Melatonin-Producing Endophytic Bacteria from Grapevine Roots Promote the Abiotic Stress-Induced Production of Endogenous Melatonin in Their Hosts

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.

Enhancing rice growth and yield with weed endophytic bacteria Alcaligenes faecalis and Metabacillus indicus under reduced chemical fertilization

Endophytic bacteria, recognized as eco-friendly biofertilizers, have demonstrated the potential to enhance crop growth and yield. While the plant growth-promoting effects of endophytic bacteria have been extensively studied, the impact of weed endophytes remains less explored. In this study, we aimed to isolate endophytic bacteria from native weeds and assess their plant growth-promoting abilities in rice under varying chemical fertilization. The evaluation encompassed measurements of mineral phosphate and potash solubilization, as well as indole-3-acetic acid (IAA) production activity by the selected isolates. Two promising strains, tentatively identified as Alcaligenes faecalis (BTCP01) from Eleusine indica (Goose grass) and Metabacillus indicus (BTDR03) from Cynodon dactylon (Bermuda grass) based on 16S rRNA gene phylogeny, exhibited noteworthy phosphate and potassium solubilization activity, respectively. BTCP01 demonstrated superior phosphate solubilizing activity, while BTDR03 exhibited the highest potassium (K) solubilizing activity. Both isolates synthesized IAA in the presence of L-tryptophan, with the detection of nifH and ipdC genes in their genomes. Application of isolates BTCP01 and BTDR03 through root dipping and spraying at the flowering stage significantly enhanced the agronomic performance of rice variety CV. BRRI dhan29. Notably, combining both strains with 50% of recommended N, P, and K fertilizer doses led to a substantial increase in rice grain yields compared to control plants receiving 100% of recommended doses. Taken together, our results indicate that weed endophytic bacterial strains BTCP01 and BTDR03 hold promise as biofertilizers, potentially reducing the dependency on chemical fertilizers by up to 50%, thereby fostering sustainable rice production.

Novel melatonin-producing Bacillus safensis EH143 mitigates salt and cadmium stress in soybean

Recently, microorganism and exogenous melatonin application has been recognized as an efficient biological tool for enhancing salt tolerance and heavy metal detoxification in agriculture crops. Thus, the goal of this study was to isolate and evaluate a novel melatonin-producing plant growth promoting bacterium. With high-throughput whole genome sequencing, phytohormone measurements, expression profiling, and biochemical analysis, we can identify a novel PGPB that produces melatonin and unravel how it promotes soybean growth and development and protects against salt and Cd stress. We identify the melatonin synthesis pathway (tryptophan→tryptamine→serotonin melatonin) of the halotolerant (NaCl > 800 mM) and heavy metal-resistant (Cd >3 mM) rhizobacterium Bacillus safensis EH143 and use it to treat soybean plants subjected to Cd and NaCl stresses. Results show that EH143 will highly bioaccumulate heavy metals and significantly improve P and Ca2+ uptake and the K+/Na+ (93%↑under salt stress) ratio while reducing Cd uptake (49% under Cd stress) in shoots. This activity was supported by the expression of the ion regulator HKT1, MYPB67, and the calcium sensors CDPK5 and CaMK1 which ultimately led to increased plant growth. EH143 significantly decreased ABA content in shoots by 13%, 20%, and 34% and increased SA biosynthesis in shoots by 14.8%, 31%, and 48.2% in control, salt, and Cd-treated plants, upregulating CYP707A1 and CYP707A2 and PAL1 and ICS, respectively. The melatonin content significantly decreased along with a reduced expression of ASMT3 following treatment with EH143; moreover, reduced expression of peroxidase (POD) and superoxide dismutase (SOD) by 134.5% and 39% under salt+Cd stress, respectively and increased level of total amino acids were observed. Whole-genome sequencing and annotation of EH143 revealed the presence of the melatonin precursor tryptophan synthase (trpA, trpB, trpS), metal and other ion regulators (Cd: cadA, potassium: KtrA and KtrB, phosphate: glpT, calcium: yloB, the sodium/glucose cotransporter: sgIT, and the magnesium transporter: mgtE), and enzyme activators (including the siderophore transport proteins yfiZ and yfhA, the SOD sodA, the catalase katA1, and the glutathione regulator KefG) that may be involved in programming the plant metabolic system. As a consequence, EH143 treatment significantly reduced the contents of lipid peroxidation (O2-, MDA, and H2O2) up to 69%, 46%, and 29% in plants under salt+Cd stress, respectively. These findings suggest that EH143 could be a potent biofertilizer to alleviate NaCl and Cd toxicity in crops and serve as an alternative substitute for exogenous melatonin application.

Evolutionary formation of melatonin and vitamin D in early life forms: insects take centre stage

Melatonin, a product of tryptophan metabolism via serotonin, is a molecule with an indole backbone that is widely produced by bacteria, unicellular eukaryotic organisms, plants, fungi and all animal taxa. Aside from its role in the regulation of circadian rhythms, it has diverse biological actions including regulation of cytoprotective responses and other functions crucial for survival across different species. The latter properties are also shared by its metabolites including kynuric products generated by reactive oxygen species or phototransfomation induced by ultraviolet radiation. Vitamins D and related photoproducts originate from phototransformation of ∆5,7 sterols, of which 7-dehydrocholesterol and ergosterol are examples. Their ∆5,7 bonds in the B ring absorb solar ultraviolet radiation [290-315 nm, ultraviolet B (UVB) radiation] resulting in B ring opening to produce previtamin D, also referred to as a secosteroid. Once formed, previtamin D can either undergo thermal-induced isomerization to vitamin D or absorb UVB radiation to be transformed into photoproducts including lumisterol and tachysterol. Vitamin D, as well as the previtamin D photoproducts lumisterol and tachysterol, are hydroxylated by cyochrome P450 (CYP) enzymes to produce biologically active hydroxyderivatives. The best known of these is 1,25-dihydroxyvitamin D (1,25(OH)2D) for which the major function in vertebrates is regulation of calcium and phosphorus metabolism. Herein we review data on melatonin production and metabolism and discuss their functions in insects. We discuss production of previtamin D and vitamin D, and their photoproducts in fungi, plants and insects, as well as mechanisms for their enzymatic activation and suggest possible biological functions for them in these groups of organisms. For the detection of these secosteroids and their precursors and photoderivatives, as well as melatonin metabolites, we focus on honey produced by bees and on body extracts of Drosophila melanogaster. Common biological functions for melatonin derivatives and secosteroids such as cytoprotective and photoprotective actions in insects are discussed. We provide hypotheses for the photoproduction of other secosteroids and of kynuric metabolites of melatonin, based on the known photobiology of ∆5,7 sterols and of the indole ring, respectively. We also offer possible mechanisms of actions for these unique molecules and summarise differences and similarities of melatoninergic and secosteroidogenic pathways in diverse organisms including insects.

