Ocimum kilimandscharicum 4CL11 negatively regulates adventitious root development via accumulation of flavonoid glycosides

4-Coumarate-CoA Ligase (4CL) is an important enzyme in the phenylpropanoid biosynthesis pathway. Multiple 4CLs are identified in Ocimum species; however, their in planta functions remain enigmatic. In this study, we independently overexpressed three Ok4CL isoforms from Ocimum kilimandscharicum (Ok4CL7, -11, and -15) in Nicotiana benthamiana. Interestingly, Ok4CL11 overexpression (OE) caused a rootless or reduced root growth phenotype, whereas overexpression of Ok4CL15 produced normal adventitious root (AR) growth. Ok4CL11 overexpression in N. benthamiana resulted in upregulation of genes involved in flavonoid biosynthesis and associated glycosyltransferases accompanied by accumulation of specific flavonoid-glycosides (kaempferol-3-rhamnoside, kaempferol-3,7-O-bis-alpha-l-rhamnoside [K3,7R], and quercetin-3-O-rutinoside) that possibly reduced auxin levels in plants, and such effects were not seen for Ok4CL7 and -15. Docking analysis suggested that auxin transporters (PINs/LAXs) have higher binding affinity to these specific flavonoid-glycosides, and thus could disrupt auxin transport/signaling, which cumulatively resulted in a rootless phenotype. Reduced auxin levels, increased K3,7R in the middle and basal stem sections, and grafting experiments (intra and inter-species) indicated a disruption of auxin transport by K3,7R and its negative effect on AR development. Supplementation of flavonoids and the specific glycosides accumulated by Ok4CL11-OE to the wild-type N. benthamiana explants delayed the AR emergence and also inhibited AR growth. While overexpression of all three Ok4CLs increased lignin accumulation, flavonoids, and their specific glycosides were accumulated only in Ok4CL11-OE lines. In summary, our study reveals unique indirect function of Ok4CL11 to increase specific flavonoids and their glycosides, which are negative regulators of root growth, likely involved in inhibition of auxin transport and signaling.

Ocimum sanctum: The Journey from Sacred Herb to Functional Food

In recent years, the growing demand for herbal-based formulations, including functional foods, has acquired significant attention. This study highlights historical, botanical, ecological, and phytochemical descriptions and different extraction mechanisms of Ocimum sanctum utilized in its processing. Besides this, it explores the utilization of Ocimum sanctum as a functional food ingredient in various food products such as bakery products (biscuits, bread), dairy products (herbal milk, cheese), and beverages (tea, juice, wine) while focusing on their evaluation parameters, preparation techniques, and pharmacological activities. In terms of other pharmacological properties, Ocimum sanctum-infused functional foods exhibited cognitiveenhancing properties, adaptogenic qualities, anti-obesity effects, gastroprotective, antiinflammatory, hypoglycemic, and immuno-modulatory effects. Thus, the diverse properties of Ocimum sanctum offer exciting opportunities for the development of functional foods that can promote specific health issues, so future research should focus on developing and analyzing novel Ocimum sanctum-based functional foods to meet the growing demand of the functional food industry.

Characterizing the circadian connectome of Ocimum tenuiflorum using an integrated network theoretic framework

Across the three domains of life, circadian clock is known to regulate vital physiological processes, like, growth, development, defence etc. by anticipating environmental cues. In this work, we report an integrated network theoretic methodology comprising of random walk with restart and graphlet degree vectors to characterize genome wide core circadian clock and clock associated raw candidate proteins in a plant for which protein interaction information is available. As a case study, we have implemented this framework in Ocimum tenuiflorum (Tulsi); one of the most valuable medicinal plants that has been utilized since ancient times in the management of a large number of diseases. For that, 24 core clock (CC) proteins were mined in 56 template plant genomes to build their hidden Markov models (HMMs). These HMMs were then used to identify 24 core clock proteins in O. tenuiflorum. The local topology of the interologous Tulsi protein interaction network was explored to predict the CC associated raw candidate proteins. Statistical and biological significance of the raw candidates was determined using permutation and enrichment tests. A total of 66 putative CC associated proteins were identified and their functional annotation was performed.

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.

