Mingle Wang

Summer tea (Camellia sinensis) is less favored due to its inferior taste compared to spring tea. The application of selenium (Se) has proven effective in enhancing tea flavor. However, the specific mechanisms underlying the Se-mediated improvement of summer tea quality remain unclear. This study examines the alteration of trace elements, the metabolome, and the transcriptome in tea plants subjected to Se treatment. Se application increased the concentrations of B, Fe, Zn, and Se in the summer tea shoots of certain cultivars. Metabolomic analysis revealed that exogenous Se elevated the levels of theanine and flavonoids while reducing the catechin bitterness taste index in most of the selected cultivars. Transcriptomic analysis further demonstrated that Se treatment modulated the expression of CsSULTRs, CsPHTs, CsIRTs, CsZIPs, and CsBOTs, indicating a potential link between the accumulation of these elements and the corresponding transporter genes. Based on qRT-PCR results, CsSULTR1.1, 1.2, and 4.1 are likely involved in Se transport. Additionally, differentially expressed genes (DEGs) were predominantly enriched in the flavonoid and amino acid biosynthesis pathways following Se treatment. In conclusion, the addition of Se enhances the flavor profile of summer tea by modulating genes participating in flavonoid and amino acid metabolism, underpinning its potential for improving summer tea quality.

Tea plant is a fluoride (F)-hyperaccumulator, which poses a potential threat to human health via tea consumption. Reducing F accumulation in fresh tea leaves is crucial for enhancing the safety of tea production at its source. This study aims to isolate novel genes responsible for F accumulation or transport in tea plants. We identified an aluminum (Al)-activated malate transporter gene, CsALMT6, which was hypothesized to be a candidate for differential F accumulation in Camellia sinensis, by employing a combination of transcriptome-wide association study and genome-wide identification of the CsALMT gene family. CsALMT6 exhibited high expression levels in old leaves, and its expression was significantly upregulated in tea plants subjected to F-stress conditions. Furthermore, heterologous expression of CsALMT6 in yeast, Arabidopsis, and Populus conferred F tolerance. However, the expression of F-tolerant hub genes, CsFEX1 and CsFEX2, remained unaffected in CsALMT6-silenced tea plants. Additionally, under F toxicity conditions, the transcription of CsALMT6 was negatively associated with F accumulation in tea plants. In conclusion, CsALMT6 plays a vital role in reducing F accumulation in C. sinensis, thus conferring F tolerance to plant cells.

Zinc (Zn) and nitrogen (N) are the two crucial nutrients for tea plant growth and development and contribute to the quality formation of tea fresh leaves. In this study, a zinc/iron-regulated transporter-like protein 4 gene (i.e., CsZIP4) was functionally characterized. Expression profiling showed that CsZIP4 could be induced by Zn stresses and a N deficiency. Heterologous expression of CsZIP4 in yeast revealed that CsZIP4 possessed the capacity for Zn transport but not ammonium. Moreover, CsZIP4 overexpression in Arabidopsis thaliana promoted Zn and N uptake and transport and contributed to alleviate Zn stresses by collaborating with N supply, which might be interrelated to the expression of N or Zn metabolism-related genes, such as AtNRT1.1 and AtZIP4. Additionally, CsZIP4 was localized in the plasma membrane and chloroplast, which was helpful in maintaining cellular homeostasis under a Zn excess. Furthermore, silencing of CsZIP4 in tea plants by virus-induced gene silencing increased the chlorophyll content but decreased the Zn content. Finally, the yeast one-hybrid assay demonstrated that CsbZIP2 bound to the CsZIP4 promoter. These results will shed light on the functions of CsZIP4 in the N and Zn interaction in tea plants.

Magnesium (Mg²⁺) is a crucial nutrient for the growth and development of Camellia sinensis and is closely related to the quality of tea. However, the underlying mechanisms responding to low-Mg²⁺ stress in tea plants remain largely unknown. In this study, the photosynthetic parameters, metabolomics, and transcriptomics were utilized to explore the potential effects of low-Mg²⁺ on the growth and metabolism of C. sinensis. Low-Mg²⁺ treatment increased the ratio of shoot dry weight to root dry weight but decreased the photosynthesis of C. sinensis. Forty and thirty metabolites were impacted by Mg²⁺ shortage in C. sinensis shoots and roots, respectively. Integrated transcriptome and metabolome analyses revealed the possible reasons for the decreased contents of chlorophyll (Chl) and catechins and the increased theanine content in C. sinensis roots. Weighted gene co-expression network analysis indicated that Mg²⁺ transport system was essential in regulation of Mg²⁺ homeostasis in C. sinensis, in which CsMGT5 was identified to be the key regulator according to CsMGT5-overexpressing and complementary assays in Arabidopsis thaliana. Moreover, silencing of CsMGT5 in vivo reduced the content of Chl in C. sinensis shoots. In addition, CsMGT5 might collaborate with ammonium transporters to keep the steady of amino acids contents, suggesting its potential application for tea quality improvement. All these findings demonstrate the key roles of CsMGTs for Mg²⁺ homeostasis in C. sinensis, providing theoretical basis for Mg²⁺ efficient utilization in plants.

MiR156 play important roles in regulation of plant growth and development, secondary metabolite synthesis, and other biological processes by targeting the SQUAMOSA promoter binding protein-like (SPL) family. Our previous sequencing data analysis suggested that Csn-miR156d may regulate flowering and anthocyanin accumulation by cleavage and degradation of the expression of the SPL in tea plant, but it remains to be elucidated. In this study, 5′RLM-RACE experiment, tobacco transient transformation, qRT-PCR, and antisense oligonucleotide (asODN) were used to verify that CsSPL1 is the target gene of Csn-miR156d. Stable transformation of Arabidopsis revealed that Csn-miR156d could delay flowering by negatively regulating the transcript levels of FT, AP1, FUL, and SOC1, while overexpression of CsSPL1 showed an opposite effect. Additionally, overexpression of Csn-miR156d in Arabidopsis could enhance the transcription of the anthocyanin biosynthesis-related structural genes DFR, ANS, F3H, UGT78D2, and LDOX, as well as regulatory genes PAP1, MYB113, GL3, MYB11, and MYB12, leading to anthocyanin accumulation. Moreover, asODN experiment revealed that Csn-miR156d could increase the anthocyanin content in tea plant. These results suggest that Csn-miR156d regulates flowering and anthocyanin accumulation in tea plant by suppressing the expression of CsSPL1. Our study provides new insights into the development and anthocyanin accumulation in tea plant and lays a theoretical foundation for further research on the molecular mechanism of miRNAs in regulating tea plant growth and secondary metabolism.