Mitochondria are the main sites for oxidative phosphorylation and synthesis of adenosine triphosphate in cells, and are known as cellular power factories. The phrase “secondary mitochondrial diseases” essentially refers to any abnormal mitochondrial function other than primary mitochondrial diseases, i.e., the process caused by the genes encoding the electron transport chain (ETC) proteins directly or impacting the production of the machinery needed for ETC. Mitochondrial diseases can cause adenosine triphosphate (ATP) synthesis disorder, an increase in oxygen free radicals, and intracellular redox imbalance. It can also induce apoptosis and, eventually, multi-system damage, which leads to neurodegenerative disease. The catechin compounds rich in tea have attracted much attention due to their effective antioxidant activity. Catechins, especially acetylated catechins such as epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), are able to protect mitochondria from reactive oxygen species. This review focuses on the role of catechins in regulating cell homeostasis, in which catechins act as a free radical scavenger and metal ion chelator, their protective mechanism on mitochondria, and the protective effect of catechins on mitochondrial deoxyribonucleic acid (DNA). This review highlights catechins and their effects on mitochondrial functional metabolic networks: regulating mitochondrial function and biogenesis, improving insulin resistance, regulating intracellular calcium homeostasis, and regulating epigenetic processes. Finally, the indirect beneficial effects of catechins on mitochondrial diseases are also illustrated by the warburg and the apoptosis effect. Some possible mechanisms are shown graphically. In addition, the bioavailability of catechins and peracetylated-catechins, free radical scavenging activity, mitochondrial activation ability of the high-molecular-weight polyphenol, and the mitochondrial activation factor were also discussed.

Leaf color is one of the key factors involved in determining the processing suitability of tea. It relates to differential accumulation of flavor compounds due to the different metabolic mechanisms. In recent years, photosensitive etiolation or albefaction is an interesting direction in tea research field. However, the molecular mechanism of color formation remains unclear since albino or etiolated mutants have different genetic backgrounds. In this study, wide-target metabolomic and transcriptomic analyses were used to reveal the biological mechanism of leaf etiolation for ‘Huangyu’, a bud mutant of ‘Yinghong 9’. The results indicated that the reduction in the content of chlorophyll and the ratio of chlorophyll to carotenoids might be the biochemical reasons for the etiolation of ‘Huangyu’ tea leaves, while the content of zeaxanthin was significantly higher. The differentially expressed genes (DEGs) involved in chlorophyll and chloroplast biogenesis were the biomolecular reasons for the formation of green or yellow color in tea leaves. In addition, our results also revealed that the changes of DEGs involved in light-induced proteins and circadian rhythm promoted the adaptation of etiolated tea leaves to light stress. Variant colors of tea leaves indicated different directions in metabolic flux and accumulation of flavor compounds.

Anthocyanins in tea (Camellia sinensis) leaves enhance tea quality due to their unique health benefits. MYB transcription factors are crucial in regulating anthocyanin biosynthesis in various plant species. In this research, a typical R2R3 repressive transcription factor CsMYB308 was identified which includes an EAR motif that belongs to the SG4 subfamily and was localized in the nucleus. Antisense oligonucleotide (asODN)-mediated CsMYB308 silencing revealed that the anthocyanin synthesis of structural genes was up-regulated. Furthermore, DNA affinity purification sequencing (DAP-seq) screened downstream genes regulated by CsMYB308. Dual-luciferase reporter (DLR) results showed that CsMYB308 suppressed anthocyanin biosynthesis by regulating the transcriptional activity of CsF3'5'H, CsDFR, and CsANS and electrophoretic mobility shift assay (EMSA) proved the concrete binding sites. In addition, we elucidated the molecular mechanism of Zijuan accumulating anthocyanin at an optimal concentration by shading experiment in summer. The results could provide an agronomic strategy to enhance the utilization of fresh leaves in summer. This study also presented a new insight of the regulatory pathway involved in anthocyanin biosynthesis in tea plants.