Characterization of a sweet basil acyltransferase involved in eugenol biosynthesis

Bioactivity of Eugenol: A Potential Antibiotic Adjuvant with Minimal Ecotoxicological Impact

Combining commercial antibiotics with adjuvants to lower their minimum inhibitory concentration (MIC) is vital in combating antimicrobial resistance. Evaluating the ecotoxicity of such compounds is crucial due to environmental and health risks. Here, eugenol was assessed as an adjuvant for 7 commercial antibiotics against 14 pathogenic bacteria in vitro, also examining its acute ecotoxicity on various soil and water organisms (microbiota, Vibrio fischeri, Daphnia magna, Eisenia foetida, and Allium cepa). Using microdilution methods, checkerboard assays, and kinetic studies, the MICs for eugenol were determined together with the nature of its combinations with antibiotics against bacteria, some unexposed to eugenol previously. The lethal dose for the non-target organisms was also determined, as well as the Average Well Color Development and the Community-Level Physiological Profiling for soil and water microbiota. Our findings indicate that eugenol significantly reduces MICs by 75 to 98%, which means that it could be a potent adjuvant. Ecotoxicological assessments showed eugenol to be less harmful to water and soil microbiota compared to studied antibiotics. While Vibrio fischeri and Daphnia magna were susceptible, Allium cepa and Eisenia foetida were minimally affected. Given that only 0.1% of eugenol is excreted by humans without metabolism, its environmental risk when used with antibiotics appears minimal.

Increase of secondary metabolites in sweet basil (Ocimum basilicum L.) leaves by exposure to N2O5 with plasma technology

Exposure to N2O5 generated by plasma technology activates immunity in Arabidopsis through tryptophan metabolites. However, little is known about the effects of N2O5 exposure on other plant species. Sweet basil synthesizes many valuable secondary metabolites in its leaves. Therefore, metabolomic analyses were performed at three different exposure levels [9.7 (Ex1), 19.4 (Ex2) and 29.1 (Ex3) μmol] to assess the effects of N2O5 on basil leaves. As a result, cinnamaldehyde and phenolic acids increased with increasing doses. Certain flavonoids, columbianetin, and caryophyllene oxide increased with lower Ex1 exposure, cineole and methyl eugenol increased with moderate Ex2 exposure and L-glutathione GSH also increased with higher Ex3 exposure. Furthermore, gene expression analysis by quantitative RT-PCR showed that certain genes involved in the syntheses of secondary metabolites and jasmonic acid were significantly up-regulated early after N2O5 exposure. These results suggest that N2O5 exposure increases several valuable secondary metabolites in sweet basil leaves via plant defense responses in a controllable system.

Anti-cancer bioactivity of sweet basil leaf derived extracellular vesicles on pancreatic cancer cells

Most living organisms secrete tiny lipid bilayer particles encapsulating various biomolecular entities, including nucleic acids and proteins. These secreted extracellular vesicles (EVs) are shown to aid in communication between cells and their environment. EVs are mainly involved in the signalling and manipulation of physiological processes. Plant EVs display similar functional activity as seen in mammalian EVs. Medicinal plants have many bioactive constituents with potential applications in cancer treatment. Particularly, Basil (Ocimum basilicum), has wide therapeutic properties including anti-inflammatory, anti-cancer, and anti-infection, among others. In this study, we focused on using EVs purified from Apoplast Washing Fluid (AWF) of Basil plant leaves as a biological therapeutic agent against cancer. Characterization of Basil EVs revealed a size range of 100-250 nm, which were later assessed for their cell uptake and apoptosis inducing abilities in pancreatic cancer cells. Basil plant EVs (BasEVs) showed a significant cytotoxic effect on pancreatic cancer cell line MIA PaCa-2 at a concentration of 80 and 160 μg/mL in cell viability, as well as clonogenic assays. Similarly, RT-PCR and western blot analysis has shown up regulation in apoptotic gene and protein expression of Bax, respectively, in BasEV treatment groups compared to untreated controls of MIA PaCa-2. Overall, our results suggest that EVs from basil plants have potent anti-cancer effects in pancreatic cancer cells and can serve as a drug delivery system, demanding an investigation into the therapeutic potential of other medicinal plant EVs.

