Abstract
BackgroundMajor secondary metabolites, including flavonoids, caffeine, and theanine, are important components of tea products and are closely related to the taste, flavor, and health benefits of tea. Secondary metabolite biosynthesis in Camellia sinensis is differentially regulated in different tissues during growth and development. Until now, little was known about the expression patterns of genes involved in secondary metabolic pathways or their regulatory mechanisms. This study aimed to generate expression profiles for C. sinensis tissues and to build a gene regulation model of the secondary metabolic pathways.ResultsRNA sequencing was performed on 13 different tissue samples from various organs and developmental stages of tea plants, including buds and leaves of different ages, stems, flowers, seeds, and roots. A total of 43.7 Gbp of raw sequencing data were generated, from which 347,827 unigenes were assembled and annotated. There were 46,693, 8446, 3814, 10,206, and 4948 unigenes specifically expressed in the buds and leaves, stems, flowers, seeds, and roots, respectively. In total, 1719 unigenes were identified as being involved in the secondary metabolic pathways in C. sinensis, and the expression patterns of the genes involved in flavonoid, caffeine, and theanine biosynthesis were characterized, revealing the dynamic nature of their regulation during plant growth and development. The possible transcription factor regulation network for the biosynthesis of flavonoid, caffeine, and theanine was built, encompassing 339 transcription factors from 35 families, namely bHLH, MYB, and NAC, among others. Remarkably, not only did the data reveal the possible critical check points in the flavonoid, caffeine, and theanine biosynthesis pathways, but also implicated the key transcription factors and related mechanisms in the regulation of secondary metabolite biosynthesis.ConclusionsOur study generated gene expression profiles for different tissues at different developmental stages in tea plants. The gene network responsible for the regulation of the secondary metabolic pathways was analyzed. Our work elucidated the possible cross talk in gene regulation between the secondary metabolite biosynthetic pathways in C. sinensis. The results increase our understanding of how secondary metabolic pathways are regulated during plant development and growth cycles, and help pave the way for genetic selection and engineering for germplasm improvement.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1773-0) contains supplementary material, which is available to authorized users.
Highlights
Major secondary metabolites, including flavonoids, caffeine, and theanine, are important components of tea products and are closely related to the taste, flavor, and health benefits of tea
The flavor of tea products varies with the age of the leaves and buds, as the chemical compositions change with age
The flowers are pollinated in the autumn, and the mature seeds are harvested in the autumn of the following year
Summary
Major secondary metabolites, including flavonoids, caffeine, and theanine, are important components of tea products and are closely related to the taste, flavor, and health benefits of tea. Kuntze) contributes to the rich flavors, clean taste, and nutrient content of tea [1, 2], one of the most popular beverages worldwide These secondary metabolites are known to be beneficial to human health. Flavonoids are phenylalanine-derived, physiologically active secondary metabolites, and include flavones, flavonols, isoflavones, flavanones, flavanols, and anthocyanidins [6] These compounds have a wide range of functions, such as antioxidant activity, ultraviolet light protection, and defense against phytopathogens. Theanine is a unique free amino acid and accounts for approximately 50 % of the total free amino acids in tea This compound gives tea a unique taste known as “umami” [9]. It acts as a neurotransmitter in the brain and has a relaxation-inducing effect in humans [10]
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