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Lilium ‘Siberia’ is a perennial herbaceous plant belonging to Liliaceae family, cultivated both as a cut flower and garden plant. The snowy white flower emits a pleasant aroma which is mainly caused by monoterpenes present in the floral volatile profile. Previously terpene synthase (TPS) genes have been isolated and characterized from various plant species but less have been identified from Liliaceae family. Here, two terpene synthase genes (LoTPS1 and LoTPS3), which are highly expressed in sepals and petals of Lilium ‘Siberia’ flower were functionally characterized recombinant LoTPS1 specifically catalyzes the formation of (Z)-β-ocimene and (±)-linalool as its main volatile compounds from geranyl pyrophosphate (GPP), whereas LoTPS3 is a promiscuous monoterpene synthase which utilizes both GPP and farnesyl pyrophosphate (FPP) as a substrate to generate (±)-linalool and cis-nerolidol, respectively. Transcript levels of both genes were prominent in flowering parts, especially in sepals and petals which are the main source of floral scent production. The gas chromatography–mass spectrometry (GC–MS) and quantitative real-time PCR analysis revealed that the compounds were emitted throughout the day, prominently during the daytime and lower levels at night following a strong circadian rhythm in their emission pattern. Regarding mechanical wounding, both genes showed considerable involvement in floral defense by inducing the emission of (Z)-β-ocimene and (±)-linalool, elevating the transcript accumulation of LoTPS1 and LoTPS3. Furthermore, the subcellular localization experiment revealed that LoTPS1 was localized in plastids, whilst LoTPS3 in mitochondria. Our findings on these two TPSs characterized from Lilium ‘Siberia’ provide new insights into molecular mechanisms of terpene biosynthesis in this species and also provide an opportunity for biotechnological modification of floral scent profile of Lilium.

β-Ocimene is a very common plant volatile released in important amounts from the leaves and flowers of many plant species. This acyclic monoterpene can play several biological functions in plants, by potentially affecting floral visitors and also by mediating defensive responses to herbivory. The ubiquity and high relative abundance of β-ocimene in the floral scents of species from most plant families and from different pollination syndromes (ranging from generalism to specialism) strongly suggest that this terpenoid may play an important role in the attraction of pollinators to flowers. We compiled abundant evidence from published studies that supports β-ocimene as a generalist attractant of a wide spectrum of pollinators. We found no studies testing behavioural responses of pollinators to β-ocimene, that could directly demonstrate or deny the function of β-ocimene in pollinator attraction; but several case studies support that the emissions of β-ocimene in flowers of different species follow marked temporal and spatial patterns of emission, which are typical from floral volatile organic compound (VOC) emissions that are involved in pollinator attraction. Furthermore, important β-ocimene emissions are induced from vegetative plant tissues after herbivory in many species, which have relevant functions in the establishment of tritrophic interactions. We thus conclude that β-ocimene is a key plant volatile with multiple relevant functions in plants, depending on the organ and the time of emission. Experimental behavioural studies on pure β-ocimene conducted with pollinating insects will be necessary to prove the assumptions made here.

In nature, plants have evolved sophisticated defense mechanisms against the attack of pathogens and insect herbivores. Plant volatile-mediated plant-to-plant communication has been assessed in multitrophic systems in different plant species and different pest species. β-ocimene is recognized as an herbivore-induced plant volatile that play an important role in the chemical communication between plants and pests. However, it is still unclear whether β-ocimene can active the defense mechanism of Chinese cabbage against the peach aphid . In this study, we found that treatment of Chinese cabbage with β-ocimene inhibited the growth of in terms of weight gain and reproduction. Moreover, β-ocimene treatment negatively influenced the feeding behavior of by shortening the total feeding period and phloem ingestion and increasing the frequency of stylet puncture. When given a choice, winged aphids preferred to settle on healthy Chinese cabbage compared with β-ocimene-treated plants. In addition, performance of the parasitoid in terms of Y-tube olfaction and landings was better on β-ocimene-treated Chinese cabbage than on healthy plants. Furthermore, β-ocimene significantly increased the expression levels of salicylic acid and jasmonic acid marker genes and the accumulation of glucosinolates. Surprisingly, the transcriptional levels of detoxifying enzymes (CYP6CY3, CYP4, and GST) in aphids reared on β-ocimene-treated Chinese cabbage were significantly higher than those of aphids reared on healthy plants. In summary, our results indicated that β-ocimene can activate the defense response of Chinese cabbage against , and that can also adjust its detoxifying enzymes machinery to counter the host plant defense reaction.

