O-methyltransferases involved in the biosynthesis of volatile phenolic derivatives in rose petals

Floral volatile benzenoids/phenylpropanoids: biosynthetic pathway, regulation and ecological value

Benzenoids/phenylpropanoids, the second most diverse group of plant volatiles, exhibit significant structural diversity and play crucial roles in attracting pollinators and protecting against pathogens, insects, and herbivores. This review summarizes their complex biosynthetic pathways and regulatory mechanisms, highlighting their links to plant growth, development, hormone levels, circadian rhythms, and flower coloration. External factors like light, humidity, and temperature also influence their biosynthesis. Their ecological value is discussed, offering insights for enhancing floral scent, pollinator attraction, pest resistance, and metabolic engineering through genetic modification.

The scent of roses, a bouquet of fragrance diversity

Roses have been domesticated since antiquity for their therapeutic, cosmetic, and ornamental properties. Their floral fragrance has great economic value, which has influenced the production of rose varieties. The production of rose water and essential oil is one of the most lucrative activities, supplying bioactive molecules to the cosmetic, pharmaceutical, and therapeutic industries. In recent years, major advances in molecular genetics, genomic, and biochemical tools have paved the way for the identification of molecules that make up the specific fragrance of various rose cultivars. The aim of this review is to highlight current knowledge on metabolite profiles, and more specifically on fragrance compounds, as well as the specificities and differences between rose species and cultivars belonging to different rose sections and how they contribute to modern roses fragrance.

Beneficial medicinal effects and material applications of rose

Rose is a beautiful and fragrant plant with a variety of medicinal and substance uses. Various parts of rose such as fruits, flowers, leaves, and bark can be used in various product development, including cosmetics, food, pharmaceuticals, and engineering. The medical benefits of roses include the treatment of inflammation, diabetes, dysmenorrhea, depression, stress, seizures, and aging. Rose water is precious beauty water for skin care and has antibacterial effects on various microbiota. The surface of a rose petal exhibits a hierarchical structure comprising microscale papillae, with each papilla further featuring intricate nanofolds. With this structural feature, rose petals have high water contact angles together with antagonistic wetting properties. The hierarchical structures of rose petals were shown to have anti-reflection and light-harvesting abilities, which have the potential to be materials for various electronic products. Rose petals are an excellent biomimetic/bioinspired material that can be applied to the popular material graphene. This paper reviews the medical function and material application of roses. During the COVID-19 pandemic, medical materials or food shortages have become a global issue. Natural biomaterials could be a good alternative. Roses, with so many benefits, definitely deserve more exploration and promotion.

Diverse O-methyltransferases catalyze the biosynthesis of floral benzenoids that repel aphids from the flowers of waterlily Nymphaea prolifera

Nymphaea is a key genus of the ANA grade (Amborellales, Nymphaeales, and Austrobaileyales) of basal flowering plants, which serve as a key model to study the early evolution of floral traits. In this study, we comprehensively investigated the emission, biosynthesis, and biological function of the floral scent in a night-blossoming waterlily Nymphaea prolifera. The headspace volatile collection combined with GC-MS analysis showed that the floral scent of N. prolifera is predominately comprised by methylated benzenoids including anisole, veratrole, guaiacol, and methoxyanisole. Moreover, the emission of these floral benzenoids in N. prolifera exhibited temporal and spatial pattern with circadian rhythm and tissue specificity. By creating and mining transcriptomes of N. prolifera flowers, 12 oxygen methyltransferases (NpOMTs) were functionally identified. By in vitro enzymatic assay, NpOMT3, 6, and 7 could produce anisole and NpOMT5, 7, 9, produce guaiacol, whereas NpOMT3, 6, 9, 11 catalyzed the formation of veratrole. Methoxyanisole was identified as the universal product of all NpOMTs. Expression patterns of NpOMTs provided implication for their roles in the production of the respective benzenoids. Phylogenetic analysis of OMTs suggested a Nymphaea-specific expansion of the OMT family, indicating the evolution of lineage-specific functions. In bioassays, anisole, veratrole, and guaiacol in the floral benzenoids were revealed to play the critical role in repelling waterlily aphids. Overall, this study indicates that the basal flowering plant N. prolifera has evolved a diversity and complexity of OMT genes for the biosynthesis of methylated benzenoids that can repel insects from feeding the flowers. These findings provide new insights into the evolutional mechanism and ecological significance of the floral scent from early-diverged flowering plants.

Callus Derived from Petals of the Rosa hybrida Breeding Line 15R-12-2 as New Material Useful for Fragrance Production

Rose (Rosa hybrida) is a major flower crop worldwide and has long been loved for its variety of colors and scents. Roses are mainly used for gardening or cutting flowers and are also used as raw materials for perfumes, cosmetics, and food. Essential oils, which are extracted from the flowers of plants, including roses, have various scents, and the essential oil market has been growing steadily owing to the growing awareness of the benefits of natural and organic products. Therefore, it is necessary to develop a system that stably supplies raw materials with uniform ingredients in line with the continuous increase in demand. In this study, conditions for the efficient induction of callus were established from the petals of the rose breeding line 15R-12-2, which has a strong scent developed by the National Institute of Horticultural and Herbal Science, Rural Development Administration. The highest callus induction rate (65%) was observed when the petals of the fully open flower (FOF) were placed on the SH11DP medium so that the abaxial surface was in contact with the medium. In addition, the VOCs contained in the petals of 15R-12-2 and the petal-derived callus were analyzed by HS-SPME-GC-MS. Thirty components, including esters and alcohols, were detected in the petal-derived callus. Among them, 2-ethylhexan-1-ol, which showed 59.01% relative content when extracted with hexane as a solvent, was the same component as detected in petals. Therefore, petal-derived callus is expected to be of high industrial value and can be suggested as an alternative pathway to obtaining VOCs.

Genetic and Biochemical Aspects of Floral Scents in Roses

Floral scents possess high ornamental and economic values to rose production in the floricultural industry. In the past two decades, molecular bases of floral scent production have been studied in the rose as well as their genetic inheritance. Some significant achievements have been acquired, such as the comprehensive rose genome and the finding of a novel geraniol synthase in plants. In this review, we summarize the composition of floral scents in modern roses, focusing on the recent advances in the molecular mechanisms of floral scent production and emission, as well as the latest developments in molecular breeding and metabolic engineering of rose scents. It could provide useful information for both studying and improving the floral scent production in the rose.

Identification of a lichen depside polyketide synthase gene by heterologous expression in Saccharomyces cerevisiae

Lichen-forming fungi produce a variety of secondary metabolites including bioactive polyketides. Advances in DNA and RNA sequencing have led to a growing database of new lichen gene clusters encoding polyketide synthases (PKS) and associated ancillary activities. Definitive assignment of a PKS gene to a metabolic product has been challenging in the lichen field due to a lack of established gene knockout or heterologous gene expression systems. Here, we report the reconstitution of a non-reducing PKS gene from the lichen Pseudevernia furfuracea and successful heterologous expression of the synthetic lichen PKS gene in engineered Saccharomyces cerevisiae. We show that P. furfuracea PFUR17_02294 produces lecanoric acid, the depside dimer of orsellinic acid, at 360 mg/L in small-scale yeast cultures. Our results unequivocally identify PFUR17_02294 as a lecanoric acid synthase and establish that a single lichen PKS synthesizes two phenolic rings and joins them by an ester linkage to form the depside product.

