The gene for fragrance in rice

The flavour or fragrance of basmati and jasmine rice is associated with the presence of 2-acetyl-1-pyrroline. A recessive gene (fgr) on chromosome 8 of rice has been linked to this important trait. Here, we show that a gene with homology to the gene that encodes betaine aldehyde dehydrogenase (BAD) has significant polymorphisms in the coding region of fragrant genotypes relative to non-fragrant genotypes. The accumulation of 2-acetyl-1-pyrroline in fragrant rice genotypes may be explained by the presence of mutations resulting in a loss of function of the fgr gene product. The allele in fragrant genotypes has a mutation introducing a stop codon upstream of key amino acid sequences conserved in other BADs. The fgr gene corresponds to the gene encoding BAD2 in rice, while BAD1 is encoded by a gene on chromosome 4. BAD has been linked to stress tolerance in plants. However, the apparent loss of function of BAD2 does not seem to limit the growth of fragrant rice genotypes. Fragrance in domesticated rice has apparently originated from a common ancestor and may have evolved in a genetically isolated population, or may be the outcome of a separate domestication event. This is an example of effective human selection for a recessive trait during domestication.     

Marine fragrance chemistry

The main marine message in perfumery is projected by Calone 1951 (7-methyl-2H-1,5-benzodioxepin-3(4H)-one). Kraft (Givaudan) and Gaudin (Firmenich) further maximized the marine fragrance molecular membership by extending the carbon chain of the 7-Me group. Our research targeted the polar group of the benzodioxepinone parent compound to investigate how this region of molecular makeup resonates with the dominant marine fragrance of the Calone 1951 structure. The olfactory evaluation of analogues prepared by chemical modification or removal of the CO group resulted in the introduction of aldehydic, sweet and floral-fruity notes with a diluted/diminished potency of the marine odor. To further analyze the olfactory properties of benzodioxepinones containing a diverse range of aromatic ring substituents, a novel synthesis route was developed. We found that a 7-alkyl group in Calone 1951 was essential for the maintenance of the significant marine odor characteristic, and our studies support the concept that the odorant structure occupying the hydrophobic binding pocket adjacent to the aromatic ring-binding site of the olfactory receptor is pivotal in the design and discovery of more potent and characteristic marine fragrances. How the structure of benzodioxepinones connects to marine sea-breeze fragrances is our continuing challenging research focus at the chemistry-biology interface.     

The search for new fragrance ingredients for functional perfumery

Functional perfumery is an integral part of the fragrance business. It demands that the ingredients chosen for compounding withstand the aggressive nature of some of the bases used for soaps, detergents, softeners, bleach, and personal-care products. The synthetic efforts in this area reported in this short personal account, presented in a talk at the RSC/SCI conference Flavours & Fragrances 2004 (Manchester), have resulted in the discovery of the two new proprietary molecules Fleuranil (5/6) and Khusinil (7), which fulfill the criteria of functional perfumery. The structure-odor relationships of several analogs of Fleuranil and Khusinil prepared in the course of these investigations are also presented.     

Homogeneous asymmetric catalysis in fragrance chemistry

Opposite enantiomers of a chiral fragrance may exhibit different olfactory activities making a synthesis in high enantiomeric purity commercially and scientifically interesting. Accordingly, the asymmetric synthesis of four chiral odorants, Fixolide, Phenoxanol, Citralis, and Citralis Nitrile, has been investigated with the aim to develop practically feasible processes. In the devised synthetic schemes, the key step that leads to the formation of the stereogenic center is the homogeneous asymmetric hydrogenation of a prochiral olefin. By an appropriate choice of the catalyst and the reaction conditions, Phenoxanol, Citralis, and Citralis Nitrile were obtained in high enantiomeric purity, and odor profiles of the single enantiomers were determined.     

