Metabolite profiling and transcriptomic analyses reveal an essential role of UVR8-mediated signal transduction pathway in regulating flavonoid biosynthesis in tea plants (Camellia sinensis) in response to shading

Abstract

BackgroundTea is the most popular nonalcoholic beverage worldwide for its pleasant characteristics and healthful properties. Catechins, theanine and caffeine are the major natural products in tea buds and leaves that determine tea qualities such as infusion colors, tastes and fragrances, as well as their health benefits. Shading is a traditional and effective practice to modify natural product accumulation and to enhance the tea quality in tea plantation. However, the mechanism underlying the shading effects is not fully understood. This study aims to explore the regulation of flavonoid biosynthesis in Camellia sinensis under shading by using both metabolomic and transcriptional analyses.ResultsWhile shading enhanced chlorophyll accumulation, major catechins, including C, EC, GC and EGC, decreased significantly in tea buds throughout the whole shading period. The reduction of catechins and flavonols were consistent with the simultaneous down-regulation of biosynthetic genes and TFs associated with flavonoid biosynthesis. Of 16 genes involved in the flavonoid biosynthetic pathway, F3’H and FLS significantly decreased throughout shading while the others (PAL, CHSs, DFR, ANS, ANR and LAR, etc.) temporally decreased in early or late shading stages. Gene co-expression cluster analysis suggested that a number of photoreceptors and potential genes involved in UV-B signal transductions (UVR8_L, HY5, COP1 and RUP1/2) showed decreasing expression patterns consistent with structural genes (F3’H, FLS, ANS, ANR, LAR, DFR and CHSs) and potential TFs (MYB4, MYB12, MYB14 and MYB111) involved in flavonoid biosynthesis, when compared with genes in the UV-A/blue and red/far-red light signal transductions. The KEGG enrichment and matrix correlation analyses also attributed the regulation of catechin biosynthesis to the UVR8-mediated signal transduction pathway. Further UV-B treatment in the controlled environment confirmed UV-B induction on flavonols and EGCG accumulation in tea leaves.ConclusionsWe proposed that catechin biosynthesis in C. sinensis leaves is predominantly regulated by UV through the UVR8-mediated signal transduction pathway to MYB12/MYB4 downstream effectors, to modulate flavonoid accumulation. Our study provides new insights into our understanding of regulatory mechanisms for shading-enhanced tea quality.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1440-0) contains supplementary material, which is available to authorized users.

UV-B Induces Distinct Transcriptional Re-programing in UVR8-Signal Transduction, Flavonoid, and Terpenoids Pathways in Camellia sinensis

“…For example, only EGCG was induced, while the abundance of other catechins remains unchanged. In addition, the genes (UVR-8, COP1, HY5) in the UV-B signaling transduction module are not consistently UV-B up-regulated (Liu L. et al, 2018) as found in many other plant species (Rizzini et al, 2011;Jenkins, 2017).…”

“…Interestingly, the UV-B induced changes in the tested catechins in both cultivars are related to their original catechin abundances: the higher original catechin abundances in tea leaves, the less increase of UV-B induced catechin production after the first 30 min treatment and the more significant decrease of the UV-B induced catechin production after 360 min treatment. Besides, a recently published study indicated that long periods (1 to 16 days, 8 h per day) of a mild UV-B treatment (20 µW/cm 2 ) applied to tea plants did not affect the abundance of the majority of flavonoid compounds, except for that of EGCG, kaempferol-7-O-glucoside, and GC (Liu L. et al, 2018). However, the detected GC enhancement only after 16 days of UV-B treatment relative to the control plants grown in hydroponic culture might result from a substantial decrease in all tested metabolites in control, not from UV-B treatment.…”

“…Interestingly, phenolic metabolites including diverse flavonoids, which are deposited in plant epidermal tissues (Greenberg et al, 1996;Rozema et al, 1997), absorbing light in the wavelength ranges 250-270 nm and 330-350 nm (Kumar et al, 2018) with an absorption peak around 300 nm (Gábor, 2013), function as a UV-absorbing sunscreen and, in turn, offer protection to plants from UV-B damage (Li et al, 1993;Brown et al, 2005;Liu et al, 2015). A recent study applying UV-B treatment to tea plants revealed their distinct responses compared to some other plants (Liu L. et al, 2018). For example, only EGCG was induced, while the abundance of other catechins remains unchanged.…”

Stress Responses of Shade-Treated Tea Leaves to High Light Exposure after Removal of Shading

“…In this traditional cultivation method, tea trees are covered with shading nets when new shoots emerge, and they are grown under the shade before being harvested after between 14 and 30 days. During this period, the contents of chlorophylls (Chls) and free amino acids including theanine are increased, and that of catechins is decreased, in the tea shoot [6][7][8][9][10][11]. Tea trees usually produce new shoots thrice in a year from spring to fall in Japanese tea plantations.…”

Identification and distribution of a single nucleotide polymorphism responsible for the catechin content in tea plants

“…In conventional tea plants, flavonoid metabolism is enhanced under strong light, but the opposite results are observed in light-sensitive tea plants 19 . Catechins are usually decreased in green-leaf tea plants with shading treatment due to an alternation in the transcription level of the genes responsible for catechin biosynthesis 43 . In the present study, tea plants were grown in the same surroundings.…”