Engineered co-culture for consolidated production of phenylpropanoids directly from aromatic-rich biomass

Consolidated bioprocesses for the in situ hydrolysis and conversion of biomass feedstocks into value-added products offers great potential for both process and cost reduction. However, to date few consolidated bioprocesses have been developed that target aromatic rich feedstock fractions. Reported here is the development of synthetic co-cultivation for the consolidated hydrolysis and valorisation of corncob hydroxycinnamic acids. Biomass hydrolysis was achieved via a secretion module developed in B. subtilis using a genetically encoded biosensor-actuator to secrete hydrolytic enzymes. Conversion was achieved via a biotransformation module developed in E. coli using a suite of plug-and-play encoded enzymes to convert the released hydroxycinnamic acids into high-value phenylpropanoid target compounds. Finally, employing cellulolytic pre-treatment, extractive fermentation and in situ product recovery multiple aromatic products, coniferol and chavicol, were isolated from the same process in high purity.

Genome-wide identification and expression of BAHD acyltransferase gene family shed novel insights into the regulation of linalyl acetate and lavandulyl acetate in lavender

The BAHD acyltransferase superfamily has a variety of biological functions, especially in catalyzing the synthesis of ester compounds and improving plant stress resistance. Linalyl acetate and lavandulyl acetate, the most important volatile esters in lavender, are generated by LaBAHDs. However, the systematic identification, expression characteristics of LaBAHD genes and their correlations with ester formation remain elusive. Here, 166 LaBAHD genes were identified from the lavender genome. Based on detailed phylogenetic analysis, the LaBAHD family genes were divided into five groups, among which the LaBAHDs involved in volatile ester biosynthesis belong to the IIIa and Va clades. Whole-genome duplications (WGDs) and tandem duplications (TDs) jointly drive the expansion of LaBAHD superfamily. The promoter regions of LaBAHDs contained a variety of stress- and hormone-related motifs, as well as binding sites with five types of transcription factors (TFs). Then, linalyl acetate- and lavandulyl acetate-regulated coexpression modules were established and some candidate TFs that may function in inducing ester formation were identified. Based on the correlation analysis between the ester contents and expression profiles of BAHD genes in different tissues, five candidate genes were screened for further examination. Drought, salt and MeJA treatments increased the accumulation of linalyl acetate and lavandulyl acetate, and induced the expression of LaBAHDs. Our results indicated that LaBAHD57, LaBAHD63, LaBAHD104, LaBAHD105 and LaBAHD119 are crucial candidate genes involved in linalyl acetate and lavandulyl acetate biosynthesis. Our findings offer a theoretical foundation for further studying the specific biological functions of LaBAHD family and improving the quality of lavender essential oil.

Caffeoyl-coenzyme A O-methyltransferase mediates regulation of carbon flux fluctuations during phenylpropenes and lignin biosynthesis in the vegetative organ roots of Asarum sieboldii Miq

