Apple tree flowering is mediated by low level of melatonin under the regulation of seasonal light signal

Views and perspectives on the indoleamines serotonin and melatonin in plants: past, present and future

In the decades since their discovery in plants in the mid-to-late 1900s, melatonin (N-acetyl-5-methoxytryptamine) and serotonin (5-methoxytryptamine) have been established as their own class of phytohormone and have become popular targets for examination and study as stress ameliorating compounds. The indoleamines play roles across the plant life cycle from reproduction to morphogenesis and plant environmental perception. There is growing interest in harnessing the power of these plant neurotransmitters in applied and agricultural settings, particularly as we face increasingly volatile climates for food production; however, there is still a lot to learn about the mechanisms of indoleamine action in plants. A recent explosion of interest in these compounds has led to exponential growth in the field of melatonin research in particular. This concept paper aims to summarize the current status of indoleamine research and highlight some emerging trends.

Phytomelatonin: From Intracellular Signaling to Global Horticulture Market

Melatonin (N-acetyl-5-methoxytryptamine), a well-known mammalian hormone, has been having a great relevance in the Plant World in recent years. Many of its physiological actions in plants are leading to possible features of agronomic interest, especially those related to improvements in tolerance to stressors and in the postharvest life of fruits and vegetables. Thus, through the exogenous application of melatonin or by modifying the endogenous biosynthesis of phytomelatonin, some change can be made in the functional levels of melatonin in tissues and their responses. Also, acting in the respective phytomelatonin biosynthesis enzymes, regulating the expression of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), N-acetylserotonin O-methyltransferase (ASMT), and caffeic acid O-methyltransferase (COMT), and recently the possible action of deacetylases on some intermediates offers promising opportunities for improving fruits and vegetables in postharvest and its marketability. Other regulators/effectors such as different transcription factors, protein kinases, phosphatases, miRNAs, protein-protein interactions, and some gasotransmitters such as nitric oxide or hydrogen sulfide were also considered in an exhaustive vision. Other interesting aspects such as the role of phytomelatonin in autophagic responses, the posttranslational reprogramming by protein-phosphorylation, ubiquitylation, SUMOylation, PARylation, persulfidation, and nitrosylation described in the phytomelatonin-mediated responses were also discussed, including the relationship of phytomelatonin and several plant hormones, for chilling injury and fungal decay alleviating. The current data about the phytomelatonin receptor in plants (CAND2/PMTR1), the effect of UV-B light and cold storage on the postharvest damage are presented and discussed. All this on the focus of a possible new action in the preservation of the quality of fruits and vegetables.

Melatonin Interaction with Other Phytohormones in the Regulation of Abiotic Stresses in Horticultural Plants

Horticultural crops play a vital role in global food production, nutrition, and the economy. Horticultural crops are highly vulnerable to abiotic stresses. These abiotic stresses hinder plant growth and development by affecting seed germination, impairing photosynthetic activity, and damaging root development, thus leading to a decrease in fruit yield, quality, and productivity. Scientists have conducted extensive research to investigate the mechanisms of resilience and the ability to cope with environmental stresses. In contrast, the use of phytohormones to alleviate the detrimental impacts of abiotic stresses on horticulture plants has been generally recognized as an effective method. Among phytohormones, melatonin (MT) is a novel plant hormone that regulates various plants' physiological functions such as seedling development, root system architecture, photosynthetic efficiency, balanced redox homeostasis, secondary metabolites production, accumulation of mineral nutrient uptake, and activated antioxidant defense system. Importantly, MT application significantly restricted heavy metals (HMs) uptake and increased mineral nutrient accumulation by modifying the root architecture system. In addition, MT is a naturally occurring, multifunctional, nontoxic biomolecule having antioxidant properties. Furthermore, this review described the hormonal interaction between MT and other signaling molecules in order to enhance abiotic stress tolerance in horticulture crops. This review focuses on current research advancements and prospective approaches for enhancing crop tolerance to abiotic stress.

Nanovehicles for melatonin: a new journey for agriculture

The important role of melatonin in plant growth and metabolism together with recent advances in the potential use of nanomaterials have opened up interesting applications in agriculture. Various nanovehicles have been explored as melatonin carriers in animals, and it is now important to explore their application in plants. Recent findings have substantiated the use of silicon and chitosan nanoparticles (NPs) in targeting melatonin to plant tissues. Although melatonin is an amphipathic molecule, nanocarriers can accelerate its uptake and transport to various plant organs, thereby relieving stress and improving plant shelf-life in the post-harvest stages. We review the scope and biosafety concerns of various nanomaterials to devise novel methods for melatonin application in crops and post-harvest products.

Straw Mulch Induced Indoleamines Alleviate Reproductive Depression in Cold Sensitive Hazelnut Cultivars

Climate change is forcing physiological changes, especially in temperate trees, in which the reproduction phase has been affected harshly, eventually resulting in poor performance. Erratic fluctuations during the flowering periods, predominantly in cold-sensitive, yet industry-desired (sourced), hazelnut cultivars have been causing at least a 10-fold decline in the nut yield. Indoleamines have been noted to provide protection during such abiotic stress conditions. In this study, we investigated the potential involvement of the indoleamine pathway in countering reproductive depression in cold-sensitive hazelnuts by blanketing the ground with wheat straw mulch. The female flower ratio; titers of tryptophan, serotonin, and melatonin; and indoleamine pathway gene regulation were the endpoints for assessing the effects of straw mulch. In the preceding year, we noted that the occurrence of phenological events through the modulation of indoleamines was necessitated via percolation of snowmelt into the rootzone. Otherwise, reproductive depression was noted, especially in harsh conditions, such as 'no snow' or when the rootzone was covered with a plastic sheet to disallow water percolation. When cold-sensitive hazelnut cultivars that were subjected to such deleterious treatments in the preceding years' experiments were treated with straw mulch, the female flower ratio was unaffected and remained on par with that of the cold-hardy locally adapted cultivars. Tryptophan accumulation improved in the (cold-sensitive) sourced cultivars treated with straw mulch and was available as serotonin to counter the cold stress. Lower titers of melatonin explained the slight improvement in female ratio in the sourced cultivars blanketed with straw mulch. ASMT gene regulation via straw mulch treatment emphasized its role in abiotic stress mitigation. A negative trend was noted when improved flowering was compared to the decreased expression of the ASMT gene. Horticultural changes, such as mulch, should provide mitigating solutions to relieve reproductive depression in cold-sensitive hazelnuts, alongside implications in other horticultural crops. The indoleamine toolkit (cellular markers) developed in this study provides insights into the mechanisms of cold sensitivity (abiotic stress) and plausible solutions, such as exogenous application of indoleamines, to propagate climate resilient plant materials with an enhanced capacity to mitigate abiotic stress conditions.

