage since gene transcription and insect control bioactivation is stable and reliable.…”