Volatile Organic Compounds from Orchids: From Synthesis and Function to Gene Regulation

Abstract

Orchids are one of the most significant plants that have ecologically adapted to every habitat on earth. Orchids show a high level of variation in their floral morphologies, which makes them popular as ornamental plants in the global market. Floral scent and color are key traits for many floricultural crops. Volatile organic compounds (VOCs) play vital roles in pollinator attraction, defense, and interaction with the environment. Recent progress in omics technology has led to the isolation of genes encoding candidate enzymes responsible for the biosynthesis and regulatory circuits of plant VOCs. Uncovering the biosynthetic pathways and regulatory mechanisms underlying the production of floral scents is necessary not only for a better understanding of the function of relevant genes but also for the generation of new cultivars with desirable traits through molecular breeding approaches. However, little is known about the pathways responsible for floral scents in orchids because of their long life cycle as well as the complex and large genome; only partial terpenoid pathways have been reported in orchids. Here, we review the biosynthesis and regulation of floral volatile compounds in orchids. In particular, we focused on the genes responsible for volatile compounds in various tissues and developmental stages in Cymbidium orchids. We also described the emission of orchid floral volatiles and their function in pollination ecology. Taken together, this review will provide a broad scope for the study of orchid floral scents.

Genome-Wide Identification and Expression Profile of TPS Gene Family in Dendrobium officinale and the Role of DoTPS10 in Linalool Biosynthesis

“…The high volatility of terpene compounds promotes the scent in orchids. For instance, geraniol and linalool are major floral scent compounds in Phalaenopsis bellina [6,7]. Orchid floral volatiles, as well as flower color, shape, and fragrance are key horticultural ornamental traits in orchids, and also serve to attract pollinators in various ecological habitats [6].…”

Functional Characterization of a Dendrobium officinale Geraniol Synthase DoGES1 Involved in Floral Scent Formation

“…In higher plants, the emission of volatile terpenes is often temporal and spatially specific [ 3 , 4 , 36 ]. For example, PbGDPS , which participates in the generation of geraniol and linalool in P. bellina , was specifically expressed in flowers and highly expressed on the fifth day after flower initiation [ 4 , 5 , 14 ]. The released of a high content of linalool in Osmanthus fragrans ‘Dangui’ petals is caused by the overexpression of mono-TPS ( LIS1 encoding linalool synthase) [ 37 ].…”

“…Plants emit an astonishing number of volatile metabolites during growth and development, and these have various roles, some with biological effects, that are considered beneficial to plants and humans [ 1 ]. For ornamental plants, floral volatiles have a dual function, to attract pollinators, and in defense against pests, herbivores, and pathogens [ 2 , 3 , 4 ]. Orchids, economically important floricultural crops, possess an abundance of floral volatile terpenes.…”

“…Orchids, economically important floricultural crops, possess an abundance of floral volatile terpenes. Among them, monoterpenes, especially geraniol, linalool, and their oxygenated derivatives, are predominant components of floral scents [ 4 , 5 ]. Geraniol is an acyclic monoterpene alcohol released from several ornamental plants, such as citronella, geranium, herbs, roses, and orchids ( Phalaenopsis bellina and Dendrobium officinale ) [ 5 , 6 , 7 , 8 ], and is extensively used in fragrance and cosmetics industries because of its pleasant rose-like scent.…”

Chemical composition, antimicrobial, and lipase enzyme activity of essential oil and solvent extracts from Serapiasorientalis subsp. orientalis

“…Some of the Orchidaceae species have been used as an herbal medicine to treat headaches, dizziness, tetanus and epilepsy. Some orchid species shown to exert sedative, anticonvulsive and antiepileptic effects which was listed in the oldest Chinese Materia Medica [4][5]. In recent years, neuroprotective functions of some Orchidaceae species are one of their traditional uses [6].…”