Inhibition of caffeine biosynthesis in tea (Camellia sinensis) and coffee (Coffea arabica) plants by ribavirin

Multi-omics analysis of the mechanisms of abundant theacrine and EGCG3"Me in tea (Camellia sinensis)

Theacrine and epigallocatechin-3-O-(3-O-methyl) gallate (EGCG3"Me) are notable secondary metabolites in tea (Camellia sinensis), celebrated for their unique flavors and significant health effects. Theacrine has a mild effect on nerve stimulation, while EGCG3"Me exhibits better stability, higher oral bioavailability and stronger biological activity. However, tea plant varieties naturally rich in both theacrine and EGCG3"Me are rare. This study unveils a unique tea variety 'Anxi kucha', which is abundant in both theacrine and EGCG3"Me. Through integrated transcriptome-proteome-metabolome analysis, SAMS3, APRT1, IMPDH, and TCS1 were identified as critical enzymes for theacrine synthesis; while CHI1, CHI2, FLS2 and LAR1 were key for EGCG3"Me synthesis. Additionally, transcription factor analysis revealed that MYB4 and bHLH74 were positively correlated with the contents of theacrine and EGCG3"Me. This study provides valuable materials for further exploring theacrine and EGCG3"Me in tea plants, and establishes a theoretical basis for their biosynthesis.

Caffeine and Purine Derivatives: A Comprehensive Review on the Chemistry, Biosynthetic Pathways, Synthesis-Related Reactions, Biomedical Prospectives and Clinical Applications

Caffeine and purine derivatives represent interesting chemical moieties, which show various biological activities. Caffeine is an alkaloid that belongs to the family of methylxanthine alkaloids and it is present in food, beverages, and drugs. Coffee, tea, and some other beverages are a major source of caffeine in the human diet. Caffeine can be extracted from tea or coffee using hot water with dichloromethane or chloroform and the leftover is known as decaffeinated coffee or tea. Caffeine and its derivatives were synthesized via different procedures on small and large scales. It competitively antagonizes the adenosine receptors (ARs), which are G protein-coupled receptors largely distributed in the human body, including the heart, vessels, brain, and kidneys. Recently, many reports showed the effect of caffeine derivatives in the treatment of many diseases such as Alzheimer's, asthma, parkinsonism, and cancer. Also, it is used as an antioxidant, anti-inflammatory, analgesic, and hypocholesterolemic agent. The present review article discusses the synthesis, reactivity, and biological and pharmacological properties of caffeine and its derivatives. The biosynthesis and biotransformation of caffeine in coffee and tea leaves and the human body were summarized in the review.

An inosine triphosphate pyrophosphatase safeguards plant nucleic acids from aberrant purine nucleotides

In plants, inosine is enzymatically introduced in some tRNAs, but not in other RNAs or DNA. Nonetheless, our data show that RNA and DNA from Arabidopsis thaliana contain (deoxy)inosine, probably derived from nonenzymatic adenosine deamination in nucleic acids and usage of (deoxy)inosine triphosphate (dITP and ITP) during nucleic acid synthesis. We combined biochemical approaches, LC-MS, as well as RNA-Seq to characterize a plant INOSINE TRIPHOSPHATE PYROPHOSPHATASE (ITPA) from A. thaliana, which is conserved in many organisms, and investigated the sources of deaminated purine nucleotides in plants. Inosine triphosphate pyrophosphatase dephosphorylates deaminated nucleoside di- and triphosphates to the respective monophosphates. ITPA loss-of-function causes inosine di- and triphosphate accumulation in vivo and an elevated inosine and deoxyinosine content in RNA and DNA, respectively, as well as salicylic acid (SA) accumulation, early senescence, and upregulation of transcripts associated with immunity and senescence. Cadmium-induced oxidative stress and biochemical inhibition of the INOSINE MONOPHOSPHATE DEHYDROGENASE leads to more IDP and ITP in the wild-type (WT), and this effect is enhanced in itpa mutants, suggesting that ITP originates from ATP deamination and IMP phosphorylation. Inosine triphosphate pyrophosphatase is part of a molecular protection system in plants, preventing the accumulation of (d)ITP and its usage for nucleic acid synthesis.

