Summary• Flowers have a high risk of pathogen attack because of their rich nutrient and moisture content, and high frequency of insect visitors. We investigated the role of (E)-b-caryophyllene in floral defense against a microbial pathogen. This sesquiterpene is a common volatile compound emitted from flowers, and is a major volatile released from the stigma of Arabidopsis thaliana flowers.• Arabidopsis thaliana lines lacking a functional (E)-b-caryophyllene synthase or constitutively overexpressing this gene were challenged with Pseudomonas syringae pv. tomato DC3000, which is a bacterial pathogen of brassicaceous plants.• Flowers of plant lines lacking (E)-b-caryophyllene emission showed greater bacterial growth on their stigmas than did wild-type flowers, and their seeds were lighter and misshapen. By contrast, plant lines with ectopic (E)-b-caryophyllene emission from vegetative parts were more resistant than wild-type plants to pathogen infection of leaves, and showed reduced cell damage and higher seed production. Based on in vitro experiments, (E)-b-caryophyllene seems to act by direct inhibition of bacterial growth, rather than by triggering defense signaling pathways.• (E)-b-Caryophyllene thus appears to serve as a defense against pathogens that invade floral tissues and, like other floral volatiles, may play multiple roles in defense and pollinator attraction.

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Terpene volatiles play important roles in plant-organism interactions as attractants of pollinators or as defense compounds against herbivores. Among the most common plant volatiles are homoterpenes, which are often emitted from night-scented flowers and from aerial tissues upon herbivore attack. Homoterpene volatiles released from herbivore-damaged tissue are thought to contribute to indirect plant defense by attracting natural enemies of pests. Moreover, homoterpenes have been demonstrated to induce defensive responses in plant-plant interaction. Although early steps in the biosynthesis of homoterpenes have been elucidated, the identity of the enzyme responsible for the direct formation of these volatiles has remained unknown. Here, we demonstrate that CYP82G1 (At3g25180), a cytochrome P450 monooxygenase of the Arabidopsis CYP82 family, is responsible for the breakdown of the C 20 -precursor (E,E)-geranyllinalool to the insect-induced C 16 -homoterpene (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT). Recombinant CYP82G1 shows narrow substrate specificity for (E,E)-geranyllinalool and its C 15 -analog (E)-nerolidol, which is converted to the respective C 11 -homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT). Homology-based modeling and substrate docking support an oxidative bond cleavage of the alcohol substrate via syn-elimination of the polar head, together with an allylic C-5 hydrogen atom. CYP82G1 is constitutively expressed in Arabidopsis stems and inflorescences and shows highly coordinated herbivoreinduced expression with geranyllinalool synthase in leaves depending on the F-box protein COI-1. CYP82G1 represents a unique characterized enzyme in the plant CYP82 family with a function as a DMNT/TMTT homoterpene synthase.floral scent | herbivory | terpene biosynthesis P lants interact with the environment by producing a variety of chemical compounds. In particular, volatile compounds emitted from flowers and vegetative plant tissues serve as attractants for pollinators or exert defensive activities against herbivores, thereby contributing to plant survival and reproductive success. Among the most common plant volatiles are the irregular C 16 -homoterpene (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) and its C 11 -analog (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), both of which are widespread floral odor constituents contributing to the "white-floral image" of night scented flowers (1). Moreover, TMTT and DMNT are released in response to herbivore attack from the foliage of gymnosperms (2) and numerous angiosperms, both monocots and dicots (3-7). Several studies have indicated a role of homoterpene volatiles in the attraction of herbivore predators in indirect plant defense. For example, de Boer et al. (8) demonstrated that TMTT influenced the foraging behavior of predatory mites when emitted in the presence of other induced volatiles from lima bean leaves infested by spider mites (Tetranychus urticae). In addition, treatment of lima bean with the terpenoid pathway inhibitor fosmidomycin, wh...

The effect of light on melatonin biosynthesis was examined in detached rice (Oryza sativa cv. Asahi) leaves during the senescence process. The detached leaves were exposed to senescence treatment either in constant darkness or in constant light, and subjected to HPLC analysis for melatonin and its precursors. Higher melatonin levels were detected in rice leaves under constant light while very low levels were observed in constant darkness. Levels of the melatonin intermediates, tryptamine, serotonin, and N-acetylserotonin significantly decreased in the dark compared to those in the light. Furthermore, relative mRNA levels of melatonin biosynthetic genes and their corresponding proteins decreased accordingly in constant darkness. The most striking difference between constant light and dark was observed in levels of the protein tryptamine 5-hydroxylase. These results suggest that melatonin biosynthesis during senescence is dependent on light signals in rice leaves, contrary to the response found in animals.

