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Thymol and carvacrol are phenolic monoterpenes found in thyme, oregano, and several other species of the Lamiaceae. Long valued for their smell and taste, these substances also have antibacterial and anti-spasmolytic properties. They are also suggested to be precursors of thymohydroquinone and thymoquinone, monoterpenes with anti-inflammatory, antioxidant, and antitumor activities. Thymol and carvacrol biosynthesis has been proposed to proceed by the cyclization of geranyl diphosphate to γ-terpinene, followed by a series of oxidations via p-cymene. Here, we show that γ-terpinene is oxidized by cytochrome P450 monooxygenases (P450s) of the CYP71D subfamily to produce unstable cyclohexadienol intermediates, which are then dehydrogenated by a short-chain dehydrogenase/reductase (SDR) to the corresponding ketones. The subsequent formation of the aromatic compounds occurs via keto–enol tautomerisms. Combining these enzymes with γ-terpinene in in vitro assays or in vivo in Nicotiana benthamiana yielded thymol and carvacrol as products. In the absence of the SDRs, only p-cymene was formed by rearrangement of the cyclohexadienol intermediates. The nature of these unstable intermediates was inferred from reactions with the γ-terpinene isomer limonene and by analogy to reactions catalyzed by related enzymes. We also identified and characterized two P450s of the CYP76S and CYP736A subfamilies that catalyze the hydroxylation of thymol and carvacrol to thymohydroquinone when heterologously expressed in yeast and N. benthamiana. Our findings alter previous views of thymol and carvacrol formation, identify the enzymes involved in the biosynthesis of these phenolic monoterpenes and thymohydroquinone in the Lamiaceae, and provide targets for metabolic engineering of high-value terpenes in plants.

Acute kidney injury (AKI) is a syndrome characterized by an accelerating decrease in renal function in a short time. Thymol is one of the main components of thyme species and has a variety of pharmacological effects. Here, we investigated whether thymol could ameliorate rhabdomyolysis (RM)-induced AKI and its related mechanism. Glycerol was used to induce RM-associated AKI in rats. Rats received thymol (20 mg/kg/day or 40 mg/kg/day) gavage 24 h before glycerol injection until 72 h after injection daily. Kidney injury was identified by measuring serum creatinine (Scr) and urea levels and by H&E and PAS staining and immunohistochemistry (the expression of proliferating cell nuclear antigen (PCNA)). Renal superoxide dismutase (SOD), malondialdehyde (MDA), and oxidative stress-related Nrf2/HO-1 signaling pathways were measured. The expression of the inflammatory markers TNF-α, IL-6, MCP-1, and NF-κB was assessed by ELISA and western blotting. Finally, the expression of the PI3K/Akt signaling pathway was detected by western blotting. Glycerol administration induced obvious renal histologic damage and increased Scr, urea, and PCNA expression. Notably, thymol treatment attenuated these structural and functional changes and prevented renal oxidative stress, inflammatory damage and PI3K/Akt pathway downregulation associated with glycerol-induced AKI. In conclusion, thymol might have potential applications in the amelioration of AKI via its antioxidant and anti-inflammatory effects and upregulation of the PI3K/Akt signaling pathway.

Volatile organic compounds (VOCs) released under cold stress have emerged as important mediators of stress tolerance. However, the specific functional VOCs and the mechanisms through which they confer cold tolerance remain largely unknown. In this study, we established a Fluo‐8‐based calcium detection system in tea ( Camellia sinensis ) protoplasts to investigate the interplay between cold‐induced VOCs, calcium signalling, and cold tolerance. We identified ( Z )‐3‐hexenol and thymol as key VOCs that significantly enhance tea plant cold tolerance by activating cytosolic calcium signalling. These VOCs upregulated cold‐responsive genes ( CsICE1 , CsCBF1 , and CsCBF2 ), enhanced antioxidant enzyme activities (SOD and POD), and improved photosynthetic efficiency under cold stress. Furthermore, we revealed that CsCDPK4 , a calcium‐dependent protein kinase, acts as a key mediator of ( Z )‐3‐hexenol and thymol‐induced calcium signalling. Silencing CsCDPK4 abolished the beneficial effects of ( Z )‐3‐hexenol and thymol, underscoring its critical role in translating calcium signals into physiological adaptations. Our findings provide a mechanistic framework linking VOC perception, calcium signalling, and cold stress tolerance, offering novel strategies for enhancing crop resilience against abiotic stress in the face of climate challenges.

