Molecular Pathogens, 2025, Vol.16, No.4, 159-170 http://microbescipublisher.com/index.php/mp 161 genes into the target variety, accelerating the breeding process. Over the past few decades, with the identification of numerous disease-resistant QTLs and genes, various efficient molecular markers (such as SSR, STS, SNP, etc.) have been developed for disease-resistant breeding (Jabran et al., 2023). Molecular markers used to track the wheat wide-spectrum anti-powder mildew gene Pm21 have been widely used in breeding in my country. The Pm21-containing varieties effectively controlled the epidemic of powdery mildew in the 1980s and 2000s. For example, molecular detection methods have been established for the important resistance genes Yr18 and Yr36 of wheat stripe rust, which facilitate the accumulation of these anti-rust factors in breeding. In recent years, new technologies such as genome-wide association analysis (GWAS) and genome selection (GS) have also begun to be used to improve disease-resistant traits in wheat. Through genotyping and disease-resistant phenotype identification of large-scale germplasm resources, GWAS can localize novel loci related to disease-resistant (Wu et al., 2020). A study conducted stripe rust resistance evaluation and genome-wide association analysis on more than 14 000 wheat resources around the world, constructed a panoramic genome map containing 431 stripe rust-resistant QTL sites, and discovered a batch of new disease-resistant allelic variants and candidate genes. These results provide important reference for the formulation of disease-resistant breeding strategies. 3 Pathogen Perception and Signal Transduction Mechanisms 3.1 Pattern recognition receptors (PRRs) and pathogen-related molecular patterns (PAMPs) recognition During the evolution process, plants have formed the "first line of defense" against broad-spectrum microbial invasion - pattern recognition receptor-mediated immunity. Pattern recognition receptors (PRRs) are usually localized to the cell surface and are able to sense conserved molecular patterns (PAMPs) shared by pathogenic microorganisms. When pathogens infect wheat, their characteristic molecules released extracellularly can be recognized as PAMP by PRR on the wheat membrane. Some of the identified PRR pairings with pattern molecules in wheat include: TaCERK1 recognizes fungal chitin (chipolysan) fragments, activates downstream antifungal responses; TaRLK1 receptor kinases can sense the conserved sequence of bacterial flagellin flg22, inducing broad-spectrum antibacterial defense. When PRR binds to the corresponding PAMP molecule, it will trigger a series of intracellular cascades and initiate innate immunity. This immunity triggered by PAMP plays an important role in the fight against disease (Lang et al., 2025). 3.2 Immune (PTI) signaling pathway triggered by PAMP When the PRR of wheat recognizes the corresponding PAMP, it initiates the immune (PTI) signaling pathway triggered by PAMP, triggering a series of defense responses. First is the receptor kinase-mediated phosphorylation cascade: the intracellular kinase domain of PRR undergoes conformational changes after binding to ligands, activating downstream coenzyme BRI1-related kinases, which in turn phosphorylate a series of signaling proteins. During this process, the Mitogen-activated protein kinase (MAPK) cascade in wheat cells is rapidly activated, causing changes in the expression of multiple defense genes. At the same time, PTI is accompanied by transient increase in intracellular calcium ions and the accumulation of outbreaks of reactive oxygen species (ROS) (Weralupitiya et al., 2024). The study found that under the trigger of the pathogen PAMP, the calcium ion channel on the wheat cell membrane is opened, allowing Ca2+ inflow to be used as the second messenger to amplify the signal. The accumulation of ROS is produced by enzymatic reactions such as NADPH oxidase in the membrane, which directly kills bacteria and strengthens the cell wall. In the early stage of PTI, wheat cells also undergo plasma membrane protein recombination and cell wall reinforcement: for example, the secretion of polysaccharides forms callose (papilla) at the invasion site, blocking bacterial invasion. A large number of defense-related genes are also induced under the action of PTI signaling, including genes encoding antibacterial proteins (such as chitinase, glucanase), and genes involved in the synthesis of plant defense compounds (Yamaguchi and Kawasaki, 2021). 3.3 Immunity (ETI) and signal amplification mechanism triggered by effectors For highly adaptive pathogens that overcome PTI defense, wheat has also evolved effector-triggered immunity (ETI). When obligate pathogens such as rust bacteria and powdery white bacteria invade the host, effector proteins will be secreted to interfere with plant immunity. However, NLR-like disease-resistant proteins in wheat cells can
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