Rice Genomics and Genetics 2024, Vol.15, No.2, 69-79 http://cropscipublisher.com/index.php/rgg 76 mechanism in bacteria and archaea that record information about previously infected viruses or foreign DNA fragments. The Cas9 protein is a lipoendonuclease that can recognize and cut foreign DNA that matches the CRISPR sequence. During the gene editing process, scientists first design an RNA sequence that matches the DNA sequence of the target gene. This RNA sequence is guided by the CRISPR sequence and combines with the Cas9 protein to form a CRISPR-Cas9 complex. Once the complex matches the DNA sequence of the target gene, the Cas9 protein cuts the DNA sequence, causing the gene to be knocked out or added. In terms of gene knockout, CRISPR-Cas9 technology is widely used in the study of rice disease resistance-related genes. For example, by designing an RNA sequence that matched a specific rice blast resistance gene, scientists successfully used CRISPR-Cas9 technology to knock out the gene. This method provides an effective means to study the role of specific disease resistance genes in rice disease resistance mechanisms. By observing the performance of rice plants after knockout, scientists can gain a deeper understanding of the impact of this gene on rice disease resistance traits (Romero and Gatica-Arias, 2019). On the contrary, gene addition is another application direction of CRISPR-Cas9 technology, especially in the introduction of foreign genes to improve rice disease resistance. For example, scientists could engineer an RNA sequence to match a disease-resistant gene from another crop or plant. By using CRISPR-Cas9 technology, this RNA sequence is introduced into the rice genome to add exogenous disease resistance genes. This method provides an effective means for rice breeding to enhance disease resistance of rice by introducing exogenous genes. Taking the improved resistance of rice to rice stripe rust as an example, scientists have successfully transferred specific resistance genes from other plants to the rice genome through CRISPR-Cas9 technology. The addition of this foreign gene makes the rice plants more resistant to rice stripe rust. This method of gene addition provides an innovative approach to rice disease resistance breeding by introducing exogenous disease resistance genes to improve rice immunity to specific diseases. Although CRISPR-Cas9 technology shows great potential in rice disease resistance research, there are still some potential problems that need to be paid attention to in practical applications, such as non-specific modification and incomplete gene editing. Nonspecific modifications may lead to undesirable side effects, while incomplete gene editing may produce polymorphic genotypes. Therefore, during the application of CRISPR-Cas9 technology, careful design and verification are required to ensure that the resulting rice varieties have the expected disease resistance traits. 4.3 Introduction of disease resistance genes Transgenic technology is a method of introducing foreign genes into the cells of a target organism by changing the genetic material of the organism, thereby giving it new traits or functions. In the plant field, especially in crop breeding, transgenic technology is widely used to improve disease resistance. This study will outline the basic principles of transgenic technology and use examples to evaluate the effect of introducing disease resistance genes from other plants or microorganisms on plant disease resistance. The basic principle of transgenic technology includes constructing a vector of foreign genes, introducing it into the cells of the target plant, and then integrating the foreign gene into the genome of the target plant through appropriate selection and screening methods. Among them, the most commonly used vector is Agrobacterium tumefaciens, which can introduce foreign genes into plant cells and integrate them into the plant genome. In addition, direct transgenic methods also include biological particle gun methods. In terms of introducing disease resistance genes from other plants or microorganisms, a typical example is the introduction of exogenous disease resistance genes into rice. Taking the improved resistance of rice to rice blast as an example, scientists have successfully introduced the rice blast resistance gene Xa21 through transgenic technology. This gene is derived from a naturally disease-resistant variety of rice and has strong resistance to rice blast. By introducing the Xa21 gene into other rice varieties, we hope to improve the resistance of these rice varieties to rice blast (Sham et al., 2020).
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