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Background Low temperature restricts the planting range of all crops, but cold acclimation induces adaption to cold stress in many plants. Camellia sinensis , a perennial evergreen tree that is the source of tea, is mainly grown in warm areas. Camellia sinensis var. sinensis (CSS) has greater cold tolerance than Camellia sinensis var. assamica (CSA). To gain deep insight into the molecular mechanisms underlying cold adaptation, we investigated the physiological responses and transcriptome profiles by RNA-Seq in two tea varieties, cold resistant SCZ (classified as CSS) and cold susceptible YH9 (classified as CSA), during cold acclimation. Results Under freezing stress, lower relative electrical conductivity and higher chlorophyll fluorescence (Fv/Fm) values were detected in SCZ than in YH9 when subjected to freezing acclimation. During cold treatment, 6072 and 7749 DEGs were observed for SCZ and YH9, respectively. A total of 978 DEGs were common for both SCZ and YH9 during the entire cold acclimation process. DEGs were enriched in pathways of photosynthesis, hormone signal transduction, and transcriptional regulation of plant-pathogen interactions. Further analyses indicated that decreased expression of Lhca2 and higher expression of SnRK2.8 are correlated with cold tolerance in SCZ. Conclusions Compared with CSA, CSS was significantly more resistant to freezing after cold acclimation, and this increased resistance was associated with an earlier expression of cold-induced genes. Because the greater transcriptional differentiation during cold acclimation in SCZ may contribute to its greater cold tolerance, our studies identify specific genes involved in photoinhibition, ABA signal conduction, and plant immunity that should be studied for understanding the processes involved in cold tolerance. Marker-assisted breeding focused on the allelic variation at these loci provides an avenue for the possible generation of CSA cultivars that have CSS-level cold tolerance.

Drought stress triggers a series of physiological and biochemical changes in tea plants. It is well known that flavonoids, lignin and long-chain fatty acids play important roles in drought resistance. However, changes in proteins related to these three metabolic pathways in tea plants under drought stress have not been reported. We analysed the proteomic profiles of tea plants by tandem mass tag and liquid chromatography-tandem mass spectrometry. A total of 4789 proteins were identified, of which 11 and 100 showed up- and downregulation, respectively. The proteins related to the biosynthesis of lignin, flavonoids and long-chain fatty acids, including phenylalanine ammonia lyase, cinnamoyl-CoA reductase, peroxidase, chalcone synthase, flavanone 3-hydroxylase, flavonol synthase, acetyl-CoA carboxylase 1,3-ketoacyl-CoA synthase 6 and 3-ketoacyl-CoA reductase 1, were downregulated. However, the contents of soluble proteins, malondialdehyde, total phenols, lignin and flavonoids in the tea plants increased. These results showed that tea plants might improve drought resistance by inhibiting the accumulation of synthases related to lignin, flavonoids and long-chain fatty acids. The proteomic spectrum of tea plants provides a scientific basis for studying the pathways related to lignin, flavonoid and long-chain fatty acid metabolism in response to drought stress.

Background Tea is the most popular non-alcoholic health beverage in the world. The tea plant ( Camellia sinensis (L.) O. Kuntze) needs to undergo a cold acclimation process to enhance its freezing tolerance in winter. Changes that occur at the molecular level in response to low temperatures are poorly understood in tea plants. To elucidate the molecular mechanisms of cold acclimation, we employed RNA-Seq and digital gene expression (DGE) technologies to the study of genome-wide expression profiles during cold acclimation in tea plants. Results Using the Illumina sequencing platform, we obtained approximately 57.35 million RNA-Seq reads. These reads were assembled into 216,831 transcripts, with an average length of 356 bp and an N50 of 529 bp. In total, 1,770 differentially expressed transcripts were identified, of which 1,168 were up-regulated and 602 down-regulated. These include a group of cold sensor or signal transduction genes, cold-responsive transcription factor genes, plasma membrane stabilization related genes, osmosensing-responsive genes, and detoxification enzyme genes. DGE and quantitative RT-PCR analysis further confirmed the results from RNA-Seq analysis. Pathway analysis indicated that the “carbohydrate metabolism pathway” and the “calcium signaling pathway” might play a vital role in tea plants’ responses to cold stress. Conclusions Our study presents a global survey of transcriptome profiles of tea plants in response to low, non-freezing temperatures and yields insights into the molecular mechanisms of tea plants during the cold acclimation process. It could also serve as a valuable resource for relevant research on cold-tolerance and help to explore the cold-related genes in improving the understanding of low-temperature tolerance and plant-environment interactions.

