The Effects of Ultraviolet A/B Treatments on Anthocyanin Accumulation and Gene Expression in Dark-Purple Tea Cultivar ‘Ziyan’ (Camellia sinensis)

Abstract

‘Ziyan’ is a novel anthocyanin-rich tea cultivar with dark purple young shoots. However, how its anthocyanin accumulation is affected by environmental factors, such as ultraviolet (UV), remains unclear. In this study, we observed that UV light treatments stimulated anthocyanin accumulation in ‘Ziyan’ leaves, and we further analyzed the underlying mechanisms at gene expression and enzyme activity levels. In addition, the catechins and chlorophyll contents of young shoots under different light treatments were also changed. The results showed that the contents of total anthocyanins and three major anthocyanin molecules, i.e., delphinidin, cyanidin, and pelargonidin, were significantly higher in leaves under UV-A, UV-B, and UV-AB treatments than those under white light treatment alone. However, the total catechins and chlorophyll contents in these purple tea plant leaves displayed the opposite trends. The anthocyanin content was the highest under UV-A treatment, which was higher by about 66% than control. Compared with the white light treatment alone, the enzyme activities of chalcone synthase (CHS), flavonoid 3′,5′-hydroxylase (F3′5′H), and anthocyanidin synthase (ANS) under UV treatments increased significantly, whereas the leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) activities reduced. There was no significant difference in dihydroflavonol 4-reductase (DFR) activity under all treatments. Comparative transcriptome analyses unveiled that there were 565 differentially expressed genes (DEGs) of 29,648 genes in three pair-wise comparisons (white light versus UV-A, W vs. UV-A; white light versus UV-B, W vs. UV-A; white light versus UV-AB, W vs. UV-AB). The structural genes in anthocyanin pathway such as flavanone 3-hydroxylase (F3H), F3′5′H, DFR, and ANS, and regulatory gene TT8 were upregulated under UV-A treatment; F3′5′H, DFR, ANS, and UFGT and regulatory genes EGL1 and TT2 were upregulated under UV-AB treatment. However, most structural genes involved in phenylpropanoid and flavonoid pathways were downregulated under UV-B treatment compared with control. The expression of LAR and ANR were repressed in all UV treatments. Our results indicated that UV-A and UV-B radiations can induce anthocyanin accumulation in tea plant ‘Ziyan’ by upregulating the structural and regulatory genes involved in anthocyanin biosynthesis. In addition, UV radiation repressed the expression levels of LAR, ANR, and FLS, resulting in reduced ANR activity and a metabolic flux shift toward anthocyanin biosynthesis.

Transcriptional analysis reveals key insights into seasonal induced anthocyanin degradation and leaf color transition in purple tea (Camellia sinensis (L.) O. Kuntze)

“…Furthermore, negative correlation recorded between genes involved in ethylene signaling (ETR, EBF1/2, ERF), TAC and day-length, highlighted photoperiod-dependent regulation of anthocyanin accumulation in tea 29 . Our findings corroborate recent study on light-mediated anthocyanin accumulation via induced expression of key regulatory and structural genes involved in anthocyanin biosynthesis 51 .…”

Screening tea hybrid with abundant anthocyanins and investigating the effect of tea processing on foliar anthocyanins in tea

“…Tea cultivar 'Mooma 1' had 0.5918 μg • g -1 DW) of foliar anthocyanins (He et al, 2018). Li et al (2020) reported that a purple leaf tea cultivar 'Ziyan' had total content of anthocyanins up to 1,079.8 μg • g -1 (DW). Purple shoots of cultivar 'Zixin' contained 35 μmol • g -1 anthocyanins (equivalent 20,860 μg • g -1 pelargonidin 3,5-di-o-glucoside) (Shen et al, 2018).…”

“…The 'ZJ' plants in the present study are grown in Hangzhou of Zhejiang Province (latitude 30.27°N, mean altitude 20 m). Ultraviolet A and ultraviolet B upregulate the expression of structural genes such as F3'5 'H encoding flavonoid 3',5'-hydroxylase, DFR encoding dihydroflavonol 4-reductase and ANS encoding anthocyanidin synthase, as well as regulatory gene TT2 (TRANSPARENT TESTA 8) in the anthocyanin pathway, resulting in high accumulation of anthocyanins (Li et al, 2020). Ultraviolet radiation is usually stronger at high altitude areas than low altitude areas.…”

CsbZIP1-CsMYB12 mediates the production of bitter-tasting flavonols in tea plants (Camellia sinensis) through a coordinated activator–repressor network

“…Light intensity and light quality significantly affect the accumulation of characteristic secondary metabolites in tea plant leaves 8,9 . Both red and blue light promote the production of catechins and caffeine 9 , while UV-A and UV-B promote the production of anthocyanins 10 . Thus, shading of tea plants has been frequently applied in tea gardens to reduce the contents of these bitter-tasting and astringent flavonoids in tea plant leaves 8,11,12 .…”