Exogenous tannic acid relieves imidacloprid-induced oxidative stress in tea tree by activating antioxidant responses and the flavonoid biosynthetic pathway.

Pesticide stress on plants is receiving increased scrutiny due to its effect on plant secondary metabolism and nutritional quality. Tannic acid (TA) is a natural polyphenolic compound showing excellent antioxidant properties and is involved in alleviating stress. The present study thoroughly investigated the effects and mechanism of exogenous TA on relieving imidacloprid (IMI) stress in tea plants. Our research found that TA(10 mg/L) activated the antioxidant defense system, enhanced the antioxidant ability, reduced the accumulation of ROS and membrane peroxidation, and notably promoted tea plant tolerance to imidacloprid stress. Additionally, TA boosted photosynthetic capacity, strengthened the accumulation of nutrients. regulated detoxification metabolism, and accelerated the digestion and metabolism of imidacloprid in tea plants. Furthermore, TA induced significant changes in 90 important metabolites in tea, targeting 17 metabolic pathways through extensively targeted metabolomics. Specifically, TA activated the flavonoid biosynthetic pathway, resulting in a 1.3- to 3.1-fold increase in the levels of 17 compounds and a 1.5- to 63.8-fold increase in the transcript level of related genes, such as ANR, LAR and CHS in this pathway. As a potential tea health activator, TA alleviates the oxidative damage caused by imidacloprid and improves the yield and quality of tea under pesticide stress.

Fulvic acid enhances drought resistance in tea plants by regulating the starch and sucrose metabolism and certain secondary metabolism.

The aim of this work was to gain insight into the molecular mechanisms underlying the effect of fulvic acid on drought-exposed tea plants. We performed proteomic analysis of fulvic acid-treated tea leaves from the target plants using tandem mass tag quantitative labeling technology and compared the results with those of a previous transcriptomic analysis. We identified 48 and 611 differentially abundant proteins in the leaves of tea plants treated with fulvic acid compared with the control under mild and severe drought, respectively. Comparative analysis showed that, under severe drought, 55 genes had similar expression patterns at the transcriptome and proteome levels, such as PAL, GBE, GBSS and bAS. Bioinformatic analysis revealed that those genes were mainly related to the starch and sucrose metabolism, phenylpropanoid biosynthesis and triterpenoid biosynthesis. SIGNIFICANCE: This study broadens the understanding of the molecular mechanisms underlying the improved drought resistance seen in tea plants in the presence of fulvic acid and provides a basis for further research on the genomics of drought tolerance in these plants. In addition, these findings could be used to develop new guidance strategies for improved drought management systems in tea plantation.

Fulvic acid ameliorates drought stress-induced damage in tea plants by regulating the ascorbate metabolism and flavonoids biosynthesis.

BACKGROUND: Fulvic acid (FA) is a kind of plant growth regulator, which can promote plant growth, play an important role in fighting against drought, improve plant stress resistance, increase production and improve quality. However, the function of FA in tea plants during drought stress remain largely unknown. RESULTS: Here, we examined the effects of 0.1 g/L FA on genes and metabolites in tea plants at different periods of drought stress using transcriptomics and metabolomics profiles. Totally, 30,702 genes and 892 metabolites were identified. Compared with controlled groups, 604 and 3331 differentially expressed metabolite genes (DEGs) were found in FA-treated tea plants at 4 days and 8 days under drought stress, respectively; 54 and 125 differentially expressed metabolites (DEMs) were also found at two time points, respectively. Bioinformatics analysis showed that DEGs and DEMs participated in diverse biological processes such as ascorbate metabolism (GME, AO, ALDH and L-ascorbate), glutathione metabolism (GST, G6PDH, glutathione reduced form and CYS-GYL), and flavonoids biosynthesis (C4H, CHS, F3'5'H, F3H, kaempferol, quercetin and myricetin). Moreover, the results of co-expression analysis showed that the interactions of identified DEGs and DEMs diversely involved in ascorbate metabolism, glutathione metabolism, and flavonoids biosynthesis, indicating that FA may be involved in the regulation of these processes during drought stress. CONCLUSION: The results indicated that FA enhanced the drought tolerance of tea plants by (i) enhancement of the ascorbate metabolism, (ii) improvement of the glutathione metabolism, as well as (iii) promotion of the flavonoids biosynthesis that significantly improved the antioxidant defense of tea plants during drought stress. This study not only confirmed the main strategies of FA to protect tea plants from drought stress, but also deepened the understanding of the complex molecular mechanism of FA to deal with tea plants to better avoid drought damage.

