Molecular Pathogens 2024, Vol.15, No.1, 30-39 http://microbescipublisher.com/index.php/mp 33 3.2 Pathogen recognition mechanisms Pathogen recognition in tea plants involves a two-tiered immune system. The first layer, known as PAMP-triggered immunity (PTI), is mediated by pattern recognition receptors (PRRs) that detect conserved microbial elicitors called pathogen-associated molecular patterns (PAMPs). The second layer, effector-triggered immunity (ETI), involves the recognition of specific pathogen effectors by intracellular R proteins, leading to a stronger and more specific defense response (Roux et al., 2014). The interaction between R genes and pathogen avirulence (Avr) genes is a key component of this recognition process, where the presence of both genes triggers a defense response. The molecular signals involved in pathogen recognition and the subsequent activation of defense mechanisms are crucial for the effective resistance of tea plants to pathogens (Zhang et al., 2013). 3.3 Genetic mapping and QTL analysis Genetic mapping and quantitative trait locus (QTL) analysis are essential tools for identifying the genetic basis of disease resistance in tea plants. QTL analysis helps in locating regions of the genome that are associated with resistance traits, which can be influenced by multiple genes with minor effects (Zhang et al., 2013; Roux et al., 2014). The genetic background of the plant can significantly impact the expression and durability of resistance traits, as epistatic interactions between resistance genes can alter the overall resistance phenotype. High-density genome-wide genetic maps, including resistance gene analogs (RGAs), are useful for identifying QTLs and designing diagnostic markers for plant disease resistance (Sekhwal et al., 2015). These tools enable breeders to develop tea plant varieties with enhanced resistance to major pathogens by incorporating multiple resistance genes and QTLs into the breeding programs (Gallois et al., 2018). By understanding the genetic basis of disease resistance, pathogen recognition mechanisms, and utilizing genetic mapping and QTL analysis, researchers can develop effective strategies to enhance the resistance of tea plants to major pathogens. This integrated approach will contribute to sustainable tea production and reduce the economic impact of plant diseases. 4 Signaling Pathways in Tea Plant Immunity 4.1 Salicylic acid pathway Salicylic acid (SA) is a crucial phytohormone involved in the regulation of plant immune responses. It plays a significant role in the activation of systemic acquired resistance (SAR), a defense mechanism that provides long-lasting protection against a broad spectrum of pathogens. The SA pathway is essential for the defense against biotrophic pathogens, which feed on living host tissue. SA-mediated signaling involves the accumulation of pathogenesis-related (PR) proteins and the activation of various defense genes (An and Mou, 2011). Additionally, SA interacts with other hormones such as jasmonic acid (JA) and ethylene (ET) to fine-tune the immune response. 4.2 Jasmonic acid and ethylene pathways Jasmonic acid (JA) and ethylene (ET) are key players in plant defense against necrotrophic pathogens, which kill host tissue and feed on the dead matter. These hormones often work synergistically to activate defense responses. The JA pathway is particularly important for induced systemic resistance (ISR), which is triggered by beneficial microbes and provides protection against a wide range of pathogens (Yang et al., 2021; Yu et al., 2022). The transcription factor ORA59 is a critical regulator in the JA/ET signaling pathway, modulating the expression of defense genes in response to pathogen attack. Furthermore, JA signaling is involved in the production of secondary metabolites that contribute to plant defense (Lin et al., 2022). 4.3 Cross-talk between signaling pathways The interaction between SA, JA, and ET pathways, known as hormonal crosstalk, is a complex network that allows plants to fine-tune their immune responses based on the type of pathogen encountered. Crosstalk can be either synergistic or antagonistic. For instance, while SA and JA pathways often exhibit antagonistic interactions, leading to the suppression of JA-mediated defenses by SA, there are scenarios where simultaneous activation of both pathways can enhance resistance (Yang et al., 2015; Hou and Tsuda, 2022). This intricate balance is crucial
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