Transcriptional response of Asarum heterotropoides Fr. Schmidt var. mandshuricum (Maxim.) Kitag. leaves grown under full and partial daylight conditions

BACKGROUND

Asarum heterotropides Fr. Schmidt var. mandshuricum (Maxim.) Kitag. is an important medicinal and industrial plant, which is used in the treatment of various diseases. The main bioactive ingredient is the volatile oil having more than 82 identified components of which methyleugenol, safrole, myristicin, and toluene account for about 70% of the total volume. As a sciophyte plant, the amount of light it absorbs through leaves is an important factor for growth and metabolism.

RESULTS

We grew Asarum plants under full, 50, 28, and 12% sunlight conditions to investigate the effect of different light irradiances on the four major volatile oil components. We employed de novo transcriptome sequencing to understand the transcriptional behavior of Asarum leaves regarding the biosynthetic pathways of the four volatile oil components, photosynthesis and biomass accumulation, and hormone signaling. Our results demonstrated that the increasing light conditions promoted higher percent of the four components. Under full sunlight conditions, cinnamyl alcohol dehydrogenase and cytochrome p450719As were upregulated and led the increased methyleugenol, safrole, and myristicin. The transcriptomic data also showed that Asarum leaves, under full sunlight conditions, adjust their photosynthesis-antenna proteins as a photoprotective response with the help of carotenoids. Plant hormone-signaling related genes were also differentially expressed between full sunlight and low light conditions.

CONCLUSIONS

High light induces accumulation of major bioactive ingredients A. heterotropides volatile oil and this is ascribed to upregulation of key genes such as cinnamyl alcohol dehydrogenase and cytochrome p450719As. The transcriptome data presented here lays the foundation of further understanding of light responses in sciophytes and provides guidance for increasing bioactive molecules in Asarum.

Auxin-Responsive R2R3-MYB Transcription Factors HcMYB1 and HcMYB2 Activate Volatile Biosynthesis in Hedychium coronarium Flowers

Auxin, an important plant hormone, induces the biosynthesis of various secondary metabolites by modulating the expression of auxin-responsive genes. In the ornamental plant Hedychium coronarium, linalool and methyl benzoate are biosynthesized by the terpene synthase (TPS) HcTPS5 and the benzoic/salicylic acid methyltransferase (BSMT) HcBSMT2, respectively. However, the transcriptional regulation of this process remains unclear. Here, we identified and functionally characterized the R2R3-MYB transcription factors HcMYB1 and HcMYB2 in regulating the biosynthesis of these floral aroma compounds. HcMYB1 and HcMYB2 are specifically expressed in flowers, their expression is correlated with the emission of volatile compounds in flowers, and is induced by auxin. Moreover, HcMYB1 and HcMYB2 interact with the HcBSMT2 promoter region. HcMYB2 activates the expression of the linalool synthase gene HcTPS5. In flowers with HcMYB1 or HcMYB2 silenced, the levels of floral scent compounds were significantly reduced, and HcBSMT2 and HcTPS5 were downregulated compared with the wild type. Moreover, HcMYB1 form protein-protein interaction with key scent-related HcIAA4 protein to regulate floral aroma production. Taken together, these results indicate that HcMYB1 and HcMYB2 play crucial roles in regulating the formation of scent compounds in Hedychium coronarium (H. coronarium) flowers in response to auxin signaling.

Improving 3-methylphenol (m-cresol) production in yeast via in vivo glycosylation or methylation

Heterologous expression of 6-methylsalicylic acid synthase (MSAS) together with 6-MSA decarboxylase enables de novo production of the platform chemical and antiseptic additive 3-methylphenol (3-MP) in the yeast Saccharomyces cerevisiae. However, toxicity of 3-MP prevents higher production levels. In this study, we evaluated in vivo detoxification strategies to overcome limitations of 3-MP production. An orcinol-O-methyltransferase from Chinese rose hybrids (OOMT2) was expressed in the 3-MP producing yeast strain to convert 3-MP to 3-methylanisole (3-MA). Together with in situ extraction by dodecane of the highly volatile 3-MA this resulted in up to 211 mg/L 3-MA (1.7 mM) accumulation. Expression of a UDP-glycosyltransferase (UGT72B27) from Vitis vinifera led to the synthesis of up to 533 mg/L 3-MP as glucoside (4.9 mM). Conversion of 3-MP to 3-MA and 3-MP glucoside was not complete. Finally, deletion of phosphoglucose isomerase PGI1 together with methylation or glycosylation and feeding a fructose/glucose mixture to redirect carbon fluxes resulted in strongly increased product titers, with up to 897 mg/L 3-MA/3-MP (9 mM) and 873 mg/L 3-MP/3-MP as glucoside (8.1 mM) compared to less than 313 mg/L (2.9 mM) product titers in the wild type controls. The results show that methylation or glycosylation are promising tools to overcome limitations in further enhancing the biotechnological production of 3-MP.

A thorough analysis and categorization of bacterial interrupted adenylation domains, including previously unidentified families

Interrupted adenylation (A) domains are key to the immense structural diversity seen in the nonribosomal peptide (NRP) class of natural products (NPs). Interrupted A domains are A domains that contain within them the catalytic portion of another domain, most commonly a methylation (M) domain. It has been well documented that methylation events occur with extreme specificity on either the backbone (N-) or side chain (O- or S-) of the amino acid (or amino acid-like) building blocks of NRPs. Here, through taxonomic and phylogenetic analyses as well as multiple sequence alignments, we evaluated the similarities and differences between interrupted A domains. We probed their taxonomic distribution amongst bacterial organisms, their evolutionary relatedness, and described conserved motifs of each type of M domain found to be embedded in interrupted A domains. Additionally, we categorized interrupted A domains and the M domains within them into a total of seven distinct families and six different types, respectively. The families of interrupted A domains include two new families, 6 and 7, that possess new architectures. Rather than being interrupted between the previously described a2–a3 or a8–a9 of the ten conserved A domain sequence motifs (a1–a10), family 6 contains an M domain between a6–a7, a previously unknown interruption site. Family 7 demonstrates that di-interrupted A domains exist in Nature, containing an M domain between a2–a3 as well as one between a6–a7, displaying a novel arrangement. These in-depth investigations of amino acid sequences deposited in the NCBI database highlighted the prevalence of interrupted A domains in bacterial organisms, with each family of interrupted A domains having a different taxonomic distribution. They also emphasized the importance of utilizing a broad range of bacteria for NP discovery. Categorization of the families of interrupted A domains and types of M domains allowed for a better understanding of the trends of naturally occurring interrupted A domains, which illuminated patterns and insights on how to harness them for future engineering studies.

In-depth study of intriguing bacterial interrupted adenylation domains from seven distinct families and six different types.

Identification of QTL for perenniality and floral scent in cowpea (Vigna unguiculata [L.] Walp.)