Genetic and evolutionary dissection of melatonin response signaling facilitates the regulation of plant growth and stress responses

The expansion of gene families during evolution could generate functional diversity among their members to regulate plant growth and development. Melatonin, a phylogenetically ancient molecule, is vital for many aspects of a plant's life. Understanding the functional diversity of the molecular players involved in melatonin biosynthesis, signaling, and metabolism will facilitate the regulation of plant phenotypes. However, the molecular mechanism of melatonin response signaling elements in regulating this network still has many challenges. Here, we provide an in-depth analysis of the functional diversity and evolution of molecular components in melatonin signaling pathway. Genetic analysis of multiple mutants in plant species will shed light on the role of gene families in melatonin regulatory pathways. Phylogenetic analysis of these genes was performed, which will facilitate the identification of melatonin-related genes for future study. Based on the abovementioned signal networks, the mechanism of these genes was summarized to provide reference for studying the regulatory mechanism of melatonin in plant phenotypes. We hope that this work will facilitate melatonin research in higher plants and finely tuned spatio-temporal regulation of melatonin signaling.

Functions of Melatonin during Postharvest of Horticultural Crops

Melatonin, a tryptophan-derived molecule, is endogenously generated in animal, plant, fungal and prokaryotic cells. Given its antioxidant properties, it is involved in a myriad of signaling functions associated with various aspects of plant growth and development. In higher plants, melatonin (Mel) interacts with plant regulators such as phytohormones, as well as reactive oxygen and nitrogen species including hydrogen peroxide (H2O2), nitric oxide (NO) and hydrogen sulfide (H2S). It shows great potential as a biotechnological tool to alleviate biotic and abiotic stress, to delay senescence and to conserve the sensory and nutritional quality of postharvest horticultural products which are of considerable economic importance worldwide. This review provides a comprehensive overview of the biochemistry of Mel, whose endogenous induction and exogenous application can play an important biotechnological role in enhancing the marketability and hence earnings from postharvest horticultural crops.

Melatonin: Both a Messenger of Darkness and a Participant in the Cellular Actions of Non-Visible Solar Radiation of Near Infrared Light

Throughout the history of melatonin research, almost exclusive focus has been on nocturnally-generated pineal melatonin production, which accounts for its circadian rhythm in the blood and cerebrospinal fluid; these light/dark melatonin cycles drive the daily and seasonal photoperiodic alterations in organismal physiology. Because pineal melatonin is produced and secreted primarily at night, it is referred to as the chemical expression of darkness. The importance of the other sources of melatonin has almost been ignored. Based on current evidence, there are at least four sources of melatonin in vertebrates that contribute to the whole-body melatonin pool. These include melatonin produced by (1) the pineal gland; (2) extrapineal cells, tissues, and organs; (3) the microbiota of the skin, mouth, nose, digestive tract, and vagina as well as (4) melatonin present in the diet. These multiple sources of melatonin exhibit differentially regulated mechanisms for its synthesis. Visible light striking the retina or an intense physical stimulus can suppress nocturnal pineal melatonin levels; in contrast, there are examples where extrapineal melatonin levels are increased during heavy exercise in daylight, which contains the whole range of NIR radiation. The cumulative impact of all cells producing augmented extrapineal melatonin is sufficient to elevate sweat concentrations, and potentially, if the exposure is sustained, to also increasing the circulating values. The transient increases in sweat and plasma melatonin support the premise that extrapineal melatonin has a production capacity that exceeds by far what can be produced by the pineal gland, and is used to maintain intercellular homeostasis and responds to rapid changes in ROS density. The potential regulatory mechanisms of near infrared light (NIR) on melatonin synthesis are discussed in detail herein. Combined with the discovery of high levels of melanopsin in most fat cells and their response to light further calls into question pineal centric theories. While the regulatory processes related to microbiota-derived melatonin are currently unknown, there does seem to be crosstalk between melatonin derived from the host and that originating from microbiota.

Exogenous melatonin enhances the growth and production of bioactive metabolites in Lemna aequinoctialis culture by modulating metabolic and lipidomic profiles

BACKGROUND

Lemna species are cosmopolitan floating plants that have great application potential in the food/feed, pharmaceutical, phytoremediation, biofuel, and bioplastic industries. In this study, the effects of exogenous melatonin (0.1, 1, and 10 µM) on the growth and production of various bioactive metabolites and intact lipid species were investigated in Lemna aequinoctialis culture.

RESULTS

Melatonin treatment significantly enhanced the growth (total dry weight) of the Lemna aequinoctialis culture. Melatonin treatment also increased cellular production of metabolites including β-alanine, ascorbic acid, aspartic acid, citric acid, chlorophyll, glutamic acid, phytosterols, serotonin, and sucrose, and intact lipid species; digalactosyldiacylglycerols, monogalactosyldiacylglycerols, phosphatidylinositols, and sulfoquinovosyldiacylglycerols. Among those metabolites, the productivity of campesterol (1.79 mg/L) and stigmasterol (10.94 mg/L) were the highest at day 28, when 10 µM melatonin was treated at day 7.

CONCLUSION

These results suggest that melatonin treatment could be employed for enhanced production of biomass or various bioactive metabolites and intact lipid species in large-scale L. aequinoctialis cultivation as a resource for food, feed, and pharmaceutical industries.

Dark secrets of phytomelatonin

Phytomelatonin is a newly identified plant hormone, and its primary functions in plant growth and development remain relatively poorly appraised. Phytomelatonin is a master regulator of reactive oxygen species (ROS) signaling and acts as a darkness signal in circadian stomatal closure. Plants exhibit at least three interrelated patterns of interaction between phytomelatonin and ROS production. Exogenous melatonin can induce flavonoid biosynthesis, which might be required for maintenance of antioxidant capacity under stress, after harvest, and in leaf senescence conditions. However, several genetic studies have provided direct evidence that phytomelatonin plays a negative role in the biosynthesis of flavonoids under non-stress conditions. Phytomelatonin delays flowering time in both dicot and monocot plants, probably via its receptor PMTR1 and interactions with the gibberellin, strigolactone, and ROS signaling pathways. Furthermore, phytomelatonin signaling also functions in hypocotyl and shoot growth in skotomorphogenesis and ultraviolet B (UV-B) exposure; the G protein α-subunit (Arabidopsis GPA1 and rice RGA1) and constitutive photomorphogenic1 (COP1) are important signal components during this process. Taken together, these findings indicate that phytomelatonin acts as a darkness signal with important regulatory roles in circadian stomatal closure, flavonoid biosynthesis, flowering, and hypocotyl and shoot growth.