Comprehensive insights into the impact of bacterial indole-3-acetic acid on sensory preferences in Drosophila melanogaster

Several bacteria of environmental and clinical origins, including some human-associated strains secrete a cross-kingdom signaling molecule indole-3-acetic acid (IAA). IAA is a tryptophan (trp) derivative mainly known for regulating plant growth and development as a hormone. However, the nutritional sources that boost IAA secretion in bacteria and the impact of secreted IAA on non-plant eukaryotic hosts remained less explored. Here, we demonstrate significant trp-dependent IAA production in Pseudomonas juntendi NEEL19 when provided with ethanol as a carbon source in liquid cultures. IAA was further characterized to modulate the odor discrimination, motility and survivability in Drosophila melanogaster. A detailed analysis of IAA-fed fly brain proteome using high-resolution mass spectrometry showed significant (fold change, ± 2; p ≤ 0.05) alteration in the proteins governing neuromuscular features, audio-visual perception and energy metabolism as compared to IAA-unfed controls. Sex-wise variations in differentially regulated proteins were witnessed despite having similar visible changes in chemo perception and psychomotor responses in IAA-fed flies. This study not only revealed ethanol-specific enhancement in trp-dependent IAA production in P. juntendi, but also showed marked behavioral alterations in flies for which variations in an array of proteins governing odor discrimination, psychomotor responses, and energy metabolism are held responsible. Our study provided novel insights into disruptive attributes of bacterial IAA that can potentially influence the eukaryotic gut-brain axis having broad environmental and clinical implications.

Nano zero-valent iron and melatonin synergistically alters uptake and translocation of Cd and As in soil-rice system and mechanism in soil chemistry and microbiology

Nanoscale zero-valent iron (Fe) is a promising nanomaterial for remediating heavy metal-contaminated soils. Melatonin (MT) is essential to alleviate environmental stress in plants. However, the conjunction effects of Fe and MT (FeMT) on rice Cd, As accumulation and the mechanism of soil chemical and microbial factors interaction are unclear. Here, a pot experiment was conducted to evaluated the effects of the FeMT for rice Cd, As accumulation and underlying mechanisms. The findings showed that FeMT significantly reduced grains Cd by 92%-87% and As by over 90%, whereas improving grains Fe by over 213%. Soil available-Cd and iron plaques-Cd (extracted by dithionite-citrate-bicarbonate solution, DCB-Cd) significantly regulated roots Cd, thus affected Cd transport to grains. Soil pH significantly affected soil As and DCB-As, which further influenced roots As uptake and the transport to shoots and grains. The interactions between the soil bacterial community and soil Fe, available Fe, and DCB-Fe together affected root Fe absorption and transportation in rice. FeMT significantly influenced rhizosphere soil bacterial α- and β-diversity. Firmicutes as the dominant phylum exhibited a significant positive response to FeMT measure, and acted a key role in reducing soil Cd and As availability mainly by improving iron-manganese plaques. The increase of soil pH caused by FeMT was beneficial only for Actinobacteriota growth, which reduced Cd, As availability probably through complexation and adsorption. FeMT also showed greater potential in reducing human health and ecological risks by rice consumption and straw returning. These results showed the important role of both soil chemical and microbial factors in FeMT-mediated rice Cd, As reduction efficiency. This study opens a novel strategy for safe rice production and improvement of rice iron nutrition level in heavy-metals polluted soil, but also provides new insights into the intricate regulatory relationships among soil biochemistry, toxic elements, microorganism, and plants.

Melatonin-mediated actions and circadian functions that improve implantation, fetal health and pregnancy outcome

This review summarizes data related to the potential importance of the ubiquitously functioning antioxidant, melatonin, in resisting oxidative stress and protecting against common pathophysiological disorders that accompany implantation, gestation and fetal development. Melatonin from the maternal pineal gland, but also trophoblasts in the placenta, perhaps in the mitochondria, produce this molecule as a hedge against impairment of the uteroplacental unit. We also discuss the role of circadian disruption on reproductive disorders of pregnancy. The common disorders of pregnancy, i.e., stillborn fetus, recurrent fetal loss, preeclampsia, fetal growth retardation, premature delivery, and fetal teratology are all conditions in which elevated oxidative stress plays a role and experimental supplementation with melatonin has been shown to reduce the frequency or severity of these conditions. Moreover, circadian disruption often occurs during pregnancy and has a negative impact on fetal health; conversely, melatonin has circadian rhythm synchronizing actions to overcome the consequences of chronodisruption which often appear postnatally. In view of the extensive findings supporting the ability of melatonin, an endogenously-produced and non-toxic molecule, to protect against experimental placental, fetal, and maternal pathologies, it should be given serious consideration as a supplement to forestall the disorders of pregnancy. Until recently, the collective idea was that melatonin supplements should be avoided during pregnancy. The data summarized herein suggests otherwise. The current findings coupled with the evidence, published elsewhere, showing that melatonin is highly protective of the fertilized oocyte from oxidative damage argues in favor of its use for improving pregnancy outcome generally.

Melatonin Prevents Alcohol- and Metabolic Dysfunction- Associated Steatotic Liver Disease by Mitigating Gut Dysbiosis, Intestinal Barrier Dysfunction, and Endotoxemia

Melatonin (MT) has often been used to support good sleep quality, especially during the COVID-19 pandemic, as many have suffered from stress-related disrupted sleep patterns. It is less known that MT is an antioxidant, anti-inflammatory compound, and modulator of gut barrier dysfunction, which plays a significant role in many disease states. Furthermore, MT is produced at 400-500 times greater concentrations in intestinal enterochromaffin cells, supporting the role of MT in maintaining the functions of the intestines and gut-organ axes. Given this information, the focus of this article is to review the functions of MT and the molecular mechanisms by which it prevents alcohol-associated liver disease (ALD) and metabolic dysfunction-associated steatotic liver disease (MASLD), including its metabolism and interactions with mitochondria to exert its antioxidant and anti-inflammatory activities in the gut-liver axis. We detail various mechanisms by which MT acts as an antioxidant, anti-inflammatory compound, and modulator of intestinal barrier function to prevent the progression of ALD and MASLD via the gut-liver axis, with a focus on how these conditions are modeled in animal studies. Using the mechanisms of MT prevention and animal studies described, we suggest behavioral modifications and several exogenous sources of MT, including food and supplements. Further clinical research should be performed to develop the field of MT in preventing the progression of liver diseases via the gut-liver axis, so we mention a few considerations regarding MT supplementation in the context of clinical trials in order to advance this field of research.