Rhythms of fragrance emission in flowers

A method for the sampling of volatiles emitted by individual flowers is described. Sampling over periods of 3 h allowed the examination of diurnal changes in quantity and quality of fragrance. In the species studied, Odontoglossum constrictum Lindl., Citrus medica L., Hoya carnosa R. Br., and Stephanotis floribunda Brongs., the fragrance was characterized by a few major components accompanied by a larger number of minor components. Flowers of all species produced volatiles in a rhythmical, diurnal fashion. Whereas in detached flowers of O. constrictum and C. medica rhythmicity could be observed for up to four cycles, flowers of H. carnosa showed this phenomenon only when attached to the plant. Maxima of emission were observed during the day in C. medica and O. constrictum whereas in H. carnosa it occurred during the night. In S. floribunda a conspicuous asynchronism of the emission of different volatiles was observed, resulting in the rhythmical change of fragrance quality.     

Inactivation of an aminoaldehyde dehydrogenase is responsible for fragrance in rice

Rice (Oryza sativa) has two betaine aldehyde dehydrogenase homologs, BAD1 and BAD2, encoded on chromosome four and chromosome eight respectively. BAD2 is responsible for the characteristic aroma of fragrant rice. Complementary DNA clones of both BAD1 and BAD2 were isolated and expressed in E. coli. BAD2 had optimum activity at pH 10, little to no affinity towards N-acetyl-gamma-aminobutyraldehyde (NAGABald) with a Km of approximately 10 mM and moderate affinity towards gamma-guanidinobutyraldehyde (GGBald) and betaine aldehyde (bet-ald) with Km values of approximately 260 microM and 63 microM respectively. A lower Km of approximately 9 microM was observed with gamma-aminobutyraldehyde (GABald), suggesting BAD2 has a higher affinity towards this substate in vivo. The enzyme encoded on chromosome four, BAD1, had optimum activity at pH 9.5, showed little to no affinity towards bet-ald with a Km of 3 mM and had moderate affinity towards GGBald, NAGABald and GABald with Km values of approximately 545, 420 and 497 microM respectively. BAD1 had a half life roughly double that of BAD2. We discuss the implications of these findings on the pathway of fragrance generation in Basmati and Jasmine rice and the potential of rice to accumulate the osmoprotectant glycine betaine.     

Genetic aspects of floral fragrance in plants

It is generally assumed that compounds are emitted from flowers in order to attract and guide pollinators. Due to the invisibility and the highly variable nature of floral scent, no efficient and reliable methods to screen for genetic variation have been developed. Moreover, no convenient plant model systems are available for flower scent studies. In the past decade, several floral fragrance-related genes have been cloned; the biosynthesis and metabolic engineering of floral volatiles have been studied with the development of biotechnology. This review summarizes the reported floral fragrance-related genes and the biosynthesis of floral scent compounds, introduces the origin of new modification enzymes for flower scent, compares different methods for floral fragrance-related gene cloning, and discusses the metabolic engineering of floral scent. Finally, the perspectives and prospects of research on floral fragrance are presented. Published in Russian in Biokhimiya, 2007, Vol. 72, No. 4, pp. 437–446.     

The fragrance of Biblical Mandrake

Mandrake (Mandragora officinaruim), nearly forgotten today, is one of the most famous plants known to humanity. For thousands of years, this plant was revered by many cultures, which ascribed to it mysterious and demonic qualities. Mandrake is mentioned in the Bible (Gen. 30:14-16) and its Biblical use is generally attributed to its supposed fertility power. A detailed study of Pentateuch text and the various commentaries allowed us to re-evaluate the role of mandrake in Biblical events. Sufficient evidence was found to conclude that the appearance of this plant on the Biblical scene is not due, as was commonly believed, to alleged magic power of its root, but to the unique fragrance furnished by the fruits of mandrake. It seems that the Scripture clearly connects the fragrance of mandrake with sexuality, which is the only known account of direct link between odor and human sexual response. Fifty-five principle odoriferous constituents were identified in rather bizarre chemical composition of mandrake aroma. It will be of assistance for a suggested scientific study of potential aphrodisiac effect of mandrake fragrance.     

