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In plants, the contribution of the plasmotype (mitochondria and chloroplast) in controlling the circadian clock plasticity and possible consequences on cytonuclear genetic makeup have yet to be fully elucidated. A genome‐wide association study in the wild barley (Hordeum vulgare ssp. spontaneum) B1K collection identified overlap with our previously mapped DRIVERS OF CLOCKS (DOCs) loci in wild‐cultivated interspecific population. Moreover, we identified non‐random segregation and epistatic interactions between nuclear DOCs loci and the chloroplastic RpoC1 gene, indicating an adaptive value for specific cytonuclear gene combinations. Furthermore, we show that DOC1.1, which harbours the candidate SIGMA FACTOR‐B (SIG‐B) gene, is linked with the differential expression of SIG‐B and CCA1 genes and contributes to the circadian gating response to heat. High‐resolution temporal growth and photosynthesis measurements of B1K also link the DOCs loci to differential growth, Chl content and quantum yield. To validate the involvement of the Plastid encoded polymerase (PEP) complex, we over‐expressed the two barley chloroplastic RpoC1 alleles in Arabidopsis and identified significant differential plasticity under elevated temperatures. Finally, enhanced clock plasticity of de novo ENU (N‐Ethyl‐N‐nitrosourea) ‐induced barley rpoB1 mutant further implicates the PEP complex as a key player in regulating the circadian clock output. Overall, this study highlights the contribution of specific cytonuclear interaction between rpoC1 (PEP gene) and SIG‐B with distinct circadian timing regulation under heat, and their pleiotropic effects on growth implicate an adaptive value. [ABSTRACT FROM AUTHOR]

Diversification and breeding following domestication and under current climate change across the globe are the two most significant evolutionary events experienced by major crops. Diversification of crops from their wild ancestors has favored dramatic changes in the sensitivity of the plants to the environment, particularly significantly in transducing light inputs to the circadian clock, which has allowed the growth of major crops in the relatively short growing season experienced in the Northern Hemisphere. Historically, mutants and the mapping of quantitative trait loci (QTL) have facilitated the identification and the cloning of genes that underlie major changes of the clock and the regulation of flowering. Recent studies have suggested that the thermal plasticity of the circadian clock output, and not just the core genes that follow temperature compensation, has also been under selection during diversification and breeding. Wild alleles that accelerate output rhythmicity could be beneficial for crop resilience. Furthermore, wild alleles with beneficial and flowering-independent effects under stress indicate their possible role in maintaining a balanced source–sink relationship, thereby allowing productivity under climatic change. Because the chloroplast genome also regulates the plasticity of the clock output, mapping populations including cytonuclear interactions should be utilized within an integrated field and clock phenomics framework. In this review, we highlight the need to integrate physiological and developmental approaches (physio-devo) to gain a better understanding when re-domesticating wild gene alleles into modern cultivars to increase their robustness under abiotic heat and drought stresses. [ABSTRACT FROM AUTHOR]

