Tea plant is an important economic crop, which is used to produce the world's oldest and most widely consumed tea beverages. Here, we present a high-quality reference genome assembly of the tea plant (Camellia sinensis var. sinensis) consisting of 15 pseudo-chromosomes. LTR retrotransposons (LTR-RTs) account for 70.38% of the genome, and we present evidence that LTR-RTs play critical roles in genome size expansion and the transcriptional diversification of tea plant genes through preferential insertion in promoter regions and introns. Genes, particularly those coding for terpene biosynthesis proteins, associated with tea aroma and stress resistance were significantly amplified through recent tandem duplications and exist as gene clusters in tea plant genome. Phylogenetic analysis of the sequences of 81 tea plant accessions with diverse origins revealed three well-differentiated tea plant populations, supporting the proposition for the southwest origin of the Chinese cultivated tea plant and its later spread to western Asia through introduction. Domestication and modern breeding left significant signatures on hundreds of genes in the tea plant genome, particularly those associated with tea quality and stress resistance. The genomic sequences of the reported reference and resequenced tea plant accessions provide valuable resources for future functional genomics study and molecular breeding of improved cultivars of tea plants.

Summary Plants produce and emit terpenes, including sesquiterpenes, during growth and development, which serve different functions in plants. The sesquiterpene nerolidol has health‐promoting properties and adds a floral scent to plants. However, the glycosylation mechanism of nerolidol and its biological roles in plants remained unknown. Sesquiterpene UDP‐glucosyltransferases were selected by using metabolites‐genes correlation analysis, and its roles in response to cold stress were studied. We discovered the first plant UGT (UGT91Q2) in tea plant, whose expression is strongly induced by cold stress and which specifically catalyzes the glucosylation of nerolidol. The accumulation of nerolidol glucoside was consistent with the expression level of UGT91Q2 in response to cold stress, as well as in different tea cultivars. The reactive oxygen species (ROS) scavenging capacity of nerolidol glucoside was significantly higher than that of free nerolidol. Down‐regulation of UGT91Q2 resulted in reduced accumulation of nerolidol glucoside, ROS scavenging capacity and tea plant cold tolerance. Tea plants absorbed airborne nerolidol and converted it to its glucoside, subsequently enhancing tea plant cold stress tolerance. Nerolidol plays a role in response to cold stress as well as in triggering plant–plant communication in response to cold stress. Our findings reveal previously unidentified roles of volatiles in response to abiotic stress in plants.

Plants emit a variety of volatiles in response to herbivore attack, and (Z)‐3‐hexenol and its glycosides have been shown to function as defence compounds. Although the ability to incorporate and convert (Z)‐3‐hexenol to glycosides is widely conserved in plants, the enzymes responsible for the glycosylation of (Z)‐3‐hexenol remained unknown until today. In this study, uridine‐diphosphate‐dependent glycosyltransferase (UGT) candidate genes were selected by correlation analysis and their response to airborne (Z)‐3‐hexenol, which has been shown to be taken up by the tea plant. The allelic proteins UGT85A53‐1 and UGT85A53‐2 showed the highest activity towards (Z)‐3‐hexenol and are distinct from UGT85A53‐3, which displayed a similar catalytic efficiency for (Z)‐3‐hexenol and nerol. A single amino acid exchange E59D enhanced the activity towards (Z)‐3‐hexenol, whereas a L445M mutation reduced the catalytic activity towards all substrates tested. Transient overexpression of CsUGT85A53‐1 in tobacco significantly increased the level of (Z)‐3‐hexenyl glucoside. The functional characterization of CsUGT85A53 as a (Z)‐3‐hexenol UGT not only provides the foundation for the biotechnological production of (Z)‐3‐hexenyl glucoside but also delivers insights for the development of novel insect pest control strategies in tea plant and might be generally applicable to other plants.

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Plants emit an overabundance of volatile compounds, which act in their producers either as appreciated attractants to lure beneficial animals or as repellent toxins to deter pests in a species-specific and concentration-dependent manner. Plants have evolved solutions to provide sufficient volatiles without poisoning themselves. Uridine-diphosphate sugar-dependent glycosyltransferases (UGTs) acting on volatiles is one important part of this sophisticated system, which balances the levels of bioactive metabolites and prepares them for cellular and long-distance transport and storage but enables the remobilization of disarmed toxins for the benefit of plant protection. This review provides an overview of the research history of glycosidically bound volatiles (GBVs), a relatively new group of plant secondary metabolites, and discusses the role of UGTs in the production of GBVs for plant protection.