Molecular Pathogens, 2025, Vol.16, No.5, 236-245 http://microbescipublisher.com/index.php/mp 240 monitoring the introduction of genes during backcross improvement. Through background selection markers, most of the genetic background of the recipient variety can be quickly restored while introducing disease resistance genes, thereby avoiding excessive influence on agronomic traits (Fu et al., 2012). 5 New Progress in Gene Editing and Precision Disease Resistance Breeding 5.1 Application of CRISPR/Cas system in targeted modification of disease resistance genes The CRISPR/Cas gene editing technology that has emerged in recent years provides a new tool for rice disease resistance breeding. In rice disease resistance breeding, an important application of CRISPR technology is to knock out susceptibility genes (S genes) to improve resistance. S genes refer to those host genes in the plant genome that are used by pathogens to promote infection. Knocking out or loss of function of these genes often confers broad-spectrum and long-lasting disease resistance to plants. Pi21 is a known susceptibility gene in rice, and its encoded protein inhibits blast resistance-related defense responses. After using CRISPR/Cas9 to perform site-specific knockout of the Pi21 gene of the highly susceptible variety Kongyu 131, the resulting mutant line significantly enhanced resistance to rice blast (Nawaz et al., 2020; Yang et al., 2023). In addition to knocking out the S gene, CRISPR technology can also be used to refine the disease-resistant Rgene itself. For example, editing the promoter or coding region of some existing Rgenes can improve their expression or functional properties, thereby enhancing resistance without reducing yield. Some studies have focused on the bacterial blight-resistant Xa13 (itself a susceptibility gene, and loss of function provides resistance). By editing its promoter to lose elements activated by pathogenic TAL effectors, new materials resistant to bacterial blight that do not require exogenous genes have been cultivated (Li et al., 2019; Li et al., 2022). 5.2 Cases of improving resistance through gene knockout and promoter editing Specific cases of using gene editing to improve disease resistance have emerged in recent years, covering a variety of rice disease types and gene targets. In terms of susceptible gene knockout, the OsSWEET gene of the betaine transporter family is a hot spot in bacterial blight resistance research (Zeng et al., 2020). OsSWEET11, OsSWEET13, OsSWEET14 and other genes distributed on the rice chromosome encode sucrose transmembrane transport proteins, which were originally involved in nutrient export from leaves to phloem (Figure 2). However, the TAL effector protein secreted by the Xoo strain specifically activates the expression of these SWEET genes, causing the host cells to continuously leak nutrients for the reproduction of pathogens, thus forming lesions (Xu et al., 2019). Other cases focus on the knockout of negative regulators of disease resistance signaling. There are some genes encoding negative regulatory proteins in the rice genome, which under normal circumstances suppress excessive immune responses to avoid wasting energy in the plant. However, when pathogens invade, the presence of these negative regulators may reduce the disease resistance effect. In addition to DNA-level editing, base editing and gene transcription activation methods have recently been used to improve disease resistance. A team used the dCas9-SunTag system to bring rice's own disease resistance gene activator to the target promoter region, thereby upregulating the expression of some resistance-related genes without introducing foreign genes. This exquisite regulation is expected to activate multiple immune-related elements at the same time and build broad-spectrum resistance (Tao et al., 2025). 5.3 Prospects for future editing strategies for multi-gene compound resistance Looking to the future, the application of gene editing technology in rice disease resistance breeding will further develop in the direction of "multi-gene, directional". The first is multi-gene parallel editing. Existing technology can already edit 2 to 3 genes simultaneously in one transformation event. In the future, by optimizing sgRNA expression vectors and screening strategies, it is expected to edit more genes at once (Yang et al., 2023). For example, a multi-target CRISPR program can be designed to target multiple susceptibility genes for one disease or representative susceptibility genes for different diseases to eliminate multiple susceptibility pathways in a single strain. This kind of "combination punch" editing is expected to achieve truly broad-spectrum and long-lasting resistance. The second is genome design breeding. Through the integration of rice genome-wide association analysis and functional genomics, ideal disease resistance gene combinations and key regulatory switches can be
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