Perennial habit and floral scent are major traits that distinguish domesticated cowpeas from their wild relatives. However, the genetic basis of these two important traits remains largely unknown in cowpea. Plant longevity, a perenniality-related trait, and floral scent, an outcrossing trait, were investigated using a RIL population derived from a cross between a domesticated and a wild cowpea. QTL analysis revealed three significant loci, one on chromosome 8 associated with plant longevity and two, on chromosomes 1 and 11, for floral scent. Genes within the QTL regions were identified. Genes encoding an F-box protein (Vigun08g215300) and two kinases (Vigun08g217000, Vigun08g217800), and involved in physiological processes including regulation of flowering time and plant longevity, were identified within the perenniality QTL region. A cluster of O-methyltransferase genes (Vigun11g096800, Vigun11g096900, Vigun11g097000, Vigun11g097600, and Vigun11g097800) was identified within the floral scent QTL region. These O-methyltransferase cowpea genes are orthologs of the Arabidopsis N-acetylserotonin O-methyltransferase (ASMT) gene, which is involved in the biosynthesis of melatonin. Melatonin is an indole derivative, which is an essential molecule for plant interactions with pollinators. These findings lay the foundation for further exploration of the genetic mechanisms of perenniality and floral scent in cowpea. Knowledge from this study can help in the development of new extended-growth cycle lines with increased yield or lines with increased outcrossing for population breeding.

Dissecting the Genome-Wide Evolution and Function of R2R3-MYB Transcription Factor Family in Rosa chinensis

Rosa chinensis, an important ancestor species of Rosa hybrida, the most popular ornamental plant species worldwide, produces flowers with diverse colors and fragrances. The R2R3-MYB transcription factor family controls a wide variety of plant-specific metabolic processes, especially phenylpropanoid metabolism. Despite their importance for the ornamental value of flowers, the evolution of R2R3-MYB genes in plants has not been comprehensively characterized. In this study, 121 predicted R2R3-MYB gene sequences were identified in the rose genome. Additionally, a phylogenomic synteny network (synnet) was applied for the R2R3-MYB gene families in 35 complete plant genomes. We also analyzed the R2R3-MYB genes regarding their genomic locations, Ka/Ks ratio, encoded conserved motifs, and spatiotemporal expression. Our results indicated that R2R3-MYBs have multiple synteny clusters. The RcMYB114a gene was included in the Rosaceae-specific Cluster 54, with independent evolutionary patterns. On the basis of these results and an analysis of RcMYB114a-overexpressing tobacco leaf samples, we predicted that RcMYB114a functions in the phenylpropanoid pathway. We clarified the relationship between R2R3-MYB gene evolution and function from a new perspective. Our study data may be relevant for elucidating the regulation of floral metabolism in roses at the transcript level.

Genome-wide identification, characterization, expression and enzyme activity analysis of coniferyl alcohol acetyltransferase genes involved in eugenol biosynthesis in Prunus mume

Prunus mume, a traditional Chinese flower, is the only species of Prunus known to produce a strong floral fragrance, of which eugenol is one of the principal components. To explore the molecular mechanism of eugenol biosynthesis in P. mume, patterns of dynamic, spatial and temporal variation in eugenol were analysed using GC-MS. Coniferyl alcohol acetyltransferase (CFAT), a member of the BAHD acyltransferase family, catalyses the substrate of coniferyl alcohol to coniferyl acetate, which is an important substrate for synthesizing eugenol. In a genome-wide analysis, we found 90 PmBAHD genes that were phylogenetically clustered into five major groups with motif compositions relatively conserved in each cluster. The phylogenetic tree showed that the PmBAHD67-70 proteins were close to the functional CFATs identified in other species, indicating that these four proteins might function as CFATs. In this work, 2 PmCFAT genes, named PmCFAT1 and PmCFAT2, were cloned from P. mume ‘Sanlunyudie’, which has a strong fragrance. Multiple sequences indicated that PmCFAT1 contained two conserved domains, HxxxD and DFGWG, whereas DFGWG in PmCFAT2 was changed to DFGFG. The expression levels of PmCFAT1 and PmCFAT2 were examined in different flower organs and during the flowering stages of P. mume ‘Sanlunyudie’. The results showed that PmCFAT1 was highly expressed in petals and stamens, and this expression increased from the budding stage to the full bloom stage and decreased in the withering stage, consistent with the patterns of eugenol synthesis and emission. However, the peak of gene expression appeared earlier than those of eugenol synthesis and emission. In addition, the expression level of PmCFAT2 was higher in pistils and sepals than in other organs and decreased from the budding stage to the blooming stage and then increased in the withering stage, which was not consistent with eugenol synthesis. Subcellular localization analysis indicated that PmCFAT1 and PmCFAT2 were located in the cytoplasm and nucleus, while enzyme activity assays showed that PmCFAT1 is involved in eugenol biosynthesis in vitro. Overall, the results suggested that PmCFAT1, but not PmCFAT2, contributed to eugenol synthesis in P. mume.

The Biology of Essential Oils in the Pollination of Flowers

Pollination is an essential biological process in higher plant reproduction that involves the transfer of pollen to the female sexual organs of flowers or cones. It plays a critical role in the reproductive success and evolution of most plant species by allowing plants to share genetic material from other members of the same or closely-related species, thus increasing genetic diversity. In many cases, non-plant organisms are involved in carrying out this cross-pollination, including insects, bats, mammals, and birds. In order to attract such pollinators, plants have evolved the ability to produce a mind-boggling array of volatile compounds that have also found abundant use for humans when collected as essential oils. In this review, we focus on the role of essential oil compounds that are produced by flowers as chemical attractants used to draw in their often highly-specific pollinators. We examine in some detail various questions behind the biology of floral scent, including how these compounds are produced in flowers, how they are detected by potential pollinators, and how biotechnology can be used to alter their activity.

Biosynthesis of 2-Phenylethanol in Rose Petals Is Linked to the Expression of One Allele of RhPAAS

Floral scent is one of the most important characters in horticultural plants. Roses (Rosa spp.) have been cultivated for their scent since antiquity. However, probably by selecting for cultivars with long vase life, breeders have lost the fragrant character in many modern roses, especially the ones bred for the cut flower market. The genetic inheritance of scent characters has remained elusive so far. In-depth knowledge of this quantitative trait is thus very much needed to breed more fragrant commercial cultivars. Furthermore, rose hybrids harbor a composite genomic structure, which complexifies quantitative trait studies. To understand rose scent inheritance, we characterized a segregating population from two diploid cultivars, Rosa × hybrida cv H190 and Rosa wichurana, which have contrasting scent profiles. Several quantitative trait loci for the major volatile compounds in this progeny were identified. One among these loci contributing to the production of 2-phenylethanol, responsible for the characteristic odor of rose, was found to be colocalized with a candidate gene belonging to the 2-phenylethanol biosynthesis pathway: the PHENYLACETALDEHYDE SYNTHASE gene RhPAAS An in-depth allele-specific expression analysis in the progeny demonstrated that only one allele was highly expressed and was responsible for the production of 2-phenylethanol. Unexpectedly, its expression was found to start early during flower development, before the production of the volatile 2-phenylethanol, leading to the accumulation of glycosylated compounds in petals.

Insight on Rosaceae Family with Genome Sequencing and Functional Genomics Perspective

Rosaceae is one of the important families possessing a variety of diversified plant species. It includes many economically valuable crops that provide nutritional and health benefits for the human. Whole genome sequences of valuable crop plants were released in recent years. Understanding of genomics helps to decipher the plant physiology and developmental process. With the information of cultivating species and its wild relative genomes, genome sequence-based molecular markers and mapping loci for economically important traits can be used to accelerate the genome assisted breeding. Identification and characterization of disease resistant capacities and abiotic stress tolerance related genes are feasible to study across species with genome information. Further breeding studies based on the identification of gene loci for aesthetic values, flowering molecular circuit controls, fruit firmness, nonacid fruits, etc. is required for producing new cultivars with valuable traits. This review discusses the whole genome sequencing reports of Malus, Pyrus, Fragaria, Prunus, and Rosa and status of functional genomics of representative traits in individual crops.

