The Impact of Environmental Stress on Bt Crop Performance

An Extended Investigation of Unexpected Helicoverpa zea (Boddie) Survival and Ear Injury on a Transgenic Maize Hybrid Expressing Cry1A/Cry2A/Vip3A Toxins

The wide occurrence of resistance to Cry1A and Cry2A insecticidal toxins from Bacillus thuringiensis (Bt) in the corn earworm/bollworm Helicoverpa zea (Boddie) leaves the Vip3A toxin produced during the vegetative stage of Bt as the only fully active toxin expressed in transgenic crops to control H. zea in the U.S.A. During 2021, the first unexpected survival of H. zea and injury (UXI) on a maize hybrid expressing Cry1A.105, Cry2Ab2, and Vip3Aa in Louisiana, U.S.A. were observed in two sentinel plots used for resistance monitoring. A follow-up intensive investigation was conducted with two H. zea populations established from larvae collected from the two UXI plots. The main goal of this study was to reveal if the unexpected damage was due to resistance development in the insect to the Bt toxins expressed in the maize hybrid. Diet-overlay bioassays showed that the two populations were highly resistant to Cry1A.105, moderately resistant to Cry2Ab2, but still highly susceptible to Vip3Aa when compared to a reference susceptible strain. In 10 d assays with detached ears, the larvae of the two UXI populations exhibited survival on ears expressing only Cry toxins but presented near 100% mortality on maize hybrids containing both cry and vip3A transgenes. Multiple field trials over three years demonstrated that natural H. zea populations in Louisiana were highly resistant to maize expressing only Cry toxins but remained susceptible to all tested hybrids containing cry and vip3A genes. Altogether, the results of this study suggest that the observed UXIs in Louisiana were associated with a resistance to Cry toxins but were not due to a resistance to Vip3A. The possible causes of the UXIs are discussed. The results generated and procedures adopted in this study help in determining thresholds for defining UXIs, assessing resistance risks, and documenting field resistance.

Performance of the domestic Bt corn event expressing pyramided Cry1Ab and Vip3Aa19 against the invasive Spodoptera frugiperda (J. E. Smith) in China

BACKGROUND

The invasive fall armyworm, Spodoptera frugiperda (J.E. Smith), has caused serious corn yield losses and increased the frequency of insecticide spraying on corn in Africa and Asia. Drawing lessons from the use of Bt corn to manage fall armyworm in the Americas, China released a certificate for the genetically modified corn event DBN3601T pyramidally expressing Cry1Ab and Vip3Aa19 for industrialization in 2021. Performance of the DBN3601T event against invasive fall armyworm in China was evaluated by plant tissue-based bioassays and field trials during 2019-2021.

RESULTS

In the bioassays, tissues and organs of DBN3601T corn differed significantly in lethality to fall armyworm neonates in the order: leaf > husk > tassel and kernel > silk. In field trials, compared with non-Bt corn, DBN3601T corn greatly suppressed fall armyworm populations and damage; larval density, damage incidence, and leaf damage scores for DBN3601T corn were significantly lower than for non-Bt corn at different vegetative stages, and efficacy against larval populations during the 3 years ranged from 95.24% to 98.30%.

CONCLUSION

A laboratory bioassay and 3-year field trials confirmed that DBN3601T corn greatly suppressed fall armyworm populations and has high potential as a control of this invasive pest, making it a key tactic for integrated management of fall armyworm in China. © 2022 Society of Chemical Industry.

Exploring the interaction between Cry1Ac protein and Zn2+, Cd2+ metal ions by fluorescence quenching and molecular docking approaches

Bacillus Thuringiensis (Bt) protein has a strong ability to complex with metal ions, which may increase the transport of metal ions in the soil multi-media system. In this study, the interactions between Cry1Ac protein and metal ions (Zn²⁺ and Cd²⁺) were investigated through spectroscopies and molecular docking methods. The spectra results showed that both Zn²⁺ and Cd²⁺ quenched the fluorescence intensity of Cry1Ac protein through the static quenching. The binding constants with 4-5 orders of magnitude also indicated the interactions between the ions and the Cry1Ac protein. The thermodynamic analysis showed that hydrogen bonds and van der Waals forces were predominant during the processes. In terms of the Förster non-radiation energy transfer theory, the binding distances between metal ions and Cry1Ac protein were approximately 0.21-0.24 nm, indicating the existence of a non-radiative energy transfer between them. Furthermore, molecular docking revealed that the metal ions participated in ligand binding with the Cry1Ac at the locations Asp569, Thr560, Asn564 and Gln566. The present work provided reasonable models helping us further understand the transport effect of heavy metals in the presence of Cry1Ac. The results could provide mechanistic insights into the nature of metal ions-Cry1Ac interactions and offer important information on the toxicity risk of metal ions-Cry1Ac binding interactions.