Summary Linalool not only is one of characteristic flavour volatiles of tea, contributing to floral aroma, but also a kind of defensive compounds, playing essential roles in resistance against biotic/abiotic stresses. Although the linalool synthases have been identified, much is unknown about the regulation mechanism in tea plants. We identified two pairs of MYB paralogs as linalool biosynthesis activators, in which one pair (CsMYB148/CsMYB193) specifically expressed in flowers, and another (CsMYB68/CsMYB147) highly expressed in flowers, leaves, fruits and roots. These activators interacted with CsMYC2 to form MYC2‐MYB complexes to regulate linalool synthase. While Jasmonate ZIM‐domain (JAZ) proteins served as the linalool biosynthesis repressors by interfering MYC2‐MYB complex. Further, we found that the transcripts of CsMYB68/CsMYB147 were significantly upregulated by jasmonic acid (JA) to improve linalool products during tea processing and that linalool pathway may as one of the downstream pathways of JA signalling and DNA methylation processes to participate in cold resistance. Under cold stress, JA signalling was activated to elevate the abundance of MYC‐MYB complexes; meanwhile, DNA demethylation was also activated, leading to declining methylation levels and increasing transcripts of CsMYB68/CsMYB147. Our study provides a new insight into synergistically improving tea quality and tea plant resistance.

Background Caffeine is a key secondary metabolite in tea plants, and its content is directly related to tea quality and the ability to relieve fatigue by stimulating neurons. Although studies have focused on the characteristics of caffeine accumulation, the specific effects of the CsDRMH3 gene on caffeine content in dormant and non-dormant buds of tea plants have not been systematically characterized. The purpose of the present study was to systematically analyze the effect of CsDRMH3 on caffeine accumulation in dormant and non-dormant buds and to clarify the correlation between the two, thereby laying an important theoretical foundation for directional regulation of caffeine content and improvement of tea quality. Results The present study systematically analyzed the correlation between CsDRMH3 and caffeine accumulation in dormant and non-dormant buds of tea plants. CsDRMH3 belongs to the DRM1/ARP family with functions related to dormancy and auxin repression and is localized to the nucleus, as confirmed by subcellular localization. Transient overexpression of CsDRMH3 resulted in a significant reduction in caffeine accumulation in buds, whereas silencing CsDRMH3 through virus-induced gene silencing (VIGS) significantly increases caffeine content. Moreover, CsDRMH3 expression exhibited responsive patterns to abscisic acid (ABA) and methyl jasmonate (MeJA) signals in the two types of buds. Conclusions The results present a systematic characterization of the links among CsDRMH3 expression features, dynamic variations in caffeine accumulation in dormant and non-dormant buds, and the responsiveness of caffeine accumulation to exogenous hormone signals, providing valuable references and insights for clarifying the role of CsDRMH3 in mediating bud-specific differences in caffeine content.

Drought priming is a critical agronomic strategy for enhancing plant drought tolerance, yet the optimal priming intensity and transcriptional regulatory mechanisms underlying subsequent drought responses in the tea plant ( Camellia sinensis ) remain poorly characterised. In this study, we systematically evaluated tea plants exposed to recurrent drought stress under varying priming intensities. Results demonstrated that moderate drought priming specifically conferred superior drought tolerance compared to non‐primed controls. Integrated metabolomic and transcriptomic profiling identified flavonoid biosynthesis as the key pathway associated with priming‐induced drought resilience. Exogenous flavonoid application and overexpression of six biosynthesis genes ( CsCHS , CsCHI , CsFLS , CsDFR , CsANS and CsANR ) functionally validated flavonoids' role in drought adaptation. Notably, transcriptional regulators CsYABBY1 and CsMYB114 were identified as hub transcription factors demonstrating transcriptional activation potential towards flavonoid biosynthesis. Combinatorial transient overexpression and silencing assays revealed that both CsYABBY1 and CsMYB114 coordinately upregulate flavonoid biosynthesis genes, redirecting metabolic flux towards flavonoid accumulation to enhance drought tolerance. Multimodal validation through yeast one‐hybrid assays, dual‐luciferase reporter systems and electrophoretic mobility shift assays, as well as molecular docking, confirmed or simulated direct binding of CsYABBY1 and CsMYB114 to promoter regions of flavonoid biosynthesis genes for transcriptional activation. These findings establish a synergistic regulatory model where CsYABBY1 and CsMYB114 cooperatively enhance flavonoid accumulation through transcriptional reprogramming, thereby conferring acquired drought tolerance. This study provides mechanistic insights for developing adaptive cultivation practices and advances molecular breeding strategies for drought‐resilient tea cultivars.