Plant Growth Regulators Improve the Production of Volatile Organic Compounds in Two Rose Varieties

The study focused on the influence of the plant growth regulators (PGRs) benzyladenine (BA) and naphthalene acetic acid (NAA) on the production of volatile organic compounds (VOCs) from the flowers of two modern rose varieties, Hybrid Tea and Floribunda. Thirty-six plants of Hybrid Tea and Floribunda were tested. Benzyladenine and naphthalene acetic acid were applied at 0, 100 and 200 mg/L to both rose varieties. Gas chromatography, coupled with flame ionization detection and mass spectrometry, was used to analyze and identify the volatile organic compounds from the flowers. A three-phase fiber 50/30 µm divinylbenzene/carboxen/polydimethylsiloxane was used to capture VOCs, at 2, 4 and 8 weeks, and 4 weeks was selected as it had the highest peak area. In total, 81 and 76 VOCs were detected after treatment of both rose varieties with BA and NAA, respectively. In addition, 20 compounds, which had significant differences between different treatments, were identified from both rose varieties. The majority of VOCs were extracted after the application of 200 mg (BA and NAA) /L of formulation, and four important compounds, cis-muurola-4(141)5-diene, y-candinene, y-muurolene and prenyl acetate, increased significantly compared to the controls. These compounds are commercially important aroma chemicals. This study used the rapid and solvent-free SPME method to show that BA and NAA treatments can result in significant VOC production in the flowers of two rose varieties, enhancing the aromatic value of the flowers. This method has the potential to be applied to other valuable aromatic floricultural plant species.

Rosa hybrida orcinol O-methyl transferase-mediated production of pterostilbene in metabolically engineered grapevine cell cultures

Stilbenes are naturally scarce high-added-value plant compounds with chemopreventive, pharmacological and cosmetic properties. Bioproduction strategies include engineering the metabolisms of bacterial, fungal and plant cell systems. Strikingly, one of the most effective strategies consists in the elicitation of wild grapevine cell cultures, which leads to vast stilbene resveratrol accumulation in the extracellular medium. The combination of both cell culture elicitation and metabolic engineering strategies to produce resveratrol analogs proved more efficient for the hydroxylated derivative piceatannol than for the dimethylated derivative pterostilbene, for which human hydroxylase HsCYP1B1- and grapevine O-methyltransferase VvROMT-transformed cell cultures were respectively used. Rose orcinol O-methyltransferase (OOMT) displays enzymatic properties, which makes it an appealing candidate to substitute VvROMT in the combined strategy to enhance the pterostilbene production level by engineered grapevine cells upon elicitation. Here we cloned a Rosa hybrida OOMT gene, and created a genetic construction suitable for Agrobacterium-mediated plant transformation. OOMT's ability to catalyze the conversion of resveratrol into pterostilbene was first assessed in vitro using protein extracts of agroinfiltrated N. benthamiana leaves and transformed grapevine callus. The grapevine cell cultures transformed with RhOOMT produced about 16 mg/L culture of pterostilbene and reached an extracellular distribution of up to 34% of total production at the best, which is by far the highest production reported to date in a plant system. A bonus large resveratrol production of ca. 1500-3000 mg/L was simultaneously obtained. Our results demonstrate a viable successful metabolic engineering strategy to produce pterostilbene, a resveratrol analog with enhanced pharmacological properties.

Camptotheca acuminata 10-hydroxycamptothecin O-methyltransferase: an alkaloid biosynthetic enzyme co-opted from flavonoid metabolism

The medicinal plant Camptotheca acuminata accumulates camptothecin, 10-hydroxycamptothecin, and 10-methoxycamptothecin as its major bioactive monoterpene indole alkaloids. Here, we describe identification and functional characterization of 10-hydroxycamptothecin O-methyltransferase (Ca10OMT), a member of the Diverse subclade of class II OMTs. Ca10OMT is highly active toward both its alkaloid substrate and a wide range of flavonoids in vitro and in this way contrasts with other alkaloid OMTs in the subclade that only utilize alkaloid substrates. Ca10OMT shows a strong preference for the A-ring 7-OH of flavonoids, which is structurally equivalent to the 10-OH of 10-hydroxycamptothecin. The substrates of other alkaloid OMTs in the subclade bear little similarity to flavonoids, but the 3-D positioning of the 7-OH, A- and C-rings of flavonoids is nearly identical to the 10-OH, A- and B-rings of 10-hydroxycamptothecin. This structural similarity likely explains the retention of flavonoid OMT activity by Ca10OMT and also why kaempferol and quercetin aglycones are potent inhibitors of its 10-hydroxycamptothecin activity. The catalytic promiscuity and strong inhibition of Ca10OMT by flavonoid aglycones in vitro prompted us to investigate the potential physiological roles of the enzyme in vivo. Based on its regioselectivity, kinetic parameters and absence of 7-OMT flavonoids in vivo, we conclude that the major and likely only substrate of Ca10OMTin vivo is 10-hydroxycamptothecin. This is likely accomplished by Ca10OMT being kept spatially separated at the tissue levels from potentially inhibitory flavonoid aglycones, and flavonoid aglycones being rapidly glycosylated to non-inhibitory flavonoid glycosides.

Molecular Cloning and Characterization of a meta/para-O-Methyltransferase from Lycoris aurea

O-methyltransferases (OMTs) have been demonstrated to play key roles in the biosynthesis of plant secondary metabolites, such as alkaloids, isoprenoids, and phenolic compounds. Here, we isolated and characterized an OMT gene from Lycoris aurea (namely LaOMT1), based on our previous transcriptome sequencing data. Sequence alignment and phylogenetic analysis showed that LaOMT1 belongs to the class I OMT, and shares high identity to other known plant OMTs. Also, LaOMT1 is highly identical in its amino acid sequence to NpN4OMT, a norbelladine 4′-OMT from Narcissus sp. aff. pseudonarcissus involved in the biosynthesis of Amaryllidaceae alkaloids. Biochemical analysis indicated that the recombinant LaOMT1 displayed both para and metaO-methylation activities with caffeic acid and 3,4-dihydroxybenzaldehyde, and showed a strong preference for the meta position. Besides, LaOMT1 also catalyzes the O-methylation of norbelladine to form 4′-O-methylnorbelladine, which has been demonstrated to be a universal precursor of all the primary Amaryllidaceae alkaloid skeletons. The results from quantitative real-time PCR assay indicated that LaOMT1 was ubiquitously expressed in different tissues of L. aurea, and its highest expression level was observed in the ovary. Meanwhile, the largest concentration of lycorine and galanthamine were found in the ovary, whereas the highest level of narciclasine was observed in the bulb. In addition, sodium chloride (NaCl), cold, polyethylene glycol (PEG), sodium nitroprusside (SNP), and methyl jasmonate (MeJA) treatments could significantly increase LaOMT1 transcripts, while abscisic acid (ABA) treatment dramatically decreased the expression level of LaOMT1. Subcellular localization showed that LaOMT1 is mainly localized in cytoplasm and endosome. Our results in this study indicate that LaOMT1 may play a multifunctional role, and lay the foundation for Amaryllidaceae alkaloid biosynthesis in L. aurea.

