Ziyin Yang

Mechanical harvesting is essential for alleviating labor shortages in tea production, yet the physiological mechanisms of tea plant responses remain unclear. Here, we show that continuous mechanical harvesting inhibits internode elongation in tea (Camellia sinensis) by reducing cell size and cell number. This inhibition was associated with a sustained decrease in free indole-3-acetic acid (IAA) and an increase in IAA-amino acid conjugates. We identified four auxin-related CsGH3 genes, divided into the CsGH3.1 and CsGH3.6 subfamilies. CsGH3.1 subfamilies gene expression correlated negatively with free IAA, whereas CsGH3.6 expression correlated positively with indole-3-acetyl-aspartic acid (IAA-Asp). Both in vitro and in vivo assays confirmed their IAA-amido synthetase activity, with CsGH3.1-2 exhibiting the highest catalytic efficiency in vitro. Overexpression of CsGH3.1-2 in tobacco significantly reduced free IAA, and induced apoplastic alkalization to inhibit cell expansion, resulting in a dwarf phenotype in transgenic plants. We further identified a NAC transcription factor, CsNAC21, as a positive regulator of CsGH3.1-2. Mechanical harvesting induced CsNAC21 expression, and transient overexpression of CsNAC21 in tea shoots up-regulated CsGH3.1-2 and promoted IAA conjugation to IAA-Asp. These findings establish the CsNAC21–CsGH3.1-2 module as a core adaptive mechanism by which mechanical harvesting reprograms auxin metabolism to regulate shoot growth.

Our previous study demonstrated that (Z)-3-hexenyl vicianoside and (Z)-3-hexenyl primeveroside display antiherbivore activity against tea gray geometrids, yet their biosynthetic glycosyltransferases (GTs) remained uncharacterized. Here, we identified CsUGT91A1 (CsGT3) from tea plants, which localizes to the cytoplasm and nucleus. Recombinant CsGT3 converted (Z)-3-hexenyl glucoside into vicianoside and primeveroside, with optimal activity at 30 °C and pH 7.5. Kinetic and docking studies indicated higher catalytic efficiency for UDParabinose than UDPxylose. Transient overexpression in tobacco and tea plants confirmed CsGT3 catalyzes this conversion. Moreover, infestation by tea green leafhoppers, tea gray geometrids, or tea aphids consistently increased the accumulation of (Z)-3-hexenyl glycosides, associated with the increased precursor (Z)-3-hexenol. These findings elucidate the role of CsGT3 in the biosynthesis of (Z)-3-hexenyl disaccharides and enhance the understanding of volatile glycoside metabolism in tea plants.

While tea quality traits are largely attributed to leaf-derived metabolites, the role of roots in determining tea (Camellia sinensis L.) productivity and quality has been relatively understudied. Tea roots are central to nitrogen assimilation, carbohydrate storage, and phytohormone biosynthesis, thereby influencing shoot development and environmental responses. Although recent efforts have focused on identifying key genes coordinating quality, yield, and stress resilience, the long lifespan of tea plants limits the practicality of genetic replacement in mature plantations. This review instead emphasizes agronomic and environmental regulation of root metabolites as an alternative approach for enhancing plant performance. Based on the findings (including multiomics studies) about root metabolites and their effects on aboveground traits, we propose a rhizosphere-to-canopy optimization framework incorporating microbiome modulation, nutrient management, and precision agronomy. Root-centered interventions represent a promising, sustainable approach to enhance tea quality, yield, and stress tolerance without replacing established cultivars.

Benzyl nitrile from tea plants attacked by various pests displays a diurnal pattern, which may be closely regulated by the endogenous circadian clock. However, the molecular mechanism by the circadian clock of tea plants that regulates the biosynthesis and release of volatiles remains unclear. In this study, the circadian clock gene CsPCL1 can activate both the expression of the benzyl nitrile biosynthesis-related gene CsCYP79 and the jasmonic acid signaling-related transcription factor CsMYC2 involved in upregulating CsCYP79 gene, thereby resulting in the accumulation and release of benzyl nitrile. Therefore, the anti-insect function of benzyl nitrile was explored in the laboratory. The application of slow-release beads of benzyl nitrile in tea plantations significantly reduced the number of tea geometrids and had positive effects on the yield of fresh tea leaves. These findings reveal the potential utility of herbivore-induced plant volatiles for the green control of pests in tea plantations.

Tea green leafhoppers are insects widely distributed in major tea‐growing areas. At present, less attention has been paid to the study on effect of tea green leafhopper infestation on tea growth phenotype. In this study, tea green leafhoppers were used to treat tea branches in laboratory and co‐treated with brassinolide (BL), the highest bioactivity of brassinosteroids (BRs), in tea garden. The results showed that the expression of genes related to BRs synthesis was inhibited and BL content was reduced in tea shoots after infestation by tea green leafhoppers. In addition, area of each leaf position, length and diameter of internodes, and the biomass of the tender shoots of tea plant were decreased after infestation by tea green leafhoppers. The number of trichomes, leaf thickness, palisade tissue thickness and cuticle thickness of tea shoots were increased after tea green leafhoppers infestation. BL spraying could partially recover the phenotypic changes of tea branches caused by tea green leafhoppers infestation. Further studies showed that tea green leafhoppers infestation may regulate the expression of CsDWF4 (a key gene for BL synthesis) through transcription factors CsFP1 and CsTCP1a, which finally affect the BL content. Moreover, BL was applied to inhibit the tea green leafhoppers infestation on tea shoots. In conclusion, our study revealed the effect of plant hormone BL‐mediated tea green leafhoppers infestation on the growth phenotype of tea plants.