A core root bacteria contribute to plant growth and anisodine accumulation of Anisodus tanguticus

BACKGROUND

Although it is well recognized that core root microorganisms contribute to plant health and productivity, little is known about their role to the accumulation of secondary metabolites. The roots of Anisodus tanguticus, a traditional herbal medication utilized by Tibetan medicine, are rich in tropane alkaloids. We collected wild A. tanguticus populations throughout a 1500 km transect on the Qinghai-Tibetan Plateau.

RESULTS

Our results showed that despite sampling at a distance of 1500 km, the root of A. tanguticus selectively recruits core root bacteria. We obtained 102 root bacterial core OTUs, and although their number only accounted for 2.99% of the total, their relative abundance accounted for 73% of the total. Spearman correlation and random forest analyses revealed that the composition of core root microbiomes was related to anisodine contents, aboveground biomass and nitrogen contents of Anisodus tanguticus. Among them, the main role is played by Rhizobacter, Variovorax, Polaromonas, and Mycobacterium genus that are significantly enriched in roots. Functional prediction by FAPROTAX showed that nitrogen-cycling microorganisms and pathogenic bacteria are strongly associated with anisodine contents, aboveground biomass and nitrogen contents of Anisodus tanguticus.

CONCLUSIONS

Our findings show that the root selectively recruits core root bacteria and revealed that the core microbiomes and microbial functions potentially contributed to the anisodine contents, aboveground biomass and nitrogen contents of the plant. This work may increase our understanding of the interactions between microorganisms and plants and improve our ability to manage root microbiota to promote sustainable production of herbal medicines.

Melatonin disturbed rumen microflora structure and metabolic pathways in vitro

IMPORTANCE

In in vitro studies, it has been found that the effects of MLT on rumen microorganisms and metabolites can change the rumen flora structure, significantly inhibit the relative abundance of harmful Acinetobacter, and improve the relative abundance of beneficial bacteria. MLT may regulate the "arginine-glutathione" pathway, "phenylalanine, tyrosine and tryptophan biosynthesis-tryptophan generation" branch, "tryptophan-kynurenine" metabolism, and "tryptophan-tryptamine-serotonin" pathway through microorganisms.

Identification of bioactive compounds of Bacillus velezensis HNA3 that contribute to its dual effects as plant growth promoter and biocontrol against post-harvested fungi

IMPORTANCE

The current study is an extension to our previous work on the plant growth-promoting rhizobacteria (PGPR) Bacillus velezensis HNA3 strain, which comes to confirm and reveals the huge stock of active secondary metabolites produced by HNA3. HNA3-emitted volatile organic compounds (VOCs) have demonstrated the capacity to impede the growth of phytopathogens affecting some fruits and vegetables, even in the absence of direct contact. Additionally, these volatiles enhanced soybean seed germination by breaking seed dormancy and inducing root system development. Furthermore, they promoted seedling growth, giving it prominence in soybean cultivation. The relevance of active volatiles derives from the fact that they can be developed as natural-safe biocontrol agents and plant promoters. This research validates the remarkable bioactivities exhibited by the Bacillus velezensis HNA3 and their potential applications in agriculture as an inoculant, encompassing biocontrol, plant growth promotion, and seed germination activities, thereby offering a safer alternative to hazardous chemicals.

Communication between Plants and Rhizosphere Microbiome: Exploring the Root Microbiome for Sustainable Agriculture

Plant roots host numerous microorganisms around and inside their roots, forming a community known as the root microbiome. An increasing bulk of research is underlining the influences root-associated microbial communities can have on plant health and development. However, knowledge on how plant roots and their associated microbes interact to bring about crop growth and yield is limited. Here, we presented (i) the communication strategies between plant roots and root-associated microbes and (ii) the applications of plant root-associated microbes in enhancing plant growth and yield. This review has been divided into three main sections: communications between root microbiome and plant root; the mechanism employed by root-associated microbes; and the chemical communication mechanisms between plants and microbes and their application in plant growth and yield. Understanding how plant root and root-associated microbes communicate is vital in designing ecofriendly strategies for targeted disease suppression and improved plant growth that will help in sustainable agriculture. Ensuring that plants become healthy and productive entails keeping plants under surveillance around the roots to recognize disease-causing microbes and similarly exploit the services of beneficial microorganisms in nutrient acquisition, stress mitigation, and growth promotion.

Melatonin: Facts, Extrapolations and Clinical Trials

Melatonin is a fascinating molecule that has captured the imagination of many scientists since its discovery in 1958. In recent times, the focus has changed from investigating its natural role as a transducer of biological time for physiological systems to hypothesized roles in virtually all clinical conditions. This goes along with the appearance of extensive literature claiming the (generally) positive benefits of high doses of melatonin in animal models and various clinical situations that would not be receptor-mediated. Based on the assumption that melatonin is safe, high doses have been administered to patients, including the elderly and children, in clinical trials. In this review, we critically review the corresponding literature, including the hypotheses that melatonin acts as a scavenger molecule, in particular in mitochondria, by trying not only to contextualize these interests but also by attempting to separate the wheat from the chaff (or the wishful thinking from the facts). We conclude that most claims remain hypotheses and that the experimental evidence used to promote them is limited and sometimes flawed. Our review will hopefully encourage clinical researchers to reflect on what melatonin can and cannot do and help move the field forward on a solid basis.

Escherichia coli RimI Encodes Serotonin N-Acetyltransferase Activity and Its Overexpression Leads to Enhanced Growth and Melatonin Biosynthesis

Serotonin N-acetyltransferase (SNAT) functions as the penultimate or final enzyme in melatonin biosynthesis, depending on the substrate. The Escherichia coli orthologue of archaeal SNAT from Thermoplasma volcanium was identified as RimI (EcRimI), with 42% amino acid similarity to archaeal SNAT. EcRimI has been reported to be an N-acetyltransferase enzyme. Here, we investigated whether EcRimI also exhibits SNAT enzyme activity. To achieve this goal, we purified recombinant EcRimI and examined its SNAT enzyme kinetics. As expected, EcRimI showed SNAT activity toward various amine substrates including serotonin and 5-methoxytryptamine, with K_m and V_max values of 531 μM and 528 pmol/min/mg protein toward serotonin and 201 μM and 587 pmol/min/mg protein toward 5-methoxytryptamine, respectively. In contrast to the rimI mutant E. coli strain that showed no growth defect, the EcRimI overexpression strain exhibited a 2-fold higher growth rate than the control strain after 24 h incubation in nutrient-rich medium. The EcRimI overexpression strain produced more melatonin than the control strain in the presence of 5-methoxytryptamine. The enhanced growth effect of EcRimI overexpression was also observed under cadmium stress. The higher growth rate associated with EcRimI expression was attributed to increased protein N-acetyltransferase activity, increased synthesis of melatonin, or the combined effects of both.

