Integrated metabolomics and transcriptomics analysis highlight key pathways involved in the somatic embryogenesis of Darjeeling tea.

BACKGROUND: Darjeeling tea is a globally renowned beverage, which faces numerous obstacles in sexual reproduction, such as self-incompatibility, poor seed germination, and viability, as well as issues with vegetative propagation. Somatic embryogenesis (SE) is a valuable method for rapid clonal propagation of Darjeeling tea. However, the metabolic regulatory mechanisms underlying SE in Darjeeling tea remain largely unknown. To address this, we conducted an integrated metabolomics and transcriptomics analysis of embryogenic callus (EC), globular embryo (GE), and heart-shaped embryo (HE). RESULTS: The integrated analyses showed that various genes and metabolites involved in the phenylpropanoid pathway, auxin biosynthesis pathway, gibberellin, brassinosteroid and amino acids biosynthesis pathways were differentially enriched in EC, GE, and HE. Our results revealed that despite highly up-regulated auxin biosynthesis genes YUC1, TAR1 and AAO1 in EC, endogenous indole-3-acetic acid (IAA) was significantly lower in EC than GE and HE. However, bioactive Gibberellin A4 displayed higher accumulation in EC. We also found higher BABY BOOM (BBM) and Leafy cotyledon1 (LEC1) gene expression in GE along with high accumulation of castasterone, a brassinosteroid. Total flavonoids and phenolics levels were elevated in GE and HE compared to EC, especially the phenolic compound chlorogenic acid was highly accumulated in GE. CONCLUSIONS: Integrated metabolome and transcriptome analysis revealed enriched metabolic pathways, including auxin biosynthesis and signal transduction, brassinosteroid, gibberellin, phenylpropanoid biosynthesis, amino acids metabolism, and transcription factors (TFs) during SE in Darjeeling tea. Notably, EC displayed lower endogenous IAA levels, conducive to maintaining differentiation, while higher IAA concentration in GE and HE was crucial for preserving embryo identity. Additionally, a negative correlation between bioactive gibberellin A4 (GA4) and IAA was observed, impacting callus growth in EC. The high accumulation of chlorogenic acid, a phenolic compound, might contribute to the low success rate in GE and HE formation in Darjeeling tea. TFs such as BBM1, LEC1, FUS3, LEA, WOX3, and WOX11 appeared to regulate gene expression, influencing SE in Darjeeling tea.

Genome-wide SNP discovery from Darjeeling tea cultivars - their functional impacts and application toward population structure and trait associations.

Genotyping by sequencing and identification of functionally relevant nucleotide variations in crop accessions are the key steps to unravel genetic control of desirable traits. Elite cultivars of Darjeeling tea were undergone SNP genotyping by double-digest restriction-site associated DNA sequencing method. This study reports a set of 54,206 high-quality SNP markers discovered from ~10.4 GB sequence data, encompassing 15 chromosomes of the reference tea genome. Genetic relatedness among the accessions conforms to the analyses of Bayesian clustering, UPGMA, and PCoA methods. Genomic positions of the discovered SNPs and their putative effect on annotated genes designated a thoughtful understanding of their functional aspects in tea system biology. A group of 95 genes was identified to be affected by high impact variants. Genome-wide association analyses of 21 agronomic and biochemical phenotypes resulted in trait-linked polymorphic loci with strong confidence (p < 0.05 and 0.001).

Phytochemical analysis of mite-infested tea leaves of Darjeeling Hills, India.

INTRODUCTION: Darjeeling tea of India is one of the most famous beverages globally. However, a large amount of tea crop is damaged every year by the attack of mites. OBJECTIVES: The study aimed to determine the changes in different pigments and biochemical components of tea leaves due to mite infestation. MATERIALS AND METHODS: We used UV-visible and Fourier-transform infrared (FTIR) spectroscopy simultaneously to understand the damages in pigment contents of the leaves of tea (Camellia sinensis (L.) Kuntze) due to attack of phytophagus mite, Oligonychus coffeae Nietner. Furthermore, chemical analysis of infested tea leaves was also performed to compare the nutrients of the plants, namely total phenol, protein and soluble sugar. RESULTS: The UV-visible study reveals severe reduction of the pigments such as chlorophyll (Chl), carotenoids and xanthophylls in the tea leaf due to mite infestation. The findings of the FTIR study, also shows variation in different physiochemical components in the leaf Chl. The sugar and protein content of the infested leaves have been reduced compared to uninfested ones. Results in the case of tea leaves plucked during first (March) and third (November) flushes show similar trends. CONCLUSION: The increase in phenolic and alcoholic components and decrease in Chl contents may affect the quality of Darjeeling tea. The extent of damages done by the pests measured here could aid the pest management in tea gardens.

Antioxidants and ROS scavenging ability in ten Darjeeling tea clones may serve as markers for selection of potentially adapted clones against abiotic stress.

Ten Darjeeling tea clones (BT15/263, RR17/144, B777, T253, B157, Sundaram, HV39, AV2, K1/1 and TTV1) were collected from the experimental garden of Darjeeling Tea Research and Development Centre, Kurseong. Total phenol, flavonoids and two antioxidating enzymes (peroxidase and superoxide dismutase) were estimated. The total phenol ranged between 241 and 28 GAE mg g(-1) of leaf dry weight. The highest amount obtained in four clones, B15/263 (241.47), RR17/144 (221.2), B777 (154.54) and B157 (140.23 mg g(-1)). Flavonoids were estimated as Catechin equivalent (CE) and ranged between 56.88 and 20.81 CE mg g(-1) leaf dry weight. Higher amounts occurred in BT15/263 (56.88 mg g(-1)), B777 (56.69) and RR17/144 (48.63). Antioxidant activities were measured following DPPH and ABTS free radicle scavenging procedures and the results were well according to total polyphenol content among the clones (in total phenols, ranges of correlation in DPPH assay were r (2) = 0.990-0.989, p ≤ 0.05; in flavonoids r (2) = 0.954, p ≤ 0.01-0.987, p ≤ 0.05). Similarly, ABTS percent scavenging results were quiet significant. The IC50 values were determined for both DPPH and ABTS assay. PAGE expressions of isoforms in two antioxidative enzymes and quantification of them also varied much among the investigated clones. The incidence of total phenols, flavonoids, PRX and SOD and ROS scavenging assay in in-situ condition, might be used as biochemical markers towards the superior adaptability against abiotic stress. In the present work, four clones (B15/263, B777, RR17/144 and B157) would be designated as comparatively better suited to the predicted abiotic stress.