Functions and prospects of melatonin in plant growth, yield, and quality

Melatonin (N-acetyl-5-methoxytryptamine) is an indole molecule widely found in animals and plants. It is well known that melatonin improves plant resistance to various biotic and abiotic stresses due to its potent free radical scavenging ability while being able to modulate plant signaling and response pathways through mostly unknown mechanisms. In recent years, an increasing number of studies have shown that melatonin plays a crucial role in improving crop quality and yield by participating in the regulation of various aspects of plant growth and development. Here, we review the effects of melatonin on plant vegetative growth and reproductive development, and systematically summarize its molecular regulatory network. Moreover, the effective concentrations of exogenously applied melatonin in different crops or at different growth stages of the same crop are analysed. In addition, we compare endogenous phytomelatonin concentrations in various crops and different organs, and evaluate a potential function of phytomelatonin in plant circadian rhythms. The prospects of different approaches in regulating crop yield and quality through exogenous application of appropriate concentrations of melatonin, endogenous modification of phytomelatonin metabolism-related genes, and the use of nanomaterials and other technologies to improve melatonin utilization efficiency are also discussed.

Molecular mechanisms and evolutionary history of phytomelatonin in flowering

Flowering is a critical stage in plant life history, which is coordinated by environmental signals and endogenous cues. Phytomelatonin is a widely distributed indoleamine present in all living organisms and plays pleiotropic roles in plant growth and development. Recent evidence has established that phytomelatonin could modulate flowering in many species, probably in a concentration-dependent manner. Phytomelatonin seems to associate with floral meristem identification and floral organ formation, and the fluctuation of phytomelatonin might be important for flowering. Regarding the underlying mechanisms, phytomelatonin interacts with the central components of floral gene regulatory networks directly or indirectly, including the MADS-box gene family, phytohormones, and reactive oxygen species (ROS). From an evolutionary point of view, the actions of phytomelatonin in flowering probably evolved during the period of the diversification of flowering plants and could be regarded as a functional extension of its primary activities. The presumed evolutionary history of phytomelatonin-modulated flowering is proposed, presented in the chronological order of the appearance of phytomelatonin and core flowering regulators, namely DELLA proteins, ROS, and phytohormones. Further efforts are needed to address some intriguing aspects, such as the exploration of the association between phytomelatonin and photoperiodic flowering, phytomelatonin-related floral MADS-box genes, the crosstalk between phytomelatonin and phytohormones, as well as its potential applications in agriculture.

ELONGATED HYPOCOTYL 5-mediated suppression of melatonin biosynthesis is alleviated by darkness and promotes cotyledon opening

Melatonin (N-acetyl-5-methoxytryptamine) biosynthesis in plants is induced by darkness and high-intensity light; however, the underlying transcriptional mechanisms and upstream signalling pathways are unknown. We identified a dark-induced and highly expressed melatonin synthetase in Arabidopsis thaliana, AtSNAT6, encoding serotonin N-acetyltransferase. We assessed melatonin content and AtSNAT6 expression in mutants lacking key regulators of light/dark signalling. AtCOP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) and AtHY5 (ELONGATED HYPOCOTYL 5), which control light/dark transition and photomorphogenesis, promoted and suppressed melatonin biosynthesis, respectively. Using EMSA and ChIP-qPCR analysis, we showed that AtHY5 inhibits AtSNAT6 expression directly. An analysis of melatonin content in snat6 hy5 double mutant and AtHY5+AtSNAT6-overexpressing plants confirmed the regulatory function of AtHY5 and AtSNAT6 in melatonin biosynthesis. Exogenous melatonin further inhibited cotyledon opening in hy5 mutant and AtSNAT6-overexpressing seedlings, but partially reversed the promotion of cotyledon opening in AtHY5-overexpressing seedlings and snat6. Additionally, CRISPR/Cas9-mediated mutation of AtSNAT6 increased cotyledon opening in hy5 mutant, and overexpression of AtSNAT6 decreased cotyledon opening in AtHY5-overexpressing seedlings via changing melatonin biosynthesis, confirming that AtHY5 decreased melatonin-mediated inhibition of cotyledon opening. Our data provide new insights into the regulation of melatonin biosynthesis and its function in cotyledon opening.

The phytomelatonin receptor PMTR1 regulates seed development and germination by modulating abscisic acid homeostasis in Arabidopsis thaliana

Melatonin is known to involve multiple physiological actions in plants. Herein, we found that exogenous melatonin inhibited the Arabidopsis seedling growth through the elevated abscisic acid (ABA) levels, and the elevated ABA was ascribed to the upregulation of 9-cis-epoxycarotenoid dioxygenase genes (NCEDs) in the ABA biosynthesis pathway. We also found that the overexpression lines of the melatonin receptor gene PMTR1 (also known as Cand2) yielded smaller seeds and germinated slower than the wild type, whereas PMTR1-knockout mutants produced larger seeds and germinated faster than the wild type. During the seed development, the accumulation peak of ABA was higher in the PMTR1-knockout mutant, while it was lower in the PMTR1-overexpression line than that in the wild type. In the dry seeds and imbibed seeds, the PMTR1-overexpression line accumulated higher ABA levels, while the PMTR1-knockout contained less ABA than the wild type. In summary, our findings suggest that PMTR1 is involved in ABA-mediated seed development and germination in Arabidopsis.

