Bt Research 2025, Vol.16, No.3, 118-124 http://microbescipublisher.com/index.php/bt 120 Figure 1 Regulation of histone modifications by ncRNAs. H3, H4, H2B, H2A—histone proteins; K—lysine residue; S—serine residue. The part of the figure with the repressive histone marks is highlighted in blue; the part with the activating histone marks is highlighted in red (Adopted from Bure et al., 2022) 3.2 Impact on sporulation and virulence The spore formation of Bt and the expression of virulence proteins (such as Cry protein) are regulated at multiple levels, including transcriptional, post-transcriptional, metabolic and post-translational levels. At present, there is no direct evidence to prove that DNA methylation or histone modification directly regulates the cry gene. However, some key regulatory factors, such as Spo0A and different σ factors, play important roles in the regulation of spore formation and virulence genes (Deng et al., 2014). In addition, the diversity of plasmids and the presence of movable genetic elements also provide a genetic basis for the virulence and adaptability of Bt. The stability and expression patterns of these components are likely to be affected by epigenetic mechanisms (Gillis et al., 2018). 3.3 Stress response and adaptability Bt shows strong adaptability in the face of environmental pressure, which is closely related to its rich active gene pool and diverse plasmids. Although there are not many studies on the involvement of epigenetic modifications in Bt stress responses at present, in insect hosts, studies have demonstrated that histone acetylation, DNA methylation and miRNA regulation affect immunity and stress responses (Mukherjee et al., 2017). These mechanisms may enable Bt to survive and maintain pathogenicity in complex environments by altering the expression of stress-related genes. Furthermore, tools such as CRISPR-Cas9 have been used for genomic modification of Bt. Although mainly for tag insertion and tracking, they also provide methods for studying its epigenetic regulation (Higgins et al., 2024). 4 Impact on Gene Expression and Toxin Production 4.1 Cry andCyt gene regulation The expression of both Cry and Cyt toxin genes is influenced by epigenetic mechanisms. DNA methylation and histone modification mainly alter chromatin structure, affect the transcriptional levels of related genes, and ultimately achieve the purpose of regulating toxin production (Gu et al., 2024). Non-coding Rnas (such as mirnas) also have a similar process. It inhibits or activates the expression of Cry and Cyt genes by acting on mRNA (Perri et al., 2017). These regulations are all important ways for Bt to flexibly adjust the amount of toxins in different environments and adapt to external pressure.
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