The overdominant model of heterosis explains the superior phenotype of hybrids by synergistic allelic interaction within heterozygous loci. To map such genetic variation in yeast, we used a population doubling time dataset of Saccharomyces cerevisiae 16 x 16 diallel and searched for major contributing heterotic trait loci (HTL). Heterosis was observed for the majority of hybrids, as they surpassed their best parent growth rate. However, most of the local heterozygous loci identified by genome scan were surprisingly underdominant, i.e., reduced growth. We speculated that in these loci adverse effects on growth resulted from incompatible allelic interactions. To test this assumption, we eliminated these allelic interactions by creating hybrids with local hemizygosity for the underdominant HTLs, as well as for control random loci. Growth of hybrids was indeed elevated for most hemizygous to HTL genes but not for control genes, hence validating the results of our genome scan. Assessing the consequences of local heterozygosity by reciprocal hemizygosity and allele replacement assays revealed the influence of genetic background on the underdominant effects of HTLs. Overall, this genome-wide study on a multi-parental hybrid population provides a strong argument against single gene overdominance as a major contributor to heterosis, and favors the dominance complementation model. Keywords: heterosis, Saccharomyces cerevisiae, nonadditive inheritance, genome-wide association, underdominance. Le modele de surdominance pour l'heterosis explique le phenotype superieur des hybrides comme etant le resultat d'interactions alleliques synergiques au sein de locus heterozygotes. Pour cartographier une telle variation genetique chez la levure, les auteurs ont utilise un jeu de donnees sur le temps de doublement au sein d'une population de Saccharomyces cerevisiae issue d'un diallele 16 x 16. Les auteurs ont ensuite recherche des locus majeurs contribuant a l'heterosis (HTL pour << heterotic trait loci >>). L'heterosis a ete observee pour la majorite des hybrides, puisqu'ils presentaient un taux de croissance superieur a leurs parents. Cependant, la plupart des locus heterozygotes locaux identifies lors d'un balayage genomique presentaient, etonnamment, de la sous-dominance puisqu'ils etaient associes aune croissance reduite. Les auteurs ont specule que, chez ces locus, des effets negatifs sur la croissance seraient le resultat d'interactions alleliques incompatibles. Pour verifier cette hypothese, ces interactions alleliques ont ete eliminees en creant des hybrides hemizygotes pour les HTL sous-dominants, de meme que pour des locus aleatoires comme temoins. La croissance des hybrides s'est en effet averee plus rapide pour la plupart des hybrides hemizygotes pour les genes HTL, mais pas pour les temoins, validant ainsi les resultats du balayage genomique. L'evaluation des consequences d'une heterozygotie locale via le recours a l'hemizygotie reciproque et au remplacement allelique a revele l'influence du fond genetique sur les effets de sous-dominance des HTL. Globalement, cette etude pan-genomique sur une population d'hybrides multiparentaux fournit des evidences fortes a l'encontre de la surdominance de genes individuels comme processus majeur contribuant a l'heterosis et vient plutot appuyer le modele de complementation de la dominance. [Traduit par la Redaction] Mots-cles : heterosis, Saccharomyces cerevisiae, heredite nonadditive, association pan-genomique, sous-dominance., Introduction The genetic basis of heterosis, or hybrid vigor, a phenomenon where the performance of a hybrid surpass those of its inbred parents, is still under debate (Crow 2008; Charlesworth [...]

To explore natural biodiversity we developed and examined introgression lines (ILs) containing chromosome segments of wild species (Solanum pennellii) in the background of the cultivated tomato (S. lycopersicum). We identified Brix9-2-5, which is a S. pennellii quantitative trait locus (QTL) that increases sugar yield of tomatoes and was mapped within a flower- and fruit-specific invertase (LIN5). QTL analysis representing five different tomato species delimited the functional polymorphism of Brix9-2-5 to an amino acid near the catalytic site of the invertase crystal, affecting enzyme kinetics and fruit sink strength. These results underline the power of diverse ILs for high-resolution perspectives on complex phenotypes., The genetic basis of many natural phenotypes takes the form of a continuous range rather than discrete classes. The complexity of traits showing continuous distribution often results from the segregation [...]

Facing the challenges of the world's food sources posed by a growing global population and a warming climate will require improvements in plant breeding and technology. Enhancing crop resiliency and yield via genome engineering will undoubtedly be a key part of the solution. The advent of new tools, such as CRIPSR/Cas, has ushered in significant advances in plant genome engineering. However, several serious challenges remain in achieving this goal. Among them are efficient transformation and plant regeneration for most crop species, low frequency of some editing applications, and high attrition rates. On March 8 and 9, 2021, experts in plant genome engineering and breeding from academia and industry met virtually for the Keystone eSymposium "Plant Genome Engineering: From Lab to Field" to discuss advances in genome editing tools, plant transformation, plant breeding, and crop trait development, all vital for transferring the benefits of novel technologies to the field. [ABSTRACT FROM AUTHOR]