Melatonin Maintains Fruit Quality and Reduces Anthracnose in Postharvest Papaya via Enhancement of Antioxidants and Inhibition of Pathogen Development

Papaya fruit is widely grown in tropical regions because of its sweet taste, vibrant color, and the huge number of health benefits it provides. Melatonin is an essential hormone that governs many plants′ biological processes. In the current study, the impact of melatonin on fruit ripening and deterioration in postharvest papaya fruit was explored. An optimum melatonin dose (400 μmol L⁻¹, 2 h) was found to be effective in delaying fruit softening and reducing anthracnose incidence. Melatonin enhanced antioxidant activity and decreased fruit oxidative injury by lowering superoxide anion, hydrogen peroxide, and malondialdehyde content by enhancing the enzymatic and non-enzymatic antioxidants, and by improving the antioxidant capacity of papaya fruit. Melatonin increased catalase, ascorbate peroxidase, NADH oxidase, glutathione reductase, polyphenol oxidase, superoxide dismutase, and peroxidase activity, as well as induced total phenol, total flavonoid, and ascorbic acid accumulation. Melatonin also enhanced the activity of defense-related enzymes, such as chitinase, 4-coumaric acid-CoA-ligase, and phenylalanine ammonia lyase, while it repressed lipid metabolism. Additionally, melatonin inhibited the development of anthracnose in vitro and in vivo. These findings suggest that exogenous melatonin application improves papaya fruit quality by boosting antioxidant and defense-related mechanisms.

Walnut N-Acetylserotonin Methyltransferase Gene Family Genome-Wide Identification and Diverse Functions Characterization During Flower Bud Development

Melatonin widely mediates multiple developmental dynamics in plants as a vital growth stimulator, stress protector, and developmental regulator. N-acetylserotonin methyltransferase (ASMT) is the key enzyme that catalyzes the final step of melatonin biosynthesis in plants and plays an essential role in the plant melatonin regulatory network. Studies of ASMT have contributed to understanding the mechanism of melatonin biosynthesis in plants. However, AMST gene is currently uncharacterized in most plants. In this study, we characterized the JrASMT gene family using bioinformatics in a melatonin-rich plant, walnut. Phylogenetic, gene structure, conserved motifs, promoter elements, interacting proteins and miRNA analyses were also performed. The expansion and differentiation of the ASMT family occurred before the onset of the plant terrestrialization. ASMT genes were more differentiated in dicotyledonous plants. Forty-six ASMT genes were distributed in clusters on 10 chromosomes of walnut. Four JrASMT genes had homologous relationships both within walnut and between species. Cis-regulatory elements showed that JrASMT was mainly induced by light and hormones, and targeted cleavage of miRNA172 and miR399 may be an important pathway to suppress JrASMT expression. Transcriptome data showed that 13 JrASMT were differentially expressed at different periods of walnut bud development. WGCNA showed that JrASMT1/10/13/23 were coexpressed with genes regulating cell fate and epigenetic modifications during early physiological differentiation of walnut female flower buds. JrASMT12/28/37/40 were highly expressed during morphological differentiation of flower buds, associated with altered stress capacity of walnut flower buds, and predicted to be involved in the regulatory network of abscisic acid, salicylic acid, and cytokinin in walnut. The qRT-PCR validated the results of differential expression analysis and further provided three JrASMT genes with different expression profiles in walnut flower bud development. Our study explored the evolutionary relationships of the plant ASMT gene family and the functional characteristics of walnut JrASMT. It provides a valuable perspective for further understanding the complex melatonin mechanisms in plant developmental regulation.

Potential roles of melatonin and ABA on apple dwarfing in semi-arid area of Xinjiang China

Dwarfing is a typic breeding trait for mechanical strengthening and relatively high yield in modern apple orchards. Clarification of the mechanisms associated with dwarfing is important for use of molecular technology to breed apple. Herein, we identified four dwarfing apple germplasms in semi-arid area of Xinjiang, China. The internodal distance of these four germplasms were significantly shorter than non-dwarfing control. Their high melatonin (MT) contents are negatively associated with their malondialdehyde (MDA) levels and oxidative damage. In addition, among the detected hormones including auxin (IAA), gibberellin (GA), brassinolide (BR), zeatin-riboside (ZR), and abscisic acid (ABA), only ABA and ZR levels were in good correlation with the dwarfing phenotype. The qPCR results showed that the expression of melatonin synthetic enzyme genes MdASMT1 and MdSNAT5, ABA synthetic enzyme gene MdAAO3 and degradative gene MdCYP707A, ZR synthetic enzyme gene MdIPT5 all correlated well with the enhanced levels of MT, ABA and the reduced level of of ZR in the dwarfing germplasms. Furthermore, the significantly higher expression of ABA marker genes (MdRD22 and MdRD29) and the lower expression of ZR marker genes (MdRR1 and MdRR2) in all the four dwarf germplasms were consistent with the ABA and ZR levels. Considering the yearly long-term drought occurring in Xinjiang, China, it seems that dwarfing with high contents of MT and ABA may be a good strategy for these germplasms to survive against drought stress. This trait of dwarfing may also benefit apple production and breeding in this semi-arid area.

Melatonin alleviates aluminum-induced growth inhibition by modulating carbon and nitrogen metabolism, and reestablishing redox homeostasis in Zea mays L

Melatonin, a regulatory molecule, performs pleiotropic functions in plants, including aluminum (Al) stress mitigation. Here, we conducted transcriptomic and physiological analyses to identify metabolic processes associated with the alleviated Al-induced growth inhibition of the melatonin-treated (MT) maize (Zea mays L.) seedlings. Melatonin decreased Al concentration in maize roots and leaves under Al stress. Al stress reduced the total dry weight (DW) by 41.2% after 7 days of treatment. By contrast, the total DW was decreased by only 19.4% in MT plants. According to RNA-Seq, enzyme activity, and metabolite content data, MT plants exhibited a higher level of relatively stable carbon and nitrogen metabolism than non-treated (NT) plants. Under Al stress, MT plants showed higher photosynthetic rate and sucrose content by 29.9% and 20.5% than NT plants, respectively. Similarly, the nitrate reductase activity and protein content of MT plants were 34.0% and 15.0% higher than those of NT plants, respectively. Furthermore, exogenous supply of melatonin mitigated Al-induced oxidative stress. Overall, our results suggest that melatonin alleviates aluminum-induced growth inhibition through modulating carbon and nitrogen metabolism, and reestablishing redox homeostasis in maize. Graphical Abstarct.

Melatonin Treatment Improves Postharvest Preservation and Resistance of Guava Fruit (Psidium guajava L.)

