Bioscience Evidence 2025, Vol.15, No.6, 270-279 http://bioscipublisher.com/index.php/be 274 5 The Molecular Defense Mechanisms of the Main Diseases of Sorghum 5.1 Anthrax (Colletotrichum sublineolum) The defense of sorghum against anthracnose mainly relies on epigenetic regulation, resistance genes (such as ARG1), PR protein, as well as phenylpropane and flavonoid metabolic pathways. The ARG1 gene can function in multiple ways, such as being regulated by the natural antisense transcript CARG and also affected by histone methylation, so it can bring about a relatively broad-spectrum resistance. After the pathogen enters, the phenylpropane and flavonoid pathways will be rapidly activated, generating many antifungal 3-deoxyanthocyanins, such as apigeninidin and luteolinidin. In addition, receptor kinases such as BAK1/SERK4 can trigger PAMP immunity and also promote programmed cell death, thereby enhancing defense (Vela et al., 2025). Some post-transcriptional regulatory modalities (such as alternative splicing) can also affect the expression levels of defense genes. 5.2 Charcoal rot (Macrophomina phaseolina) The charcoal rot pathogen can induce the upregulation of genes related to the cell wall degrading enzyme (CWDE) in sorghum itself, which makes the cell wall more vulnerable to damage and makes susceptible varieties more susceptible to the disease. However, resistant varieties can inhibit the upregulation of these enzymes, thereby maintaining the cell wall structure. In resistant materials, some antifungal genes (such as chitinase and styrene synthase) are expressed more frequently, which can effectively limit the spread of pathogens. Susceptible materials often experience more severe oxidative stress after infection, with excessive accumulation of ROS and RNS, leading to cell death and making the disease even more severe. Resistant varieties can enhance the activity of antioxidant enzymes, such as peroxidase and catalase, thereby reducing damage. 5.3 Valley mold complex The resistance of trichoderma oryzae is regulated by multiple genes, involving pathogen recognition receptors (such as SbLYK5), PR protein, defensins, MAPK signaling pathway, and the production of antibacterial secondary metabolites such as 3-deoxyanthocyanins. MYB transcription factors (such as Y1 and Y3) regulate some flavonoid genes (such as DFR3), thereby affecting the accumulation of resistant substances (Nida et al., 2021). In varieties with high resistance, genes such as PR protein, defenin and antimicrobial peptide are rapidly upregulated after Aspergillus oryzae infection, enhancing the physical and chemical defense of grains. Some grain-specific proteins, such as KAFIRIN and LEA3, are also considered to be related to resistance. 5.4 Bacterial stripe disease (Xanthomonas vasicola) The defense of sorghum against bacterial stripe disease is mainly achieved by regulating the cell wall structure and metabolic signals. Pathogens secrete various cell wall degrading enzymes (CWDE) to assist in infection, while sorghum strengthens the cell wall barrier by up-regulating lignin synthesis genes such as Bmr12 (also known as COMT) (Wang et al., 2025). The Bmr12 mutant is more susceptible to diseases, indicating that lignin metabolites (such as sinapaldehyde) have a direct inhibitory effect on the pathogen. Meanwhile, in the resistance response, the expression of the PR gene and some defense metabolites increases, and some of these metabolites can also suppress the pathogenic factors of the pathogen (Wang et al., 2021). 5.5 Viral diseases (MDMV, SCMV) The defense of sorghum against viral diseases (such as MDMV and SCMV) involves PR genes, phenylpropane metabolism, hormone signaling (especially salicylic acid), and small RNA regulation. After the administration of salicylic acid, the expression of defense genes such as PR1, NPR1, and PAL will increase significantly, thereby enhancing resistance (Lu et al., 2023; Zhou et al., 2024). Viral infection can affect signaling pathways such as Ca2+, ROS, and ethylene, and also alter the expression of transcription factors like WRKY and ERF. Small Rnas (such as mirnas) are also involved in early immune regulation and affect resistance levels by regulating the expression of target genes (Su et al., 2022).
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