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Magnolia grandiflora (Southern Magnolia) is a primitive evergreen tree that has attracted attention because of its horticultural distinctiveness, the wealth of natural products associated with it, and its evolutionary position as a basal angiosperm. Three cDNAs corresponding to terpene synthase (TPS) genes expressed in young leaves were isolated, and the corresponding enzymes were functionally characterized in vitro. Recombinant Mg25 converted farnesyl diphosphate (C 15 ) predominantly to b-cubebene, while Mg17 converted geranyl diphosphate (C 5 ) to a-terpineol. Efforts to functionally characterize Mg11 were unsuccessful. Transcript levels for all three genes were prominent in young leaf tissue and significantly elevated for Mg25 and Mg11 messenger RNAs in stamens. A putative amino-terminal signal peptide of Mg17 targeted the reporter green fluorescent protein to both chloroplasts and mitochondria when transiently expressed in epidermal cells of Nicotiana tabacum leaves. Phylogenetic analyses indicated that Mg25 and Mg11 belonged to the angiosperm sesquiterpene synthase subclass TPS-a, while Mg17 aligned more closely to the angiosperm monoterpene synthase subclass TPS-b. Unexpectedly, the intron-exon organizations for the three Magnolia TPS genes were different from one another and from other well-characterized TPS gene sets. The Mg17 gene consists of six introns arranged in a manner similar to many other angiosperm sesquiterpene synthases, but Mg11 contains only four introns, and Mg25 has only a single intron located near the 5# terminus of the gene. Our results suggest that the structural diversity observed in the Magnolia TPS genes could have occurred either by a rapid loss of introns from a common ancestor TPS gene or by a gain of introns into an intron-deficient progenote TPS gene.Many reports on the identification of a new terpene compound or the characterization of a terpene biosynthetic enzyme begin with a comment about the structural complexity and diversity of terpene metabolism in general. That complexity arises, in part, from the genetic and regulatory complexity of the gene families involved Trapp and Croteau, 2001;Gang, 2005), but more so from the terpene synthases (TPSs) themselves that initiate the biosynthesis of different classes of terpenes (i.e. monoterpenes, sesquiterpenes, and diterpenes) and impart exquisite regiospecificity and stereospecificity into the biosynthesis of specific members within a terpene family (Davis and Croteau, 2000;Christianson, 2006). Valencene synthase (Sharon-Asa et al., 2003) and 5-epiaristolochene synthase (Back and Chappell, 1996), for example, are related to one another based on the biosynthesis of sesquiterpenes within the eremophilene class of compounds. Sesquiterpenes in the eremophilane class are fused (bicyclic), decalin ring structures that harbor methyl and isopropenyl substituents in the same regio positions, but with alternative stereo configurations. Valencene also contains a double bond in the A-ring, which is mirrored in the B-ring of aristolochene....

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Serotonin derivatives belong to a class of phenylpropanoid amides found at low levels in a wide range of plant species. Representative serotonin derivatives include feruloylserotonin (FS) and 4-coumaroylserotonin (CS). Since the first identification of serotonin derivatives in safflower seeds, their occurrence, biological significance, and pharmacological properties have been reported. Recently, serotonin N-hydroxycinnamoyl transferase (SHT), which is responsible for the synthesis of serotonin derivatives, was cloned from pepper (Capsicum annuum) and characterized in terms of its enzyme kinetics. Using the SHT gene, many attempts have been made to either increase the level of serotonin derivatives in transgenic plants or produce serotonin derivatives de novo in microbes by dual expression of key genes such as SHT and 4-coumarate-CoA ligase (4CL). Due to the strong antioxidant activity and other therapeutic properties of serotonin derivatives, these compounds may have high potential in treatment and prophylaxis, as cosmetic ingredients, and as major components of functional foods or feeds that have health-improving effects. This review examines the biosynthesis of serotonin derivatives, corresponding enzymes, heterologous production in plants or microbes, and their applications.