Guava fruit has a short postharvest shelf life at room temperature. Melatonin is widely used for preservation of various postharvest fruit and vegetables. In this study, an optimal melatonin treatment (600 μmol·L⁻¹, 2 h) was identified, which effectively delayed fruit softening and reduced the incidence of anthracnose on guava fruit. Melatonin effectively enhanced the antioxidant capacity and reduced the oxidative damage to the fruit by reducing the contents of superoxide anions, hydrogen peroxide and malondialdehyde; improving the overall antioxidant capacity and enhancing the enzymatic antioxidants and non-enzymatic antioxidants. Melatonin significantly enhanced the activities of catalase, superoxide dismutase, ascorbate peroxidase and glutathione reductase. The contents of total flavonoids and ascorbic acid were maintained by melatonin. This treatment also enhanced the defense-related enzymatic activities of chitinase and phenylpropanoid pathway enzymes, including phenylalanine ammonia lyase and 4-coumaric acid-CoA-ligase. The activities of lipase, lipoxygenase and phospholipase D related to lipid metabolism were repressed by melatonin. These results showed that exogenous melatonin can maintain the quality of guava fruit and enhance its resistance to disease by improving the antioxidant and defense systems of the fruit.

Melatonin-Mediated Abiotic Stress Tolerance in Plants

Melatonin is a multi-functional molecule that is ubiquitous in all living organisms. Melatonin performs essential roles in plant stress tolerance; its application can reduce the harmful effects of abiotic stresses. Plant melatonin biosynthesis, which usually occurs within chloroplasts, and its related metabolic pathways have been extensively characterized. Melatonin regulates plant stress responses by directly inhibiting the accumulation of reactive oxygen and nitrogen species, and by indirectly affecting stress response pathways. In this review, we summarize recent research concerning melatonin biosynthesis, metabolism, and antioxidation; we focus on melatonin-mediated tolerance to abiotic stresses including drought, waterlogging, salt, heat, cold, heavy metal toxicity, light and others. We also examine exogenous melatonin treatment in plants under abiotic stress. Finally, we discuss future perspectives in melatonin research and its applications in plants.

Spontaneous Recovery of Circadian Organization in Mice Lacking a Core Component of the Molecular Clockwork

Circadian rhythms are generated by interlocked transcriptional-translational feedback loops of circadian clock genes and their protein products. Mice homozygous for a functional deletion in the Period-2 gene (Per2^m/m mice) exhibit short free-running circadian periods and eventually lose behavioral circadian rhythmicity in constant darkness (DD). We investigated Per2^m/m mice in DD for several months and identified a categorical sex difference in the dependence on Per2 for maintenance of circadian rhythms. Nearly all female Per2^m/m mice became circadian arrhythmic in DD, whereas free-running rhythms persisted in 37% of males. Remarkably, with extended testing, Per2^m/m mice did not remain arrhythmic in DD, but after varying intervals spontaneously recovered robust, free-running circadian rhythms, with periods shorter than those expressed prior to arrhythmia. Spontaneous recovery was strikingly sex-biased, occurring in 95% of females and 33% of males. Castration in adulthood resulted in male Per2^m/m mice exhibiting female-like levels of arrhythmia in DD, but did not affect spontaneous recovery. The circadian pacemaker of many gonad-intact males, but not females, can persist in DD for long intervals without a functional PER2 protein; their circadian clocks may be in an unstable equilibrium, incapable of sustaining persistent coherent circadian organization, resulting in transient cycles of circadian organization and arrhythmia.

Genome-wide identification and characteristic analysis of the downstream melatonin metabolism gene GhM2H in Gossypium hirsutum L

Background

Melatonin 2-hydroxylase (M2H) is the first enzyme in the catabolism pathway of melatonin, which catalyzes the production of 2-hydroxymelatonin (2-OHM) from melatonin. The content of 2-hydroxymelatonin in plants is much higher than that of melatonin. So M2H may be a key enzyme in the metabolic pathway of melatonin.

Method

We conducted a systematic analysis of the M2H gene family in Gossypium hirsutum based on the whole genome sequence by integrating the structural characteristics, phylogenetic relationships, expression profile, and biological stress of the members of the Gossypium hirsutum M2H gene family.

Result

We identified 265 M2H genes in the whole genome of Gossypium hirsutum, which were divided into 7 clades (clades I-VII) according to phylogenetic analysis. Most M2H members in each group had similar motif composition and gene structure characteristics. More than half of GhM2H members contain ABA-responsive elements and MeJA-responsive elements. Under different stress conditions, the expression levels of the gene changed, indicating that GhM2H members were involved in the regulation of abiotic stress. Some genes in the GhM2H family were involved in regulating melatonin levels in cotton under salt stress, and some genes were regulated by exogenous melatonin.

Conclusion

This study is helpful to explore the function of GhM2H, the downstream metabolism gene of melatonin in cotton, and lay the foundation for better exploring the molecular mechanism of melatonin improving cotton's response to abiotic stress.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40659-021-00358-y.

The case of tryptamine and serotonin in plants: a mysterious precursor for an illustrious metabolite

Indolamines are tryptophan-derived specialized metabolites belonging to the huge and ubiquitous indole alkaloids group. Serotonin and melatonin are the best-characterized members of this family, given their many hormonal and physiological roles in animals. Following their discovery in plants, the study of plant indolamines has flourished and their involvement in important processes, including stress responses, growth and development, and reproduction, has been proposed, leading to their classification as a new category of phytohormones. However, the complex indolamine puzzle is far from resolved, particularly the biological roles of tryptamine, the early serotonin precursor representing the central hub of many downstream indole alkaloids. Tryptophan decarboxylase, which catalyzes the synthesis of tryptamine, strictly regulates the flux of carbon and nitrogen from the tryptophan pool into the indolamine pathway. Furthermore, tryptamine accumulates to high levels in the reproductive organs of many plant species and therefore cannot be classed as a mere intermediate but rather as an end product with potentially important functions in fruits and seeds. This review summarizes current knowledge on the role of tryptamine and its close relative serotonin, emphasizing the need for a clear understanding of the functions of, and mutual relations between, these indolamines and their biosynthesis pathways in plants.

