Farmers across the globe have increasingly adopted genetically modified crops that incorporate proteins derived from Bacillus thuringiensis (Bt) bacteria. These Bt proteins have become integral to pest management strategies, primarily because they selectively target specific agricultural pests while being harmless to humans and wildlife. By drastically reducing the need for insecticide applications, such innovations have ushered in substantial economic and environmental benefits, enabling farmers to cultivate crops more sustainably. However, as reliance on Bt crops has grown, so too has the emergence of pest resistance, with at least 11 notable pest species developing adaptive traits that diminish the effectiveness of these crops. This evolving resistance presents a persistent challenge, necessitating the exploration of innovative strategies to counteract these trends.
A recent study published in the Proceedings of the National Academy of Sciences offers crucial insights into an effective natural strategy for mitigating pest resistance to Bt proteins. Conducted by researchers at both the University of Arizona and Nanjing Agricultural University, the study unearthed an intriguing mechanism behind the efficacy of the Cry1Ab protein, one of the most widely used Bt proteins against pests like the Asian corn borer. Researchers discovered that this specific protein kills caterpillar pests through two distinct pathways rather than relying on a single one. Bruce Tabashnik, a significant contributor to this research and lead of the Department of Entomology at the University of Arizona, highlighted the importance of this dual-pathway mechanism in prolonging the efficacy of Cry1Ab. He explained that if pest populations acquire mutations that block one of these pathways, the alternative pathway remains fully capable of delivering a lethal effect. Consequently, it is only when both pathways are simultaneously compromised that pest resistance develops.
To clarify how important the gene editing aspects of their study were, the researchers investigated how disrupting the receptors ABCC2, ABCC3, and cadherin influenced the caterpillar’s responses to Bt proteins Cry1Ab and Cry1Fa. The receptors in question are akin to locks that Bt proteins must fit into to exert their lethal effects on the pests. The innovative gene editing techniques employed allowed the team to systematically disable these receptors in the Asian corn borer caterpillars, cultivating a more profound understanding of the precise mechanism through which the Bt proteins operate.
The defining experiment began by examining how these targeted disruptions in receptors impacted the caterpillar’s susceptibility to the two distinct Bt proteins. During their investigation, researchers found that Cry1Ab operated through two different pathways, with one critically depending on the receptor ABCC2, while the other pathway required both cadherin and ABCC3 to facilitate the lethal interaction. The redundancy embedded in the toxic pathway of Cry1Ab significantly increases the challenge for pests to evolve resistance. The necessity for simultaneous mutations disrupting both pathways to grant survival is essentially a barrier against rapid resistance development.
Conversely, Cry1Fa functions differently; it utilizes a single pathway contingent on the presence of ABCC2. The implication is that should the pest develop a mutation disrupting ABCC2, it can quickly achieve high levels of resistance to Cry1Fa. This delineation of resistance mechanisms points to a critical understanding of the evolutionary dynamics unfolding in pest populations exposed to these Bt proteins.
To further validate their findings, the researchers engineered a cell line derived from a different lepidopteran pest—the fall armyworm—to express the receptors found in the Asian corn borer. Once modified, these cells allowed for a practical verification of the pathways suspected to underlie Cry1Ab’s increased efficacy. The outcomes of the modified cells echoed the initial hypotheses. Revealingly, cells that produced ABCC2 exhibited susceptibility to both Bt proteins, reinforcing the notion that ABCC2 serves as a pivotal receptor in mediating toxic effects. The experiments demonstrated that while cadherin and ABCC3 receptors facilitated susceptibility to Cry1Ab, they were not involved in the interaction with Cry1Fa, corroborating the hypothesis of pathway redundancy.
The study’s implications extend beyond theoretical musings; they touch on practical agricultural realities, especially regarding pest management practices in North America and Europe. Observations regarding the European corn borer’s resistance patterns align closely with the findings derived from the Asian corn borer. Notably, the evolution of resistance to Cry1Ab has been significantly slower over 21 years compared to the 12 years observed for Cry1Fa in Canada. This discrepancy suggests that, akin to its Asian counterpart, the European corn borer potentially benefits from having two toxic pathways for Cry1Ab, albeit just one for Cry1Fa. Exploring this hypothesis through similar experiments as those conducted with the Asian corn borer could yield valuable insights.
This emerging understanding of functional redundancy represents a promising avenue for improving Bt crop sustainability. As pathogens and pests continue to adapt and evolve, the agricultural sector stands to gain from more nuanced approaches that incorporate multiple-target strategies. By identifying native Bt proteins or engineering new variants capable of exploiting multiple toxic pathways against pests, researchers can create a robust framework for enhancing pest management systems. These dual-pathway Bt proteins could offer a critical measure in the fight against the rise of resistant pest populations, ultimately bolstering food security in a rapidly changing agricultural landscape.
In conclusion, the innovative research undertaken by this international team stands as a beacon of hope against the mounting challenge of pest resistance. The discovery of functional redundancy in the toxic pathways of Bt proteins embodies a pivotal breakthrough that can shape future agricultural strategies. By embracing these insights, the path is paved toward a more sustainable cultivation of crops, preserving the delicate balance between modern agriculture and environmental health.
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Article Title: Functional redundancy in the toxic pathway of Bt protein Cry1Ab but not Cry1Fa against the Asian corn borer
News Publication Date: 18-Apr-2025
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Keywords: Bt crops, pest resistance, Cry1Ab, Cry1Fa, Bacillus thuringiensis, agriculture, sustainability, gene editing, functional redundancy, Asian corn borer.
Tags: adaptive traits in agricultural pestsagricultural research advancementsBacillus thuringiensis proteinsCry1Ab protein efficacyeconomic benefits of Bt cropsenvironmental benefits of Bt cropsgenetically modified cropsinnovative pest control methodsnatural strategies against pest resistancepest management strategiespest resistance challengessustainable farming practices
