Tea (Camelliasinensis) is the world’s most widely consumed non-alcoholic beverage with essential economic and health benefits since it is an excellent source of polyphenols, catechins, amino acids, flavonoids, carotenoids, vitamins, and polysaccharides. The aim of this review is to summarize the main secondary metabolites in tea plants, and the content and distribution of these compounds in six different types of tea and different organs of tea plant were further investigated. The application of these secondary metabolites on food processing, cosmetics industry, and pharmaceutical industry was reviewed in this study. With the rapid advancements in biotechnology and sequencing technology, omics analyses, including genome, transcriptome, and metabolome, were widely used to detect the main secondary metabolites and their molecular regulatory mechanisms in tea plants. Numerous functional genes and regulatory factors have been discovered, studied, and applied to improve tea plants. Research advances, including secondary metabolites, applications, omics research, and functional gene mining, are comprehensively reviewed here. Further exploration and application trends are briefly described. This review provides a reference for basic and applied research on tea plants.

The 2-oxoglutarate and Fe (II)-dependent dioxygenase (2ODD-C) family of 2-oxoglutarate-dependent dioxygenases potentially participates in the biosynthesis of various metabolites under various abiotic stresses. However, there is scarce information on the expression profiles and roles of 2ODD-C genes in Camellia sinensis. We identified 153 Cs2ODD-C genes from C. sinensis, and they were distributed unevenly on 15 chromosomes. According to the phylogenetic tree topology, these genes were divided into 21 groups distinguished by conserved motifs and an intron/exon structure. Gene-duplication analyses revealed that 75 Cs2ODD-C genes were expanded and retained after WGD/segmental and tandem duplications. The expression profiles of Cs2ODD-C genes were explored under methyl jasmonate (MeJA), polyethylene glycol (PEG), and salt (NaCl) stress treatments. The expression analysis showed that 14, 13, and 49 Cs2ODD-C genes displayed the same expression pattern under MeJA and PEG treatments, MeJA and NaCl treatments, and PEG and NaCl treatments, respectively. A further analysis showed that two genes, Cs2ODD-C36 and Cs2ODD-C21, were significantly upregulated and downregulated after MeJA, PEG, and NaCl treatments, indicating that these two genes played positive and negative roles in enhancing the multi-stress tolerance. These results provide candidate genes for the use of genetic engineering technology to modify plants by enhancing multi-stress tolerance to promote phytoremediation efficiency.