Summary: Circadian clock rhythms are shown to be intertwined with crop adaptation. To realize the adaptive value of changes in these rhythms under crop domestication and improvement, there is a need to compare the genetics of clock and yield traits.We compared circadian clock rhythmicity based on Chl leaf fluorescence and transcriptomics among wild ancestors, landraces, and breeding lines of barley under optimal and high temperatures. We conducted a genome scan to identify pleiotropic loci regulating the clock and field phenotypes. We also compared the allelic diversity in wild and cultivated barley to test for selective sweeps.We found significant loss of thermal plasticity in circadian rhythms under domestication. However, transcriptome analysis indicated that this loss was only for output genes and that temperature compensation in the core clock machinery was maintained. Drivers of the circadian clock (DOC) loci were identified via genome‐wide association study. Notably, these loci also modified growth and reproductive outputs in the field. Diversity analysis indicated selective sweep in these pleiotropic DOC loci.These results indicate a selection against thermal clock plasticity under barley domestication and improvement and highlight the importance of identifying genes underlying for understanding the biochemical basis of crop adaptation to changing environments. [ABSTRACT FROM AUTHOR]

Abstract Background Rapid RNA extraction is commonly performed with commercial kits, which are very expensive and can involve toxic reagents. Most of these kits can be used with healthy plant tissues, but do not produce consistently high-quality RNA from necrotic fungus-infected tissues or fungal mycelium. Findings We report on the development of a rapid and relatively inexpensive method for total RNA extraction from plants and fungus-infected tissues, as well as from insects and fungi, based on guanidine hydrochloride buffer and common DNA extraction columns originally used for the extraction and purification of plasmids and cosmids. Conclusions The proposed method can be used reproducibly for RNA isolation from a variety of plant species. It can also be used with infected plant tissue and fungal mycelia, which are typically recalcitrant to standard nucleic acid extraction procedures.

Temperature compensation, expressed as the ability to maintain clock characteristics (mainly period) in face of temperature changes, that is, robustness, is considered a key feature of circadian clock systems. In this study, we explore the genetic basis for lack of robustness, that is, plasticity, of circadian clock as reflected by photosynthesis rhythmicity. The clock rhythmicity of a new wild barley reciprocal doubled haploid population was analysed with a high temporal resolution of pulsed amplitude modulation of chlorophyll fluorescence under optimal (22°C) and high (32°C) temperature. This comparison between two environments pointed to the prevalence of clock acceleration under heat. Genotyping by sequencing of doubled haploid lines indicated a rich recombination landscape with minor fixation (less than 8%) for one of the parental alleles. Quantitative genetic analysis included genotype by environment interactions and binary‐threshold models. Variation in the circadian rhythm plasticity phenotypes, expressed as change (delta) of period and amplitude under two temperatures, was associated with maternal organelle genome (the plasmotype), as well as with several nuclear loci. This first reported rhythmicity driven by nuclear loci and plasmotype with few identified variants, paves the way for studying impact of cytonuclear variations on clock robustness and on plant adaptation to changing environments. Robustness of circadian rhythms towards high temperature is controlled by nuclear and plasmotype quantitative trait loci in a wild barley (Hordeum vulgare ssp. spontaneum) reciprocal doubled haploid population. [ABSTRACT FROM AUTHOR]

Regulation of the rate of transpiration is an important part of plants' adaptation to uncertain environments. Stomatal closure is the most common response to severe drought. By closing their stomata, plants reduce transpiration to better their odds of survival under dry conditions. Under mild to moderate drought conditions, there are several possible transpiration patterns that balance the risk of lost productivity with the risk of water loss. Here, we hypothesize that plant ecotypes that have evolved in environments characterized by unstable patterns of precipitation will display a wider range of patterns of transpiration regulation along with other quantitative physiological traits (QPTs), compared to ecotypes from less variable environments. We examined five accessions of wild barley (Hordeum vulgare ssp. spontaneum) from different locations in Israel (the B1K collection) with annual rainfall levels ranging from 100 to 900 mm, along with one domesticated line (cv. Morex). We measured several QPTs and morphological traits of these accessions under well‐irrigated conditions, under drought stress and during recovery from drought. Our results revealed a correlation between precipitation‐certainty conditions and QPT plasticity. Specifically, accessions from stable environments (very wet or very dry locations) were found to take greater risks in their water‐balance regulation than accessions from areas in which rainfall is less predictable. Notably, less risk‐taking genotypes recovered more quickly than more risk‐taking ones once irrigation was resumed. We discuss the relationships between environment, polymorphism, physiological plasticity and fitness, and suggest a general risk‐taking model in which transpiration‐rate plasticity is negatively correlated with population polymorphism. [ABSTRACT FROM AUTHOR]