Role of melatonin in enhancing arbuscular mycorrhizal symbiosis and mitigating cold stress in perennial ryegrass (Lolium perenne L.)

Melatonin is a biomolecule that affects plant development and is involved in protecting plants from environmental stress. However, the mechanisms of melatonin's impact on arbuscular mycorrhizal (AM) symbiosis and cold tolerance in plants are still unclear. In this research, AM fungi inoculation and exogenous melatonin (MT) were applied to perennial ryegrass (Lolium perenne L.) seedlings alone or in combination to investigate their effect on cold tolerance. The study was conducted in two parts. The initial trial examined two variables, AM inoculation, and cold stress, to investigate the involvement of the AM fungus Rhizophagus irregularis in endogenous melatonin accumulation and the transcriptional levels of its synthesis genes in the root system of perennial ryegrass under cold stress. The subsequent trial was designed as a three-factor analysis, encompassing AM inoculation, cold stress, and melatonin application, to explore the effects of exogenous melatonin application on plant growth, AM symbiosis, antioxidant activity, and protective molecules in perennial ryegrass subjected to cold stress. The results of the study showed that compared to non-mycorrhizal (NM) plants, cold stress promoted an increase in the accumulation of melatonin in the AM-colonized counterparts. Acetylserotonin methyltransferase (ASMT) catalyzed the final enzymatic reaction in melatonin production. Melatonin accumulation was associated with the level of expression of the genes, LpASMT1 and LpASMT3. Treatment with melatonin can improve the colonization of AM fungi in plants. Simultaneous utilization of AM inoculation and melatonin treatment enhanced the growth, antioxidant activity, and phenylalanine ammonia-lyase (PAL) activity, while simultaneously reducing polyphenol oxidase (PPO) activity and altering osmotic regulation in the roots. These effects are expected to aid in the mitigation of cold stress in Lolium perenne. Overall, melatonin treatment would help Lolium perenne to improve growth by promoting AM symbiosis, improving the accumulation of protective molecules, and triggering in antioxidant activity under cold stress.

Indoleamines Impart Abiotic Stress Tolerance and Improve Reproductive Traits in Hazelnuts

Hazelnuts have recently gathered tremendous attention due to the expansion of the confectionary industry. However, the sourced cultivars fail to perform in initial phase of cultivation as they enter bare survival mode due to changes in climatic zones, for example, Southern Ontario, where the climate is continental, as opposed to the milder climate in Europe and Turkey. Indoleamines have been shown to counter abiotic stress and modulate vegetative and reproductive development of plants. Here, we examined the effect of indoleamines on the flowering response of the dormant stem cuttings of sourced hazelnut cultivars in controlled environment chambers. The stem cuttings were exposed to sudden summer-like conditions (abiotic stress) and the female flower development was assessed in relation to endogenous indoleamine titers. The sourced cultivars responded well to serotonin treatment by producing more flowers compared to the controls or other treatments. The probability of buds resulting in female flowers was highest in the middle region of the stem cuttings. It is interesting to note that the tryptamine titers of the locally adapted, and N-acetyl serotonin titers of native hazelnut cultivars, provided the best explanation for adaptation to the stress environment. Titers of both compounds were compromised in the sourced cultivars which resorted mostly to serotonin concentrations to counter the stress. The indoleamines tool kit identified in this study could be deployed in assessing cultivars for stress adaptation attributes.

Melatonin improves the removal and the reduction of Cr(VI) and alleviates the chromium toxicity by antioxidative machinery in Rhodobacter sphaeroides

Bioremediation with photosynthetic bacteria (PSB) is thought to be a promising removal method for hexavalent chromium [Cr(VI)]-containing wastewater. In the present study, Rhodobacter sphaeroides (R. sphaeroides) SC01 was used for the investigation of Cr(VI) removal in Cr(VI)-contaminated solution in the presence of melatonin. It was found that exogenous melatonin alleviated oxidative damage to R. sphaeroides SC01, increased Cr (VI) absorption capacity of cell membrane, and improved the reduction efficiency of Cr(VI) via the activation of chromate reductants. The results showed that melatonin could further promote the increase in Cr(VI) removal efficiency, reaching up to 97.8%. Furthermore, melatonin application resulted in 296.9%, 44.4%, and 69.7% upregulation of ascorbic acid (AsA), glutathione (GSH), and cysteine (Cys) relative to non-melatioin treated R. sphaeroides SC01 at 48 h. In addition, the resting cells, cell-free supernatants (CFS), and cell-free extracts (CFE) with melatonin had a higher Cr(VI) removal rate of 18.6%, 82.0%, and 15.2% compared with non-melatonin treated R. sphaeroides SC01. Fourier transform infrared spectroscopy (FTIR) revealed that melatonin increased the binding of Cr(III) with PO4^3- and CO groups on cell membrane of R. sphaeroides SC01. X-ray diffractometer (XRD) analysis demonstrated that melatonin remarkably bioprecipitated the production of CrPO₄·6H₂O in R. sphaeroides SC01. Hence, these results indicated that melatonin plays the important role in the reduction and uptake of Cr(VI), demonstrating it is a great promising strategy for the management of Cr(VI) contaminated wastewater in photosynthetic bacteria.

Melatonin from Microorganisms, Algae, and Plants as Possible Alternatives to Synthetic Melatonin

Melatonin dietary supplements are widely consumed worldwide, with developed countries as the largest consumers, with an estimated annual growth rate of approximately 10% until 2027, mainly in developing countries. The wide use of melatonin against sleep disorders and particular problems, such as jet lag, has been added to other applications, such as anti-aging, anti-stress, immune system activation, anticancer, and others, which have triggered its use, normally without a prescription. The chemical industry currently covers 100% of the needs of the melatonin market. Motivated by sectors with more natural consumption habits, a few years ago, the possibility of obtaining melatonin from plants, called phytomelatonin, arose. More recently, the pharmaceutical industry has developed genetically modified microorganisms whose ability to produce biological melatonin in bioreactors has been enhanced. This paper reviews the aspects of the chemical and biological synthesis of melatonin for human consumption, mainly as dietary supplements. The pros and cons of obtaining melatonin from microorganisms and phytomelatonin from plants and algae are analyzed, as well as the advantages of natural melatonin, avoiding unwanted chemical by-products from the chemical synthesis of melatonin. Finally, the economic and quality aspects of these new products, some of which are already marketed, are analyzed.

