Sugar signal mediates flavonoid biosynthesis in tea leaves

Selenium-Mediated (-)-Epigallocatechin-3-Gallate Dynamics via Flavanone-3-Hydroxylase Regulation of Flavonoid Biosynthesis in Fu Tea (Camellia sinensis (L.) O. Kuntze)

Tea (Camellia sinensis (L.) O. Kuntze) is a highly selenium enrichment capacity plant; high selenium concentration contributes to the occurrence of oxidative stress and protein misfolding in tea plants, whereas flavonoids can chelate heavy metals to protect plants from oxidative stress caused by metal exposure. Nevertheless, the role of catechins in flavonoid synthesis and nutrient metabolism under selenium stress remains unidentified. Combining Word2vec and HNSW utilizing UHPLC-Q-Orbitrap HRMS-MS/MS to implement rapid matching annotation of the structural information on metabolites in Fu tea, we found that selenium-mediated changes in catechins in Fu tea were mainly associated with flavonoid biosynthesis pathways. The results demonstrated that selenium treatment increased benign selenol analogues (glutathioselenol) in tea and identified the novel selenopeptide PRSeMW (m/z 636.22571, Pro-Arg-SeMet-Trp) in selenium-enriched Fu tea samples to enhance the health benefits of tea. The selenium levels were negatively correlated with N5-ethyl-l-glutamine (11.63 to 4.26 mg kg-1) and (-)-epigallocatechin (13.26 to 11.19 mg kg-1), increasing the accumulation of tea polyphenols ((-)-catechin gallate, (-)-epigallocatechin 3-gallate, and (+)-gallocatechin), and decreasing the level of caffeine. These discoveries provide new insights into the mechanism of tea polyphenol-mediated transformation of selenium in Fu tea and theoretical support for the quality assessment of selenium-enriched tea.

Accumulation mechanism of metabolite markers identified by machine learning between Qingyuan and Xiushui counties in Polygonatum cyrtonema Hua

Polygonatum cyrtonema Hua is a traditional Chinese medicinal plant acclaimed for its therapeutic potential in diabetes and various chronic diseases. Its rhizomes are the main functional parts rich in secondary metabolites, such as flavonoids and saponins. But their quality varies by region, posing challenges for industrial and medicinal application of P. cyrtonema. In this study, 482 metabolites were identified in P. cyrtonema rhizome from Qingyuan and Xiushui counties. Cluster analysis showed that samples between these two regions had distinct secondary metabolite profiles. Machine learning methods, specifically support vector machine-recursive feature elimination and random forest, were utilized to further identify metabolite markers including flavonoids, phenolic acids, and lignans. Comparative transcriptomics and weighted gene co-expression analysis were performed to uncover potential candidate genes including CHI, UGT1, and PcOMT10/11/12/13 associated with these compounds. Functional assays using tobacco transient expression system revealed that PcOMT10/11/12/13 indeed impacted metabolic fluxes of the phenylpropanoid pathway and phenylpropanoid-related metabolites such as chrysoeriol-6,8-di-C-glucoside, syringaresinol-4'-O-glucopyranosid, and 1-O-Sinapoyl-D-glucose. These findings identified metabolite markers between these two regions and provided valuable genetic insights for engineering the biosynthesis of these compounds.

Genome-wide identification and expression analysis of NIN-like protein (NLP) genes: Exploring their potential roles in nitrate response in tea plant (Camellia sinensis)

NIN-like proteins (NLPs) are evolutionarily conserved transcription factors that are unique to plants and play a pivotal role in responses to nitrate uptake and assimilation. However, a comprehensive analysis of NLP members in tea plants is lacking. The present study performed a genome-wide analysis and identified 33 NLP gene family members of Camellia sinensis that were distributed unequally across 5 chromosomes. Subcellular localisation predictions revealed that all CsNLP proteins were localised in the nucleus. Conservative domain analysis revealed that all of these proteins contained conserved RWP-RK and PB1 domains. Phylogenetic analysis grouped the CsNLP gene family into four clusters. The promoter regions of CsNLPs harboured cis-acting elements associated with plant hormones and abiotic stress responses. Expression profile analysis demonstrated that CsNLP8 was significantly upregulated in roots under nitrate stress conditions. Subcellular localisation analysis found CsNLP8 localised to the nucleus. Dual-luciferase reporter assay demonstrated that CsNLP8 positively regulated the expression of a nitrate transporter gene (CsNRT2.2). These findings provide a comprehensive characterisation of NLP genes in Camellia sinensis and offer insights into the biological function of CsNLP8 in regulating the response to nitrate-induced stress.