A Systematic Review of Melatonin in Plants: An Example of Evolution of Literature

Melatonin (N-acetyl-5-methoxy-tryptamine) is a mammalian neurohormone, antioxidant and signaling molecule that was first discovered in plants in 1995. The first studies investigated plant melatonin from a human perspective quantifying melatonin in foods and medicinal plants and questioning whether its presence could explain the activity of some plants as medicines. Starting with these first handful of studies in the late 1990s, plant melatonin research has blossomed into a vibrant and active area of investigation and melatonin has been found to play critical roles in mediating plant responses and development at every stage of the plant life cycle from pollen and embryo development through seed germination, vegetative growth and stress response. Here we have utilized a systematic approach in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) protocols to reduce bias in our assessment of the literature and provide an overview of the current state of melatonin research in plants, covering 1995-2021. This review provides an overview of the biosynthesis and metabolism of melatonin as well as identifying key themes including: abiotic stress responses, root development, light responses, interkingdom communication, phytohormone and plant signaling. Additionally, potential biases in the literature are investigated and a birefringence in the literature between researchers from plant and medical based which has helped to shape the current state of melatonin research. Several exciting new opportunities for future areas of melatonin research are also identified including investigation of non-crop and non-medicinal species as well as characterization of melatonin signaling networks in plants.

Phytomelatonin: An Emerging Regulator of Plant Biotic Stress Resistance

Melatonin has diverse functions in plant development and stress tolerance, with recent evidence showing a beneficial role in plant biotic stress tolerance. It has been hypothesized that pathogenic invasion causes the immediate generation of melatonin, reactive oxygen species (ROS), and reactive nitrogen species (RNS), with these being mutually dependent, forming the integrative melatonin-ROS-RNS feedforward loop. Here we discuss how the loop, possibly located in the mitochondria and chloroplasts, maximizes disease resistance in the early pathogen ingress stage, providing on-site protection. We also review how melatonin interacts with phytohormone signaling pathways to mediate defense responses and discuss the evolutionary context from the beginnings of the melatonin receptor-mitogen-activated protein kinase (MAPK) cascade in unicellular green algae, followed by the occurrence of phytohormone pathways in land plants.

Melatonin metabolism, signaling and possible roles in plants

Melatonin is a multifunctional biomolecule found in both animals and plants. In this review, the biosynthesis, levels, signaling, and possible roles of melatonin and its metabolites in plants is summarized. Tryptamine 5-hydroxylase (T5H), which catalyzes the conversion of tryptamine into serotonin, has been proposed as a target to create a melatonin knockout mutant presenting a lesion-mimic phenotype in rice. With a reduced anabolic capacity for melatonin biosynthesis and an increased catabolic capacity for melatonin metabolism, all plants generally maintain low melatonin levels. Some plants, including Arabidopsis and Nicotiana tabacum (tobacco), do not possess tryptophan decarboxylase (TDC), the first committed step enzyme required for melatonin biosynthesis. Major melatonin metabolites include cyclic 3-hydroxymelatonin (3-OHM) and 2-hydroxymelatonin (2-OHM). Other melatonin metabolites such as N¹ -acetyl-N² -formyl-5-methoxykynuramine (AFMK), N-acetyl-5-methoxykynuramine (AMK) and 5-methoxytryptamine (5-MT) are also produced when melatonin is applied to Oryza sativa (rice). The signaling pathways of melatonin and its metabolites act via the mitogen-activated protein kinase (MAPK) cascade, possibly with Cand2 acting as a melatonin receptor, although the integrity of Cand2 remains controversial. Melatonin mediates many important functions in growth stimulation and stress tolerance through its potent antioxidant activity and function in activating the MAPK cascade. The concentration distribution of melatonin metabolites appears to be species specific because corresponding enzymes such as M2H, M3H, catalases, indoleamine 2,3-dioxygenase (IDO) and N-acetylserotonin deacetylase (ASDAC) are differentially expressed among plant species and even among different tissues within species. Differential levels of melatonin and its metabolites can lead to differential physiological effects among plants when melatonin is either applied exogenously or overproduced through ectopic overexpression.

An evolutionary view of melatonin synthesis and metabolism related to its biological functions in plants

Plant melatonin research is a rapidly developing field. A variety of isoforms of melatonin's biosynthetic enzymes are present in different plants. Due to the different origins, they exhibit independent responses to the variable environmental stimuli. The locations for melatonin biosynthesis in plants are chloroplasts and mitochondria. These organelles have inherited their melatonin biosynthetic capacities from their bacterial ancestors. Under ideal conditions, chloroplasts are the main sites of melatonin biosynthesis. If the chloroplast pathway is blocked for any reason, the mitochondrial pathway will be activated for melatonin biosynthesis to maintain its production. Melatonin metabolism in plants is a less studied field; its metabolism is quite different from that of animals even though they share similar metabolites. Several new enzymes for melatonin metabolism in plants have been cloned and these enzymes are absent in animals. It seems that the 2-hydroxymelatonin is a major metabolite of melatonin in plants and its level is ~400-fold higher than that of melatonin. In the current article, from an evolutionary point of view, we update the information on plant melatonin biosynthesis and metabolism. This review will help the reader to understand the complexity of these processes and promote research enthusiasm in these fields.

ROCK1 knockdown inhibits non-small-cell lung cancer progression by activating the LATS2-JNK signaling pathway

Rho-associated kinase 1 (ROCK1) regulates tumor metastasis by maintaining cellular cytoskeleton homeostasis. However, the precise role of ROCK1 in non-small-cell lung cancer (NSCLC) apoptosis remains largely unknown. In this study, we examined the function of ROCK1 in NSCLS survival using RNA interference-mediated knockdown. Our results showed that ROCK1 knockdown reduced A549 lung cancer cell viability in vitro. It also inhibited A549 cell migration and proliferation. Transfection of ROCK1 siRNA was associated with increased expression of large tumor suppressor kinase 2 (LATS2) and c-Jun N-terminal kinase (JNK). Moreover, ROCK1 knockdown-induced A549 cell apoptosis and inhibition of proliferation were suppressed by LATS2 knockdown or JNK inactivation, suggesting that ROCK1 deficiency triggers NSCLC apoptosis in a LATS2-JNK pathway-dependent manner. Functional analysis further demonstrated that ROCK1 knockdown dysregulated mitochondrial dynamics and inhibited mitochondrial biogenesis. This effect too was reversed by LATS2 knockdown or JNK inactivation. We have thus identified a potential pathway by which ROCK1 downregulation triggers apoptosis in NSCLC by inducing LATS2-JNK-dependent mitochondrial damage.

Overexpression of MsASMT1 Promotes Plant Growth and Decreases Flavonoids Biosynthesis in Transgenic Alfalfa (Medicago sativa L.)