Asarum sieboldii Miq. possesses remarkable medicinal value due to its essential oil enriched with phenylpropenes (e.g., methyleugenol and safrole). Although the biosynthesis of phenylpropenes shares a common pathway with lignin, the regulation mechanisms in carbon flux allocation between them are unclear. This study is the first to genetically verify the carbon flux regulation mechanism in A. sieboldii roots. We regulated the expression of Caffeoyl-coenzyme A O-methyltransferase (CCoAOMT), an essential enzyme in the common pathway, to investigate carbon flux allocation in vegetative organs. Here, the lignin and phenylpropene content fluctuation was analyzed by wet chemistry and GC-MS methods. A bona fide CCoAOMT gene from A. sieboldii was firstly cloned and verified. Preliminary heterologous expression validation in transgenic Arabidopsis thaliana showed that RNAi-induced CCoAOMT down-regulation significantly decreased lignin content by 24% and increased the S/G ratio by 30%; however, AsCCoAOMT over-expression in A. thaliana resulted in a 40% increase in lignin content and a 20% decrease in the S/G ratio when compared to the wild type. Similar trends were noted in homologous transformation in A. sieboldii, although the variations were not conspicuous. Nevertheless, the transgenic A. sieboldii plants displayed substantial differences in the level of phenylpropene compounds methyleugenol and safrole leading to a 168% increase in the methyleugenol/safrole ratio in the over-expression line and a 73% reduction in RNAi-suppression line. These findings suggest that the biosynthesis of phenylpropene constituents methyleugenol and safrole seems to be prioritized over lignin. Furthermore, this study indicated that suppression of AsCCoAOMT resulted in marked root susceptibility to pathogenic fungal disease, implying a significant additional role of CCoAOMT in protecting plant vegetative parts from diseases. Overall, the present study provides important references and suggests that future research should be aimed at elucidating the detailed mechanisms of the carbon flux allocation between phenylpropenes and lignin biosynthesis, as well as the disease resistance competency.

AaWIN1, an AP2/ERF protein, positively regulates glandular secretory trichome initiation in Artemisia annua

Exploring the genetic network of glandular trichomes and manipulating genes relevant to secondary metabolite biosynthesis are of great importance and value. Artemisinin, a key antimalarial drug ingredient, is synthesized and stored in glandular secretory trichomes (GSTs) in Artemisia annua. WIN/SHN proteins, a clade of AP2/ERF family, are known as regulators for cuticle biosynthesis. However, their function in glandular trichome development is less unknown. In this study, we identified a WIN/SHN gene from A. annua and named it as AaWIN1. AaWIN1 was predominantly expressed in buds, flowers and trichomes, and encoded a nuclear-localized protein. Overexpressing AaWIN1 in A. annua significantly increased the density of GST as well as the artemisinin content. Furthermore, AaGSW2 was reported to play an important role in promoting GST initiation, and the expression of AaGSW2 was induced in AaWIN1-overexpression lines. AaMIXTA1, a MYB protein positively regulating trichome initiation and cuticle biosynthesis, was confirmed to interact with AaWIN1. In addition, the ectopic expression of AaWIN1 resulted in slender and curled leaves, fewer trichomes, and rising expressions of cuticle biosynthesis genes in Arabidopsis thaliana. Taken together, based on phenotype observations, content measurements and gene expression detections, AaWIN1 was considered as a positive regulator for GST initiation in A. annua.

Facing energy limitations - approaches to increase basil (Ocimum basilicum L.) growth and quality by different increasing light intensities emitted by a broadband LED light spectrum (400-780 nm)

Based on the current trend towards broad-bandwidth LED light spectra for basil productions in multi-tiered controlled-environment horticulture, a recently developed white broad-bandwidth LED light spectrum (400-780 nm) including far-red wavelengths with elevated red and blue light fractions was employed to cultivate basil. Four Ocimum basilicum L. cultivars (cv. Anise, cv. Cinnamon, cv. Dark Opal and cv. Thai Magic) were exposed to two different rising light intensity conditions (I_Low and I_High). In dependence of the individual cultivar-specific plant height increase over time, basil cultivars were exposed to light intensities increasing from ~ 100 to ~ 200 µmol m^-2 s^-1 under I_Low, and from 200 to 400 µmol m^-2 s^-1 under I_High (due to the exponential light intensity increases with decreasing proximity to the LED light fixtures). Within the first experiment, basils' morphological developments, biomass yields and time to marketability under both light conditions were investigated and the energy consumptions were determined to calculate the basils' light use efficiencies. In detail, cultivar-dependent differences in plant height, leaf and branch pair developments over time are described. In comparison to the I_Low light conditions, I_High resulted in accelerated developments and greater yields of all basil cultivars and expedited their marketability by 3-5 days. However, exposure to light intensities above ~ 300 µmol m^-2 s^-1 induced light avoidance responses in the green-leafed basil cultivars cv. Anise, cv. Cinnamon and cv. Thai Magic. In contrast, I_Low resulted in consumer-preferred visual qualities and greater biomass efficiencies of the green-leafed basil cultivars and are discussed as a result of their ability to adapt well to low light conditions. Contrarily to the green-leafed cultivars, purple-leafed cv. Dark Opal developed insufficiently under I_Low, but remained light-tolerant under I_High, which is related to its high anthocyanin contents. In a second experiment, cultivars' volatile organic compound (VOC) contents and compositions over time were investigated. While VOC contents per gram of leaf dry matter gradually decreased in purple-leafed cv. Dark Opal between seedling stage to marketability, their contents gradually increased in the green cultivars. Regardless of the light treatment applied, cultivar-specific VOC compositions changed tremendously in a developmental stage-dependent manner.