Psychology of fragrance use: perception of individual odor and perfume blends reveals a mechanism for idiosyncratic effects on fragrance choice

Cross-culturally, fragrances are used to modulate body odor, but the psychology of fragrance choice has been largely overlooked. The prevalent view is that fragrances mask an individual's body odor and improve its pleasantness. In two experiments, we found positive effects of perfume on body odor perception. Importantly, however, this was modulated by significant interactions with individual odor donors. Fragrances thus appear to interact with body odor, creating an individually-specific odor mixture. In a third experiment, the odor mixture of an individual's body odor and their preferred perfume was perceived as more pleasant than a blend of the same body odor with a randomly-allocated perfume, even when there was no difference in pleasantness between the perfumes. This indicates that fragrance use extends beyond simple masking effects and that people choose perfumes that interact well with their own odor. Our results provide an explanation for the highly individual nature of perfume choice.     

The genetic origin of fragrance in NERICA1

In this study, we investigated the cause and origin of fragrance in NERICA1, a fragrant rice inbred line developed from an interspecific cross between two non-fragrant parents. The genetic cause of fragrance in NERICA1 was found to be due to a previously reported mutation in the BADH2 gene, the same allele responsible for the majority of modern fragrant rice varieties. Haplotype analysis around the BADH2 gene in NERICA1, its parents, and 95 other varieties carrying the badh2.1 allele identified the source of the badh2.1 allele in NERICA1 was a fragrant tropical japonica variety, WAB638-1, which had been growing in the vicinity of the NERICA1 nursery during varietal development. The allele-specific marker for the badh2.1 allele consistently predicted fragrance in the diverse African germplasm tested, making it very useful for marker-assisted breeding of fragrant rice varieties in Africa.     

Genetic and molecular basis of fragrance in rice

Fragrance or aroma in rice is considered as a special trait with huge economic importance that determines the premium price in global trade. With the availability of molecular maps and genome sequences, a major gene for fragrance (badh2) was identified on chromosome 8. An 8-bp deletion in the exon 7 of this gene was reported to result in truncation of betaine aldehyde dehydrogenease enzyme whose loss-of-function lead to the accumulation of a major aromatic compound, 2-acetyl 1-pyrroline (2AP) in fragrant rice. However, several studies have reported exceptions to this mutation and indicated the involvement of other genetic loci in controlling fragrance trait. These studies emphasize the need to characterize the fragrance and its underlying factors in a wide range of genetic resources available for this trait. This review summarizes the new insights gained on the genetic and molecular understanding of fragrance in rice.     

芳香族香料化合物生物合成研究进展

芳香族化合物在香料中占很大的比重,传统生产方式有化学合成和植物提取。化学合成依赖于石油资源,并具有环境不友好、反应条件恶劣等缺点。植物提取方法受限于植物资源,且占用耕地。近年来,随着代谢工程和合成生物学技术的发展,利用可再生原料,微生物合成芳香族香料化合物成为一种新的生产方式。文中介绍了大肠杆菌和酵母菌等模式微生物合成芳香族香料的研究进展,包括利用莽草酸途径合成香兰素等,聚酮途径合成覆盆子酮等。综述重点介绍了生物合成途径解析、人工合成途径创建及代谢调控等,为微生物发酵法生产芳香族香料化合物提供参考。     

