Genomics and Applied Biology 2024, Vol.15, No.3, 153-161 http://bioscipublisher.com/index.php/gab 157 5 Case Study: Epigenetic Regulation of Cry Genes inBt Bacillus thuringiensis (Bt) is a bacterium known for its insecticidal properties, primarily due to the production of Cry proteins. These proteins are widely used in biopesticides and transgenic crops to control insect pests. However, the effectiveness of Bt products is increasingly threatened by the evolution of resistance in target insect populations. Understanding the molecular mechanisms, including epigenetic factors, that regulate Cry gene expression and contribute to resistance is crucial for the sustainable use of Bt-based technologies. 5.1 Analysis of epigenetic factors affecting Cry gene expression Recent studies have highlighted the role of various transcription factors and signaling pathways in the regulation of Cry gene expression. For instance, the MAPK signaling pathway has been shown to influence the expression of Cry1Ac receptor genes. In Plutella xylostella, the transcription factor PxGATAd, activated by the MAPK pathway, directly interacts with a specific GATA-like cis-response element in the promoter region of the PxmALP gene, a Cry1Ac receptor. Mutations in this cis-acting element can repress transcriptional activity, thereby reducing susceptibility to Cry1Ac toxin (Figure 2) (Guo et al., 2022). Similarly, the transcription factor PxJun, also activated by the MAPK pathway, has been found to repress the expression of the PxABCB1 gene, another Cry1Ac receptor, contributing to resistance (Qin et al., 2021). Figure 2 Role of different TFs on the transcriptional activation of the PxmALPpromoter (Adopted from Guo et al., 2022) Image caption: (A) Schematic illustration of the putative TF CREs located in the promoter region of PxmALP. Different CREs are indicated by colored ellipses. (B) Analysis of various TFs on the activity of the PxmALPpromoter. The values shown are the means and the corresponding SEM values. The empty vector pAc5.1/V5-His B was used as control and standardized the value as 1-fold. Four independent transfections were conducted for each pair of plasmids. Holm-Sidak’s test was used for statistical analysis (***p < 0.001). (C) The expression of PxGATAd, PxGATAe andPxPOU6F2was analyzed in the midgut tissue from larvae of DBM1Ac-S and NIL-R strains. The values are presented as mean of relative expression values ± the SEM (*p < 0.05, Holm-Sidak’s test, n = 3) (Adopted from Guo et al., 2022) Figure 2 illustrates the role of the transcription factor PxGATAd in regulating the expression of the PxmALPgene. Figure 2A shows the prediction of multiple potential cis-acting elements in the promoter region. The luciferase reporter assay in Figure 2B indicates that PxGATAd significantly enhances the activity of the PxmALP promoter in the Cry1Ac-susceptible strain, while the effect is weaker in the resistant strain. The qPCR results in Figure 2C further confirm that the expression level of PxGATAd is significantly higher in the susceptible strain compared to the resistant strain. Overall, Figure 2 reveals that PxGATAd is a key regulatory factor for PxmALP gene expression, and its expression is suppressed in the resistant strain, leading to the diamondback moth's resistance to Cry1Ac toxin.
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