The clove (Syzygium aromaticum) genome provides insights into the eugenol biosynthesis pathway

The clove (Syzygium aromaticum) is an important tropical spice crop in global trade. Evolving environmental pressures necessitate modern characterization and selection techniques that are currently inaccessible to clove growers owing to the scarcity of genomic and genetic information. Here, we present a 370-Mb high-quality chromosome-scale genome assembly for clove. Comparative genomic analysis between S. aromaticum and Eucalyptus grandis—both species of the Myrtaceae family—reveals good genome structure conservation and intrachromosomal rearrangements on seven of the eleven chromosomes. We report genes that belong to families involved in the biosynthesis of eugenol, the major bioactive component of clove products. On the basis of our transcriptomic and metabolomic findings, we propose a hypothetical scenario in which eugenol acetate plays a key role in high eugenol accumulation in clove leaves and buds. The clove genome is a new contribution to omics resources for the Myrtaceae family and an important tool for clove research.

A newly assembled clove genome is compared with E. grandis to investigate genome evolution between the two genera of the Myrtaceae family, and putative genes involved in the biosynthesis of eugenol are identified through transcriptomics and metabolomics.

Sulfated Galactofucans: An Outstanding Class of Fucoidans with Promising Bioactivities

Fucoidans encompass versatile and heterogeneous sulfated biopolysaccharides of marine origin, specifically brown algae and marine invertebrates. Their chemistry and bioactivities have been extensively investigated in the last few decades. The reported studies revealed diverse chemical skeletons in which l-fucose is the main sugar monomer. However, other sugars, i.e., galactose, mannose, etc., have been identified to be interspersed, forming several heteropolymers, including galactofucans/fucogalactans (G-fucoidans). Particularly, sulfated galactofucans are associated with rich chemistry contributing to more promising bioactivities than fucans and other marine polysaccharides. The previous reports in the last 20 years showed that G-fucoidans derived from Undaria pinnatifida were the most studied; 21 bioactivities were investigated, especially antitumor and antiviral activities, and unique biomedical applications compared to other marine polysaccharides were demonstrated. Hence, the current article specifically reviews the biogenic sources, chemistry, and outstanding bioactivities of G-fucoidans providing the opportunity to discover novel drug candidates.

Dissecting dietary and semisynthetic volatile phenylpropenes: A compile of their distribution, food properties, health effects, metabolism and toxicities

Phenylpropenes represent a major subclass of plant volatiles, including eugenol, and (E)-anethole. They contribute to the flavor and aroma of many chief herbs and spices, to exert distinct notes in food, i.e., spicy anise- and clove-like to fruit. Asides from their culinary use, they appear to exert general health effects, whereas some effects are specific, e.g., eugenol being a natural local anesthetic. This review represents the most comprehensive overview of phenylpropenes with respect to their chemical structures, different health effects, and their food applications as flavor and food preservatives. Side effects and toxicities of these compounds represent the second main part of this review, as some were reported for certain metabolites generated inside the body. Several metabolic reactions mediating for phenylpropenes metabolism in rodents via cytochrome P450 (CYP450) and sulfotransferase (SULT) enzymes are presented being involved in their toxicities. Such effects can be lessened by influencing their pharmacokinetics through a matrix-derived combination effect via administration of herbal extracts containing SULT inhibitors, i.e., nevadensin in sweet basil. Moreover, structural modification of phenylpropanes appears to improve their effects and broaden their applications. Hence, such review capitalizing on phenylpropenes can help optimize their applications in nutraceuticals, cosmeceuticals, and food applications.

