Molecular Pathogens 2024, Vol.15, No.4, 179-188 http://microbescipublisher.com/index.php/mp 183 interconnected and can influence each other to fine-tune the plant's defense mechanisms (Wang and Li, 2024). For instance, the wheat gene Lr34 not only activates multiple defense pathways but also induces high levels of JA and SA, demonstrating the interplay between these hormonal pathways in enhancing disease resistance (Polturak et al., 2022). Additionally, systemic acquired resistance (SAR) in wheat involves the activation of different gene pathways, including acquired resistance (AR) and systemic immunity (SI), which are regulated by NPR1 homologs and other downstream genes (Wang et al., 2018). 4.3 Hormonal regulation of disease resistance Hormonal regulation plays a pivotal role in modulating wheat's defense responses against pathogens. Key hormones such as jasmonic acid (JA) and salicylic acid (SA) are central to the plant's immune system. The wheat resistance gene Lr34, for example, leads to the constitutive induction of JA and SA, which are crucial for activating various defense pathways (Poretti et al., 2021). Additionally, the TIME FOR COFFEE (TIC) gene in Brachypodium distachyon, a model grass, is involved in jasmonate signaling and contributes to nonhost resistance to wheat stem rust, highlighting the importance of hormonal regulation in disease resistance (Coletta et al., 2021). The interplay between these hormones and their signaling pathways ensures a robust and effective defense response. 4.4 Role of secondary metabolites in defense Secondary metabolites, these compounds, which include flavonoids and terpenes, are produced through pathogen-induced biosynthetic pathways and serve as phytoalexins or signaling molecules that enhance the plant's resistance to diseases. The production of these metabolites is often regulated by specific gene clusters, and their accumulation can deter pathogen growth and spread (Li etal., 2024). For instance, the wheat resistance gene Lr34 induces the production of lignin and hordatines, which are secondary metabolites that contribute to the plant's structural defense and antimicrobial activity (Chauhan et al., 2015). The strategic deployment of these metabolites is a crucial aspect of wheat's overall defense strategy. 5 Transcriptomic Signatures of Wheat-Pest Interactions 5.1 Specific transcriptomic responses to fungal pathogens Wheat's interaction with fungal pathogens, particularly Puccinia striiformis f. sp. tritici (Pst), involves complex transcriptomic changes. The identification of microRNAs (miRNAs) and their targets has revealed their significant roles in wheat's defense mechanisms. For instance, the miRNA-like RNA 1 (Pst-milR1) from Pst suppresses wheat defenses by targeting the pathogenesis-related 2 (PR2) gene, thereby impairing the plant's immune response (Wang et al., 2017). Additionally, the AP2/ERF transcription factor TaAP2-15 has been shown to enhance wheat resistance to Pst by regulating the expression of pathogenesis-related genes and reactive oxygen species (ROS)-scavenging genes (Hawku et al., 2021). Another study highlighted the role of the R2R3 MYB transcription factor TaMYB391, which positively regulates hypersensitive response (HR)-associated cell death and resistance to Pst through the induction of PR genes and ROS accumulation (Hawku et al., 2022). These findings underscore the importance of specific transcription factors and miRNAs in modulating wheat's transcriptomic responses to fungal pathogens. 5.2 Responses to bacterial and viral pathogens Wheat's transcriptomic responses to bacterial and viral pathogens involve distinct signaling pathways and regulatory mechanisms. The interaction between wheat and bacterial pathogens often triggers systemic acquired resistance (SAR), mediated by key transcriptional regulators such as NPR1. A conserved protein from Pst, PNPi, interacts with wheat NPR1, reducing the induction of pathogenesis-related genes and thereby manipulating the plant's defense response (Wu et al., 2022). In the context of viral pathogens, host-induced gene silencing (HIGS) has emerged as a promising strategy. For example, silencing the PsCPK1 gene in Pst through HIGS significantly enhances wheat resistance to stripe rust by reducing the pathogen's growth and development (Qi et al., 2017). These studies highlight the diverse transcriptomic responses of wheat to bacterial and viral pathogens, involving both transcriptional regulators and gene silencing mechanisms.
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