Bioscience Evidence 2025, Vol.15, No.6, 270-279 http://bioscipublisher.com/index.php/be 273 3.3 Calcium signaling and MAPK cascading Calcium ions (Ca2+) are very crucial signaling molecules in plant defense. After pathogen or insect attacks, genes such as calmodulin (CAM) and calmodulin-like protein (CMLs) are rapidly upregulated in sorghum. These genes can sense calcium signals and continue to initiate subsequent cascade reactions (Khasin et al., 2021). Meanwhile, the MAPK cascade is also very important in sorghum defense, as it can amplify signals and promote various defense responses. The expression of genes such as MAPK17/18 and MEKK3 in resistant materials is significantly increased, thereby promoting ROS generation, cell death response and the expression of defense genes. MAPK can also add phosphate to some transcription factors, enabling them to better regulate downstream defense genes. 3.4 Transcriptional regulatory factors Many transcription factors (TFs) are also involved in the defense regulation of sorghum. Members of the WRKY, MYB, AP2/ERF families can be induced to express after pathogen or insect infection. They can regulate the synthesis of defense genes, some secondary metabolites (such as flavonoids, 3-deoxyanthocyanins), and antimicrobial peptides. For example, WRKY22 and WRKY33 will continuously rise in aphid resistant sorghum, helping with signal transduction and the accumulation of defense products (Rashad et al., 2022). In addition, the expression changes of transcriptional repressor factors like JAZ also remind us that sorghum actually requires a fine balance between "growth" and "defense". 4 The Main Defense-related Genes and Metabolic Pathways of Sorghum 4.1 Disease-resistant related (PR) genes During the disease resistance process of sorghum, many PR genes will be significantly upregulated, such as Sobic.001G401200, Sobic.005G169200, etc. The proteins encoded by these genes include defensins, antimicrobial peptides, some receptor kinases, etc. They can directly suppress the growth of pathogens and also initiate more immune responses below. The higher the expression of the PR gene, the stronger the resistance of sorghum to diseases such as valley mold and aphids is usually (Mutinda et al., 2022). Furthermore, some NLR genes (such as ARG1) are also involved in resistance. They are often regulated at the epigenetic and transcriptional levels, thereby enabling sorghum to acquire a relatively broad-spectrum fungal resistance (Lee et al., 2022). 4.2 Phenylpropane pathway and secondary metabolites The phenylpropane pathway is a very important metabolic route in sorghum defense, capable of synthesizing resistant substances such as lignin, flavonoids, and 3-deoxyanthocyanins. Genes such as PAL, CCoAOMT, and DFR3 are significantly upregulated in disease-resistant varieties, helping to accumulate more lignin and antibacterial components (Khasin et al., 2021). Some of these 3-deoxyanthocyanins (such as apigeninidin, luteolinidin) show strong effects in antifungal and pest resistance. Transcription factors such as MYB also regulate the expression of these metabolic genes, thereby affecting the amount and mode of accumulation of resistant substances. 4.3 Structural barriers and cell wall modification Sorghum enhances resistance by strengthening the cell wall structure, such as thickening the cell wall, depositing more lignin, β-glucan and callose, etc. (Mutinda et al., 2022). Genes such as CCoAOMT, COMT, and CAD regulate lignin synthesis, making the cell wall stronger and more capable of blocking pathogen entry (Grover et al., 2024). In varieties with high resistance, these genes are usually upregulated more quickly after pathogen infection, making the cell wall stronger and thereby limiting pathogen spread. 4.4 Small rnas and post-transcriptional regulation Small Rnas (such as miRNA, siRNA) and natural antisense transcripts (NAT) are also important in the defense regulation of sorghum, and they mainly act in the post-transcriptional stage (Govintharaj et al., 2025). For example, the expression of the ARG1 gene is regulated by its corresponding NAT (CARG), which affects the splicing situation and epigenetic status of ARG1, and thereby influences the resistance of sorghum (Lee et al., 2022). In addition, non-coding RNA and small RNA can further affect the expression of defense genes by regulating the stability and translation efficiency of mRNA, enabling sorghum to respond to different pathogens such as fungi and parasitic plants.
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