Journal of Tea Science Research, 2024, Vol.14, No.3, 160-168 http://hortherbpublisher.com/index.php/jtsr 162 3.3 Case studies of quality enhancement Several studies have demonstrated the successful use of CRISPR/Cas9 in improving the quality of tea plants. For example, Li et al. (2023) studied the application of CRISPR/Cas9 gene editing in the tea tree genome, identified 248 million potential editing sites, and found five PAM types (AGG, TGG, CGG, GGG, NGG). Through bioinformatics analysis, the researchers revealed the distribution and characterization of these loci in the tea tree genome, particularly their importance in secondary metabolism and amino acid biosynthesis pathways (Figure 1). The results show that CRISPR/Cas9 technology can provide a powerful tool for molecular breeding of tea plants, and help to improve the quality and yield of tea. Figure 1 Functional analysis of genes in specific CRISPR-edited regions in 15 chromosomes (Adopted from Li et al., 2023) Image caption: (A): Gene ontology (GO) enrichment analysis showed that genes in these regions were mainly involved in the biological processes of terpenoid biosynthesis, gene expression regulation and methylation. (B): KEGG enrichment analysis showed that these genes are closely related to secondary metabolites and amino acid biosynthesis pathways, and these results suggest that genes in specific CRISPR-edited regions play key roles in important physiological and biochemical processes of tea plants, providing potential molecular targets for genetic improvement of tea plants (Adapted from Li et al., 2023) 4 Disease Resistance in Tea Plants 4.1 Common diseases affecting tea plants The tea plant (Camellia sinensis) is susceptible to various diseases that can significantly impact its yield and quality. Some of the most prevalent diseases include blister blight, gray blight, and red root rot. Blister blight is caused by a fungus, leading to the formation of blisters on young leaves, severely affecting photosynthesis and plant growth. Gray blight, caused by the fungus Pseudopestalotiopsis, produces gray spots on the leaves, resulting in defoliation and reduced plant vigor. Red root rot, caused by the soil-borne pathogen Poria hypobrunnea, affects the roots, leading to plant wilting and death. Additionally, while not a disease, the tea mosquito bug (Helopeltis theivora) is a significant pest that causes damage similar to disease symptoms, including leaf spots and dieback. 4.2 CRISPR strategies for developing disease-resistant varieties The advent of CRISPR/Cas9 technology has revolutionized the development of disease-resistant crops, including tea plants. CRISPR/Cas9 allows for precise genome editing, enabling the introduction of disease resistance traits without the need for traditional breeding methods, which are often time-consuming and less precise. One common strategy involves knocking out susceptibility (S) genes that make plants vulnerable to pathogens. For instance, CRISPR/Cas9 can be used to disrupt these genes, thereby enhancing resistance to fungal, bacterial, and viral diseases (Borrelli et al., 2018; Langner et al., 2018; Ahmad et al., 2020). Another approach is to enhance the plant's innate immune response by editing genes involved in pathogen recognition and defense signaling
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