De novo transcriptome and phytochemical analyses reveal differentially expressed genes and characteristic secondary metabolites in the original oolong tea (Camellia sinensis) cultivar 'Tieguanyin' compared with cultivar 'Benshan'

Background

The two original plants of the oolong tea cultivar (‘Tieguanyin’) are “Wei shuo” ‘Tieguanyin’—TGY (Wei) and “Wang shuo” ‘Tieguanyin’—TGY (Wang). Another cultivar, ‘Benshan’ (BS), is similar to TGY in its aroma, taste, and genetic make-up, but it lacks the “Yin Rhyme” flavor. We aimed to identify differences in biochemical characteristics and gene expression among these tea plants.

Results

The results of spectrophotometric, high performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS) analyses revealed that TGY (Wei) and TGY (Wang) had deeper purple-colored leaves and higher contents of anthocyanin, catechins, caffeine, and limonene compared with BS. Analyses of transcriptome data revealed 12,420 differentially expressed genes (DEGs) among the cultivars. According to a Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the flavonoid, caffeine, and limonene metabolic pathways were highly enriched. The transcript levels of the genes involved in these three metabolic pathways were not significantly different between TGY (Wei) and TGY (Wang), except for two unigenes encoding IMPDH and SAMS, which are involved in caffeine metabolism. The comparison of TGY vs. BS revealed eight up-regulated genes (PAL, C4H, CHS, F3’H, F3H, DFR, ANS, and ANR) and two down-regulated genes (FLS and CCR) in flavonoid metabolism, four up-regulated genes (AMPD, IMPDH, SAMS, and 5′-Nase) and one down-regulated XDH gene in caffeine metabolism; and two down-regulated genes (ALDH and HIBADH) in limonene degradation. In addition, the expression levels of the transcription factor (TF) PAP1 were significantly higher in TGY than in BS. Therefore, high accumulation of flavonoids, caffeine, and limonene metabolites and the expression patterns of their related genes in TGY might be beneficial for the formation of the “Yin Rhyme” flavor.

Conclusions

Transcriptomic, HPLC, and GC-MS analyses of TGY (Wei), TGY (Wang), and BS indicated that the expression levels of genes related to secondary metabolism and high contents of catechins, anthocyanin, caffeine, and limonene may contribute to the formation of the “Yin Rhyme” flavor in TGY. These findings provide new insights into the relationship between the accumulation of secondary metabolites and sensory quality, and the molecular mechanisms underlying the formation of the unique flavor “Yin Rhyme” in TGY.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5643-z) contains supplementary material, which is available to authorized users.

De novo transcriptome assembly of the wild relative of tea tree (Camellia taliensis) and comparative analysis with tea transcriptome identified putative genes associated with tea quality and stress response

Background

Camellia taliensis is one of the most important wild relatives of cultivated tea tree, C. sinensis. The species extensively occupies mountainous habitats representing a wide-range abiotic tolerance and biotic resistance and thus harbors valuable gene resources that may greatly benefit genetic improvement of cultivated tea tree. However, owning to a large genome size of ~3 Gb and structurally complex genome, there are fairly limited genetic information and particularly few genomic resources publicly available for this species. To better understand the key pathways determining tea flavor and enhance tea tree breeding programs, we performed a high-throughput transcriptome sequencing for C. taliensis.

Results

In this study, approximate 241.5 million high-quality paired-end reads, accounting for ~24 Gb of sequence data, were generated from tender shoots, young leaves, flower buds and flowers using Illumina HiSeq 2000 platform. De novo assembly with further processing and filtering yielded a set of 67,923 transcripts with an average length of 685 bp and an N50 of 995 bp. Based on sequence similarity searches against public databases, a total of 39,475 transcripts were annotated with gene descriptions, conserved protein domains or gene ontology (GO) terms. Candidate genes for major metabolic pathways involved in tea quality were identified and experimentally validated using RT-qPCR. Further gene expression profiles showed that they are differentially regulated at different developmental stages. To gain insights into the evolution of these genes, we aligned them to the previously cloned orthologous genes in C. sinensis, and found that considerable nucleotide variation within several genes involved in important secondary metabolic biosynthesis pathways, of which flavone synthase II gene (FNSII) is the most variable between these two species. Moreover, comparative analyses revealed that C. taliensis shows a remarkable expansion of LEA genes, compared to C. sinensis, which might contribute to the observed stronger stress resistance of C. taliensis.