Two-dimensional analysis provides molecular insight into flower scent of Lilium 'Siberia'

Lily is a popular flower around the world not only because of its elegant appearance, but also due to its appealing scent. Little is known about the regulation of the volatile compound biosynthesis in lily flower scent. Here, we conducted an approach combining two-dimensional analysis and weighted gene co-expression network analysis (WGCNA) to explore candidate genes regulating flower scent production. In the approach, changes of flower volatile emissions and corresponding gene expression profiles at four flower developmental stages and four circadian times were both captured by GC-MS and RNA-seq methods. By overlapping differentially-expressed genes (DEGs) that responded to flower scent changes in flower development and circadian rhythm, 3,426 DEGs were initially identified to be candidates for flower scent production, of which 1,270 were predicted as transcriptional factors (TFs). The DEGs were further correlated to individual flower volatiles by WGCNA. Finally, 37, 41 and 90 genes were identified as candidate TFs likely regulating terpenoids, phenylpropanoids and fatty acid derivatives productions, respectively. Moreover, by WGCNA several genes related to auxin, gibberellins and ABC transporter were revealed to be responsible for flower scent production. Thus, this strategy provides an important foundation for future studies on the molecular mechanisms involved in floral scent production.

Characterization of an O-methyltransferase specific to guaiacol-type benzenoids from the flowers of loquat (Eriobotrya japonica)

Volatile benzenoids, including methyl p-methoxybenzoate, p-anisaldehyde, and p-anisalcohol, are responsible for the sweet and characteristic fragrance of loquat (Eriobotrya japonica, Rosaceae) flowers. Although the full pathway of volatile benzenoid synthesis has yet to be elucidated, their chemical structures suggest that O-methyltransferases are present in loquat and function in the methylation of the para-OH groups. In the present study, we used RNA-sequencing to identify four loquat genes (EjOMT1, EjOMT2, EjOMT3, and EjOMT4) that encode O-methyltransferases. We found that EjOMT1 was highly expressed in floral tissues, with an expression pattern that coincided with changes in intracellular volatile benzenoids during flower development. Recombinant EjOMT1 protein expressed in Escherichia coli showed the highest activity towards guaiacol with a K_m value of 35 μM. Furthermore, the protein also showed lesser activities towards guaiacol-type benzenoids including eugenol, isoeugenol, vanillin, and ferulic acid, in addition to much weaker activities towards catechol and p-hydroxybenzenoid derivatives. However, no activity was shown towards phenylpropenes without m-methoxy substitution, t-anol and chavicol. Taken together, our findings indicate that EjOMT1 has a broad substrate specificity towards compounds with both para-OH and meta-OCH₃ groups, unlike previously characterized O-methyltransferases for volatile benzenoid/phenylpropanoid biosynthesis.

O-Methyltransferases involved in biphenyl and dibenzofuran biosynthesis

Biphenyls and dibenzofurans are the phytoalexins of the Malinae involving apple and pear. Biosynthesis of the defence compounds includes two O-methylation reactions. cDNAs encoding the O-methyltransferase (OMT) enzymes were isolated from rowan (Sorbus aucuparia) cell cultures after treatment with an elicitor preparation from the scab-causing fungus, Venturia inaequalis. The preferred substrate for SaOMT1 was 3,5-dihydroxybiphenyl, supplied by the first pathway-specific enzyme, biphenyl synthase (BIS). 3,5-Dihydroxybiphenyl underwent a single methylation reaction in the presence of S-adenosyl-l-methionine (SAM). The second enzyme, SaOMT2, exhibited its highest affinity for noraucuparin, however the turnover rate was greater with 5-hydroxyferulic acid. Both substrates were only methylated at the meta-positioned hydroxyl group. The substrate specificities of the OMTs and the regiospecificities of their reactions were rationalized by homology modeling and substrate docking. Interaction of the substrates with SAM also took place at a position other than the sulfur group. Expression of SaOMT1, SaOMT2 and SaBIS3 was transiently induced in rowan cell cultures by the addition of the fungal elicitor. While the immediate SaOMT1 products were not detectable in elicitor-treated cell cultures, noraucuparin and noreriobofuran accumulated transiently, followed by increasing levels of the SaOMT2 products aucuparin and eriobofuran. SaOMT1, SaOMT2 and SaBIS3 were N- and C-terminally fused with the super cyan fluorescent protein and a modified yellow fluorescent protein, respectively. All the fluorescent reporter fusions were localized to the cytoplasm of Nicotiana benthamiana leaf epidermis cells. A revised biosynthetic pathway of biphenyls and dibenzofurans in the Malinae is presented.

Developmental patterns of emission of scent compounds and related gene expression in roses of the cultivar Rosa x hybrida cv. 'Yves Piaget'

2-Phenylethanol (2PE) and 3,5-dimethoxytoluene (DMT) are characteristic scent compounds in specific roses such as Rosa x hybrida cv. 'Yves Piaget'. We analyzed the endogenous concentrations and emission of 2PE and DMT during the unfurling process in different floral organs, as well as changes in transcript levels of the two key genes, PAR and OOMT2. The emission of both 2PE and DMT increased during floral development to reach peaks at the fully unfurled stage. The relative transcripts of PAR and OOMT2 also increased during floral development. Whereas the maximum for OOMT2 was found at the fully unfurled stage (stage 4), similar expression levels of PAR were detected at stage 4 and the senescence stage (stage 6). The results demonstrate a positive correlation between the expression levels of PAR and OOMT2 and the emission of 2PE and DMT. In addition, endogenous volatiles and relative transcripts showed tissue- and development-specific patterns.

Temporal characterization of 2-phenylethanol in strongly and weakly scented genotypes of damask rose

The molecular and physiological properties of 2-phenylethanol (2-PE) in the strongly scented genotype (SSG) and a weakly scented genotype (WSG) of damask rose at six floral developmental stages were investigated. The chemical compositions of volatile emissions were determined by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analysis of the floral headspace. In both genotypes, the relative percentage of 2-PE increased more in SSG than WSG, as flowers developed. In the petals of damask rose the relative transcript levels of phenyl acetaldehyde reductase (PAR) were higher at stages 3 and 4 in SSG and WSG, respectively. Also, the expression pattern of PAR indicated a significant difference between two genotypes during flower developmental stages. In this study, enzymatic activity leading to the synthesis of 2-PE from the phenyl acetaldehyde (PAld) moderately increased during flower development up to stage 5 in SSG. However, high level of PAR enzymatic activity was observed in stage 3 of WSG. These results indicated that the pattern activity of PAR was different in two used genotypes of damask rose. For SSG, PAR activities were low in early stage of flower development and then gradually increased reaching its highest value at full bloom stage. In WSG, no significant change in enzyme activity was seen after stage 3.