Screening large populations for carriers of known or de novo rare single nucleotide polymorphisms (SNPs) is required both in Targeting induced local lesions in genomes (TILLING) experiments in plants and in screening of human populations. We previously suggested an approach that combines the mathematical field of compressed sensing with next-generation sequencing to allow such large-scale screening. Based on pooled measurements, this method identifies multiple carriers of heterozygous or homozygous rare alleles while using only a small fraction of resources. Its rigorous mathematical foundations allow scalable and robust detection, and provide error correction and resilience to experimental noise. Here we present a large-scale experimental demonstration of our computational approach, in which we targeted a TILLING population of 1024 Sorghum bicolor lines to detect carriers of de novo SNPs whose frequency was less than 0.1%, using only 48 pools. Subsequent validation confirmed that all detected lines were indeed carriers of the predicted mutations. This novel approach provides a highly cost-effective and robust tool for biologists and breeders to allow identification of novel alleles and subsequent functional analysis. [ABSTRACT FROM AUTHOR]

The genomic makeup and phenotypes of plants are diversifying, in part due to artificial or natural selection in agricultural and natural environments. Utilization of these variations to enhance crop productivity requires an understanding of the relationships between genotype and phenotype in inbreds and hybrids derived from crosses between these populations. This review highlights recent studies on hybrid vigor (heterosis) and the related phenomenon of hybrid weakness – two types of non-additive inheritance. Heterosis is a phenomenon whereby the phenotype of first-generation hybrids is superior to that of their parents. Intralocus interactions between alleles, complementation of dominant alleles, or inter-loci epistatic interactions are genetic mechanisms that may cause non-additive phenotypic inheritance in hybrids. However, there are different views on what portion of the heterotic variation is modulated by each of these mechanisms. Another aspect of plant vigor is phenotypic stability or robustness in different environments and how this is influenced by gene heterozygosity. Hybrids are not necessarily more phenotypically stable than inbreds since local heterozygosity might be associated with negative effects on biochemical activities. This review integrates genetic and biochemical considerations to illustrate how these relationships may be tightly linked with breeding system and sequence divergence. [ABSTRACT FROM AUTHOR]

Background Wild barley is adapted to highly diverse environments throughout its geographical distribution range. Transcriptome sequencing of differentially adapted wild barley ecotypes from contrasting environments contributes to the identification of genes and genetic variation involved in abiotic stress tolerance and adaptation. Results Two differentially adapted wild barley ecotypes from desert (B1K2) and Mediterranean (B1K30) environments were analyzed for drought stress response under controlled conditions. The desert ecotype lost more water under both irrigation and drought, but exhibited higher relative water content (RWC) and better water use efficiency (WUE) than the coastal ecotype. We sequenced normalized cDNA libraries from drought-stressed leaves of both ecotypes with the 454 platform to identify drought-related transcripts. Over half million reads per ecotype were de novo assembled into 20,439 putative unique transcripts (PUTs) for B1K2, 21,494 for B1K30 and 28,720 for the joint assembly. Over 50% of PUTs of each ecotype were not shared with the other ecotype. Furthermore, 16% (3,245) of B1K2 and 17% (3,674) of B1K30 transcripts did not show orthologous sequence hits in the other wild barley ecotype and cultivated barley, and are candidates of ecotype-specific transcripts. Over 800 unique transcripts from each ecotype homologous to over 30 different stress-related genes were identified. We extracted 1,017 high quality SNPs that differentiated the two ecotypes. The genetic distance between the desert ecotype and cultivated barley was 1.9-fold higher than between the Mediterranean ecotype and cultivated barley. Moreover, the desert ecotype harbored a larger proportion of non-synonymous SNPs than the Mediterranean ecotype suggesting different demographic histories of these ecotypes. Conclusions The results indicate a strong physiological and genomic differentiation between the desert and Mediterranean wild barley ecotypes and a closer relationship of the Mediterranean to cultivated barley. A significant number of novel transcripts specific to wild barley were identified. The higher SNP density and larger proportion of SNPs with functional effects in the desert ecotype suggest different demographic histories and effects of natural selection in Mediterranean and desert wild barley. The data are a valuable genomic resource for an improved genome annotation, transcriptome studies of drought adaptation and a source of new genetic markers for future barley improvement. [ABSTRACT FROM AUTHOR]