Volatile Organic Compounds from Basil Essential Oils: Plant Taxonomy, Biological Activities, and Their Applications in Tropical Fruit Productions

Basils of the genus Ocimum are aromatic plants grown widely throughout the tropical and temperate regions. The essential oils obtained from their aerial parts are enriched with volatile organic compounds with high market demand for food and pharmaceutical industries. The volatile organic compounds have been shown to exhibit biological activities. Therefore, their novel applications have been extensively explored in the last few decades. The most widely available basils in the tropical areas include white holy basil (O. sanctum var. Shyama), red holy basil (O. sanctum var. Rama), Thai basil (O. basilicum var. thyrsiflorum), lemon basil (O. citriodorum), and tree basil (O. gratissimum). Over 60 volatiles of different classes have been exclusively described, and some of them could be useful as biomarkers for genotype specification. The major volatile ingredient is the phenylpropanoids, such as methyl eugenol, which has the potential as a natural product for mitigating Oriental fruit fly (Bactrocera dorsalis) during tropical fruit production. Moreover, basil essential oils are also used to control diseases of the fruits during post-harvest storage. As a result, the application of basil essential oils as a sustainable defect control strategy for tropical fruit value chains seems intriguing. This review provides comprehensive information on plant taxonomy and volatile compositions of the essential oil fractions from different basil species. Their biological activities and applications are also discussed, mainly during the pre- and post-production of tropical fruits. Additionally, the available techniques to enhance the efficacy of the volatile active compounds are also described.

Quality Traits, Volatile Organic Compounds, and Expression of Key Flavor Genes in Strawberry Genotypes over Harvest Period

Six strawberry genotypes were examined for fruit yield and size, important chemical traits (sugars, phenolics, anthocyanins, ascorbic acid, volatiles) and antioxidant properties (ferric reducing power). In addition, we determined the expression of genes and transcription factors (SAAT, FaNES1, FaFAD1, FaEGS2, FaEOBII and FaMYB10) controlling the main flavor and aroma traits, and finally evaluated the effect of the genotype and harvest time on the examined chemical and genetic factors, as well as their intercorrelations. The commercial varieties 'Fortuna', 'Victory', 'Calderon', 'Rociera', and two advanced selections Ber22/6 and Ber23/3 were cultivated under the same conditions at Berryplasma World Ltd. plantations (Varda, Ilia, Region of Western Greece). Strawberries were harvested at three different time points over the main harvest period in Greece, i.e., early March (T1), late March (T2) and late April (T3). 'Fortuna' exhibited the highest early and total yield, while 'Calderon', the highest average berry weight. General Linear Model repeated measures ANOVA demonstrated that the interaction of the genotype and harvest time was significant (p < 0.001) on all tested quality attributes and gene expression levels, showing that each genotype behaves differently throughout the harvest period. Exceptions were observed for: (a) the volatile anhydrides, fatty acids, aromatics and phenylpropanoids (all were greatly affected by the harvest time), and (b) lactones, furaneol and FaEGS2 that were affected only by the genotype. We observed significant intercorrelations among those factors, e.g., the positive correlation of FaFAD1 expression with decalactone and nerolidol, of SAAT with furaneol, trans-cinnamic acid and phenylpropanoids, and of FaEGS2 with decalactone and FaFAD1. Moreover, a strong positive correlation between SAAT and FaMYB10 and a moderate negative one between SAAT and glucose were also detected. Those correlations can be further investigated to reveal potential markers for&nbsp;strawberry breeding. Overall, our study contributes to a better understanding of strawberry physiology, which would facilitate breeding efforts for the development of new strawberry varieties with superior qualitative traits.

Activation of Microbiota Sensing - Free Fatty Acid Receptor 2 Signaling Ameliorates Amyloid-β Induced Neurotoxicity by Modulating Proteolysis-Senescence Axis

Multiple emerging evidence indicates that the gut microbiota contributes to the pathology of Alzheimer's disease (AD)-a debilitating public health problem in older adults. However, strategies to beneficially modulate gut microbiota and its sensing signaling pathways remain largely unknown. Here, we screened, validated, and established the agonists of free fatty acid receptor 2 (FFAR2) signaling, which senses beneficial signals from short chain fatty acids (SCFAs) produced by microbiota. The abundance of SCFAs, is often low in the gut of older adults with AD. We demonstrated that inhibition of FFAR2 signaling increases amyloid-beta (Aβ) stimulated neuronal toxicity. Thus, we screened FFAR2 agonists using an in-silico library of more than 144,000 natural compounds and selected 15 of them based on binding with FFAR2-agonist active sites. Fenchol (a natural compound commonly present in basil) was recognized as a potential FFAR2 stimulator in neuronal cells and demonstrated protective effects against Aβ-stimulated neurodegeneration in an FFAR2-dependent manner. In addition, Fenchol reduced AD-like phenotypes, such as Aβ-accumulation, and impaired chemotaxis behavior in Caenorhabditis (C.) elegans and mice models, by increasing Aβ-clearance via the promotion of proteolysis and reduced senescence in neuronal cells. These results suggest that the inhibition of FFAR2 signaling promotes Aβ-induced neurodegeneration, while the activation of FFAR2 by Fenchol ameliorates these abnormalities by promoting proteolytic Aβ-clearance and reducing cellular senescence. Thus, stimulation of FFAR2 signaling by Fenchol as a natural compound can be a therapeutic approach to ameliorate AD pathology.