Purple-leaf tea is a phenotype with unique color because of its high anthocyanin content. The special flavor of purple-leaf tea is highly different from that of green-leaf tea, and its main ingredient is also of economic value. To probe the genetic mechanism of the phenotypic characteristics of tea leaf color, we conducted widely targeted metabolic and transcriptomic profiling. The metabolites in the flavonoid biosynthetic pathway of purple- and green-leaf tea were compared, and results showed that phenolic compounds, including phenolic acids, flavonoids, and tannins, accumulated in purple-leaf tea. The high expression of genes related to flavonoid biosynthesis (e.g., PAL and LAR) exhibits the specific expression of biosynthesis and the accumulation of these metabolites. Our result also shows that two CsUFGTs were positively related to the accumulation of anthocyanin. Moreover, genes encoding transcription factors that regulate flavonoids were identified by coexpression analysis. These results may help to identify the metabolic factors that influence leaf color differentiation and provide reference for future research on leaf color biology and the genetic improvement of tea.

Lateral organ boundaries domain (LBD) proteins are plant-specific transcription factors that play a crucial role in growth and development, as well as metabolic processes. However, knowledge of the function of LBD proteins in Camellia sinensis is limited, and no systematic investigations of the LBD family have been reported. In this study, we identified 54 LBD genes in Camellia sinensis . The expression patterns of CsLBDs in different tissues and their transcription responses to exogenous hormones and abiotic stress were determined by RNA-seq, which showed that CsLBDs may have diverse functions. Analysis of the structural gene promoters revealed that the promoters of CsC4H , CsDFR and CsUGT84A , the structural genes involved in flavonoid biosynthesis, contained LBD recognition binding sites. The integrative analysis of CsLBD expression levels and metabolite accumulation also suggested that CsLBDs are involved in the regulation of flavonoid synthesis. Among them, CsLOB_3, CsLBD36_2 and CsLBD41_2, localized in the nucleus, were selected for functional characterization. Yeast two-hybrid assays revealed that CsLBD36_2 and CsLBD41_2 have self-activation activities, and CsLOB_3 and CsLBD36_2 can directly bind to the cis -element and significantly increase the activity of the CsC4H , CsDFR and CsUGT84A promoter. Our results present a comprehensive characterization of the 54 CsLBDs in Camellia sinensis and provide new insight into the important role that CsLBDs play in abiotic and flavonoid biosynthesis.

Volatile organic compounds (VOCs) released under cold stress have emerged as important mediators of stress tolerance. However, the specific functional VOCs and the mechanisms through which they confer cold tolerance remain largely unknown. In this study, we established a Fluo‐8‐based calcium detection system in tea ( Camellia sinensis ) protoplasts to investigate the interplay between cold‐induced VOCs, calcium signalling, and cold tolerance. We identified ( Z )‐3‐hexenol and thymol as key VOCs that significantly enhance tea plant cold tolerance by activating cytosolic calcium signalling. These VOCs upregulated cold‐responsive genes ( CsICE1 , CsCBF1 , and CsCBF2 ), enhanced antioxidant enzyme activities (SOD and POD), and improved photosynthetic efficiency under cold stress. Furthermore, we revealed that CsCDPK4 , a calcium‐dependent protein kinase, acts as a key mediator of ( Z )‐3‐hexenol and thymol‐induced calcium signalling. Silencing CsCDPK4 abolished the beneficial effects of ( Z )‐3‐hexenol and thymol, underscoring its critical role in translating calcium signals into physiological adaptations. Our findings provide a mechanistic framework linking VOC perception, calcium signalling, and cold stress tolerance, offering novel strategies for enhancing crop resilience against abiotic stress in the face of climate challenges.

Salt stress is one of the abiotic stresses affecting crop quality and yield, and the application of exogenous brassinosteroids (BRs) can be used in response to salt stress. However, the function of BR in tea plants under salt stress remains to be elucidated. This study investigated the effects of exogenous spraying of BR on the malondialdehyde, soluble sugar, soluble protein, and antioxidant enzyme activities in tea plants under salt stress and explored the expression changes in genes related to the synthesis pathways of proline and secondary metabolites (flavonoids and theanine). The results show that 200 mM NaCl solution inhibits the physiology of tea plants, but 0.2 mg/L BR could partially reduce the damage by increasing photosynthetic pigments, osmoregulatory substances (such as soluble sugar, soluble protein, and proline), and the activity of antioxidant enzymes (including peroxidase, catalase, and superoxide dismutase), while decreasing the malondialdehyde content in salt-stressed leaves. The qRT-PCR experiment also shows that the genes related to the synthesis pathways of proline and secondary metabolites (flavonoids and theanine) were upregulated under salt stress, and the proline degradation genes were downregulated, thus promoting the accumulation of proline under salt stress in both varieties. When tea plants were subjected to salt stress, the expression of genes related to the synthesis of secondary metabolites was regulated accordingly to resist salt stress. Moreover, spraying BR had an obvious effect on improving the salt tolerance of tea plants. Therefore, exploring a way to improve the salt tolerance of tea trees provides a reference for the subsequent study of its salt tolerance mechanism, which is of great significance for expanding the introduction area of tea trees, increasing the planting area of tea trees, and improving the yield and quality of tea.