Melatonin (N-acetyl-5-methoxytryptamine) is a pleiotropic signaling molecule that plays important roles in plant growth, development and stress responses. Alfalfa (Medicago sativa L.) is an important and widely cultivated leguminous forage crop with high biomass yield and rich nutritional value. The effects of exogenous melatonin content regulation on alfalfa stress tolerance have been investigated in recent years. Here, we isolated and introduced the MsASMT1 (N-acetylserotonin methyltransferase) gene into alfalfa, which significantly improved the endogenous melatonin content. Compared with wild-type (WT) plants, MsASMT1 overexpression (OE-MsASMT1) plants exhibited a series of phenotypic changes, including vigorous growth, increased plant height, enlarged leaves and robust stems with increased cell sizes, cell numbers and vascular bundles, as well as more branches. We also found that the flavonoid content and lignin composition of syringyl to guaiacyl ratio (S/G) were decreased and the cellulose content was increased in OE-MsASMT1 transgenic alfalfa. Further transcriptomic and metabolomic exploration revealed that a large group of genes in phenylalanine pathway related to flavonoids and lignin biosynthesis were significantly altered, accompanied by significantly reduced concentrations of the glycosides of quercetin, kaempferol, formononetin and biochanin in OE-MsASMT1 transgenic alfalfa. Our study first uncovers the effects of endogenous melatonin on alfalfa growth and metabolism. This report provides insights into the regulation effects of melatonin on plant growth and phenylalanine metabolism, especially flavonoids and lignin biosynthesis.

Exendin-4 attenuates inflammation-mediated endothelial cell apoptosis in varicose veins through inhibiting the MAPK-JNK signaling pathway

Context: Inflammation response has been found to be associated with endothelial cell death in the progression of varicose veins. Exendin-4 is able to reduce inflammation and thus attenuate cell apoptosis.Aim: The aim of our study is to explore the influence of Exendin-4 on LPS-treated endothelial cells.Methods: Cells were treated with LPS. Exendin-4 was added into the medium of cells. Western blots, qPCR, and ELISA were used to analyze the role of Exendin-4 in LPS-mediated cell death.Results: We found that LPS treatment caused significantly cell death. Whereas this trend could be attenuated by Exendin-4. After treatment with Exendin-4, inflammation factors upregulation and oxidative stress activation were significantly repressed, an effect that was followed by a drop in the levels of glucose production and lactic acid generation. At the molecular levels, Exendin-4 treatment inhibited the activity of MAPK-JNK signaling pathway in the presence of LPS treatment.Conclusions: LPS causes cell apoptosis through inducing inflammation response, oxidative stress and energy stress. Exendin-4 treatment enhances cell survival, reduces inflammation, and improves energy stress through inhibiting the MAPK-JNK signaling pathway.

Effects of Light Quality and Phytochrome Form on Melatonin Biosynthesis in Rice

Light is an important factor influencing melatonin synthesis in response to cadmium treatment in rice. However, the effects of light quality on, and the involvement of phytochrome light receptors in, melatonin production have not been explored. In this study, we used light-emitting diodes (LEDs) to investigate the effect of light wavelength on melatonin synthesis, and the role of phytochromes in light-dependent melatonin induction in rice. Upon cadmium treatment, peak melatonin production was observed under combined red and blue (R + B) light, followed by red (R) and blue light (B). However, both far-red (FR) LED light and dark treatment (D) failed to induce melatonin production. Similarly, rice seedlings grown under the R + B treatment showed the highest melatonin synthesis, followed by those grown under B and R. These findings were consistent with the results of our cadmium treatment experiment. To further confirm the effects of light quality on melatonin synthesis, we employed rice photoreceptor mutants lacking functional phytochrome genes. Melatonin induction was most inhibited in the phytochrome A mutant (phyA) followed by the phyB mutant under R + B treatment, whereas phyB produced the least amount of melatonin under R treatment. These results indicate that PhyB is an R light receptor. Expression analyses of genes involved in melatonin biosynthesis clearly demonstrated that tryptophan decarboxylase (TDC) played a key role in phytochrome-mediated melatonin induction when rice seedlings were challenged with cadmium.

Melatonin promotes seed germination under salinity and enhances the biosynthesis of steviol glycosides in Stevia rebaudiana Bertoni leaves

Melatonin (MEL) can act as a plant growth regulator and biostimulator in stressful situations. Using MEL in seed pretreatment also affects the future growth of plants. Therefore, this research investigated the effects of MEL on seed germination and seedling growth under NaCl in in vitro conditions. The additional effects of MEL on the accumulation of steviol glycosides (SGs) and on the expression of appropriate genes were also studied. Five μM of MEL was the best concentration for seed germination, while 20 μM exerted a positive impact on the biomass of stevia plantlets. NaCl significantly decreased seed germination, but MEL alleviated this effect when seeds were germinated in 50 mM of NaCl. Under salinity, the values of almost all morphological traits decreased as MEL concentration increased. The highest amounts of stevioside and rebaudioside A (Reb A) were observed as a result of treating seeds with 5 and 20 μM of MEL, respectively. When adding NaCl, positive impacts of MEL on the accumulation of both SGs were also observed. Expression analyses of the genes involved in SGs biosynthesis was explored in seeds and leaves, and the transcripts of key enzymes occurred in both the tissues. However, quantitative polymerase chain reaction (qPCR) analysis showed that all tested genes were upregulated in younger leaves, contrary to older ones. Also in younger, rather than older, leaves SG gene expression varied according to MEL concentration. This study, therefore, presents the promising potential of MEL for improving stevia seed germination under salinity conditions and for enhancing the production of SGs in stevia plants.

Melatonin Relations with Energy Metabolism as Possibly Involved in Fatal Mountain Road Traffic Accidents

Previous results evidenced acute exposure to high altitude (HA) weakening the relation between daily melatonin cycle and the respiratory quotient. This review deals with the threat extreme environments pose on body time order, particularly concerning energy metabolism. Working at HA, at poles, or in space challenge our ancestral inborn body timing system. This conflict may also mark many aspects of our current lifestyle, involving shift work, rapid time zone crossing, and even prolonged office work in closed buildings. Misalignments between external and internal rhythms, in the short term, traduce into risk of mental and physical performance shortfalls, mood changes, quarrels, drug and alcohol abuse, failure to accomplish with the mission and, finally, high rates of fatal accidents. Relations of melatonin with energy metabolism being altered under a condition of hypoxia focused our attention on interactions of the indoleamine with redox state, as well as, with autonomic regulations. Individual tolerance/susceptibility to such interactions may hint at adequately dealing with body timing disorders under extreme conditions.