Identifying intra-locus interactions underlying heterotic variation among whole-genome hybrids is a key to understanding mechanisms of heterosis and exploiting it for crop and livestock improvement. In this study, we present the development and first use of the heterotic trait locus (HTL) mapping approach to associate specific intra-locus interactions with an overdominant heterotic mode of inheritance in a diallel population using Sorghum bicolor as the model. This method combines the advantages of ample genetic diversity and the possibility of studying non-additive inheritance. Furthermore, this design enables dissecting the latter to identify specific intra-locus interactions. We identified three HTLs (3.5% of loci tested) with synergistic intra-locus effects on overdominant grain yield heterosis in 2 years of field trials. These loci account for 19.0% of the heterotic variation, including a significant interaction found between two of them. Moreover, analysis of one of these loci (hDPW4.1) in a consecutive F2 population confirmed a significant 21% increase in grain yield of heterozygous vs. homozygous plants in this locus. Notably, two of the three HTLs for grain yield are in synteny with previously reported overdominant quantitative trait loci for grain yield in maize. A mechanism for the reproductive heterosis found in this study is suggested, in which grain yield increase is achieved by releasing the compensatory tradeoffs between biomass and reproductive output, and between seed number and weight. These results highlight the power of analyzing a diverse set of inbreds and their hybrids for unraveling hitherto unknown allelic interactions mediating heterosis. [ABSTRACT FROM AUTHOR]

Today, plant breeders are being met with new opportunities to develop superior varieties. Fruitful genetic research into populations with novel diversity using genotyping by sequencing combined with genotype-to-phenotype bioinformatics has generated much knowledge that is directly relevant to crop improvement. These advances can assist the breeders in associating genetic makeup with traits of commercial value. The greatest challenge now is to find ways to attract the best young people to work in plant breeding for its innovation, open field experience and ability to support food security. We discuss the need, opportunities and conflicts associated with revamping plant breeding teaching programs to bridge the art and science of this profession with a rapidly expanding job market. [Copyright &y& Elsevier]

The trichomes of the wild tomato species Solanum habrochaites subsp, glabratum synthesize and store high levels of methylketones, primarily 2-tridecanone and 2-undecanone, that protect the plants against various herbivorous insects. Previously, we identified cDNAs encoding two proteins necessary for methylketone biosynthesis, designated methylketone synthase 1 (ShMKS1) and ShMKS2. Here, we report the isolation of genomic sequences encoding ShMKS1 and ShMKS2 as well as the homologous genes from the cultivated tomato, Solanum lycopersicum. We show that a full-length transcript of ShMKS2 encodes a protein that is localized in the plastids. By expressing ShMKS1 and ShMKS2 in Escherichia coli and analyzing the products formed, as well as by performing in vitro assays with both ShMKS1 and ShMKS2, we conclude that ShMKS2 acts as a thioesterase hydrolyzing 3-ketoacyl-acyl carrier proteins (plastid-localized intermediates of fatty acid biosynthesis) to release 3-ketoacids and that ShMKS1 subsequently catalyzes the decarboxylation of these liberated 3-ketoacids, forming the methylketone products. Genes encoding proteins with high similarity to ShMKS2, a member of the "hot-dog fold" protein family that is known to include other thioesterases in nonplant organisms, are present in plant species outside the genus Solanum. We show that a related enzyme from Arabidopsis (Arabidopsis thaliana) also produces 3-ketoacids when recombinantly expressed in E. coli. Thus, the thioesterase activity of proteins in this family appears to be ancient. In contrast, the 3-ketoacid decarboxylase activity of ShMKS1, which belongs to the α/β-hydrolase fold superfamily, appears to have emerged more recently, possibly within the genus Solanum. [ABSTRACT FROM AUTHOR]