Genome-Wide Identification of BAHD Superfamily and Functional Characterization of Bornyl Acetyltransferases Involved in the Bornyl Acetate Biosynthesis in Wurfbainia villosa

Bornyl acetate (BA) is known as a natural aromatic monoterpene ester with a wide range of pharmacological and biological activities. Borneol acetyltransferase (BAT), catalyzing borneol and acetyl-CoA to synthesize BA, is alcohol acetyltransferase, which belongs to the BAHD super acyltransferase family, however, BAT, responsible for the biosynthesis of BA, has not yet been characterized. The seeds of Wurfbainia villosa (homotypic synonym: Amomum villosum) are rich in BA. Here we identified 64 members of the BAHD gene family from the genome of W. villosa using both PF02458 (transferase) and PF07247 (AATase) as Hidden Markov Model (HMM) to screen the BAHD genes. A total of sixty-four WvBAHDs are distributed on 14 chromosomes and nine unanchored contigs, clustering into six clades; three WvBAHDs with PF07247 have formed a separated and novel clade: clade VI. Twelve candidate genes belonging to clade I-a, I-b, and VI were selected to clone and characterize in vitro, among which eight genes have been identified to encode BATs acetylating at least one type of borneol to synthesize BA. All eight WvBATs can utilize (-)-borneol as substrates, but only five WvBATs can catalyze (+)-borneol, which is the endogenous borneol substrate in the seeds of W. villosa; WvBAT3 and WvBAT4 present the better catalytic efficiency on (+)-borneol than the others. The temporal and spatial expression patterns of WvBATs indicate that WvBAT3 and WvBAT4 are seed-specific expression genes, and their expression levels are correlated with the accumulation of BA, suggesting WvBAT3 and WvBAT4 might be the two key BATs for BA synthesis in the seeds of W. villosa. This is the first report on BAT responsible for the last biosynthetic step of BA, which will contribute to further studies on BA biosynthesis and metabolism engineering of BA in other plants or heterologous hosts.

The chromosome-based lavender genome provides new insights into Lamiaceae evolution and terpenoid biosynthesis

The aromatic shrub Lavandula angustifolia produces various volatile terpenoids that serve as resources for essential oils and function in plant-insect communication. To better understand the genetic basis of the terpenoid diversity in lavender, we present a high-quality reference genome for the Chinese lavender cultivar "Jingxun 2" using PacBio and Hi-C technologies to anchor the 894.50 Mb genome assembly into 27 pseudochromosomes. In addition to the γ triplication event, lavender underwent two rounds of whole-genome duplication (WGD) during the Eocene-Oligocene (29.6 MYA) and Miocene-Pliocene (6.9 MYA) transitions. As a result of tandem duplications and lineage-specific WGDs, gene families related to terpenoid biosynthesis in lavender are substantially expanded compared to those of five other species in Lamiaceae. Many terpenoid biosynthesis transcripts are abundant in glandular trichomes. We further integrated the contents of ecologically functional terpenoids and coexpressed terpenoid biosynthetic genes to construct terpenoid-gene networks. Typical gene clusters, including TPS-TPS, TPS-CYP450, and TPS-BAHD, linked with compounds that primarily function as attractants or repellents, were identified by their similar patterns of change during flower development or in response to methyl jasmonate. Comprehensive analysis of the genetic basis of the production of volatiles in lavender could serve as a foundation for future research into lavender evolution, phytochemistry, and ecology.