Melatonin production by rhizobacteria native strains: Towards sustainable plant growth promotion strategies

In the current context of climate change and water deficit, the selection of native beneficial microorganisms, such as plant growth-promoting rhizobacteria (PGPR), has become a trend for sustainable agriculture due to their ability to improve plant-bacteria interaction with a minimal adverse effect on the soil microbiota compared to commercial PGPR. Until now, the production of phytohormones like melatonin (MT) by native PGPR and their effect on endogenous MT levels in plants have been poorly studied. MT is a ubiquitous phytohormone that protects plants against biotic and abiotic stress by improving the tolerance of stressed plants. In this work, the production of MT by two native PGPR, Enterobacter 64S1 and Pseudomonas 42P4, was evaluated and both PGPR were applied in Arabidopsis thaliana plants grown under drought conditions to assess the inoculation effects. Parameters such as plant growth, leaf cellular membrane damage, leaf protective compounds, and endogenous MT levels under drought and irrigation conditions were evaluated. The results demonstrated that the native strains Pseudomonas 42P4 and Enterobacter 64S1 produce MT and increase the content of endogenous MT in A. thaliana plants under drought. These native strains improved the tolerance of arabidopsis plants to drought by preventing oxidative and membrane damages and improving plant growth. To the best of our knowledge, this is the first report on MT production by native PGPR and their effects on endogenous MT levels in arabidopsis plants, setting the bases to elucidate the role of native PGPR on water deficit conditions.

Composition and biodiversity of soil and root-associated microbiome in Vitis vinifera cultivar Lambrusco distinguish the microbial terroir of the Lambrusco DOC protected designation of origin area on a local scale

Introduction

Wines produced from the same grape cultivars but in different locations possess distinctive qualities leading to different consumer's appreciation, preferences, and thus purchase choices. Here, we explore the possible importance of microbiomes at the soil-plant interface as a determinant of the terroir properties in grapevine production, which confer specific growth performances and wine chemo-sensory properties at the local scale.

Methods

In particular, we investigated the variation in microbial communities associated with the roots of Vitis vinifera cultivar Lambrusco, as well as with surrounding bulk soils, in different vineyards across the "Consorzio Tutela Lambrusco DOC" protected designation of origin area (PDO, Emilia Romagna, Italy), considering viticultural sites located both inside and outside the consortium in two different seasons (June and November 2021).

Results

According to our findings, rhizospheric and soil microbiomes show significant structural differences in relation to the sampling site, regardless of seasonality, while endophytic microbiomes seem to be completely unaffected by such variables. Furthermore, a deeper insight into the microbial terroir of PDO areas highlighted the presence of some rhizospheric microorganisms enriched inside the consortium and characterizing the PDO regardless of both sampling season and farming strategy. These include Bacillus, Paenibacillus, and Azospirillum, which are all well-known plant growth-promoting bacteria.

Discussion

Taken together, our results suggest a connection between soil and root microbiomes of V. vinifera cultivar Lambrusco and the local designation of origin, emphasizing the potential role of PDO-enriched plant growth-promoting bacteria in vine growing and final quality of the Lambrusco DOC wine.

Plant responses to high temperature and drought: A bibliometrics analysis

Global climate change is expected to further increase the frequency and severity of extreme events, such as high temperature/heat waves as well as drought in the future. Thus, how plant responds to high temperature and drought has become a key research topic. In this study, we extracted data from Web of Science Core Collections database, and synthesized plant responses to high temperature and drought based on bibliometric methods using software of R and VOSviewer. The results showed that a stabilized increasing trend of the publications (1199 papers) was found during the period of 2008 to 2014, and then showed a rapid increase (2583 papers) from year 2015 to 2021. Secondly, the top five dominant research fields of plant responses to high temperature and drought were Plant Science, Agroforestry Science, Environmental Science, Biochemistry, and Molecular Biology, respectively. The largest amount of published article has been found in the Frontiers in Plant Science journal, which has the highest global total citations and H-index. We also found that the journal of Plant Physiology has the highest local citations. From the most cited papers and references, the most important research focus was the improvement of crop yield and vegetation stress resistance. Furthermore, "drought" has been the most prominent keyword over the last 14 years, and more attention has been paid to "climate change" over the last 5 years. Under future climate change, how to regulate growth and development of food crops subjected to high temperature and drought stress may become a hotspot, and increasing research is critical to provide more insights into plant responses to high temperature and drought by linking plant above-below ground components. To summarize, this research will contribute to a comprehensive understanding of the past, present, and future research on plant responses to high temperature and drought.

Phytomelatonin and plant mineral nutrition

Plant mineral nutrition is critical for agricultural productivity and for human nutrition; however, the availability of mineral elements is spatially and temporally heterogeneous in many ecosystems and agricultural landscapes. Nutrient imbalances trigger intricate signalling networks that modulate plant acclimation responses. One signalling agent of particular importance in such networks is phytomelatonin, a pleiotropic molecule with multiple functions. Evidence indicates that deficiencies or excesses of nutrients generally increase phytomelatonin levels in certain tissues, and it is increasingly thought to participate in the regulation of plant mineral nutrition. Alterations in endogenous phytomelatonin levels can protect plants from oxidative stress, influence root architecture, and influence nutrient uptake and efficiency of use through transcriptional and post-transcriptional regulation; such changes optimize mineral nutrient acquisition and ion homeostasis inside plant cells and thereby help to promote growth. This review summarizes current knowledge on the regulation of plant mineral nutrition by melatonin and highlights how endogenous phytomelatonin alters plant responses to specific mineral elements. In addition, we comprehensively discuss how melatonin influences uptake and transport under conditions of nutrient shortage.

Psychobiotics: the Influence of Gut Microbiota on the Gut-Brain Axis in Neurological Disorders

Nervous system disorders are one of the common problems that affect many people around the world every year. Regarding the beneficial effects of the probiotics on the gut and the gut-brain axis, their application along with current medications has been the subject of intense interest. Psychobiotics are a probiotic strain capable to affect the gut-brain axis. The effective role of Psychobiotics in several neurological disorders is documented. Consumption of the Psychobiotics containing nutrients has positive effects on the improvement of microbiota as well as alleviation of some symptoms of central nervous system (CNS) disorders. In the present study, the effects of probiotic strains on some CNS disorders in terms of controlling the disease symptoms were reviewed. Finding suggests that Psychobiotics can efficiently alleviate the symptoms of several CNS disorders such as autism spectrum disorders, Parkinson’s disease, multiple sclerosis, insomnia, depression, diabetic neuropathy, and anorexia nervosa. It can be concluded that functional foods containing psychotropic strains can help to improve mental health.

