Plant Gene and Traits 2024, Vol.15, No.4, 207-219 http://genbreedpublisher.com/index.php/pgt 208 sinensis is primarily cultivated for tea production. It includes two main varieties, C. sinensis var. Sinensis and C. sinensis var. assamica, which have been independently domesticated and exhibit significant genetic diversity due to extensive intra- and interspecific introgressions (Xia et al., 2020; Zhang et al., 2021). The tea plant is clonally propagated, and its genetic and evolutionary history has been extensively studied to enhance desirable traits such as flavor and stress resistance (Zhang et al., 2021). Camellia oleifera is known as the tea-oil camellia, this species is a crucial woody oil crop in southern China and Southeast Asia. It is valued for its high oil content and resistance to environmental stresses such as drought and nutrient deficiency (Dong et al., 2017; Ye et al., 2023). Recent genomic studies have provided insights into its complex genome and identified genes related to economic traits and stress tolerances (Ye et al., 2023). 2.2 Key traits of interest inCamellia breeding Breeding programs for Camellia species focus on several key traits to enhance their economic value and adaptability. In C. oleifera, high oil content and quality are primary breeding goals. Studies have identified genes involved in oil biosynthesis, such as acetyl-coenzyme A carboxylase and diacylglycerol acyltransferase, which are crucial for high oil and oleic acid content (Figure 1) (Gong et al., 2022). For C. sinensis, traits related to tea quality, such as catechin and caffeine content, are of paramount importance. Genomic studies have revealed genes associated with these secondary metabolites, which are critical for the flavor and quality of tea (Lubanga et al., 2021; Wu et al., 2022). Resistance to diseases like anthracnose is a significant breeding objective for C. oleifera. Transcriptomic and metabolomic analyses have identified key metabolites and genes involved in flavonoid biosynthesis that contribute to disease resistance (Yang et al., 2022). Both C. sinensis and C. oleifera are bred for enhanced resistance to environmental stresses. For instance, drought tolerance in C. oleifera has been linked to genes involved in abscisic acid synthesis and protective enzyme activity (Dong et al., 2017). 2.3 Traditional breeding approaches and their limitations inCamellia species Traditional breeding approaches in Camellia species have primarily relied on phenotypic selection and cross-breeding. However, these methods face several limitations. Camellia species are perennial plants with long generation times, making traditional breeding time-consuming and labor-intensive (Ye et al., 2023). Many desirable traits, such as tea quality and oil content, are complex and controlled by multiple genes. Traditional breeding methods struggle to effectively select for these traits due to their polygenic nature (Lubanga et al., 2021). The genetic base of cultivated Camellia species is often narrow, limiting the potential for improvement through traditional breeding. This is particularly true for clonally propagated species like C. sinensis (Zhang et al., 2021). Phenotypic traits can be significantly influenced by environmental conditions, complicating the selection process and reducing the accuracy of traditional breeding methods (Chen et al., 2023). 3 Genomic Resources Available for CamelliaBreeding 3.1 Genomic sequencing projects inCamellia Genomic sequencing projects have significantly advanced our understanding of Camellia species, particularly Camellia sinensis, which is crucial for tea production. The draft genome sequence of Camellia sinensis var. sinensis has provided insights into the evolution of the tea genome and the biosynthesis of key metabolites such as catechins, theanine, and caffeine. This high-quality genome assembly, which includes 33 932 high-confidence protein-coding genes, has revealed two rounds of whole-genome duplications that have played a critical role in the evolution of these metabolites (Wei et al., 2018). Additionally, the chromosome-level genome of Camellia lanceoleosa has been sequenced, offering valuable resources for understanding genome evolution and self-incompatibility mechanisms in Camellia species (Gong et al., 2022). 3.2 Transcriptomic, proteomic, and metabolomic data inCamellia species Transcriptomic, proteomic, and metabolomic analyses have been extensively conducted in various Camellia species to understand their genetic diversity and metabolic pathways. For instance, a comprehensive transcriptome dataset of Camellia sinensis has been generated using high-throughput RNA sequencing, identifying numerous genes involved in primary and secondary metabolic pathways, including those critical for tea quality such as flavonoid, theanine, and caffeine biosynthesis. Comparative transcriptomic analysis of 116 Camellia plants has
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