Molecular Link between Leaf Coloration and Gene Expression of Flavonoid and Carotenoid Biosynthesis in Camellia sinensis Cultivar 'Huangjinya'.

'Huangjinya' is an excellent albino tea germplasm cultivated in China because of its bright color and high amino acid content. It is light sensitive, with yellow leaves under intense light while green leaves under weak light. As well, the flavonoid and carotenoid levels increased after moderate shading treatment. However, the mechanism underlying this interesting phenomenon remains unclear. In this study, the transcriptome of 'Huangjinya' plants exposed to sunlight and shade were analyzed by high-throughput sequencing followed by de novo assembly. Shading 'Huangjinya' made its leaf color turn green. De novo assembly showed that the transcriptome of 'Huangjinya' leaves comprises of 127,253 unigenes, with an average length of 914 nt. Among the 81,128 functionally annotated unigenes, 207 differentially expressed genes were identified, including 110 up-regulated and 97 down-regulated genes under moderate shading compared to full light. Gene ontology (GO) indicated that the differentially expressed genes are mainly involved in protein and ion binding and oxidoreductase activity. Antioxidation-related pathways, including flavonoid and carotenoid biosynthesis, were highly enriched in these functions. Shading inhibited the expression of flavonoid biosynthesis-associated genes and induced carotenoid biosynthesis-related genes. This would suggest that decreased flavonoid biosynthetic gene expression coincides with increased flavonoids (e.g., catechin) content upon moderate shading, while carotenoid levels and biosynthetic gene expression are positively correlated in 'Huangjinya.' In conclusion, the leaf color changes in 'Huangjinya' are largely determined by the combined effects of flavonoid and carotenoid biosynthesis.

Zinc stress affects ionome and metabolome in tea plants.

The research of physiological responses to Zn stress in plants has been extensively studied. However, the ionomics and metabolomics responses of plants to Zn stress remain largely unknown. In present study, the nutrient elements were identified involved in ion homeostasis and metabolomics changes related to Zn deficiency or excess in tea plants. Nutrient element analysis demonstrated that the concentrations of Zn affected the ion-uptake in roots and the nutrient element transportation to leaves, leading to the different distribution of P, S, Al, Ca, Fe and Cu in the tea leaves or roots. Metabolomics analysis revealed that Zn deficiency or excess differentially influenced the metabolic pathways in the tea leaves. More specifically, Zn deficiency affected the metabolism of carbohydrates, and Zn excess affected flavonoids metabolism. Additionally, the results showed that both Zn deficiency and Zn excess led to reduced nicotinamide levels, which speeded up NAD+ degradation and thus reduced energy metabolism. Furthermore, element-metabolite correlation analysis illustrated that Zn contents in the tea leaves were positively correlated with organic acids, nitrogenous metabolites and some carbohydrate metabolites, and negatively correlated with the metabolites involved in secondary metabolism and some other carbohydrate metabolites. Meanwhile, metabolite-metabolite correlation analysis demonstrated that organic acids, sugars, amino acids and flavonoids played dominant roles in the regulation of the tea leaf metabolism under Zn stress. Therefore, the conclusion should be drawn that the tea plants responded to Zn stress by coordinating ion-uptake and regulation of metabolism of carbohydrates, nitrogenous metabolites, and flavonoids.

Aluminum induced metabolic responses in two tea cultivars.

Tea [Camellia sinensis (L.)], is an aluminum (Al(3+)) hyperaccumulator plant and grows well in acid soils. In the present study, roots of two tea cultivars, JHC and YS were treated with different concentrations of Al(3+). After treatments, the root length, dry matter, root activity and chlorophyll content (SPAD value) of JHC had greater increase than that of YS. We also detected metabolic changes of two varieties using GC-MS method. Comparison between two cultivars indicated that shikimic pathway was more enhanced in YS roots by Al(3+) with higher levels of catechine, quinic acid and shikimic acid. While, more active amino acid synthesis was found in JHC roots and JHC leaves remained the higher level contents of metabolites related to cysteine synthesis. The comparison also showed that a large amount of sugar alcohols were accumulated in roots of two varieties, whereas most of them were reduced in YS leaves. Other well-known ligands, such as phosphoric acid and malic acid were observed in two cultivars that showed significantly altered abundances under Al(3+) treatments. The results indicated that Al(3+) adaptation of two cultivars may be correlated with their differential metabolism of amino acids, sugars and shikimic acids.