Insight into melatonin-mediated response and signaling in the regulation of plant defense under biotic stress

Melatonin plays a crucial role in the mitigation of plant biotic stress through induced defense responses and pathogen attenuation. Utilizing the current knowledge of signaling and associated mechanism of this phytoprotectant will be invaluable in sustainable plant disease management. Biotic stress in plants involves complex regulatory networks of various sensory and signaling molecules. In this context, the polyfunctional, ubiquitous-signaling molecule melatonin has shown a regulatory role in biotic stress mitigation in plants. The present review conceptualized the current knowledge concerning the melatonin-mediated activation of the defense signaling network that leads to the resistant or tolerant phenotype of the infected plants. Fundamentals of signaling networks involved in melatonin-induced reactive oxygen species (ROS) or reactive nitrogen species (RNS) scavenging through enzymatic and non-enzymatic antioxidants have also been discussed. Increasing evidence has suggested that melatonin acts upstream of mitogen-activated proteinase kinases in activation of defense-related genes and heat shock proteins that provide immunity against pathogen attack. Besides, the direct application of melatonin on virulent fungi and bacteria showed disrupted spore morphology, destabilization of cell ultrastructure, reduced biofilm formation, and enhanced mortality that led to attenuate disease symptoms on melatonin-treated plants. The transcriptome analysis has revealed the down-regulation of pathogenicity genes, metabolism-related genes, and up-regulation of fungicide susceptibility genes in melatonin-treated pathogens. The activation of melatonin-mediated systemic acquired resistance (SAR) through cross-talk with salicylic acid (SA), jasmonic acid (JA) has been essential for viral disease management. The high endogenous melatonin concentration has also been correlated with the up-regulation of genes involved in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI). The present review highlights the versatile functions of melatonin towards direct inhibition of pathogen propagule along with active participation in mediating oxidative burst and simulating PTI, ETI and SAR responses. The hormonal cross-talk involving melatonin mediated biotic stress tolerance through defense signaling network suggests its suitability in a sustainable plant protection system.

Melatonin-Induced Protection Against Plant Abiotic Stress: Mechanisms and Prospects

Global warming in this century increases incidences of various abiotic stresses restricting plant growth and productivity and posing a severe threat to global food production and security. The plant produces different osmolytes and hormones to combat the harmful effects of these abiotic stresses. Melatonin (MT) is a plant hormone that possesses excellent properties to improve plant performance under different abiotic stresses. It is associated with improved physiological and molecular processes linked with seed germination, growth and development, photosynthesis, carbon fixation, and plant defence against other abiotic stresses. In parallel, MT also increased the accumulation of multiple osmolytes, sugars and endogenous hormones (auxin, gibberellic acid, and cytokinins) to mediate resistance to stress. Stress condition in plants often produces reactive oxygen species. MT has excellent antioxidant properties and substantially scavenges reactive oxygen species by increasing the activity of enzymatic and non-enzymatic antioxidants under stress conditions. Moreover, the upregulation of stress-responsive and antioxidant enzyme genes makes it an excellent stress-inducing molecule. However, MT produced in plants is not sufficient to induce stress tolerance. Therefore, the development of transgenic plants with improved MT biosynthesis could be a promising approach to enhancing stress tolerance. This review, therefore, focuses on the possible role of MT in the induction of various abiotic stresses in plants. We further discussed MT biosynthesis and the critical role of MT as a potential antioxidant for improving abiotic stress tolerance. In addition, we also addressed MT biosynthesis and shed light on future research directions. Therefore, this review would help readers learn more about MT in a changing environment and provide new suggestions on how this knowledge could be used to develop stress tolerance.

Grapevine rootstock and soil microbiome interactions: Keys for a resilient viticulture

Soil microbiota has increasingly been shown to play an integral role in viticulture resilience. The emergence of new metagenomic and culturomic technologies has led to significant advances in the study of microbial biodiversity. In the agricultural sector, soil and plant microbiomes have been found to significantly improve resistance to environmental stressors and diseases, as well as influencing crop yields and fruit quality thus improving sustainability under shifting environments. Grapevines are usually cultivated as a scion grafted on rootstocks, which are selected according to pedoclimatic conditions and cultural practices, known as terroir. The rootstock connects the surrounding soil to the vine's aerial part and impacts scion growth and berry quality. Understanding rootstock and soil microbiome dynamics is a relevant and important field of study, which may be critical to improve viticulture sustainability and resilience. This review aims to highlight the relationship between grapevine roots and telluric microbiota diversity and activity. In addition, this review explores the concept of core microbiome regarding potential applications of soil microbiome engineering with the goal of enhancing grapevine adaptation to biotic and abiotic stress.

How do plants defend themselves against pathogens-Biochemical mechanisms and genetic interventions

In agro-ecosystem, plant pathogens hamper food quality, crop yield, and global food security. Manipulation of naturally occurring defense mechanisms in host plants is an effective and sustainable approach for plant disease management. Various natural compounds, ranging from cell wall components to metabolic enzymes have been reported to protect plants from infection by pathogens and hence provide specific resistance to hosts against pathogens, termed as induced resistance. It involves various biochemical components, that play an important role in molecular and cellular signaling events occurring either before (elicitation) or after pathogen infection. The induction of reactive oxygen species, activation of defensive machinery of plants comprising of enzymatic and non-enzymatic antioxidative components, secondary metabolites, pathogenesis-related protein expression (e.g. chitinases and glucanases), phytoalexin production, modification in cell wall composition, melatonin production, carotenoids accumulation, and altered activity of polyamines are major induced changes in host plants during pathogen infection. Hence, the altered concentration of biochemical components in host plants restricts disease development. Such biochemical or metabolic markers can be harnessed for the development of "pathogen-proof" plants. Effective utilization of the key metabolites-based metabolic markers can pave the path for candidate gene identification. This present review discusses the valuable information for understanding the biochemical response mechanism of plants to cope with pathogens and genomics-metabolomics-based sustainable development of pathogen proof cultivars along with knowledge gaps and future perspectives to enhance sustainable agricultural production.

Transcriptomic and Metabolomic Approaches Deepen Our Knowledge of Plant-Endophyte Interactions

In natural systems, plant-symbiont-pathogen interactions play important roles in mitigating abiotic and biotic stresses in plants. Symbionts have their own special recognition ways, but they may share some similar characteristics with pathogens based on studies of model microbes and plants. Multi-omics technologies could be applied to study plant-microbe interactions, especially plant-endophyte interactions. Endophytes are naturally occurring microbes that inhabit plants, but do not cause apparent symptoms in them, and arise as an advantageous source of novel metabolites, agriculturally important promoters, and stress resisters in their host plants. Although biochemical, physiological, and molecular investigations have demonstrated that endophytes confer benefits to their hosts, especially in terms of promoting plant growth, increasing metabolic capabilities, and enhancing stress resistance, plant-endophyte interactions consist of complex mechanisms between the two symbionts. Further knowledge of these mechanisms may be gained by adopting a multi-omics approach. The involved interaction, which can range from colonization to protection against adverse conditions, has been investigated by transcriptomics and metabolomics. This review aims to provide effective means and ways of applying multi-omics studies to solve the current problems in the characterization of plant-microbe interactions, involving recognition and colonization. The obtained results should be useful for identifying the key determinants in such interactions and would also provide a timely theoretical and material basis for the study of interaction mechanisms and their applications.

