New Insights into Stress-Induced β-Ocimene Biosynthesis in Tea (Camellia sinensis) Leaves during Oolong Tea Processing

Abstract

As the major contributors to the floral odors of tea products, terpenoid volatiles play critical roles in the defense response of plants to multiple stresses. Until now, only a few TPS genes in tea plants (Camellia sinensis) have been functionally validated. In this study, by comparative studies conducted at gene, protein, and metabolite levels during oolong tea processing, we isolated an ocimene synthase gene, CsOCS, which displays a low similarity to previously characterized tea ocimene synthases. Further prokaryotic expression and subcellular localization analysis showed that it is plastid-located and could produce (E)-β-ocimene and (Z)-β-ocimene using GPP as the substrate. The optimum temperature and pH of the enzyme were 30 °C and 7.5, respectively. Treatment with exogenous methyl jasmonate elevated the transcript level of CsOCS and enhanced the emission of ocimene from tea leaves. Collectively, CsOCS is implicated as a key enzyme for β-ocimene synthesis during oolong tea processing.

Quantitative Measurement Reveals Dynamic Volatile Changes and Potential Biochemical Mechanisms during Green Tea Spreading Treatment

“…A tea CsOCS (TEA014989.1) and snapdragon ( ama0a23 ) encodes (E)-β-ocimene synthase; both catalyze GPP to produce predominantly (E)-β-ocimene and a small amount of (Z)-β-ocimene. 40 , 45 In this study, both (E)-β-ocimene and (Z)-β-ocimene were detected, and both showed biphasic peaks at 4 and 8 h spreading ( Figures 1 and 5 b). From 0 to 6 h, the ratio of (E)-β-ocimene to (Z)-β-ocimene was around 2 and increased to 5 at 8 h of spreading ( Figure 5 c).…”

“…Thus, additional FPP should be generated de novo to drive the increase. Meanwhile, other factors should be taken into account which could support this hypothesis: (1) the targeted metabolic profiling in this study could miss some unidentified sesquiterpenes which are involved in the sesquiterpene interconversion; (2) sesquiterpene glycosides and esters have been found from other plant species; − they could also be present in fresh tea leaves. During 4 to 10 h spreading, these compounds could be released by glycosidases and contribute to the total sesquiterpene increase.…”

“…From 0 to 6 h, the ratio of (E)-β-ocimene to (Z)-β-ocimene was around 2 and increased to 5 at 8 h of spreading ( Figure 5 c). The in vitro enzyme activity assay demonstrated that recombinant ama0a23 or CsOCS protein produces (E)-β-ocimene and (Z)-β-ocimene in a ratio of 97:2; 40 , 45 in contrast, recombinant CsOCS2 (TEA004606.1) produces both (E)-β-ocimene and (Z)-β-ocimene in a relative abundance about 2:1. 46 Our data suggest that before 4 h of spreading, CsOCS2 was the dominant enzyme responsible for ocimene synthesis; after 4 h of spreading, CsOCS could be induced and result in the (E)-β-ocimene increase.…”

Study on the Suitability of Tea Cultivars for Processing Oolong Tea from the Perspective of Aroma Based on Olfactory Sensory, Electronic Nose, and GC-MS Data Correlation Analysis

“…In tea leaves, α-Farnesene and Ocimene have been found to be synthesized de novo in tea leaves treated with jasmonic acid and mechanical damage (JAMD) and pass between tea plants to initiate volatile defense mechanisms of undamaged tea plants [ 29 ]. In another report, CsOCS was mentioned as a key synthase to promote the de novo synthesis of β-ocimene in oolong tea processing, which is one of the important defense signals of the tea plant against adversity [ 30 ]. These reports suggested that although some of the aforementioned terpene substances (such as α-Farnesene, etc.)…”

Comparative transcriptomics of Pinus massoniana organs provides insights on terpene biosynthesis regulation

“…Furthermore, bifunction and multifunction is another common phenomenon in TPS, meaning that two or more products can be catalyzed by a single TPS (Liu et al, 2021; Zerbe et al, 2012). Deep analysis and discovery of TPS function associated with specific terpenoid is a key topic of investigation in plants (Chen et al, 2021). Although it is still unclear how terpenoids are synthesized in P .…”