Integrated metabolomic and transcriptomic analyses reveal the molecular mechanism of amino acid transport between source and sink during tea shoot development

KEY MESSAGE

The weighted gene co-expression network analysis and antisense oligonucleotide-mediated transient gene silencing revealed that CsAAP6 plays an important role in amino acid transport during tea shoot development. Nitrogen transport from source to sink is crucial for tea shoot growth and quality formation. Amino acid represents the major transport form of reduced nitrogen in the phloem between source and sink, but the molecular mechanism of amino acid transport from source leaves to new shoots is not yet clear. Therefore, the composition of metabolites in phloem exudates collected by the EDTA-facilitated method was analyzed through widely targeted metabolomics. A total of 326 metabolites were identified in the phloem exudates with the richest variety of amino acids and their derivatives (93), accounting for approximately 39.13% of the total metabolites. Moreover, through targeted metabolomics, it was found that the content of glutamine, glutamic acid, and theanine was the most abundant, and gradually increased with the development of new shoots. Meanwhile, transcriptome analysis suggested that the expression of amino acid transport genes changed significantly. The WGCNA analysis identified that the expression levels of CsAVT1, CsLHTL8, and CsAAP6 genes located in the MEterquoise module were positively correlated with the content of amino acids such as glutamine, glutamic acid, and theanine in phloem exudates. Reducing the CsAAP6 in mature leaves resulted in a significant decrease in the content of glutamic acid, aspartic acid, alanine, leucine, asparagine, glutamine, and arginine in the phloem exudates, indicating that CsAAP6 played an important role in the source to sink transport of amino acids in the phloem. The research results will provide the theoretical basis and genetic resources for the improvement of nitrogen use efficiency and tea quality.

Comprehensive analysis of pigment alterations and associated flavor development in strip and needle green teas

Strip/needle green teas (SGT/NGT) processed using innovative technologies are in high demand; however, mechanisms behind their color and flavor have not been comprehensively studied. We aimed to reveal the dynamics of major pigmented components (carotenoids, lipids, flavonoids, and Maillard products) and their contributions to the flavor of green teas. The total content of flavonoids in SGT and NGT were 255 ± 4.51 and 201 ± 3.91 mg·g-1, respectively; these values are slightly lower than that in fresh leaves (FLs), resulting in a fresh and sweet aftertaste. In average, carotene content in SGT/NGT (24.8 μg·g-1) was higher than in FL (17.4 μg·g-1), whilst xanthophyll content (603 μg·g-1) decreased to one-half of that in FL (310 μg·g-1). Among the 218 primary metabolites, glutamine, glutamic acid, and arginine were found to accumulate and were dominate contributors for the umami and sweet taste. Notably, more than 96 volatiles were screened and revealed their correlations with carotenoids, lipids, and amino acids. Overall, the synergism between pigments and their non-enzymatic derivates' contribution to GT characterized flavor was illustrated.

Role of miRNAs in sucrose stress response, reactive oxygen species, and anthocyanin biosynthesis in Arabidopsis thaliana