Phenylalanine 4-Hydroxylase Contributes to Endophytic Bacterium Pseudomonas fluorescens' Melatonin Biosynthesis

Melatonin acts both as an antioxidant and as a growth regulatory substance in plants. Pseudomonas fluorescens endophytic bacterium has been shown to produce melatonin and increase plant resistance to abiotic stressors through increasing endogenous melatonin. However, in bacteria, genes are still not known to be melatonin-related. Here, we reported that the bacterial phenylalanine 4-hydroxylase (PAH) may be involved in the 5-hydroxytryptophan (5-HTP) biosynthesis and further influenced the subsequent production of melatonin in P. fluorescens. The purified PAH protein of P. fluorescens not only hydroxylated phenylalanine but also exhibited l-tryptophan (l-Trp) hydroxylase activity by converting l-Trp to 5-HTP in vitro. However, bacterial PAH displayed lower activity and affinity for l-Trp than l-phenylalanine. Notably, the PAH deletion of P. fluorescens blocked melatonin production by causing a significant decline in 5-HTP levels and thus decreased the resistance to abiotic stress. Overall, this study revealed a possible role for bacterial PAH in controlling 5-HTP and melatonin biosynthesis in bacteria, and expanded the current knowledge of melatonin production in microorganisms.

Phytomelatonin: An overview of the importance and mediating functions of melatonin against environmental stresses

Recently, melatonin has gained significant importance in plant research. The presence of melatonin in the plant kingdom has been known since 1995. It is a molecule that is conserved in a wide array of evolutionary distant organisms. Its functions and characteristics have been found to be similar in both plants and animals. The review focuses on the role of melatonin pertaining to physiological functions in higher plants. Melatonin regulates physiological functions regarding auxin activity, root, shoot, and explant growth, activates germination of seeds, promotes rhizogenesis (growth of adventitious and lateral roots), and holds up impelled leaf senescence. Melatonin is a natural bio-stimulant that creates resistance in field crops against various abiotic stress, including heat, chemical pollutants, cold, drought, salinity, and harmful ultra-violet radiation. The full potential of melatonin in regulating physiological functions in higher plants still needs to be explored by further research.

Harnessing Bacterial Endophytes for Promotion of Plant Growth and Biotechnological Applications: An Overview

Endophytic bacteria colonize plants and live inside them for part of or throughout their life without causing any harm or disease to their hosts. The symbiotic relationship improves the physiology, fitness, and metabolite profile of the plants, while the plants provide food and shelter for the bacteria. The bacteria-induced alterations of the plants offer many possibilities for biotechnological, medicinal, and agricultural applications. The endophytes promote plant growth and fitness through the production of phytohormones or biofertilizers, or by alleviating abiotic and biotic stress tolerance. Strengthening of the plant immune system and suppression of disease are associated with the production of novel antibiotics, secondary metabolites, siderophores, and fertilizers such as nitrogenous or other industrially interesting chemical compounds. Endophytic bacteria can be used for phytoremediation of environmental pollutants or the control of fungal diseases by the production of lytic enzymes such as chitinases and cellulases, and their huge host range allows a broad spectrum of applications to agriculturally and pharmaceutically interesting plant species. More recently, endophytic bacteria have also been used to produce nanoparticles for medical and industrial applications. This review highlights the biotechnological possibilities for bacterial endophyte applications and proposes future goals for their application.

Melatonin controversies, an update

Melatonin was discovered more than 60 years ago. Since then, several seminal discoveries have allowed us to define its function as a neuroendocrine hormone and its molecular targets in mammals and many other species. However, many fundamental issues have not yet been solved such as the subcellular localization of melatonin synthesis and the full spectrum of its molecular targets. In addition, a considerable number of controversies persist in the field, mainly concerning how many functions melatonin has. Altogether, this illustrates how "immature" the field still is. The intention of this opinion article is to note the controversies and limitations in the field, to initiate a discussion and to make proposals/guidelines to overcome them and move the field forward.

Chitosan modulates Pochonia chlamydosporia gene expression during nematode egg parasitism

Climate change makes plant‐parasitic nematodes (PPN) an increasing threat to commercial crops. PPN can be managed sustainably by the biocontrol fungus Pochonia chlamydosporia (Pc). Chitosan generated from chitin deacetylation enhances PPN parasitism by Pc. In this work, we investigate the molecular mechanisms of Pc for chitosan resistance and root‐knot nematode (RKN) parasitism, using transcriptomics. Chitosan and RKN modify the expression of Pc genes, mainly those involved in oxidation–reduction processes. Both agents significantly modify the expression of genes associated to 113 GO terms and 180 Pc genes. Genes encoding putative glycoproteins (Pc adhesives) to nematode eggshell, as well as genes involved in redox, carbohydrate and lipid metabolism trigger the response to chitosan. We identify genes expressed in both the parasitic and endophytic phases of the Pc lifecycle; these include proteases, chitosanases and transcription factors. Using the Pathogen—Host Interaction database (PHI‐base), our previous RNA‐seq data and RT‐PCR of Pc colonizing banana we have investigated genes expressed both in the parasitic and endophytic phases of Pc lifecycle.

Microbial production of beneficial indoleamines (serotonin and melatonin) with potential application to biotechnological products for human health

Micro-organisms have showed the ability to produce biologically active compounds associated with neurotransmission in higher organisms. In particular, serotonin- and melatonin-producing microbes are valuable sources for the development of eco-friendly bioproducts. Serotonin and melatonin are indoleamines that have received special attention due to their positive effects on human health. These biomolecules exert a critical role in several physiological or pathological processes, including some mental and neurological disorders. This article includes a review of the microbial production of serotonin and melatonin, their functions in micro-organisms and their potential uses as therapeutic and/or preventive agents to improve human health. A description of the quantification methods employed to detect indoleamines and the evidence found concerning their microbial production at laboratory and industrial scale-for application in biotechnological products-is also provided. The microbial ability to synthesize beneficial indoleamines should be further studied and harnessed, to allow the development of sustainable bioprocesses to produce foods and pharmaceuticals for human health.