Conclusion

We reported the first large-coverage transcriptome datasets for C. taliensis using the next-generation sequencing technology. Such comprehensive EST datasets provide an unprecedented opportunity for identifying genes involved in several major metabolic pathways and will accelerate functional genomic studies and genetic improvement efforts of tea trees in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1494-4) contains supplementary material, which is available to authorized users.

Effect of physicochemical parameters on enzymatic biodecaffeination during tea fermentation

We report for the first time the development of a biodecaffeination process for tea synchronised with tea fermentation process using enzymes isolated from Pseudomonas alcaligenes. Cell-free extract was used for biodecaffeination of tea during fermentation of tea and 80% of the caffeine in the tea dhool was degraded within 90 min of incubation. Several factors that tend to effect the biodecaffeination during this stage, like moisture, aeration, intermittent enzyme addition and mixing, were optimized, and inhibitory interactions of proteins with polyphenols, caffeine-polyphenol interactions, which directly influence the biodecaffeination process were prevented by the use of glycine (5% w/w) in the dhool. Tea decaffeinated through the enzymatic route retained the original flavor and aroma, and there was an increase in the total polyphenol content of the tea.

Distribution, biosynthesis and catabolism of methylxanthines in plants

Methylxanthines and methyluric acids are purine alkaloids that are synthesized in quantity in a limited number of plant species, including tea, coffee and cacao. This review summarizes the pathways, enzymes and related genes of caffeine biosynthesis. The main biosynthetic pathway is a sequence consisting of xanthosine → 7-methylxanthosine → 7-methylxanthine → theobromine → caffeine. Catabolism of caffeine starts with its conversion to theophylline. Typically, this reaction is very slow in caffeine-accumulating plants. Finally, the ecological roles of caffeine and the production of decaffeinated coffee plants are discussed.

Biosynthesis and Catabolism of Purine Alkaloids in Camellia Plants

A few Camellia plants accumulate caffeine, theobromine and theacrine. The present article reviews the distribution of purine alkaloids and biosynthetic pathways, including properties and genes of the caffeine synthase family of enzymes, and catabolism. Plant physiological studies and ecology-related studies are also summarized briefly.

Caffeine and related purine alkaloids: biosynthesis, catabolism, function and genetic engineering

Details of the recently elucidated biosynthetic pathways of caffeine and related purine alkaloids are reviewed. The main caffeine biosynthetic pathway is a sequence consisting of xanthosine-->7-methylxanthosine-->7-methylxanthine-->theobromine-->caffeine. Genes encoding N-methyltransferases involved in three of these four reactions have been isolated and the molecular structure of N-methyltransferases investigated. Pathways for the catabolism of caffeine have also been studied, although there are currently no reports of enzymatic and genetic studies having been successfully carried out. Metabolism of purine alkaloids in species including Camellia, Coffea, Theobroma and Ilex plants is summarised, and evidence for the involvement of caffeine in chemical defense and allelopathy is discussed. Finally, information is presented on metabolic engineering that has produced coffee seedlings with reduced caffeine content, and transgenic caffeine-producing tobacco plants with enhanced disease resistance.

Metabolism of alkaloids in coffee plants

Coffee beans contain two types of alkaloids, caffeine and trigonelline, as major components. This review describes the distribution and metabolism of these compounds. Caffeine is synthesised from xanthosine derived from purine nucleotides. The major biosynthetic route is xanthosine -> 7-methylxanthosine -> 7-methylxanthine -> theobromine -> caffeine. Degradation activity of caffeine in coffee plants is very low, but catabolism of theophylline is always present. Theophylline is converted to xanthine, and then enters the conventional purine degradation pathway. A recent development in caffeine research is the successful cloning of genes of N-methyltransferases and characterization of recombinant proteins of these genes. Possible biotechnological applications are discussed briefly. Trigonelline (N-methylnicotinic acid) is synthesised from nicotinic acid derived from nicotinamide adenine nucleotides. Nicotinate N-methyltransferase (trigonelline synthase) activity was detected in coffee plants, but purification of this enzyme or cloning of the genes of this N-methyltransferase has not yet been reported. The degradation activity of trigonelline in coffee plants is extremely low.