A glance at the chemodiversity of Ocimum species: Trends, implications, and strategies for the quality and yield improvement of essential oil

Ocimum species represent commercially important medicinal and aromatic plants. The essential oil biosynthesized by Ocimum species is enriched with specialized metabolites specifically, terpenoids and phenylpropanoids. Interestingly, various Ocimum species are known to exhibit diverse chemical profiles, and this chemical diversity has been at the center of many studies to identify commercially important chemotypes. Here, we present various chemotypes from the Ocimum species and emphasize trends, implications, and strategies for the quality and yield improvement of essential oil. Globally, many Ocimum species have been analyzed for their essential oil composition in over 50 countries. Asia represents the highest number of chemotypes, followed by Africa, South America, and Europe. Ocimum basilicum L. has been the most widespread and well-studied species, followed by O. gratissimum L., O. tenuiflorum L., O. canum Sims, O. americanum and O. kilimandscharicum Gürke. Moreover, various molecular reasons, benefits, adverse health effects and mechanisms behind this vast chemodiversity have been discussed. Different strategies of plant breeding, metabolic engineering, transgenic, and tissue-culture, along with anatomical modifications, are surveyed to enhance specific chemotypic profiles and essential oil yield in numerous Ocimum species. Consequently, chemical characterization of the essential oil obtained from Ocimum species has become indispensable for its proper utilization. The present chemodiversity knowledge from Ocimum species will help to exploit various applications in the industrial, agriculture, biopharmaceutical, and food sectors.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11101-021-09767-z.

Functional insights into two Ocimum kilimandscharicum 4-coumarate-CoA ligases involved in phenylpropanoid biosynthesis

Plant 4-coumarate-CoA ligase (4CL) catalyzes the ligation of CoA to cinnamic acid and its derivatives. Activated CoA esters are utilized for the biosynthesis of phenolic metabolites and lignin that play essential function in plants. Here, we characterize the diversity of Ocimum kilimandscharicum 4CLs (Ok4CLs). Phylogenetic analysis suggest that Ok4CLs could be grouped into three classes, class I - enzymes mostly involved in lignin biosynthesis, class II - non-structural phenylpropanoid biosynthesis and class III - yet to be characterized for specific role(s). We selected two Ok4CLs namely Ok4CL7 and Ok4CL15 for further characterization. Gene expression analysis suggested that Ok4CL7 is highly expressed in leaf trichomes, whereas Ok4CL15 is abundant in the roots. The recombinant Ok4CL7 and Ok4CL15 had optimal enzyme activities at 40 °C in pH 8 and 7, respectively. Ok4CL7 showed substrate preference towards p-coumaric acid, ferulic acid and caffeic acid. While, Ok4CL15 preferred p-coumaric acid, ferulic acid and sinapic acid. Feruloyl adenylate showed higher number of contacts and lowers binding energy with Ok4CL7 and 15 compared to cinnamoyl adenylate. Based on root-specific expression and preference for sinapic acid, Ok4CL15 might be involved in lignin biosynthesis. Further exploration is needed to unravel the role of diverse Ok4CLs in O. kilimandscharicum.

Leveraging Controlled-Environment Agriculture to Increase Key Basil Terpenoid and Phenylpropanoid Concentrations: The Effects of Radiation Intensity and CO2 Concentration on Consumer Preference