In plants, sucrose is the main transported disaccharide that is the primary product of photosynthesis and controls a multitude of aspects of the plant life cycle including structure, growth, development, and stress response. Sucrose is a signaling molecule facilitating various stress adaptations by crosstalk with other hormones, but the molecular mechanisms are not well understood. Accumulation of high sucrose concentrations is a hallmark of many abiotic and biotic stresses, resulting in the accumulation of reactive oxygen species and secondary metabolite anthocyanins that have antioxidant properties. Previous studies have shown that several MYeloBlastosis family/MYB transcription factors are positive and negative regulators of sucrose-induced anthocyanin accumulation and subject to microRNA (miRNA)-mediated post-transcriptional silencing, consistent with the notion that miRNAs may be "nodes" in crosstalk signaling by virtue of their sequence-guided targeting of different homologous family members. In this study, we endeavored to uncover by deep sequencing small RNA and mRNA transcriptomes the effects of exogenous high sucrose stress on miRNA abundances and their validated target transcripts in Arabidopsis. We focused on genotype-by-treatment effects of high sucrose stress in Production of Anthocyanin Pigment 1-Dominant/pap1-D, an activation-tagged dominant allele of MYB75 transcription factor, a positive effector of secondary metabolite anthocyanin pathway. In the process, we discovered links to reactive oxygen species signaling through miR158/161/173-targeted Pentatrico Peptide Repeat genes and two novel non-canonical targets of high sucrose-induced miR408 and miR398b*(star), relevant to carbon metabolic fluxes: Flavonoid 3'-Hydroxlase (F3'H), an important enzyme in determining the B-ring hydroxylation pattern of flavonoids, and ORANGE a post-translational regulator of Phytoene Synthase expression, respectively. Taken together, our results contribute to understanding the molecular mechanisms of carbon flux shifts from primary to secondary metabolites in response to high sugar stress.

Effect of sucrose as an elicitor in increasing quercetin-3-O-rhamnoside (quercitrin) content of chrysanthemum (Chrysanthemum morifolium Ramat) callus culture based on harvest time differences

Chrysanthemum (Chrysanthemum morifolium) contains secondary metabolites, such as flavonoid compounds, especially luteolin-7-glucoside and quercetin-3-O-rhamnoside (quercitrin), in its tissues. Utilizing sucrose as an elicitor through callus culture presents an alternative method to enhance the production of secondary metabolites. This research aimed to determine the best sucrose concentration and harvest time for maximizing quercitrin content in chrysanthemum callus culture. The research employed a completely randomized design with four treatment groups: 0, 30, 45, and 60 g/l of sucrose added to MS medium containing 4 ppm 2,4-dichlorophenoxyacetic acid (2,4-D). Callus samples were harvested on the 15th and 30th days of culture. The observed parameters included callus morphology (color and texture), fresh weight, dry weight, the diameter of the callus, and quercitrin content analyzed using high-performance liquid chromatography. The results showed that all callus cultures exhibited intermediate textures and varied colors, predominantly shades of brown. The treatment involving 45 g/l of sucrose with a 30th-day harvest yielded the highest fresh weight, dry weight, and quercitrin content, namely 2.108 g, 0.051 g, and 0.437 mg/g DW, respectively. Notably, the quercitrin content exhibited a 63.67% increase compared to the control.

Integrative analyses of morphology, physiology, and transcriptional expression profiling reveal miRNAs involved in culm color in bamboo

Culm color variation is an interesting phenomenon that contributes to the breeding of new varieties of ornamental plants during domestication. De-domesticated variation is considered ideal for identifying and interpreting the molecular mechanisms of plant mutations. However, the variation in culm color of bamboo remains unknown. In the present study, yellow and green culms generated from the same rhizome of Phyllostachys vivax cv. Aureocaulis (P. vivax) were used to elucidate the molecular mechanism of culm color formation. Phenotypic and physiological data showed that environmental suitability was higher in green culms than in yellow culms. High-throughput sequencing analysis showed 295 differentially expressed genes (DEGs) and 22 differentially expressed miRNAs (DEMs) in two different colored bamboo culms. There were 103 DEM-DEG interaction pairs, of which a representative "miRNA-mRNA" regulatory module involved in photosynthesis and pigment metabolism was formed by 14 DEM-DEG pairs. The interaction of the three key pairs was validated by qPCR and dual-luciferase assays. This study provides new insights into the molecular mechanism of miRNAs involved in P. vivax culm color formation, which provides evidence for plant de-domestication and is helpful for revealing the evolutionary mechanism of bamboo.