Geranyl diphosphate (GPP), the precursor of many monoterpene end products, is synthesized in plastids by a condensation of dimethylallyl diphosphate and isopentenyl diphosphate (IPP) in a reaction catalyzed by homodimeric or heterodimeric GPP synthase (GPPS). In the heterodimeric enzymes, a noncatalytic small subunit (GPPS.SSU) determines the product specificity of the catalytic large subunit, which may be either an active geranylgeranyl diphosphate synthase (GGPPS) or an inactive GGPPS-like protein. Here, we show that expression of snapdragon (Antirrhinum majus) GPPS.SSU in tobacco (Nicotiana tabacum) plants increased the total GPPS activity and monoterpene emission from leaves and flowers, indicating that the introduced catalytically inactive GPPS.SSU found endogenous large subunit partner(s) and formed an active snapdragon/tobacco GPPS in planta. Bimolecular fluorescence complementation and in vitro enzyme analysis of individual and hybrid proteins revealed that two of four GGPPS-like candidates from tobacco EST databases encode bona fide GGPPS that can interact with snapdragon GPPS.SSU and form a functional GPPS enzyme in plastids. The formation of chimeric GPPS in transgenic plants also resulted in leaf chlorosis, increased light sensitivity, and dwarfism due to decreased levels of chlorophylls, carotenoids, and gibberellins. In addition, these transgenic plants had reduced levels of sesquiterpene emission, suggesting that the export of isoprenoid intermediates from the plastids into the cytosol was decreased. These results provide genetic evidence that GPPS.SSU modifies the chain length specificity of phylogenetically distant GGPPS and can modulate IPP flux distribution between GPP and GGPP synthesis in planta. [ABSTRACT FROM AUTHOR]

Plants have evolved a plethora of chemical solutions to help them cope with dynamic biotic and abiotic environments, and much of this diversity was used throughout human history for medicinal and hedonistic purposes (seasoning, preservatives, etc.). Despite the enormous progress made in the last decade in elucidating the genes and enzymes involved in these metabolic pathways using classical biochemical approaches and biochemical genomic methods, very few studies applied targeted and non-targeted mutagenesis for isolating novel genes to study their hitherto unknown function. This minireview will discuss recent examples of forward and reverse genetics approaches taken in some medicinal plants and herbs, and will present data that we obtained from an ethylmethane sulfate mutagenesis project in Ocimum basilicum (sweet basil), aiming to identify new genes that are involved in the biosynthesis of aroma compounds. [ABSTRACT FROM AUTHOR]

A large proportion of the genes in any plant genome encode enzymes of primary and specialized (secondary) metabolism. Not all plant primary metabolites, those that are found in all or most species, have been identified. Moreover, only a small portion of the estimated hundreds of thousand specialized metabolites, those found only in restricted lineages, have been studied in any species. The correlative analysis of extensive metabolic profiling and gene expression profiling has proven a powerful approach for the identification of candidate genes and enzymes, particularly those in secondary metabolism. The final characterization of substrates, enzymatic activities, and products requires biochemical analysis, which has been most successful when candidate proteins have homology to other enzymes of known function. The challenges are to identify new types of enzymes and to develop biochemical techniques that are suitable for large-scale analysis. [Copyright &y& Elsevier]