Altering the radiation intensity in controlled environments can influence volatile organic compound (VOC) biosynthetic pathways, including those of terpenoids and phenylpropanoids. In turn, the concentrations of these compounds can have a profound effect on flavor and sensory attributes. Because sweet basil (Ocimum basilicum) is a popular culinary herb, our objectives were to (1) determine the extent radiation intensity and carbon dioxide (CO₂) concentration influence seedling terpenoid and phenylpropanoid concentrations; (2) determine if differences in phenylpropanoid and terpenoid concentrations influence consumer preference; and (3) characterize consumer preferences to better inform production and marketing strategies. "Nufar" sweet basil was grown with CO₂ concentrations of 500 or 1,000 μmol ⋅ mol^-1 under sole-source radiation intensities of 100, 200, 400, or 600 μmol ⋅ m^-2 ⋅ s^-1 with a 16 h photoperiod to create daily light integrals of 6, 12, 23, and 35 mol ⋅ m^-2 ⋅ d^-1. After 2 weeks, concentrations of the terpenoids 1,8 cineole and linalool and the phenylpropanoids eugenol and methyl chavicol were quantified, and consumer sensory panel evaluations were conducted to quantify preferences. Overall, increasing radiation intensity from 100 to 600 μmol ⋅ m^-2 ⋅ s^-1 increased 1,8 cineole, linalool, and eugenol concentrations 2. 4-, 8. 8-, and 3.3-fold, respectively, whereas CO₂ concentration did not influence VOCs. Contrary to our hypothesis, increased VOC concentrations were not correlated with consumer preference. However, overall liking was correlated with aftertaste and flavor. The conclusion that consumer preference is dependent on flavor can be drawn. However, increasing VOC concentrations to increase flavor did not improve flavor preference. Many consumer sensory preference characteristics (favorable preference for aftertaste, bitterness/sweetness, color, flavor, overall liking, and texture) were correlated with basil grown under a radiation intensity of 200 μmol ⋅ m^-2 ⋅ s^-1. This led us to determine that consumers prefer to detect the characteristic basil flavor made up of 1,8 cineole, eugenol, and linalool, which was not as prevalent in basil grown under 100 μmol ⋅ m^-2 ⋅ s^-1, but too high in basil grown under 400 and 600 μmol ⋅ m^-2 ⋅ s^-1, which led to lower consumer preference.

Biosynthesis and tissue-specific partitioning of camphor and eugenol in Ocimum kilimandscharicum

In Ocimum kilimandscharicum, the relative volatile composition of camphor in leaves was as high as 55%, while that of eugenol in roots was 57%. These metabolites were differentially partitioned between the aerial and root tissues. Global metabolomics revealed tissue-specific biochemical specialization, evident by the differential distribution of 2588 putative metabolites across nine tissues. Next-generation sequencing analysis indicated differential expression of 51 phenylpropanoid and 55 terpenoid pathway genes in aerial and root tissues. By integrating metabolomics with transcriptomics, the camphor biosynthesis pathway in O. kilimandscharicum was elucidated. In planta bioassays revealed the role of geranyl diphosphate synthase (gpps) and borneol dehydrogenase (bdh) in camphor biosynthesis. Further, the partitioning of camphor was attributed to tissue-specific gene expression of both the pathway entry point (gpps) and terminal (bdh) enzyme. Unlike camphor, eugenol accumulated more in roots; however, absence of the eugenol synthase gene in roots indicated long distance transport from aerial tissues. In silico co-expression analysis indicated the potential involvement of ATP-binding cassette, multidrug and toxic compound extrusion, and sugar transporters in eugenol transport. Similar partitioning was evident across five other Ocimum species. Overall, our work indicates that metabolite partitioning maybe a finely regulated process, which may have implications on plant growth, development, and defense.

Successive Harvests Affect Yield, Quality and Metabolic Profile of Sweet Basil (Ocimum basilicum L.)

Sweet basil (Ocimum basilicum L.) is an aromatic, tender leafy green cultivated for the fresh market and industrial processing. Like many other leafy vegetables, this species can be harvested more than once to increase productivity. Although the cut-and-come-again (CC) harvest strategy is widespread in basil, not much is known about the effect of the cut. In this work, we examined differences in biomass, physiology, nutrient use efficiency and antioxidant capacity of basil leaves from two successive harvests. Moreover, we also performed an untargeted metabolomics analysis to reveal variations in the leaf metabolite profile. The data indicated that the cut affected many of the parameters under investigation, including a modest reduction of yield (−20%), of nitrogen use efficiency (−21%) and of some quality attributes such as the antioxidant capacity (−16%) and the nitrate content in leaves (+48%). Moreover, leaves of successive cuts displayed a significant variation of the profile of bioactive compounds, characterized by an overall decrease of phenylpropanoids and an increase in terpenoids. Our data revealed the impact of CC harvesting strategy in basil, and that this strategy offers the possibility to yield leaves with different metabolomics profiles and quality attributes.

