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.
Highlights
Tea is the most popular nonalcoholic beverage worldwide for its pleasant characteristics and healthful properties
In light of the importance of flavonoids to tea characteristics, we investigated the flavonoid accumulation in tea buds in response to shading, the temporal regulation of gene and transcription factor (TF) activities involved in flavonoid biosynthesis, and potential light signal transduction pathways including the UV RESISTANCE LOCUS8 (UVR8)-mediated signal transduction pathway, UV-A/blue light and red/far-red light signal transduction pathways, as important signal regulators of gene activities in tea plants
Altered Ultraviolet-B radiation (UV-B) light signal transductions in response to shading To explore the roles of different light signal transduction pathways in determining flavonoid biosynthesis in tea plants in response to shading, we investigated the activities of potential unigenes that thought to be involved in the UVR8-mediated low fluence UV-B responses, UV-A/blue light and red/ far-red light signal transduction pathways in our assembled tea transcriptome datasets (Fig. 5b)
Summary
Tea is the most popular nonalcoholic beverage worldwide for its pleasant characteristics and healthful properties. 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. In addition to the medicinal properties, these compounds contribute to the color, aroma and mouth-feel of tea infusion, eventually determine the sensation characteristics of tea products [6, 7]. The ratio of catechins to amino acids in tea buds and leaves is one of the critical parameters evaluating the tea quality [8]. To achieve a good balance between the accumulation of catechins and amino acids in consideration of both the tea sensation and health benefits is primarily important for tea industry, which is a practical objective for tea research
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