Thymus vulgaris L. is a rich source of thymol and rosmarinic acid. Nowadays, water deficiency is one of the critical environmental factors affecting plants performance and metabolites. Melatonin, as a biostimulant, increases the tolerance of plant to environment stressors, especially drought. In order to exploit dry and low-yielding lands, this study was conducted on enhancing T. vulgaris ' growth, phytochemical and biochemical traits by means of melatonin foliar spray (0, 50, 100, and 150 µM) under various water deficiencies (100%, 70%, and 40% FC) which were carried out as a factorial completely randomized design. Foliar application of melatonin caused to improve water deficit tolerance, successfully revived the suppressed morphological traits and significantly increased biochemical capacity. The findings of present experiment demonstrated that as water deficiency increased, growing parameters reduced although, the negative effect of water deficit on vegetative parameters such as plant height/diameter, leaf length/width, and shoot fresh/dry weight were ameliorated by melatonin specially at concentration of 100 µM. The maximum essential oil content and yield was recorded respectively at 40% FC and 100% FC in combination with 100 µM melatonin. Based on GC and HPLC analyses, the amount of thymol, carvacrol and rosmarinic acid in the treatment of 40% FC and 150 μM melatonin increased by 42.25%, 81.36%, and 85.34%, respectively, compared to the control. Increase in drought severity led to increase in total phenol content, total flavonoid content, and also antioxidant capacity which were multiplied by 100 µM melatonin application. The least malondialdehyde (MDA) content, and hydrogen peroxide (H 2 O 2 ) generation as well as proline accumulation was related to the plants treated with 150 µM melatonin under normal conditions while plants grown at 40% FC without melatonin had the most concentrations of the mentioned osmolytes. Regardless to melatonin application, in T. vulgaris under 40% FC conditions the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were considerably more than those in control plants (100% FC) by 4.1, 1.8, and 0.64 times respectively. However, increased levels of melatonin had a promoting effect on POD and CAT activity, although SOD was negatively affected by melatonin concentrations. In conclusion melatonin probably with protection against oxidative damage and scavenging of free radicals through the stimulation of the enzymatic system, enrichment of plasma with phytochemicals, and regulation of osmotic status of the cells through accumulation of various solutes leads to an increase in the T. vulgaris tolerance against drought stress and ultimately increases the growth and phytochemical compounds.

Background and objective Salt stress is one of the most important abiotic stresses affecting the yield and quality of tobacco ( Nicotiana tabacum ). Thymol (a natural medicine) has been widely used in medical research because of its antibacterial and anti-inflammatory activities. However, the influence of thymol on the root growth of tobacco is not fully elucidated. In this study, the regulatory effects of different concentrations of thymol were investigated. Methodology Here, histochemical staining and biochemical methods, non-invasive micro-test technology (NMT), and qPCR assay were performed to investigate the effect of thymol and mechanism of it improving salinity tolerance in tobacco seedlings. Results In this study, our results showed that thymol rescued root growth from salt stress by ameliorating ROS accumulation, lipid peroxidation, and cell death. Furthermore, thymol enhanced contents of NO and GSH to repress ROS accumulation, further protecting the stability of the cell membrane. And, thymol improved Na + efflux and the expression of SOS1 , HKT1 , and NHX1 , thus protecting the stability of Na + and K + . Conclusion Our study confirmed the protecting effect of thymol in tobacco under salt stress, and we also identified the mechanism of it, involving dynamic regulation of antioxidant system and the maintenance of Na + homeostasis. It can be a new method to improve salinity tolerance in plants.

Background Zataria multiflora Boiss. is a medicinal and aromatic plant from the Lamiaceae family. It is extensively used in Iranian traditional medicine, mostly as a replacement for Thyme species. This study was focused on the analysis of chemical composition and the distribution and types of trichomes of Z. multiflora grown under different conditions. Equilibrium headspace analysis in combination with GC-FID-MS was used to identify volatile compounds released by aerial parts of Z. multiflora in development stages of 50 and 100% flowering under normal and drought-stress conditions. Results The main constituents were p-cymene (20.06–27.40%), γ-terpinene (12.44–16.93%), and α-pinene (6.91–16.58%) and thymol (8.52–9.99%). The highest content of p-cymene (27.40%) and thymol (9.99%) was observed in the 50% flowering stage at the 90% field capacity, while the maximum γ-terpinene (16.93%) content was recorded in the 100% flowering stage under normal conditions. Using the SEM method, it was found that peltate glandular and non-glandular trichomes are distributed on the surface of the leaf, stem, and outer side of the calyx. However, capitate trichomes only are detected on the stem and calyx in the 100% flowering and beginning of blooming stages, respectively. The type and structure of trichomes do not vary in different development stages, but they differ in density. The highest number of leaf peltate glandular trichomes was observed in the vegetative and beginning of blooming stages at 50% and 90% field capacity, respectively. Non-glandular trichomes of the stem were observed with high density in both normal and stress conditions, which are more densely in 90% field capacity. Conclusions Since this plant has strong potential to be used in the food and pharmacological industries, this study provides valuable information for its cultivation and harvesting at specific phenological stages, depending on desired compounds and their concentrations.