Plants under herbivore attack are able to initiate indirect defense by synthesizing and releasing complex blends of volatiles that attract natural enemies of the herbivore. However, little is known about how plants respond to infestation by multiple herbivores, particularly if these belong to different feeding guilds. Here, we report the interference by a phloem-feeding insect, the whitefly Bemisia tabaci, with indirect plant defenses induced by spider mites (Tetranychus urticae) in Lima bean (Phaseolus lunatus) plants. Additional whitefly infestation of spider-mite infested plants resulted in a reduced attraction of predatory mites (Phytoseiulus persimilis) compared to attraction to plants infested by spider mites only. This interference is shown to result from the reduction in (E)-β-ocimene emission from plants infested by both spider mites and whiteflies. When using exogenous salicylic acid (SA) application to mimic B. tabaci infestation, we observed similar results in behavioral and chemical analyses. Phytohormone and gene-expression analyses revealed that B. tabaci infestation, as well as SA application, inhibited spider mite-induced jasmonic acid (JA) production and reduced the expression of two JA-regulated genes, one of which encodes for the P. lunatus enzyme β-ocimene synthase that catalyzes the synthesis of (E)-β-ocimene. Remarkably, B. tabaci infestation concurrently inhibited SA production induced by spider mites. We therefore conclude that in dual-infested Lima bean plants the suppression of the JA signaling pathway by whitefly feeding is not due to enhanced SA levels.

Key messageHerein, 37 ARF genes were identified and analyzed inHedychium coronarium andHcARF5showed a potential role in the regulation of HcTPS3.Auxin is an important plant hormone, implicated in various aspects of plant growth and development processes especially in the biosynthesis of various secondary metabolites. Auxin response factors (ARF) belong to the transcription factors (TFs) gene family and play a crucial role in transcriptional activation/repression of auxin-responsive genes by directly binding to their promoter region. Nevertheless, whether ARF genes are involved in the regulatory mechanism of volatile compounds in flowering plants is largely unknown. β-ocimene is a key floral volatile compound synthesized by terpene synthase 3 (HcTPS3) in Hedychium coronarium. A comprehensive analysis of H. coronarium genome reveals 37 candidate ARF genes in the whole genome. Tissue-specific expression patterns of HcARFs family members were assessed using available transcriptome data. Among them, HcARF5 showed a higher expression level in flowers, and significantly correlated with the key structural β-ocimene synthesis gene (HcTPS3). Furthermore, transcript levels of both genes were associated with the flower development. Under hormone treatments, the response of HcARF5 and HcTPS3, and the emission level of β-ocimene contents were evaluated. Subcellular and transcriptional activity assay showed that HcARF5 localizes to the nucleus and possesses transcriptional activity. Yeast one-hybrid (Y1H) and dual-luciferase assays revealed that HcARF5 directly regulates the transcriptional activity of HcTPS3. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays showed that HcARF5 interacts with scent-related HcIAA4, HcIAA6, and HcMYB1 in vivo. Overall, these results indicate that HcARF5 is potentially involved in the regulation of β-ocimene synthesis in H. coronarium.

Isoprene is the most abundant biogenic volatile hydrocarbon compound naturally emitted by plants and plays a major role in atmospheric chemistry. It has been proposed that isoprene synthases (IspS) may readily evolve from other terpene synthases, but this hypothesis has not been experimentally investigated. We isolated and functionally validated in Arabidopsis the first isoprene synthase gene, AdoIspS, from a monocotyledonous species (Arundo donax L., Poaceae). Phylogenetic reconstruction indicates that AdoIspS and dicots isoprene synthases most likely originated by parallel evolution from TPS-b monoterpene synthases. Site-directed mutagenesis demonstrated invivo the functional and evolutionary relevance of the residues considered diagnostic for IspS function. One of these positions was identified by saturating mutagenesis as a major determinant of substrate specificity in AdoIspS able to cause invivo a dramatic change in total volatile emission from hemi- to monoterpenes and supporting evolution of isoprene synthases from ocimene synthases. The mechanism responsible for IspS neofunctionalization by active site size modulation by a single amino acid mutation demonstrated in this study might be general, as the very same amino acidic position is implicated in the parallel evolution of different short-chain terpene synthases from both angiosperms and gymnosperms. Based on these results, we present a model reconciling in a unified conceptual framework the apparently contrasting patterns previously observed for isoprene synthase evolution in plants. These results indicate that parallel evolution may be driven by relatively simple biophysical constraints, and illustrate the intimate molecular evolutionary links between the structural and functional bases of traits with global relevance.