Floral volatiles: from biosynthesis to function

Floral volatiles have attracted humans' attention since antiquity and have since then permeated many aspects of our lives. Indeed, they are heavily used in perfumes, cosmetics, flavourings and medicinal applications. However, their primary function is to mediate ecological interactions between flowers and a diverse array of visitors, including pollinators, florivores and pathogens. As such, they ultimately ensure the plants' reproductive and evolutionary success. To date, over 1700 floral volatile organic compounds (VOCs) have been identified. Interestingly, they are derived from only a few biochemical networks, which include the terpenoid, phenylpropanoid/benzenoid and fatty acid biosynthetic pathways. These pathways are intricately regulated by endogenous and external factors to enable spatially and temporally controlled emission of floral volatiles, thereby fine-tuning the ecological interactions facilitated by floral volatiles. In this review, we will focus on describing the biosynthetic pathways leading to floral VOCs, the regulation of floral volatile emission, as well as biological functions of emitted volatiles.

Biosynthesis of the biphenyl phytoalexin aucuparin in Sorbus aucuparia cell cultures treated with Venturia inaequalis

Aucuparin is the most widely distributed biphenyl phytoalexin in the rosaceous subtribe Pyrinae, which includes the economically important fruit trees apple and pear. The biphenyl scaffold is formed by biphenyl synthase, which catalyzes biosynthesis of 3,5-dihydroxybiphenyl. Conversion of this precursor to aucuparin (3,5-dimethoxy-4-hydroxybiphenyl) was studied in cell cultures of Sorbus aucuparia after treatment with an elicitor preparation from the scab-causing fungus Venturia inaequalis. The sequence of the biosynthetic steps detected was O-methylation - 4-hydroxylation - O-methylation. The two alkylation reactions were catalyzed by distinct methyltransferases, which differed in pH and temperature optima as well as stability. Biphenyl 4-hydroxylase was a microsomal cytochrome P450 monooxygenase, whose activity was appreciably decreased by the addition of established P450 inhibitors. When fed to V. inaequalis-treated S. aucuparia cell cultures, radioactively labeled 3,5-dihydroxybiphenyl was not only incorporated into aucuparin but also into the dibenzofuran eriobofuran, the accumulation of which paralleled that of aucuparin. However, biphenyl 2'-hydroxylase activity proposed to be involved in dibenzofuran formation was detected in neither microsomes nor cell-free extracts in the presence of NADPH and 2-oxoglutarate, respectively. Nevertheless, a basis for studying biphenyl biosynthesis at the gene level is provided.

A methyltransferase essential for the methoxypyrazine-derived flavour of wine

Methoxypyrazines are a family of potent volatile compounds of diverse biological significance. They are used by insects and plants in chemical defence, are present in many vegetables and fruit and, in particular, impart herbaceous/green/vegetal sensory attributes to wines of certain varieties, including Cabernet Sauvignon. While pathways for methoxypyrazine biosynthesis have been postulated, none of the steps have been confirmed genetically. We have used the F2 progeny of a cross between a rapid flowering grapevine dwarf mutant, which does not produce 3-isobutyl-2-methoxypyrazine (IBMP), and Cabernet Sauvignon to identify the major locus responsible for accumulation of IBMP in unripe grape berries. Two candidate methyltransferase genes within the locus were identified and one was significantly associated with berry IBMP levels using association mapping. The enzyme encoded by this gene (VvOMT3) has high affinity for hydroxypyrazine precursors of methoxypyrazines. The gene is not expressed in the fruit of Pinot varieties, which lack IBMP, but is expressed in Cabernet Sauvignon at the time of accumulation of IBMP in the fruit. The results suggest that VvOMT3 is responsible for the final step in methoxypyrazine synthesis in grape berries and is the major determinant of IBMP production.

Veratrole biosynthesis in white campion

White campion (Silene latifolia) is a dioecious plant that emits 1,2-dimethoxybenzene (veratrole), a potent pollinator attractant to the nocturnal moth Hadena bicruris. Little is known about veratrole biosynthesis, although methylation of 2-methoxyphenol (guaiacol), another volatile emitted from white campion flowers, has been proposed. Here, we explore the biosynthetic route to veratrole. Feeding white campion flowers with [(13)C9]l-phenylalanine increased guaiacol and veratrole emission, and a significant portion of these volatile molecules contained the stable isotope. When white campion flowers were treated with the phenylalanine ammonia lyase inhibitor 2-aminoindan-2-phosphonic acid, guaiacol and veratrole levels were reduced by 50% and 63%, respectively. Feeding with benzoic acid (BA) or salicylic acid (SA) increased veratrole emission 2-fold, while [(2)H5]BA and [(2)H6]SA feeding indicated that the benzene ring of both guaiacol and veratrole is derived from BA via SA. We further report guaiacol O-methyltransferase (GOMT) activity in the flowers of white campion. The enzyme was purified to apparent homogeneity, and the peptide sequence matched that encoded by a recently identified complementary DNA (SlGOMT1) from a white campion flower expressed sequence tag database. Screening of a small population of North American white campion plants for floral volatile emission revealed that not all plants emitted veratrole or possessed GOMT activity, and SlGOMT1 expression was only observed in veratrole emitters. Collectively these data suggest that veratrole is derived by the methylation of guaiacol, which itself originates from phenylalanine via BA and SA, and therefore implies a novel branch point of the general phenylpropanoid pathway.

Genetics and genomics of flower initiation and development in roses

Roses hold high symbolic value and great cultural importance in different societies throughout human history. They are widely used as garden ornamental plants, as cut flowers, and for the production of essential oils for the perfume and cosmetic industries. Domestication of roses has a long and complex history, and the rose species have been hybridized across vast geographic areas such as Europe, Asia, and the Middle East. The domestication processes selected several flower characters affecting floral quality, such as recurrent flowering, double flowers, petal colours, and fragrance. The molecular and genetic events that determine some of these flower characters cannot be studied using model species such as Arabidopsis thaliana, or at least only in a limited manner. In this review, we comment on the recent development of genetic, genomic, and transcriptomic tools for roses, and then focus on recent advances that have helped unravel the molecular mechanisms underlying several rose floral traits.

Transcriptome database resource and gene expression atlas for the rose

BACKGROUND

For centuries roses have been selected based on a number of traits. Little information exists on the genetic and molecular basis that contributes to these traits, mainly because information on expressed genes for this economically important ornamental plant is scarce.

RESULTS

Here, we used a combination of Illumina and 454 sequencing technologies to generate information on Rosa sp. transcripts using RNA from various tissues and in response to biotic and abiotic stresses. A total of 80714 transcript clusters were identified and 76611 peptides have been predicted among which 20997 have been clustered into 13900 protein families. BLASTp hits in closely related Rosaceae species revealed that about half of the predicted peptides in the strawberry and peach genomes have orthologs in Rosa dataset. Digital expression was obtained using RNA samples from organs at different development stages and under different stress conditions. qPCR validated the digital expression data for a selection of 23 genes with high or low expression levels. Comparative gene expression analyses between the different tissues and organs allowed the identification of clusters that are highly enriched in given tissues or under particular conditions, demonstrating the usefulness of the digital gene expression analysis. A web interface ROSAseq was created that allows data interrogation by BLAST, subsequent analysis of DNA clusters and access to thorough transcript annotation including best BLAST matches on Fragaria vesca, Prunus persica and Arabidopsis. The rose peptides dataset was used to create the ROSAcyc resource pathway database that allows access to the putative genes and enzymatic pathways.

CONCLUSIONS

The study provides useful information on Rosa expressed genes, with thorough annotation and an overview of expression patterns for transcripts with good accuracy.