Development of a facile genetic transformation system for the Spanish elite rice paella genotype Bomba

We report the development of an efficient and reproducible genetic transformation system for the recalcitrant Spanish elite rice paella genotype, Bomba. Preconditioned embryos derived from dry seeds were bombarded with gold particles carrying a plasmid containing a screenable and a selectable marker. We confirmed integration and expression of hpt and gusA in the rice genome. Transformation frequency was ca: 10% in several independent experiments. We show Mendelian inheritance of the input transgenes and zygosity determination of the transgenic lines in the T1 generation. A unique and critical step for the regeneration of plants from transformed tissue was shading during the early stages of regeneration, combined with a specific cytokinin:auxin ration at the onset of shifting callus to regeneration media.

Environmental fate of Bt proteins in soil: Transport, adsorption/desorption and degradation

During the production and application of Bacillus thuringiensis (Bt) transgenic crops, large doses of insecticidal Bt toxic proteins are expressed continuously. The multi-interfacial behaviors of Bt proteins entering the environment in multi-media affects their states of existence transformation, transport and fate as well as biological and ecological impacts. Because both soil matrix and organisms will be exposed to Bt proteins to a certain extent, knowledge of the multi-interfacial behaviors and affecting factors of Bt proteins are vital not only for understanding the source-sink distribution mechanisms, predicting their bio-availability, but also for exploring the soil safety and environmental problems caused by the interaction between Bt proteins and soil matrix. This review summarized and analyzed various internal and external factors that affect the adsorption/ desorption and degradation of Bt proteins in the environment, so as to understand the multi-interfacial behaviors of Bt proteins. In addition, the reasons of concentration changes of Bt proteins in soil are discussed. This review will also discuss the existing knowledge of the combined effects of Bt proteins and other pollutants in environment. Finally, discussing the factors that should be considered when assessing the environmental risk of Bt proteins, thus to further improve the understanding of the environmental fate of Bt proteins.

Water Deprivation Induces Biochemical Changes Without Reduction in the Insecticidal Activity of Maize and Soybean Transgenic Plants

Like conventional crops, transgenic plants expressing insecticidal toxins from Bacillus thuringiensis (Bt) are subjected to water deprivation. However, the effects of water deprivation over the insecticidal activity of Bt plants are not well understood. We submitted Bt maize and Bt soybean to water deprivation and evaluated biochemical stress markers and the insecticidal activity of plants against target insects. Bt maize (DAS-Ø15Ø7-1 × MON-89Ø34-3 × MON-ØØ6Ø3-6 × SYN-IR162-4) containing the PowerCore Ultra traits, Bt soybean (DAS-444Ø6-6 × DAS-81419-2) with the Conkesta E3 traits, and commercial non-Bt cultivars were cultivated and exposed to water deprivation in the greenhouse. Leaves were harvested for quantification of hydrogen peroxide, malondialdeyde (MDA), and total phenolics and insecticidal activity. Maize or soybean leaf disks were used to evaluate the insecticidal activity against, respectively, Spodoptera frugiperda (J.E Smith) and Chrysodeixis includens (Walker) neonates. Except for Bt soybean, water deprivation increased hydrogen peroxide and MDA contents in Bt and non-Bt plants. Both biochemical markers of water deficit were observed in lower concentrations in Bt plants than in non-Bt commercial cultivars. Water deprivation did not result in changes of phenolic contents in Bt and non-Bt maize. For Bt or non-Bt soybean, phenolic contents were similar despite plants being exposed or not to water deprivation. Water deprivation did not alter substantially insect survival in non-Bt maize or non-Bt soybean. Despite water deprivation-induced biochemical changes in plants, both Bt plants maintained their insecticidal activity (100% mortality) against the target species.

Effect of Urea Spray on Boll Shell Insecticidal Protein Content in Bt Cotton

Reproductive organs of Bacillus thuringiensis transgenic cotton, which contribute to cotton final yield, have low insect resistant efficacy, so it is important to improve their insect resistance. This study was conducted to find out the impact of different urea spray doses on the expression of Cry1A protein in boll shell of Bt cotton (Sikang 1 and Sikang 3), and nitrogen metabolism in this process was also studied to uncover the physiological mechanism. The experiment with six urea doses was organized during peak boll stage in 2017 and 2018. The results showed that urea spray could significantly increase boll shell insecticidal protein contents in both cultivars, with the highest Bt protein content observed at 28-32 kg ha^-1 urea dose. In addition, urea spray increased the contents of soluble protein and free amino acid and the activities of GS, GOGAT, GOT, and GPT, but decreased the activities of peptidase and protease in boll shell. Correlation analysis showed that the amount of boll shell Bt protein was positively correlated with levels of soluble protein and amino acid, and activities of GS, GOGAT, GOT, and GPT, but negatively correlated with peptidase and protease activities. Thus, this study demonstrated that higher protein synthesis ability and lower proteolysis ability were related to increased Bt protein content in urea-sprayed boll shell.