Fertilization plays an irreplaceable role in raising crop yields; however, there are issues with unnecessary and blind use of chemical fertilizers, which raise the risk of contamination in the atmosphere. It is hypothesized that fertilization of nitrogen (N) and sulfur (S) will together improve the essential oil (EO) yield and composition of Tagetes minuta L. Thus, 2 years field experiment were carried out to evaluate the outcomes of N (0, 60, 90, and 120 kg ha –1 ) and S levels (0, 20, 40, and 60 kg ha –1 ) on T. minuta during 2018 and 2019. The growth, biomass, EO content and composition were influenced ( P = 0.05) by N and S fertilization. N at 120 kg ha –1 and S at 60 kg ha –1 registered higher biomass (183.89 and 178.90 q ha –1 , respectively) and EO yield (102.09 and 88.60 kg ha –1 , respectively), than control. Stomatal density reduced significantly with increase of N and S levels, however, density of oil glands substantially increased with S at 40 and 60 kg ha –1 . The major component of EO ( Z -β-ocimene) significantly increased with 120 kg N ha –1 (42.59%) and 60 kg S ha –1 (42.35%), respectively. Available nutrients in soil and plant tissues substantially increased with N and S fertilization upto 120 and 60 kg ha –1 , respectively. The highest nutrient use efficiency traits were recorded at 60 kg N ha –1 and 20 kg S ha –1 . It was concluded that 120 kg N ha –1 and 40 kg S ha –1 can be proposed for T. minuta as a result of agronomic responses, which serves as a sustainable means of cropping.

( E )-β-ocimene, a ubiquitous monoterpene volatile in plants, is emitted from flowers to attract pollinators and/or from vegetative tissues as part of inducible defenses mediated by complex signaling networks when plants are attacked by insect herbivores. Wild pear species Pyrus betuleafolia used worldwide as rootstock generally displays valuable pest-resistant traits and is a promising genetic resource for pear breeding. In the current study, transcriptional changes in this wild pear species infested with a polyphagous herbivore Spodoptera litura and the underlying molecular mechanisms were fully investigated. A total of 3,118 differentially expressed genes (DEGs) were identified in damaged pear leaf samples. Spodoptera litura larvae infestation activated complex phytohormonal signaling networks in which jasmonic acid, ethylene, brassinosteroids, cytokinin, gibberellic acid and auxin pathways were induced, whereas salicylic acid and abscisic acid pathways were suppressed. All DEGs associated with growth-related photosynthesis were significantly downregulated, whereas most DEGs involved in defense-related early signaling events, transcription factors, green leaf volatiles and volatile terpenes were significantly upregulated. The PbeOCS (GWHGAAYT028729), a putative ( E )-β-ocimene synthase gene, was newly identified in P. betuleafolia transcriptome. The upregulation of PbeOCS in S. litura -infested pear leaves supports a potential role for PbeOCS in herbivore-induced plant defenses. In enzyme-catalyzed reaction, recombinant PbeOCS utilized only geranyl pyrophosphate but not neryl diphosphate, farnesyl pyrophosphate or geranylgeranyl diphosphate as a substrate, producing ( E )-β-ocimene as the major product and a trace amount of ( Z )-β-ocimene. Moreover, as a catalytic product of PbeOCS, ( E )-β-ocimene showed repellent effects on larvae of S. litura in dual-choice bioassays. What is more, ( E )-β-ocimene increased mortalities of larvae in no-choice bioassays. These findings provide an overview of transcriptomic changes in wild pears in response to chewing herbivores and insights into ( E )-β-ocimene biosynthesis in pear plants, which will help elucidate the molecular mechanisms underlying pear-insect interactions.