PAP1 transcription factor enhances production of phenylpropanoid and terpenoid scent compounds in rose flowers

• Floral scent is a complex trait of biological and applied significance. To evaluate whether scent production originating from diverse metabolic pathways (e.g. phenylpropanoids and isoprenoids) can be affected by transcriptional regulators, Arabidopsis PRODUCTION OF ANTHOCYANIN PIGMENT1 (PAP1) transcription factor was introduced into Rosa hybrida. • Color and scent profiles of PAP1-transgenic and control (β-glucuronidase-expressing) rose flowers and the expression of key genes involved in the production of secondary metabolites were analyzed. To evaluate the significance of the scent modification, olfactory trials were conducted with both humans and honeybees. • In addition to increased levels of phenylpropanoid-derived color and scent compounds when compared with control flowers, PAP1-transgenic rose lines also emitted up to 6.5 times higher levels of terpenoid scent compounds. Olfactory assay revealed that bees and humans could discriminate between the floral scents of PAP1-transgenic and control flowers. • The increase in volatile production in PAP1 transgenes was not caused solely by transcriptional activation of their respective biosynthetic genes, but probably also resulted from enhanced metabolic flux in both the phenylpropanoid and isoprenoid pathways. The mechanism(s) governing the interactions in these metabolic pathways that are responsible for the production of specialized metabolites remains to be elucidated.

Co-expression of VpROMT gene from Chinese wild Vitis pseudoreticulata with VpSTS in tobacco plants and its effects on the accumulation of pterostilbene

Plant secondary metabolites, such as stilbenes, have fungicidal potential and have been found in several plant species. Stilbenes in grapevine, such as resveratrol and pterostilbene, have recently attracted much attention, they are not only helping the plant to fight against pathogen attack, but they are also being widely used as ingredients of fungicide, anti-inflammatory drugs, antioxidant, and anti-infective agents. However, resveratrol O-methyltransferase gene, related with the synthesis of pterostilbene from resveratrol, has not been characterized effectively from Chinese wild Vitis pseudoreticulata. In this study, a candidate of resveratrol O-methyltransferase gene designated as VpROMT was isolated from a powdery mildew-resistant Chinese wild V. pseudoreticulata 'Baihe-35-1', and characterization studies were performed. Expression studies showed that VpROMT was predominantly expressed in developing roots yet not found in the leaves, stems, nor tendrils when the plants are not challenged. Results of qRT-PCR showed that VpROMT was rapidly induced by Erysiphe necator in V. pseudoreticulata and by methyl-jasmonate, UV-irradiation in suspension culture cells of Vitis romanetii. The expression level varies in different tissues of grapevine, which MeJA and UV-C treatment significantly upregulated the expression of VpROMT gene while UV-B treatment failed to. Co-expression of VpROMT and grapevine stilbene synthase (VpSTS) gene leads to the accumulation of pterostilbene in leaves of tobacco (Nicotiana tabacum) indicating that VpROMT was able to catalyze the biosynthesis of pterostilbene from resveratrol in over-expression transgenic tobacco plants.

Characterization of three O-methyltransferases involved in noscapine biosynthesis in opium poppy

Noscapine is a benzylisoquinoline alkaloid produced in opium poppy (Papaver somniferum) and other members of the Papaveraceae. It has been used as a cough suppressant and more recently was shown to possess anticancer activity. However, the biosynthesis of noscapine in opium poppy has not been established. A proposed pathway leading from (S)-reticuline to noscapine includes (S)-scoulerine, (S)-canadine, and (S)-N-methylcanadine as intermediates. Stem cDNA libraries and latex extracts of eight opium poppy cultivars displaying different alkaloid profiles were subjected to massively parallel pyrosequencing and liquid chromatography-tandem mass spectrometry, respectively. Comparative transcript and metabolite profiling revealed the occurrence of three cDNAs encoding O-methyltransferases designated as SOMT1, SOMT2, and SOMT3 that correlated with the accumulation of noscapine in the eight cultivars. SOMT transcripts were detected in all opium poppy organs but were most abundant in aerial organs, where noscapine primarily accumulates. SOMT2 and SOMT3 showed strict substrate specificity and regiospecificity as 9-O-methyltransferases targeting (S)-scoulerine. In contrast, SOMT1 was able to sequentially 9- and 2-O-methylate (S)-scoulerine, yielding (S)-tetrahydropalmatine. SOMT1 also sequentially 3'- and 7-O-methylated both (S)-norreticuline and (S)-reticuline with relatively high substrate affinity, yielding (S)-tetrahydropapaverine and (S)-laudanosine, respectively. The metabolic functions of SOMT1, SOMT2, and SOMT3 were investigated in planta using virus-induced gene silencing. Reduction of SOMT1 or SOMT2 transcript levels resulted in a significant decrease in noscapine accumulation. Reduced SOMT1 transcript levels also caused a decrease in papaverine accumulation, confirming the selective roles for these enzymes in the biosynthesis of both alkaloids in opium poppy.

Methyl eugenol: its occurrence, distribution, and role in nature, especially in relation to insect behavior and pollination

This review discusses the occurrence and distribution (within a plant) of methyl eugenol in different plant species (> 450) from 80 families spanning many plant orders, as well as various roles this chemical plays in nature, especially in the interactions between tephritid fruit flies and plants.

Genomic approach to study floral development genes in Rosa sp

Cultivated for centuries, the varieties of rose have been selected based on a number of flower traits. Understanding the genetic and molecular basis that contributes to these traits will impact on future improvements for this economically important ornamental plant. In this study, we used scanning electron microscopy and sections of meristems and flowers to establish a precise morphological calendar from early rose flower development stages to senescing flowers. Global gene expression was investigated from floral meristem initiation up to flower senescence in three rose genotypes exhibiting contrasted floral traits including continuous versus once flowering and simple versus double flower architecture, using a newly developed Affymetrix microarray (Rosa1_Affyarray) tool containing sequences representing 4765 unigenes expressed during flower development. Data analyses permitted the identification of genes associated with floral transition, floral organs initiation up to flower senescence. Quantitative real time PCR analyses validated the mRNA accumulation changes observed in microarray hybridizations for a selection of 24 genes expressed at either high or low levels. Our data describe the early flower development stages in Rosa sp, the production of a rose microarray and demonstrate its usefulness and reliability to study gene expression during extensive development phases, from the vegetative meristem to the senescent flower.

Functional characterization of rose phenylacetaldehyde reductase (PAR), an enzyme involved in the biosynthesis of the scent compound 2-phenylethanol

2-Phenylethanol (2PE) is a prominent scent compound released from flowers of Damask roses (Rosa×damascena) and some hybrid roses (Rosa 'Hoh-Jun' and Rosa 'Yves Piaget'). 2PE is biosynthesized from l-phenylalanine (l-Phe) via the intermediate phenylacetaldehyde (PAld) by two key enzymes, aromatic amino acid decarboxylase (AADC) and phenylacetaldehyde reductase (PAR). Here we describe substrate specificity and cofactor preference in addition to molecular characterization of rose-PAR and recombinant PAR from R.×damascena. The deduced amino acid sequence of the full-length cDNA encoded a protein exhibiting 77% and 75% identity with Solanum lycopersicum PAR1 and 2, respectively. The transcripts of PAR were higher in petals than calyxes and leaves and peaking at the unfurling stage 4. Recombinant PAR and rose-PAR catalyzed reduction of PAld to 2PE using NADPH as the preferred cofactor. Reductase activity of rose-PAR and recombinant PAR were higher for aromatic and aliphatic aldehydes than for keto-carbonyl groups. Both PARs showed that (S)-[4-(2)H] NADPH was preferentially used over the (R)-[4-(2)H] isomer to give [1-(2)H]-2PE from PAld, indicating that PAR can be classified as short-chain dehydrogenase reductase (SDR).