Melatonin Application Improves Salt Tolerance of Alfalfa (Medicago sativa L.) by Enhancing Antioxidant Capacity

Alfalfa (Medicago sativa L.) is an important and widely cultivated forage grass. The productivity and forage quality of alfalfa are severely affected by salt stress. Melatonin is a bioactive molecule with versatile physiological functions and plays important roles in response to various biotic and abiotic stresses. Melatonin has been proven efficient in improving alfalfa drought and waterlogging tolerance in recent studies. In our reports, we applied melatonin exogenously to explore the effects of melatonin on alfalfa growth and salt resistance. The results demonstrated that melatonin application promoted alfalfa seed germination and seedling growth, and reduced oxidative damage under salt stress. Further application research found that melatonin alleviated salt injury in alfalfa plants under salt stress. The electrolyte leakage, malondialdehyde (MDA) content and H₂O₂ content were significantly reduced, and the activities of catalase (CAT), peroxidase (POD), and Cu/Zn superoxide dismutase (Cu/Zn-SOD) were increased with melatonin pretreatment compared to control plants under salt stress with the upregulation of genes related to melatonin and antioxidant enzymes biosynthesis. Melatonin was also involved in reducing Na⁺ accumulation in alfalfa plants. Our study indicates that melatonin plays a primary role as an antioxidant in scavenging H₂O₂ and enhancing activities of antioxidant enzymes to improve the salt tolerance of alfalfa plants.

Sphingosine kinase 1 promotes cerebral ischemia-reperfusion injury through inducing ER stress and activating the NF-κB signaling pathway

Endoplasm reticulum stress and inflammation response have been found to be linked to cerebral ischemia-reperfusion (IR) injury. Sphingosine kinase 1 (SPHK1) has been reported to be a novel endoplasm reticulum regulator. The aim of our study is to figure out the role of SPHK1 in cerebral IR injury and verify whether it has an ability to regulate inflammation and endoplasm reticulum stress. Hydrogen peroxide was used to induce cerebral IR injury. Enzyme-linked immunosorbent assay, quantitative polymerase chain reaction, western blots, and immunofluorescence were used to measure the alterations of cell viability, inflammation response, and endoplasm reticulum stress. The results demonstrated that after exposure to hydrogen peroxide, cell viability was reduced whereas SPHK1 expression was significantly elevated. Knockdown of SPHK1 attenuated hydrogen peroxide-mediated cell death and reversed cell viability. Our data also demonstrated that SPHK1 deletion reduced endoplasm reticulum stress and alleviated inflammation response in hydrogen peroxide-treated cells. In addition, we also found that SHPK1 modulated endoplasm reticulum stress and inflammation response to through the NF-κB signaling pathway. Inhibition of NF-κB signaling pathway has similar results when compared with the cells with SPHK1 deletion. Altogether, our results demonstrated that SPHK1 upregulation, induced by hydrogen peroxide, is responsible for cerebral IR injury through inducing endoplasm reticulum stress and inflammation response in a manner working through the NF-κB signaling pathway. This finding provides new insight into the molecular mechanism to explain the neuron death induced by cerebral IR injury.

Direct comparison of Arabidopsis gene expression reveals different responses to melatonin versus auxin

BACKGROUND

Melatonin (N-acetyl-5-methoxytryptamine) in plants, regulates shoot and root growth and alleviates environmental stresses. Melatonin and the phyto-hormone auxin are tryptophan-derived compounds. However, it largely remains controversial as to whether melatonin and auxin act through similar or overlapping signalling and regulatory pathways.

RESULTS

Here, we have used a promoter-activation study to demonstrate that, unlike auxin (1-naphthalene acetic acid, NAA), melatonin neither induces Direct repeat 5 DR5 expression in Arabidopsis thaliana roots under normal growth conditions nor suppresses the induction of Alternative oxidase 1a AOX1a in leaves upon Antimycin A treatment, both of which are the hallmarks of auxin action. Additionally, comparative global transcriptome analysis conducted on Arabidopsis treated with melatonin or NAA revealed differences in the number and types of differentially expressed genes. Auxin (4.5 μM) altered the expression of a diverse and large number of genes whereas melatonin at 5 μM had no significant effect but melatonin at 100 μM had a modest effect on transcriptome compared to solvent-treated control. Interestingly, the prominent category of genes differentially expressed upon exposure to melatonin trended towards biotic stress defence pathways while downregulation of key genes related to photosynthesis was observed.

CONCLUSION

Together these findings indicate that though they are both indolic compounds, melatonin and auxin act through different pathways to alter gene expression in Arabidopsis thaliana. Furthermore, it appears that effects of melatonin enable Arabidopsis thaliana to prioritize biotic stress defence signalling rather than growth. These findings clear the current confusion in the literature regarding the relationship of melatonin and auxin and also have greater implications of utilizing melatonin for improved plant protection.

Melatonin delays leaf senescence of Chinese flowering cabbage by suppressing ABFs-mediated abscisic acid biosynthesis and chlorophyll degradation

Melatonin and abscisic acid (ABA) play contrasting roles in regulating leaf senescence in plants. The molecular mechanism underlying the interaction between melatonin and ABA involved in leaf senescence, however, remains poorly defined. Herein, we found that exogenous application of melatonin delayed the senescence of Chinese flowering cabbage, accompanied by reduced expression of chlorophyll catabolic and ABA biosynthetic genes, and a lower endogenous ABA level. Significantly, three nucleus-localized transcriptional activators BrABF1, BrABF4, and BrABI5 were identified, and their expressions were repressed by melatonin. In vitro and in vivo binding experiments revealed that BrABF1, BrABF4, and BrABI5 activated the transcription of a series of ABA biosynthetic and chlorophyll catabolic genes by physically binding to their promoters. Moreover, transient over-expression of BrABF1, BrABF4, and BrABI5 in tobacco leaves induced ABA accumulation and promoted chlorophyll degradation by upregulating tobacco ABA biosynthetic and chlorophyll catabolic genes, resulting in the accelerated leaf senescence. These effects were significantly attenuated by melatonin treatment. Our findings suggest that melatonin-mediated inhibition of leaf senescence involves suppression of ABFs-mediated ABA biosynthesis and chlorophyll degradation. Unraveling of the molecular regulatory mechanism of leaf senescence controlled by ABA and melatonin expands our understanding of the regulation of this phenomenon and offers potentially more effective molecular breeding strategies for extending the shelf-life of Chinese flowering cabbage.