Currently, a global analysis of the information available on the relative composition of the floral scents of a very diverse variety of plant species is missing. Such analysis may reveal general patterns on the distribution and dominance of the volatile compounds that form these mixtures, and may also allow measuring the effects of factors such as the phylogeny, pollination vectors, and climatic conditions on the floral scents of the species. To fill this gap, we compiled published data on the relative compositions and emission rates of volatile organic compounds (VOCs) in the floral scents of 305 plant species from 66 families. We also gathered information on the groups of pollinators that visited the flowers and the climatic conditions in the areas of distribution of these species. This information allowed us to characterize the occurrence and relative abundances of individual volatiles in floral scents and the effects of biotic and climatic factors on floral scent. The monoterpenes trans-β-ocimene and linalool and the benzenoid benzaldehyde were the most abundant floral VOCs, in both ubiquity and predominance in the floral blends. Floral VOC richness and relative composition were moderately preserved traits across the phylogeny. The reliance on different pollinator groups and the climate also had important effects on floral VOC richness, composition, and emission rates of the species. Our results support the hypothesis that key compounds or compounds originating from specific biosynthetic pathways mediate the attraction of the main pollinators. Our results also indicate a prevalence of monoterpenes in the floral blends of plants that grow in drier conditions, which could link with the fact that monoterpene emissions protect plants against oxidative stresses throughout drought periods and their emissions are enhanced under moderate drought stress. Sesquiterpenes, in turn, were positively correlated with mean annual temperature, supporting that sesquiterpene emissions are dominated mainly by ambient temperature. This study is the first to quantitatively summarise data on floral-scent emissions and provides new insights into the biotic and climatic factors that influence floral scents.

Hemp ( Cannabis sativa L.) is a multifunctional crop that is capable of prompt environmental adaptation. In this study, a monoecious cultivar (Futura 75) and a dioecious one (Finola) were tested in a mountain area in Valsaviore (Rhaetian Alps, Italy; elevation: 1,100 m a.s.l.) during the growing season 2018. Phytochemical behavior was evaluated by different analytical approaches: HPLC-high-resolution mass spectrometry, SDS-PAGE LC-MS/MS, HS-SPME GC-MS, and GC-FID in order to obtain complete profile of two varieties cultivated in altitude. CSR functional strategy used for ecological evaluation revealed that both genotypes are mainly competitors, although Finola is more stress tolerator (C:S:R = 57:26:17%) than Futura (C:S:R = 69:15:16%). The Finola inflorescences were characterized by higher quantities of β-ocimene and α-terpinolene, while α- and ß-pinene accompanied by extremely high ß-myrcene were found as predominant in Futura. Both varieties were rich in sesquiterpenes (45 recognized) among which trans -caryophyllene and α-humulene were the most abundant. Total tetrahydrocannabinol level was lower than 0.1%, while the most abundant cannabinoid was cannabidiolic acid (CBDA): 2.3% found in Finola vs. 2.7% revealed for Futura. The level of corresponding neutral form, cannabidiol, varied drastically: 0.27% (Finola) vs. 0.056% (Futura). Finola showed the unique cannabinoid profile with unexpectedly high cannabidivarin, 2-fold higher that corresponding acidic analogue, whereas the particularity of Futura 75 was the occurrence of cannabigerolic acid (CBGA) in the quantities that was double than those exposed for Finola. The seeds from both chemovars proved to be rich in polyunsaturated fatty acids, and Finola showed a higher ratio ω6/ω3. No difference was found in the protein content, and the SDS-PAGE profile was similar. The most abundant protein was edestin, followed by heat shock protein 70, ß-conglycinin, and vicilin. In conclusion, comprehensive phytochemical and ecological study of two fiber-type varieties cultivated in Italian Alps displayed specific, legal, and safe cannabinoids profile, followed by particular terpene composition, polyunsaturated fatty acids content, and favorable protein profile. This postulates that geographical provenience of hemp should be considered in selecting a variety that would be suitable for a specific end-use nutraceutical application.