Genomics and Applied Biology 2024, Vol.15, No.3, 153-161 http://bioscipublisher.com/index.php/gab 154 playing a critical role in various biological processes such as development, cellular differentiation, and the organism's response to environmental changes. By influencing gene expression patterns, epigenetic mechanisms help orchestrate complex processes like tissue development and adaptation to external stimuli, thus maintaining cellular and organismal homeostasis (Mathur et al., 2022; Lempiäinen and Garcia, 2023). Key concepts in epigenetics include DNA methylation, histone modifications, and the roles of non-coding RNAs. DNA methylation involves adding methyl groups to cytosine residues in DNA, often leading to gene silencing and impacting cellular identity and gene regulation. Histone modifications encompass various post-translational changes to histone proteins, such as acetylation and methylation, which can alter chromatin structure and modulate gene expression. Additionally, non-coding RNAs, such as long non-coding RNAs (lncRNAs) and microRNAs, contribute significantly to the regulation of gene expression by interacting with chromatin-modifying complexes and influencing both transcriptional and post-transcriptional processes (Jin et al., 2021; Ji et al., 2023). These mechanisms work together to create a complex and dynamic regulatory network that governs gene expression. 2.2 Mechanisms of epigenetic modifications Epigenetic modifications involve several key mechanisms that influence gene expression. One fundamental mechanism is DNA methylation, which entails the addition of a methyl group to cytosine residues in DNA. This addition typically leads to gene silencing and is crucial for maintaining cellular identity and regulating gene expression (Davalos and Esteller, 2022; Ji et al., 2023). Another significant mechanism is histone modifications, where histones, the protein components of chromatin, undergo various post-translational modifications such as acetylation, methylation, phosphorylation, and ubiquitination. These modifications can alter the chromatin structure and thereby impact gene expression. For example, histone acetylation generally promotes gene expression by loosening the chromatin structure, whereas histone methylation can either activate or repress gene expression depending on the specific residues modified (Sandholtz et al., 2020; García-Giménez et al., 2021; Zaib et al., 2021). In addition to these, non-coding RNAs, including long non-coding RNAs (lncRNAs) and microRNAs, also play crucial roles in regulating gene expression. These RNAs can operate at both the transcriptional and post-transcriptional levels. They exert their effects by recruiting chromatin-modifying complexes to specific genomic loci, thus influencing the epigenetic landscape (Kan et al., 2021; Mathur et al., 2022). 2.3 Epigenetic landscape in Bt In Bacillus thuringiensis (Bt), the epigenetic landscape is shaped by similar mechanisms observed in eukaryotic systems, albeit adapted to the prokaryotic context. DNA methylation in Bt can regulate gene expression and is involved in processes such as sporulation and toxin production. Histone-like proteins in Bt may undergo modifications that affect chromatin structure and gene regulation, although the specific types and roles of these modifications are less well-characterized compared to eukaryotes (Jin et al., 2021; Lempiäinen and Garcia, 2023). Recent studies have highlighted the importance of epigenetic regulation in Bt's ability to adapt to environmental changes and stress conditions. For example, oxidative stress can lead to alterations in the epigenetic landscape, affecting gene expression and potentially contributing to the organism's pathogenicity and resistance mechanisms (García-Giménez et al., 2021). Understanding these epigenetic modifications in Bt can provide insights into its biology and inform strategies for its use in biocontrol and other applications. 3 Types of Epigenetic Modifications in Bt 3.1 DNA methylation in Bt DNA methylation is a well-studied epigenetic modification that involves the addition of a methyl group to the DNA molecule, typically at the fifth carbon of the cytosine ring, resulting in 5-methylcytosine. This modification can lead to the repression of gene expression by altering the interaction between DNA and transcriptional machinery. DNA methylation is a primary mechanism for epigenetic variation and can induce phenotypic changes in response to environmental stresses (Akhter et al., 2021; Kumar and Mohapatra, 2021).
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