Plant Gene and Trait 2024, Vol.15, No.1, 15-22 http://genbreedpublisher.com/index.php/pgt 18 For example, in rice, a series of important disease-resistance related genes have been identified, such as Xa21, Xa4, Xa5, etc. These genes encode disease-resistant proteins that are effective against common rice pathogens, such as Fusarium oryzae (Zhang et al., 2019). Similarly, many genes related to disease resistance have been found in wheat (Triticum aestivum), maize (Zea mays), soybean (Glycine max) and other crops, providing important molecular markers and candidate genes for crop resistance breeding. The genetic basis of crop disease resistance is a complex system, which is co-regulated by several genes. The discovery of disease-resistance-related genes provides important clues for further understanding the molecular mechanism of crop disease resistance, and provides important genetic resources and molecular markers for crop disease resistance breeding. 3.2 Function and mechanism of resistance genes Resistance genes are genes that produce resistance response against pathogen infection in plants. These genes are involved in regulating plant disease resistance by encoding specific proteins or regulating gene expression. The function and mechanism of resistance genes can be divided into direct resistance and regulation of resistance response (Garrett et al., 2017). Proteins encoded by direct disease resistance genes usually have specific disease resistance effects. For example, proteins encoded by some genes can bind to specific components of pathogens, trigger plant immune responses, such as activating signal transduction pathways, producing toxins, etc., and ultimately lead to the death of pathogens or inhibit their infection. These proteins may be directly involved in the physical blocking or chemical attack of a pathogen-infected site to ensure the health of the plant. Another class of resistance genes regulates gene expression and activation of resistance response. These genes may encode proteins in signal transduction pathways (Garrett et al., 2017), such as kinases or transcription factors, that can influence a plant's disease resistance response by regulating the expression of other genes. For example, some genes can activate the synthesis of antibacterial substances, enhance the strength of cell walls, promote cell death, and so on, thereby enhancing the plant's resistance to pathogens. 3.3 Genetic diversity and evolution of resistance genes The genetic diversity and evolution of resistance genes is an important part of crop disease resistance research, which is of great significance for understanding the evolution and resistance mechanism of resistance genes. Genetic diversity of resistance genes refers to differences in the types and amounts of resistance genes present in different crop varieties or germplasm resources (Andersen et al., 2016). Because different crop varieties or germplasm resources are affected by natural selection, artificial selection and other factors, there are certain differences in the composition of resistance genes, which is reflected in the diversity of the types of resistance genes, genotype frequency and other aspects. The existence of genetic diversity provides rich genetic resources for crop disease resistance breeding and helps to breed new varieties with more disease resistance. The evolution of resistance genes refers to the origin, differentiation and propagation of resistance genes during the evolution of species (Andersen et al., 2016). Resistance genes can be produced in many ways, such as gene mutation, gene recombination, gene transfer, etc. In the long-term adaptive evolution process of species, resistance genes continue to mutate and accumulate, forming different genotypes. These genotypes are subject to selection pressures in the environment, resulting in changes in the frequency of different genotypes that affect the genetic diversity and evolution of resistance genes. 4 New Progress in GWAS Research 4.1 GWAS case studies of resistance to different crop diseases In 2020, Voichek and Weigel's research team published a paper in Nature Genetics entitled ‘Identifying genetic variants underlying phenotypic variation in plants without complete genomes’. The study explored the genetic variation behind phenotypic variation in plants by using GWAS without reference to the genome, and the results demonstrated the ability to perform GWAS before linking sequence reads to specific genomic regions. This allows the detection of a wider range of genetic variants that cause phenotypic variation (Voichek and Weigel, 2020). The method can be applied not only to species with complete genome sequences, but also to those that have not been fully sequenced, providing a new way to identify the genetic basis of important agronomic traits such as disease resistance.
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