Bioscience Evidence 2025, Vol.15, No.6, 270-279 http://bioscipublisher.com/index.php/be 272 2.3 Interaction and synergy between PTI and ETI Recent studies have found that PTI and ETI are actually not two completely separate routes, but an integrated system with high synergy (Yu et al., 2024). ETI can restore or enhance PTI by strengthening some key components in PTI (such as PRR, signal proteins, ROS-generating enzymes, etc.), forming an "amplification" effect (Nguyen et al., 2021; Yuan et al., 2021). PTI and ETI share many links in signal transduction, gene expression and defense substance production, but ETI comes faster and is stronger. This interaction enables plants to be more flexible and have more redundant protection when facing different pathogens or environmental pressures. However, although there have been many studies on the PTI-ETI interaction in model plants, in crops such as sorghum, the related molecular mechanisms still require further in-depth research (Cui et al., 2021; Fang et al., 2023). 3 The Molecular Signaling Pathways of Sorghum Defense 3.1 Hormone-mediated defense Hormones in plants play a very important regulatory role in the disease resistance process of sorghum. Hormones such as salicylic acid (SA), jasmonic acid (JA), and abscisic acid (ABA) usually rise when sorghum is attacked by fungi, bacteria or insects. Moreover, in some varieties with stronger resistance, the increase of these hormones is more obvious. Similar situations can be observed in materials resistant to aphids or valley mold disease (Huang et al., 2022; Shrestha et al., 2024) (Figure 2). Exogenous addition of some SA, JA or ABA can also reduce disease damage in originally susceptible sorghum and lower the mortality rate. This indicates that these hormones can indeed positively regulate defense (Pant and Huang, 2022). In addition, SA and JA can not only cooperate with each other but also may restrain each other. They jointly regulate the expression of subsequent defense genes and the accumulation of resistance substances. Figure 2 Schematic diagram of major plant hormone signal transduction pathway for sorghum (adapted from KEGG, yellow highlights are pathway name, dotted arrow represents multiple enzymatic steps, green highlights are genes in respective pathways). AUX-auxin influx carrier; TIR1-transport inhibitor response1; AUX/IAA-auxin/indole-3-acetic acid; ARF-auxin response factor; GH3-auxin responsive Gretchen hagen3; SAUR-small auxin upregulated RNA; COI1-coronatine-insensitive protein 1; JAZ-jasmonate ZIM-domain; MYC2-transcription factor MYC2; NPR1-regulatory protein NPR1; TGA-transcription factor TGA; PR-1-pathogenesis related-1; PYR/PYL-abscisic acid receptor PYR/PYL family; PP2C-protein phosophatase 2C; snRK2-serine/threonine-protein kinase; ABF-ABA responsive element biding factor (Adopted from Huang et al., 2022) 3.2 Reactive oxygen species (ROS) outbreak Reactive oxygen species (such as H2O2) are very typical signals of sorghum in early defense. They can not only directly inhibit the growth of pathogens, but also act as signals to continue promoting the subsequent defense routes (Puri et al., 2023). In disease-resistant varieties, when pathogens infect or aphids feed on them, genes related to ROS generation will be rapidly upregulated. Meanwhile, some antioxidant enzymes (such as peroxidase, glutathione S-transferase, etc.) will also increase simultaneously to balance the number of ROS and prevent plant self-injury. ROS signaling can also promote the synthesis of SA and further enhance the expression of some defense proteins (such as PR protein).
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