Net blotch (NB) is a major disease of barley caused by the fungus Pyrenophora teres f. teres (Ptt), and P. teres f. maculata (Ptm). Ptt and Ptm infect the cultivated crop (Hordeum vulgare) and its wild relatives (H. vulgare ssp. spontaneum and H. murinum ssp. glaucum). The main goal of this research was to study the NB-causing pathogen in the crop center of origin. To address this, we have constructed a Ptt (n = 15) and Ptm (n = 12) collection isolated from three barley species across Israel. Isolates were characterized genetically and phenotypically. Aggressiveness of the isolates was determined based on necrotrophic growth rate on detached leaves of barley. In addition, isolates were genetically characterized by the mating type, followed by phylogenetic analysis, clustering them into seven groups. The analysis showed no significant differentiation of isolates based on either geographic origin, host of origin or form (Ptt vs. Ptm). Nevertheless, there was a significant difference in aggressiveness among the isolates regardless of host species, geographic location or sampling site. Moreover, it was apparent that the isolates derived from wild hosts were more variable in their necrotrophic growth rate, compared to isolates sampled from cultivated hosts, thereby suggesting that NB plays a major role in epidemiology at the center of barley origin where most of the diversity lies. Ptm has significantly higher necrotrophic and saprotrophic growth rates than Ptt, and for both a significant negative correlation was found between light intensity exposure and growth rates. [ABSTRACT FROM AUTHOR]

Abstract: Basil glands of the Sweet Dani cultivar contain high levels of citral, a mixture of geranial and its cis-isomer neral, as well as low levels of geraniol and nerol. We have previously reported the identification of a cDNA from Sweet Dani that encodes an enzyme responsible for the formation of geraniol from geranyl diphosphate in the glands, and that these glands cannot synthesize nerol directly from geranyl diphosphate. Here, we report the identification of two basil cDNAs encoding NADP+-dependent dehydrogenases that can use geraniol as the substrate. One cDNA, designated CAD1, represents a gene whose expression is highly specific to gland cells of all three basil cultivars examined, regardless of their citral content, and encodes an enzyme with high sequence similarity to known cinnamyl alcohol dehydrogenases (CADs). The enzyme encoded by CAD1 reversibly oxidizes geraniol to produce geranial (which reversibly isomerizes to neral via keto–enol tautomerization) at half the efficiency compared with its activity with cinnamyl alcohol. CAD1 does not use nerol and neral as substrates. A second cDNA, designated GEDH1, encodes an enzyme with sequence similarity to CAD1 that is capable of reversibly oxidizing geraniol and nerol in equal efficiency, and prolonged incubation of geraniol with GEDH1 in vitro produces not only geranial and neral, but also nerol. GEDH1 is also active, although at a lower efficiency, with cinnamyl alcohol. However, GEDH1 is expressed at low levels in glands of all cultivars compared with its expression in leaves. These and additional data presented indicate that basil glands may contain additional dehydrogenases capable of oxidizing geraniol. [Copyright &y& Elsevier]

Vegetable cultivation favored the inclusion of pleasant aromas in the produce, whereas unpleasant aromas were selected against. Introgression lines, generated by hybridization of a cultivated tomato (Lycopersicon esculentum) to its wild relative L. pennellii, were used to map quantitative trait loci (QTL) that influence tomato aroma. A marked undesirable flavor was detected by taste panelists in L. pennellii fruits and was related to an introgressed segment from the short arm of chromosome 8. Analysis of the ripe fruits' volatiles of chromosome 8 introgressed lines revealed an up to 60-fold increase in the levels of 2-phenylethanol and phenylacetaldehyde, as compared to the cultivated tomato. This effect was associated with a 10 cM segment originating from the wild species. Although 2-phenylethanol and phenylacetaldehyde have favorable contribution to tomato aroma when present at low levels, phenylacetaldehyde has a nauseating objectionable aroma when present in levels >0.005 ppm. The loss of the ability to produce high levels of phenylacetaldehyde contributed to the development of desirable aroma of the cultivated tomato. The findings provide a genetic explanation for one of the aroma changes that occurred during the domestication of the tomato.