Biosynthesis of methyleugenol and methylisoeugenol in Daucus carota leaves: Characterization of eugenol/isoeugenol synthase and O-Methyltransferase

Carrot (Daucus carota subsp. sativus) is a widely cultivated root vegetable of high economic importance. The aroma of carrot roots and aboveground organs is mainly defined by terpenes. We found that leaves of orange carrot cultivar also produce considerable amounts of the phenylpropenes methyleugenol and methylisoeugenol. Notably, methyleugenol is most abundant in young leaves, while methylisoeugenol is the dominant phenylpropene in mature leaf tissue. The goal of the present study was to shed light on the biochemistry and molecular biology of these compounds' biosynthesis and accumulation. Using the available genomic and transcriptomic data, we isolated a cDNA encoding eugenol/isoeugenol synthase (DcE(I)GS1), an NADPH-dependent enzyme that converts coniferyl acetate to eugenol. This enzyme exhibits dual product specificity and yields propenylphenol isoeugenol alongside allylphenol eugenol. Furthermore, we identified a cDNA encoding S-adenosyl-L-methionine:eugenol/isoeugenol O-methyltransferase 1 (DcE(I)OMT1) that produces methyleugenol and methylisoeugenol via methylation of the para-OH-group of their respective precursors. Both DcE(I)GS1 and DcE(I)OMT1 were expressed in seeds, roots, young and mature leaves, and the DcE(I)OMT1 transcript levels were the highest in leaves. The DcE(I)GS1 protein is 67% identical to anise t-anol/isoeugenol synthase and displays an apparent K_m of 247 μM for coniferyl acetate. The catalytic efficiency of DcEOMT1 with eugenol is more than five-fold higher than that with isoeugenol, with K_m values of 40 μM for eugenol, and of 115 μM for isoeugenol. This work expands the current knowledge of the enzymes involved in phenylpropene biosynthesis and would enable studies into structural elements defining the regioselectivity of phenylpropene synthases.

The Clinical Efficacy and Safety of Tulsi in Humans: A Systematic Review of the Literature

Tulsi, also known as holy basil, is indigenous to the Indian continent and highly revered for its medicinal uses within the Ayurvedic and Siddha medical systems. Many in vitro, animal and human studies attest to tulsi having multiple therapeutic actions including adaptogenic, antimicrobial, anti-inflammatory, cardioprotective, and immunomodulatory effects, yet to date there are no systematic reviews of human research on tulsi's clinical efficacy and safety. We conducted a comprehensive literature review of human studies that reported on a clinical outcome after ingestion of tulsi. We searched for studies published in books, theses, conference proceedings, and electronic databases including Cochrane Library, Google Scholar, Embase, Medline, PubMed, Science Direct, and Indian Medical databases. A total of 24 studies were identified that reported therapeutic effects on metabolic disorders, cardiovascular disease, immunity, and neurocognition. All studies reported favourable clinical outcomes with no studies reporting any significant adverse events. The reviewed studies reinforce traditional uses and suggest tulsi is an effective treatment for lifestyle-related chronic diseases including diabetes, metabolic syndrome, and psychological stress. Further studies are required to explore mechanisms of action, clarify the dosage and dose form, and determine the populations most likely to benefit from tulsi's therapeutic effects.

Analytical method for metabolites involved in biosynthesis of plant volatile compounds

The progress in the successful techniques used for studying metabolites involved in the metabolic routes of plant volatiles is summarized.

Comparative functional characterization of eugenol synthase from four different Ocimum species: Implications on eugenol accumulation

Isoprenoids and phenylpropanoids are the major secondary metabolite constituents in Ocimum genus. Though enzymes from phenylpropanoid pathway have been characterized from few plants, limited information exists on how they modulate levels of secondary metabolites. Here, we performed phenylpropanoid profiling in different tissues from five Ocimum species, which revealed significant variations in secondary metabolites including eugenol, eugenol methyl ether, estragole and methyl cinnamate levels. Expression analysis of eugenol synthase (EGS) gene showed higher transcript levels especially in young leaves and inflorescence; and were positively correlated with eugenol contents. Additionally, transcript levels of coniferyl alcohol acyl transferase, a key enzyme diverting pool of substrate to phenylpropanoids, were in accordance with their abundance in respective species. In particular, eugenol methyl transferase expression positively correlated with higher levels of eugenol methyl ether in Ocimum tenuiflorum. Further, EGSs were functionally characterized from four Ocimum species varying in their eugenol contents. Kinetic and expression analyses indicated, higher enzyme turnover and transcripts levels, in species accumulating more eugenol. Moreover, biochemical and bioinformatics studies demonstrated that coniferyl acetate was the preferred substrate over coumaryl acetate when used, individually or together, in the enzyme assay. Overall, this study revealed the preliminary evidence for varied accumulation of eugenol and its abundance over chavicol in these Ocimum species. Current findings could potentially provide novel insights for metabolic modulations in medicinal and aromatic plants.