Two O-methyltransferases involved in the biosynthesis of methoxypyrazines: grape-derived aroma compounds important to wine flavour

Methoxypyrazines (MPs) are volatile, grape-derived aroma compounds that contribute to the distinct herbaceous characters of some wines. Although the full pathway leading to MP production has not been elucidated, there is strong evidence that the final step involves the methylation of non-volatile hydroxypyrazine (HP) precursors. Two cDNA encoding O-methyltransferases (OMTs) that have homology to an enzyme previously purified and shown to catalyse the methylation of HPs were isolated from Cabernet Sauvignon. Recombinant protein from the cDNAs (VvOMT1 and VvOMT2) was produced in E. coli and activity assays demonstrated that both encode OMTs able to methylate HPs to produce MPs, however both showed greatest activity against the flavonol quercetin. VvOMT1 has higher catalytic activity against isobutyl hydroxypyrazine compared to isopropyl hydroxypyrazine, whereas the converse is true for VvOMT2. The timing of the expression of VvOMT1 in the skin and the flesh of developing Cabernet Sauvignon grape berries was associated with the period of MP accumulation in these tissues, while VvOMT2 expression was greatest in roots, which were found to contain high levels of MPs. The MP composition of these tissues also reflects the relative levels of expression of these genes and their substrate preference. The identification of genes responsible for MP production in grapevine will help in understanding the effect of different viticultural and environmental factors on MP accumulation.

Genetic dissection of scent metabolic profiles in diploid rose populations

The scent of flowers is a very important trait in ornamental roses in terms of both quantity and quality. In cut roses, scented varieties are a rare exception. Although metabolic profiling has identified more than 500 scent volatiles from rose flowers so far, nothing is known about the inheritance of scent in roses. Therefore, we analysed scent volatiles and molecular markers in diploid segregating populations. We resolved the patterns of inheritance of three volatiles (nerol, neryl acetate and geranyl acetate) into single Mendelian traits, and we mapped these as single or oligogenic traits in the rose genome. Three other volatiles (geraniol, beta-citronellol and 2-phenylethanol) displayed quantitative variation in the progeny, and we mapped a total of six QTLs influencing the amounts of these volatiles onto the rose marker map. Because we included known scent related genes and newly generated ESTs for scent volatiles as markers, we were able to link scent related QTLs with putative candidate genes. Our results serve as a starting point for both more detailed analyses of complex scent biosynthetic pathways and the development of markers for marker-assisted breeding of scented rose varieties.

Identification of rose phenylacetaldehyde synthase by functional complementation in yeast

Rose flowers, like flowers and fruits of many other plants, produce and emit the aromatic volatiles 2-phenylacetaldehyde (PAA) and 2-phenylethylalchohol (PEA) which have a distinctive flowery/rose-like scent. Previous studies in rose have shown that, similar to petunia flowers, PAA is formed from L: -phenylalanine via pyridoxal-5'-phosphate-dependent L: -aromatic amino acid decarboxylase. Here we demonstrate the use of a Saccharomyces cerevisiae aro10 mutant to functionally characterize a Rosa hybrida cv. Fragrance Cloud sequence (RhPAAS) homologous to petunia phenylacetaldehyde synthase (PhPAAS). Volatile headspace analysis of the aro10 knockout strain showed that it produces up to eight times less PAA and PEA than the WT. Expression of RhPAAS in aro10 complemented the yeast's mutant phenotype and elevated PAA levels, similar to petunia PhPAAS. PEA production levels were also enhanced in both aro10 and WT strains transformed with RhPAAS, implying an application for metabolic engineering of PEA biosynthesis in yeast. Characterization of spatial and temporal RhPAAS transcript accumulation in rose revealed it to be specific to floral tissues, peaking in mature flowers, i.e., coinciding with floral scent production and essentially identical to other rose scent-related genes. RhPAAS transcript, as well as PAA and PEA production in flowers, displayed a daily rhythmic behavior, reaching peak levels during the late afternoon hours. Examination of oscillation of RhPAAS transcript levels under free-running conditions suggested involvement of the endogenous clock in the regulation of RhPAAS expression in rose flowers.

SAM levels, gene expression of SAM synthetase, methionine synthase and ACC oxidase, and ethylene emission from N. suaveolens flowers

S'adenosyl-L: -methionine (SAM) is a ubiquitous methyl donor and a precursor in the biosynthesis of ethylene, polyamines, biotin, and nicotianamine in plants. Only limited information is available regarding its synthesis (SAM cycle) and its concentrations in plant tissues. The SAM concentrations in flowers of Nicotiana suaveolens were determined during day/night cycles and found to fluctuate rhythmically between 10 and 50 nmol g(-1) fresh weight. Troughs of SAM levels were measured in the evening and night, which corresponds to the time when the major floral scent compound, methyl benzoate, is synthesized by a SAM dependent methyltransferase (NsBSMT) and when this enzyme possesses its highest activity. The SAM synthetase (NsSAMS1) and methionine synthase (NsMS1) are enzymes, among others, which are involved in the synthesis and regeneration of SAM. Respective genes were isolated from a N. suaveolens petal cDNA library. Transcript accumulation patterns of both SAM regenerating enzymes matched perfectly those of the bifunctional NsBSMT; maximum mRNA accumulations of NsMS1 and NsSAMS1 were attained in the evening. Ethylene, which is synthesized from SAM, reached only low levels of 1-2 ppbv in N. suaveolens flowers. It is emitted in a burst at the end of the life span of the flowers, which correlates with the increased expression of the 1-aminocyclopropane-1-carboxylate oxidase (NsACO).

Flavour compounds in tomato fruits: identification of loci and potential pathways affecting volatile composition

The unique flavour of a tomato fruit is the sum of a complex interaction among sugars, acids, and a large set of volatile compounds. While it is generally acknowledged that the flavour of commercially produced tomatoes is inferior, the biochemical and genetic complexity of the trait has made breeding for improved flavour extremely difficult. The volatiles, in particular, present a major challenge for flavour improvement, being generated from a diverse set of lipid, amino acid, and carotenoid precursors. Very few genes controlling their biosynthesis have been identified. New quantitative trait loci (QTLs) that affect the volatile emissions of red-ripe fruits are described here. A population of introgression lines derived from a cross between the cultivated tomato Solanum lycopersicum and its wild relative, S. habrochaites, was characterized over multiple seasons and locations. A total of 30 QTLs affecting the emission of one or more volatiles were mapped. The data from this mapping project, combined with previously collected data on an IL population derived from a cross between S. lycopersicum and S. pennellii populations, were used to construct a correlational database. A metabolite tree derived from these data provides new insights into the pathways for the synthesis of several of these volatiles. One QTL is a novel locus affecting fruit carotenoid content on chromosome 2. Volatile emissions from this and other lines indicate that the linear and cyclic apocarotenoid volatiles are probably derived from separate carotenoid pools.