Genomics and Applied Biology 2024, Vol.15, No.3, 153-161 http://bioscipublisher.com/index.php/gab 158 Moreover, microRNAs (miRNAs) have been implicated in the post-transcriptional regulation of Cry receptor genes. For example, miR-998-3p targets the coding sequence of the ABCC2 gene, a known Cry1Ac receptor, and down-regulates its expression in several lepidopteran pests, thereby increasing resistance to Cry1Ac toxin (Zhu et al., 2019). 5.2 Impact on the insecticidal properties of Bt The epigenetic regulation of Cry gene expression has significant implications for the insecticidal properties of Bt. The down-regulation or mutation of Cry receptor genes, mediated by transcription factors and miRNAs, can lead to reduced binding of Cry toxins to midgut cells in insects, thereby decreasing their susceptibility to these toxins. For instance, the reduced expression of PxmALP and PxABCB1 in P. xylostella due to the action of PxGATAd and PxJun, respectively, results in higher levels of resistance to Cry1Ac toxin (Qin et al., 2021; Guo et al., 2022). Similarly, the down-regulation of ABCC2 by miR-998-3p in various lepidopteran pests also contributes to increased resistance (Zhu et al., 2019). 6 Environmental Factors Influencing Epigenetic Modifications in Bt 6.1 Role of environmental stressors in epigenetic changes Environmental stressors such as drought, cold, salinity, and heat can induce significant epigenetic changes in organisms, including Bt (Bacillus thuringiensis). These stressors can lead to alterations in DNA methylation, histone modifications, and the expression of non-coding RNAs, which in turn affect gene expression and phenotypic traits. For instance, plants exposed to abiotic stresses adopt epigenetic changes to cope with these conditions, which can be temporary or stable and inheritable (Chang et al., 2019; Akhter et al., 2021). Similarly, in Bt, environmental stressors may trigger epigenetic modifications that help the bacteria adapt to and survive in challenging environments. 6.2 Interaction between Bt and host plants The interaction between Bt and host plants is another critical factor influencing epigenetic modifications. Plants and their associated microorganisms, including Bt, are exposed to fluctuating environmental conditions that necessitate adaptive responses. Epigenetic regulation plays a significant role in this interaction by modulating gene expression patterns in response to environmental cues. For example, plants exhibit phenotypic plasticity largely determined by epigenetic regulation, which allows them to adapt to varying environmental conditions (Brukhin and Albertini, 2021). This interaction can lead to epigenetic changes in Bt, potentially affecting its virulence and effectiveness as a biocontrol agent. 6.3 Influence of external chemicals and pollutants External chemicals and pollutants are known to induce epigenetic changes in various organisms, including Bt. Pollutants such as heavy metals, endocrine disruptors, and other environmental contaminants can cause oxidative stress and DNA damage, leading to epigenetic modifications like DNA methylation and histone modifications (Sharavanan et al., 2019; Han and Huang, 2021). These changes can result in gene dysregulation and altered physiological responses. For instance, exposure to pollutants has been shown to induce epigenetic changes that affect reproductive toxicity and other health outcomes in different species (Sharavanan et al., 2019). In Bt, similar mechanisms may be at play, where exposure to external chemicals and pollutants could lead to epigenetic modifications that impact its gene expression and overall functionality. 7 Implications of Epigenetic Modifications for Bt Application 7.1 Epigenetic modifications and Bt efficacy Epigenetic modifications, such as DNA methylation and histone modifications, play a crucial role in regulating gene expression without altering the underlying DNA sequence. These modifications can significantly impact the efficacy of Bacillus thuringiensis (Bt) by influencing the expression of genes involved in toxin production and resistance mechanisms. For instance, the reversible nature of epigenetic changes, such as DNA methylation and histone acetylation, can modulate the expression of genes that are critical for Bt's insecticidal activity (Han et al., 2019; Jin et al., 2021). Understanding these modifications can help in optimizing Bt strains for enhanced efficacy and stability in various environmental conditions.
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