Background Thymol and carvacrol are natural phenolic compounds with various biological activities. They are widely used in the spice and medicine industries. Production of thymol and carvacrol using microbial cell factories is considered a viable alternative to extracting them from plants of the Thymus genus or the Lamiaceae family. Results In this study, the complete synthetic pathways of thymol and carvacrol were constructed using the oleaginous yeast Yarrowia lipolytica Po1f as a chassis. The total titer of thymol and carvacrol was increased 18.44-fold by enhancing the mevalonate pathway during the modification process and reducing the metabolic flux from geranyl diphosphate (GPP) to farnesyl diphosphate (FPP) through the modification of ERG20. Next, by increasing the copy number of the TvCYP71D507 gene combination ( TvCYP71D507 + TvTPS2 + TvSDR1 ) in the synthetic pathway, the total titer was increased by 1.75-fold. Finally, the engineered strain CT18, which was reintroduced the 3-isopropylmalate dehydrogenase ( LEU2 ) gene, achieved a titer of thymol and carvacrol of 7.14 mg/L in shake flasks and 61.31 mg/L in a 5-L bioreactor. Conclusion This study demonstrates the de novo synthesis of thymol and carvacrol in Y. lipolytica for the first time and provides a valuable reference for constructing microbial cell factories for phenolic monoterpenes biosynthesis.

Thyme species are a good source of thymol and carvacrol, which play a key role in controlling diseases. For the first time, the expression patterns of γ-terpinene synthase (TPS2), CYP71D178, and CYP71D180 genes and the amount of phenolics compounds were evaluated in T. migricus and T. daenensis after different methyl jasmonate (MeJA) treatments. The highest thymol and carvacrol contents were observed in T. migricus (86.27%) and T. daenensis (17.87%) at MeJA 100 µM, which was consistent with the expression patterns of the three investigated genes. All species treated showed high total phenolic and flavonoid content compared to control plants for which the highest amounts were observed in T. vulgaris treated with 100 µM and 10 µM MeJA. Furthermore, in the 100 µM MeJA treatment, the relative expression of TPS2 and CYP71D178 in T. migricus increased 7.47 and 9.86-fold compared with the control, respectively. The highest level of CYP71D180 transcripts (5.15-fold) was also observed for T. daenensis treated. This finding highlights the notion that thymol was known as the dominant component of the essential oil rather than carvacrol in diffident thyme species. This implies that MeJA at different concentrations influenced metabolic pathways and induced expression changes, resulting in a rise in essential oil levels.

Background Poultry housing includes unavoidable stressors that impair birds’ welfare and health. Global policies are banning antimicrobial growth promoters mainly due to antimicrobial resistance. Antioxidants modulate immunity by reducing oxidative stress, which impairs immune function. Thymol (THY), tocopherol (TOC) and ascorbyl palmitate (AP) have been studied for their antioxidant, antimicrobial and anxiety/fear‐reducing properties. However, their effects on immune function and stress responses in broilers require further investigation. Objectives This study assesses whether dietary THY or a TOC and AP mix modulates immune and chronic stress‐related responses in broilers. Methods Cobb‐500 chicks (n = 960) were assigned to one of 6 dietary treatments: (1) Basal (control), (2) Promotor (Basal + flavomycin), (3) BHT (Basal + butylated hydroxytoluene), (4) Promotor‐BHT (Basal + flavomycin + BHT), (5) THY (Basal + thymol) and (6) TOC‐AP (Basal + tocopherol + AP). Immune and stress parameters were evaluated, including inflammatory response to phytohemagglutinin‐P (PHA‐P), antibody production against sheep red blood cells (SRBC) and heterophil‐to‐lymphocyte (H/L) ratio. Results Supplementation did not affect the PHA‐P inflammatory response (p = 0.72) but influenced SRBC antibody production and H/L ratio (p < 0.003). Broilers supplemented with THY or TOC‐AP exhibited significantly lower antibody responses, potentially avoiding an energy‐demanding acquired immune activation. Additionally, both groups showed significantly lower H/L ratios, suggesting that these supplements may help mitigate physiological stress induced by routine husbandry practices. Conclusion These findings provide evidence that THY and TOC‐AP may serve as natural alternative to synthetic additives for improving welfare and mitigating stress‐induced immune imbalance under commercial rearing conditions. Poultry housing stress impairs welfare and health, whereas antimicrobial growth promoters are being banned due to resistance concerns. This study evaluates thymol (THY) and a tocopherol–ascorbyl palmitate mix (TOC‐AP) supplementation in broilers, showing reduced antibody responses and heterophil‐to‐lymphocyte ratios, suggesting potential benefits for mitigating stress‐induced immune imbalances and improving welfare.

Honey bees learn to associate sugars with odorants in controlled laboratory conditions and during foraging. The memory of these associations can be impaired after exposure to contaminants such as pesticides. The sub-lethal effects of acaricides such as 5-methyl-2-(propan-2-yl)-phenol (thymol) introduced into colonies to control varroa mites are of particular concern to beekeeping, due to detrimental effects of some acaricides on bees. Here we assess whether various odorant/sugar pairs are identically memorized in a differential appetitive olfactory conditioning experiment and whether this learning is affected by thymol exposure. Responses to odorants in retrieval tests varied according to the sugar they were paired with, a property called congruency. Interestingly, congruency was altered by pre-exposure to some thymol concentrations during retrieval tests, although electroantennography recordings showed it left odorant detection intact. This highlights the importance of taking into account subtle effects such as odor/sugar congruency in the study of the effect of pesticides on non-target insects, in addition to the simpler question of memory impairment.