Journal of Tea Science Research, 2024, Vol.14, No.1, 64-78 http://hortherbpublisher.com/index.php/jtsr 68 Genomic data for Camellia species are stored in various databases and repositories, facilitating easy access and retrieval for researchers. For example, National Center for Biotechnology Information (NCBI) provides access to genomic sequences, gene annotations, and related metadata through platforms such as GenBank and the Sequence Read Archive (SRA) (Yi et al., 2024). The Tea Plant Information Archive (TPIA) is a specialized database that offers comprehensive genomic and transcriptomic data specific to Camellia sinensis. Additionally, Wu et al. (2022) have created a web-accessible database to store transcriptome sequences of 116 Camellia plants, enabling efficient conservation and utilization of Camellia germplasm for breeding programs. Chloroplast genome sequences of multiple Camellia species are also available, providing robust evidence for taxonomic studies and species identification (Huang et al., 2014). 2.3 Data analysis Common data analysis methods in Camellia genomic research include sequence alignment, phylogenetic analysis, and comparative genomics. Sequence alignment and phylogenetic analysis have been used to resolve interspecies relationships and identify rapidly evolving regions in chloroplast genomes (Yang et al., 2013; Huang et al., 2014). Comparative genomics methods are used to identify orthologous genes and conserved regions across different Camellia species, providing insights into their evolutionary relationships. The results showed that the comparative genomic analysis has revealed whole-genome duplication events and gene family expansions, providing insights into the evolutionary history and trait adaptations in Camelliaspecies (Wei et al., 2018; Shen et al., 2022). Data processing and interpretation involve several steps, including quality control, sequence assembly, and functional annotation. Quality control measures, such as using propidium iodide (PI) flow cytometry analysis, ensure high-quality results with low coefficient of variation values (Huang et al., 2013). Sequence assembly techniques, such as de novo and reference-guided assembly, are employed to construct complete and draft genome sequences (Huang et al., 2014). Functional annotation helps identify genes related to key economic traits, such as flower and fruit development and stress tolerances, which are crucial for molecular breeding programs (Yan et al., 2018). The integration of high-throughput sequencing technologies, bioinformatics tools, and comprehensive genomic resources has significantly advanced our understanding of the evolutionary history and genomic diversity of the Camellia genus. These approaches provide a solid foundation for future research and breeding efforts aimed at improving economically important traits in Camelliaspecies. 3 Evolutionary History of the Camellia Genus 3.1 Phylogenetic studies Phylogenetic studies aim to reconstruct the evolutionary relationships among species by analyzing genetic data. Phylogenetic studies of the Camellia genus have employed various molecular techniques to resolve the complex interspecies relationships. Chloroplast genome sequencing has been a prominent method, providing high-resolution data for phylogenetic analysis. For instance, complete chloroplast genomes of multiple Camellia species have been sequenced using Illumina technology, revealing conserved yet sufficiently variable regions for phylogenetic inference (Yang et al., 2013; Li et al., 2019; Lin et al., 2022). Additionally, nuclear DNA sequences such as ITS and waxy genes have been utilized, although with varying degrees of success due to issues like low divergence rates and amplification difficulties (Li et al., 2021). Phylogenetic analyses have revealed significant insights into the evolutionary relationships within the Camellia genus. Studies have shown that the genus is monophyletic, but the interspecies relationships remain complex due to frequent hybridization and polyploidization events (Li et al., 2021; Li et al., 2019; Lin et al., 2022). Comparative genomic analyses have identified specific regions in the chloroplast genome that serve as effective barcode markers for species identification and phylogenetic resolution (Lin et al., 2022). Furthermore, transcriptomic data from 116 Camellia plants have provided robust phylogenetic trees supported by nuclear gene trees and morphological traits (Figure 2), highlighting a recent whole genome duplication event in the genus (Wu et al., 2022).
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