Molecular Pathogens 2024, Vol.15, No.5, 237-245 http://microbescipublisher.com/index.php/mp 239 enhance their expression in response to pathogen attack (Zeng et al., 2015). RNAi, on the other hand, involves silencing specific genes that contribute to disease susceptibility. This technique has been used to downregulate genes that facilitate Xoo infection, thereby reducing the pathogen's ability to cause disease. Both techniques offer targeted and efficient means to develop rice varieties with improved resistance to BB, complementing traditional breeding methods (Zeng et al., 2015). 3.3 Comparative resistance strategies The development of disease-resistant rice varieties can be achieved through both transgenic and non-transgenic approaches. Transgenic strategies involve the introduction of foreign genes into the rice genome, such as the insertion of modified R genes like Xa10 (E5) to confer broad-spectrum resistance (Zeng et al., 2015). These approaches can provide robust and durable resistance but often face regulatory and public acceptance challenges. Non-transgenic approaches, including marker-assisted selection (MAS) and genomic selection, rely on the natural genetic variation within rice populations. For instance, the identification and utilization of naturally occurring R genes like Xa7 and Xa33 through MAS have led to the development of resistant varieties without the need for genetic modification (Figure 1) (Chen et al., 2021; Kumar et al., 2012). Both strategies have their advantages and limitations, and a combination of transgenic and non-transgenic methods may offer the most effective solution for achieving durable resistance against Xoo (Banerjee et al., 2018). 4 Case Analysis 4.1 Case selection criteria The selection of cases for this study was based on the presence of significant genetic engineering interventions aimed at enhancing resistance to Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial blight in rice. Specifically, we focused on cases involving the application of disease resistance genes and CRISPR technology. The selected cases were chosen to represent a range of genetic strategies, including the use of traditional resistance genes, novel gene modifications, and advanced genome editing techniques. 4.2 Application of disease resistance gene Xa21 The Xa21 gene has been widely studied and utilized for its role in conferring resistance to Xoo. This gene encodes a receptor kinase that recognizes pathogen-associated molecular patterns, triggering immune responses in rice. Studies have shown that transgenic rice plants expressing Xa21 exhibit enhanced resistance to multiple Xoo strains, making it a valuable tool in breeding programs aimed at developing durable disease-resistant rice varieties (Jiang et al., 2020; Kumar et al., 2020). The effectiveness of Xa21 in providing broad-spectrum resistance highlights its potential for sustainable disease management in rice cultivation. 4.3 Application of CRISPR technology in resistance to bacterial blight CRISPR technology has emerged as a powerful tool for precise genome editing, offering new avenues for enhancing disease resistance in crops. In the context of bacterial blight resistance, CRISPR has been employed to modify susceptibility genes and introduce resistance traits. For instance, the modification of the Xa10 promoter using CRISPR has resulted in the development of the Xa10 (E5) gene, which confers broad-spectrum and durable resistance to Xoo by responding to multiple TAL effectors (Zen et al., 2015). This approach demonstrates the potential of CRISPR technology to create rice varieties with enhanced and long-lasting resistance to bacterial blight. 4.4 Interpretation and comparison of main findings The main findings from the selected cases reveal that both traditional resistance genes and advanced genome editing techniques can significantly enhance resistance to Xoo. The application of the Xa21 gene has been effective in providing broad-spectrum resistance, which is crucial for managing the disease across different rice-growing regions (Figure 2) (Kumar et al., 2020). On the other hand, CRISPR technology offers a more targeted approach, allowing for the precise modification of specific genes to achieve desired resistance traits. The development of the Xa10 (E5) gene through CRISPR exemplifies how this technology can be used to create rice varieties with durable resistance by targeting multiple pathogen effectors (Zeng et al., 2015).
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