Volatiles are important for plant root stress resistance. The diseases in tea root are serious, causing major losses. The volatile composition in tea root and whether it can resist diseases remain unclear. In this study, the volatile composition in different tea tissues was revealed. The vanillin content was higher in the root (mainly in root cortex) than in aerial parts. The antifungal effects of vanillin on pathogenic fungi in tea root were equal to or greater than those of other metabolites. O-methyltransferase (CsOMT), a key enzyme in one of two biosynthetic pathways of vanillin, converted protocatechualdehyde to vanillin in vitro. Furthermore, its characteristics and kinetic parameters were studied. In Arabidopsis thaliana protoplasts, the transiently expressed CsOMT was localized in the cytoplasm and nucleus. These findings have clarified the formation and bioactivities of volatiles in tea roots and provided a theoretical basis for understanding how tea plants resist root diseases.

Plant volatile compounds have important physiological and ecological functions. Phenylacetaldehyde (PAld), a volatile phenylpropanoid/benzenoid, accumulates in the leaves of tea (Camellia sinensis) plants grown under continuous shading. This study was conducted to determine whether PAld production is correlated with light and to elucidate the physiological functions of PAld in tea plants. Specifically, the upstream mechanism modulating PAld biosynthesis in tea plants under different light conditions as well as the effects of PAld on chloroplast/chlorophyll were investigated. The biosynthesis of PAld was inhibited under light, whereas it was induced in darkness. The structural gene encoding aromatic amino acid aminotransferase 1 (CsAAAT1) was expressed at a high level in darkness, consistent with its importance for PAld accumulation. Additionally, the results of a transcriptional activation assay and an electrophoretic mobility shift assay indicated CsAAAT1 expression was slightly activated by phytochrome-interacting factor 3-2 (CsPIF3-2), which is a light-responsive transcription factor. Furthermore, PAld might promote the excitation of chlorophyll in dark-treated chloroplasts and mediate electron energy transfer in cells. However, the accumulated PAld can degrade chloroplasts and chlorophyll, with potentially detrimental effects on photosynthesis. Moreover, PAld biosynthesis is inhibited in tea leaves by red and blue light, thereby decreasing the adverse effects of PAld on chloroplasts during daytime. In conclusion, the regulated biosynthesis of PAld in tea plants under light and in darkness leads to chloroplast modifications. The results of this study have expanded our understanding of the biosynthesis and functions of volatile phenylpropanoids/benzenoids in tea leaves.

Polyamine oxidase (PAO) is a key enzyme maintaining polyamine homeostasis, which affects plant physiological activities. Until now, the gene members and function of PAOs in tea (Camellia sinenesis) have not been fully identified. Here, through the expression in Escherichia coli and Nicotiana benthamiana, we identified six genes annotated as CsPAO in tea genome and transcriptome and determined their enzyme reaction modes and gene expression profiles in tea cultivar "Yinghong 9'. We found that CsPAO1,2,3 could catalyze spermine, thermospermine, and norspermidine, and CsPAO2,3 could catalyze spermidine in the back-conversion mode, which indicated that the precursor of gamma-aminobutyric acid might originate from the oxidation of putrescin but not spermidine. We further investigated the changes of CsPAO activity with temperature and pH and their stability. Kinetic parameters suggested that CsPAO2 was the major PAO modifying polyamine composition in tea, and it could be inactivated by beta- hydroxyethylhydrazine and aminoguanidine. Putrescine content and CsPAO2 expression were high in tea flowers. CsPAO2 responded to wound, drought, and salt stress; CsPAO1 might be the main member responding to cold stress; anoxia induced CsPAO3. We conclude that in terms of phylogenetic tree, enzyme characteristics, and expression profile, CsPAO2 might be the dominant CsPAO in the polyamine degradation pathway.

Herbivore-induced plant volatiles (HIPVs) help the tea plant (Camellia sinensis) adapt to environmental stress, and they are also quality-related components of tea. However, the upstream mechanism regulating the herbivore-induced expression of volatile biosynthesis genes is unclear, especially at the level of epigenetic regulation. In this study, similar to the effects of a tea green leafhopper infestation, treatments with exogenous jasmonic acid (JA) and histone deacetylase inhibitors significantly increased the (E)-nerolidol content in tea and induced the expression of the associated biosynthesis gene CsNES. Furthermore, a key transcription factor related to JA signaling, myelocytomatosis 2 (CsMYC2), interacted with histone deacetylase 2 (CsHDA2) in vitro and in vivo. A tea green leafhopper infestation inhibited CsHDA2 expression and decreased CsHDA2 abundance. Moreover, the tea green leafhopper infestation increased H3 and H4 acetylation levels in the promoter region of CsNES, which in turn upregulated the expression of CsNES and increased the (E)-nerolidol content. In this study, we revealed the effects of histone acetylations on the accumulation of HIPVs, while also confirming that CsHDA2–CsMYC2 is an important transcriptional regulatory module for the accumulation of (E)-nerolidol induced by tea green leafhoppers. The results of this study may be useful for characterizing plant aromatic compounds and the main upstream stress-responsive signaling molecules. Furthermore, the study findings will assist researchers clarify the epigenetic regulation influencing plant secondary metabolism in response to external stress.