Genotype and Successive Harvests Interaction Affects Phenolic Acids and Aroma Profile of Genovese Basil for Pesto Sauce Production

Basil (Ocimum basilicum L.) is an essential ingredient of the Mediterranean cuisine due to its distinctive aroma. Genovese basil leaves are used to prepare "pesto", a condiment that has always caught the interest of consumers and producers. Usually, basil for industrial processing is harvested more than once to extract a higher yield. However, successive cuts can affect quality traits that play a crucial role in defining the product's final sensory profile. This research was aimed to evaluate the impact of cut on the quantitative and qualitative properties of three Genovese basil cultivars (Aroma 2, Eleonora and Italiano Classico) grown in an open field. Nitrate content, phenolic acids and aromatic profile were determined by ion chromatography (IC), high-performance liquid chromatography (HPLC), and gas chromatography coupled to a mass spectrometer (GC/MS) analysis, respectively. The second harvest increased fresh biomass and total phenolic acids content by 172% and 413%, respectively, with Italiano Classico recording the highest values. The combination of second-cut Aroma 2 yielded the lowest nitrate (473.8 mg kg-1 of fresh weight) and Eugenol (2.4%) levels. In the second harvest, Eleonora showed an increase in eugenol and trans-α-bergamotene of 75.3% and 48.2%, respectively; whereas, eucalyptol and β-cis-ocimene decreased by 34.4% and 51.6%, respectively. Although successive harvests may increase basil yield and quality overall, the cultivar-dependent response to successive cuts needs to be accounted for in order to accomplish standardization of industrial "pesto" sauce.

Sweet Basil Has Distinct Synthases for Eugenol Biosynthesis in Glandular Trichomes and Roots with Different Regulatory Mechanisms

Production of a volatile phenylpropene; eugenol in sweet basil is mostly associated with peltate glandular trichomes (PGTs) found aerially. Currently only one eugenol synthase (EGS), ObEGS1 which belongs to PIP family is identified from sweet basil PGTs. Reports of the presence of eugenol in roots led us to analyse other EGSs in roots. We screened for all the PIP family reductase transcripts from the RNA-Seq data. In vivo functional characterization of all the genes in E. coli showed their ability to produce eugenol and were termed as ObEGS2-8. Among all, ObEGS1 displayed highest expression in PGTs and ObEGS4 in roots. Further, eugenol was produced only in the roots of soil-grown plants, but not in roots of aseptically-grown plants. Interestingly, eugenol production could be induced in roots of aseptically-grown plants under elicitation suggesting that eugenol production might occur as a result of environmental cues in roots. The presence of ObEGS4 transcript and protein in aseptically-grown plants indicated towards post-translational modifications (PTMs) of ObEGS4. Bioinformatics analysis showed possibility of phosphorylation in ObEGS4 which was further confirmed by in vitro experiment. Our study reveals the presence of multiple eugenol synthases in sweet basil and provides new insights into their diversity and tissue specific regulation.

The genome sequence of tetraploid sweet basil, Ocimum basilicum L., provides tools for advanced genome editing and molecular breeding

Sweet basil, Ocimum basilicum L., is a well-known culinary herb grown worldwide, but its uses go beyond the kitchen to traditional medicine, cosmetics and gardening. To date, the lack of an available reference genome has limited the utilization of advanced molecular breeding methods. We present a draft version of the sweet basil genome of the cultivar ‘Perrie’, a fresh-cut Genovese-type basil. Genome sequencing showed basil to be a tetraploid organism with a genome size of 2.13 Gbp, assembled in 12,212 scaffolds, with > 90% of the assembly being composed of 107 scaffolds. About 76% of the genome is composed of repetitive elements, with the majority being long-terminal repeats. We constructed and annotated 62,067 protein-coding genes and determined their expression in different plant tissues. We analysed the currently known phenylpropanoid volatiles biosynthesis genes. We demonstrated the necessity of the reference genome for a comprehensive understanding of this important pathway in the context of tetraploidy and gene redundancy. A complete reference genome is essential to overcome this redundancy and to avoid off-targeting when designing a CRISPR: Cas9-based genome editing research. This work bears promise for developing fast and accurate breeding tools to provide better cultivars for farmers and improved products for consumers.