Phylogenetic fragrance patterns in Nicotiana sections Alatae and Suaveolentes

We analyzed floral volatiles from eight tobacco species (Nicotiana; Solanaceae) including newly discovered Brazilian taxa (Nicotiana mutabilis and "Rastroensis") in section Alatae. Eighty-four compounds were found, including mono- and sesquiterpenoids, nitrogenous compounds, benzenoid and aliphatic alcohols, aldehydes and esters. Floral scent from recent accessions of Nicotiana alata, Nicotiana bonariensis and Nicotiana langsdorffii differed from previously published data, suggesting intraspecific variation in scent composition at the level of biosynthetic class. Newly discovered taxa in Alatae, like their relatives, emit large amounts of 1,8-cineole and smaller amounts of monoterpenes on a nocturnal rhythm, constituting a chemical synapomorphy for this lineage. Fragrance data from three species of Nicotiana sect. Suaveolentes, the sister group of Alatae, (two Australian species: N. cavicola, N. ingulba; one African species: N. africana), were compared to previously reported data from their close relative, N. suaveolens. Like N. suaveolens, N. cavicola and N. ingulba emit fragrances dominated by benzenoids and phenylpropanoids, whereas the flowers of N. africana lacked a distinct floral scent and instead emitted only small amounts of an aliphatic methyl ester from foliage. Interestingly, this ester also is emitted from foliage of N. longiflora and N. plumbaginifolia (both in section Alatae s.l.), which share a common ancestor with N. africana. This result, combined with the synapomorphic pattern of 1,8 cineole emission in Alatae s.s., suggests that phylogenetic signal explains a major component of fragrance composition among tobacco species in sections Alatae and Suaveolentes. At the intraspecific level, interpopulational scent variation is widespread in sect. Alatae, and may reflect edaphic specialization, introgression, local pollinator shifts, genetic drift or artificial selection in cultivation. Further studies with genetically and geographically well-defined populations are needed to distinguish between these possibilities.     

Further observations on rhythmic emission of fragrance in flowers

Observations regarding floral fragrance and the rhythmicity of its emission in four plant species are reported. In the case of flowers of Hoya carnosa R. Br. which are characterized by circadian rhythmicity of scentedness (R. Altenburger and P. Matile, 1988, Planta 174, 248–252), temperature compensation of the free-running period as well as persistence of oscillations in permanent darkness have been demonstrated. A hitherto unidentified component of fragrance turned out to be identical to an unusual sesquiterpene recently discovered in cardamom oil (B. Maurer et al., 1986, Tetrahedron Lett. 27, 2111–2112). In Stephanotis floribunda Brongs. the rhythmic emission of fragrance is circadian in nature, but in a constant environment the oscillations of individual components are increasingly asynchronous. In excised flowers of Odontoglossum constrictum Lindl. the diurnal oscillations observed in a natural photoperiod are abolished under constant environmental conditions. They are resumed upon the return to a 1212-h photoperiod. The absence of circadian control could also be demonstrated in excised flowers of Citrus medica L. In this species, too, the daily maxima of scent emission reappear upon the transfer of flowers to a 1212-h light/ dark cycle. Results obtained upon the comparative analysis of volatiles in the headspace above the flowers and in petal extract indicate that the relative abundance of an individual compound in the floral fragrance is not a function of differential volatility.Abbreviations DL 1212 h photoperiod - DD continuous darkness - GLC gas-liquid chromatography - LL continuous illumination The authors are indebted to R. Kaiser, Givaudon Corp.for kindly carrying out the identifikation of volatiles by gas-liquid chromalography/mass spectrometry.     

PCR-based molecular markers for the fragrance gene in rice (Oryza sativa. L.)

The genomic DNA clone RG28, linked to the major fragrance gene of rice (fgr), was assessed for polymorphism in order to produce a PCR-based marker for fragrance. A small mono-nucleotide repeat, that was polymorphic between a pair of fragrant and non-fragrant cultivars, was identified and developed into a co-dominant PCR-based marker. The polymorphism-information-content determinations for three microsatellite markers, that have been genetically mapped near RG28, are also presented. These PCR-based markers will be highly useful in distinguishing fragrance-producing alleles from non-fragrance-producing alleles at the fgr locus. Received: 19 October 1999 / Accepted: 16 December 1999