Plant Health and Sound Vibration: Analyzing Implications of the Microbiome in Grape Wine Leaves

Understanding the plant microbiome is a key for plant health and controlling pathogens. Recent studies have shown that plants are responsive towards natural and synthetic sound vibration (SV) by perception and signal transduction, which resulted in resistance towards plant pathogens. However, whether or not native plant microbiomes respond to SV and the underlying mechanism thereof remains unknown. Within the present study we compared grapevine-associated microbiota that was perpetually exposed to classical music with a non-exposed control group from the same vineyard in Stellenbosch, South Africa. By analyzing the 16S rRNA gene and ITS fragment amplicon libraries we found differences between the core microbiome of SV-exposed leaves and the control group. For several of these different genera, e.g., Bacillus, Kocuria and Sphingomonas, a host-beneficial or pathogen-antagonistic effect has been well studied. Moreover, abundances of taxa identified as potential producers of volatile organic compounds that contribute to sensory characteristics of wines, e.g., Methylobacterium, Sphingomonas, Bacillus and Sporobolomyces roseus, were either increased or even unique within the core music-exposed phyllosphere population. Results show an as yet unexplored avenue for improved plant health and the terroir of wine, which are important for environmentally friendly horticulture and consumer appreciation. Although our findings explain one detail of the long-term positive experience to improve grapevine’s resilience by this unusual but innovative technique, more mechanistic studies are necessary to understand the whole interplay.

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.

Melatonin: A master regulator of plant development and stress responses

Melatonin is a pleiotropic molecule with multiple functions in plants. Since the discovery of melatonin in plants, numerous studies have provided insight into the biosynthesis, catabolism, and physiological and biochemical functions of this important molecule. Here, we describe the biosynthesis of melatonin from tryptophan, as well as its various degradation pathways in plants. The identification of a putative melatonin receptor in plants has led to the hypothesis that melatonin is a hormone involved in regulating plant growth, aerial organ development, root morphology, and the floral transition. The universal antioxidant activity of melatonin and its role in preserving chlorophyll might explain its anti-senescence capacity in aging leaves. An impressive amount of research has focused on the role of melatonin in modulating postharvest fruit ripening by regulating the expression of ethylene-related genes. Recent evidence also indicated that melatonin functions in the plant's response to biotic stress, cooperating with other phytohormones and well-known molecules such as reactive oxygen species and nitric oxide. Finally, great progress has been made towards understanding how melatonin alleviates the effects of various abiotic stresses, including salt, drought, extreme temperature, and heavy metal stress. Given its diverse roles, we propose that melatonin is a master regulator in plants.

Psychobiotic Effects of Multi-Strain Probiotics Originated from Thai Fermented Foods in a Rat Model

This work aimed to investigate the psychobiotic effects of six bacterial strains on the mind and behavior of male Wistar rats. The probiotic (PRO) group (n=7) were rats pre-treated with antibiotics for 7 days followed by 14-day probiotic administration, antibiotics (ANT) group (n=7) were rats treated with antibiotics for 21 days without probiotics. The control (CON) group (n=7) were rats that received sham treatment for 21 days. The six bacterial strains with probiotic properties were mostly isolated from Thai fermented foods; Pedicoccus pentosaceus WS11, Lactobacillus plantarum SK321, L. fermentum SK324, L. brevis TRBC 3003, Bifidobacterium adolescentis TBRC 7154 and Lactococcus lactis subsp. lactis TBRC 375. The probiotics were freeze-dried into powder (6×109 CFU/5 g) and administered to the PRO group via oral gavage. Behavioral tests were performed. The PRO group displayed significantly reduced anxiety level and increased locomotor function using a marble burying test and open field test, respectively and significantly improved short-term memory performance using a novel object recognition test. Antibiotics significantly reduced microbial counts in rat feces in the ANT group by 100 fold compared to the PRO group. Probiotics significantly enhanced antioxidant enzymatic and non-enzymatic defenses in rat brains as assessed using catalase activity and ferric reducing antioxidant power assay, respectively. Probiotics also showed neuroprotective effects with less pyknotic cells and lower frequency of vacuolization in cerebral cortex. This multi-strain probiotic formulation from Thai fermented foods may offer a potential to develop psychobiotic-rich functional foods to modulate human mind and behaviors.

Melatonin-Induced Water Stress Tolerance in Plants: Recent Advances

Water stress (drought and waterlogging) is severe abiotic stress to plant growth and development. Melatonin, a bioactive plant hormone, has been widely tested in drought situations in diverse plant species, while few studies on the role of melatonin in waterlogging stress conditions have been published. In the current review, we analyze the biostimulatory functions of melatonin on plants under both drought and waterlogging stresses. Melatonin controls the levels of reactive oxygen and nitrogen species and positively changes the molecular defense to improve plant tolerance against water stress. Moreover, the crosstalk of melatonin and other phytohormones is a key element of plant survival under drought stress, while this relationship needs further investigation under waterlogging stress. In this review, we draw the complete story of water stress on both sides-drought and waterlogging-through discussing the previous critical studies under both conditions. Moreover, we suggest several research directions, especially for waterlogging, which remains a big and vague piece of the melatonin and water stress puzzle.

Melatonin-Induced Water Stress Tolerance in Plants: Recent Advances

Water stress (drought and waterlogging) is severe abiotic stress to plant growth and development. Melatonin, a bioactive plant hormone, has been widely tested in drought situations in diverse plant species, while few studies on the role of melatonin in waterlogging stress conditions have been published. In the current review, we analyze the biostimulatory functions of melatonin on plants under both drought and waterlogging stresses. Melatonin controls the levels of reactive oxygen and nitrogen species and positively changes the molecular defense to improve plant tolerance against water stress. Moreover, the crosstalk of melatonin and other phytohormones is a key element of plant survival under drought stress, while this relationship needs further investigation under waterlogging stress. In this review, we draw the complete story of water stress on both sides-drought and waterlogging-through discussing the previous critical studies under both conditions. Moreover, we suggest several research directions, especially for waterlogging, which remains a big and vague piece of the melatonin and water stress puzzle.

Plants endophytes: unveiling hidden agenda for bioprospecting toward sustainable agriculture

Endophytic microbes are present in nearly all of the plant species known to date but how they enter and flourish inside a host plant and display multiple benefits like plant growth promotion (PGP), biodegradation, and stress alleviation are still unexplored. Until now, the majority of the research has been conducted assuming that the host-endophyte interaction is analogous to the PGP microbes, although, studies related to the mechanisms of their infection, colonization as well as conferring important traits to the plants are limited. It would be fascinating to explore the role of these endophytic microbes in host gene expression, metabolism, and the modulation of phenotypic traits, under abiotic and biotic stress conditions. In this review, we critically focused on the following areas: (i) endophytic lifestyle and the mechanism of their entry into plant tissues, (ii) how endophytes modulate the immune system of plants and affect the genotypic and phenotypic expression of host plants under abiotic and biotic stress condition, and (iii) the role of omics and other integrated genomic approaches in unraveling complex host-endophyte signaling crosstalk. Furthermore, we discussed their role in phytoremediation of heavy metal stress and whole genomic analysis based on an understanding of different metabolic pathways these endophytes utilize to combat stress.

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.

Endophytic bacteria promote the quality of Lyophyllum decastes by improving non-volatile taste components of mycelia

Endophytic bacteria are always related to the host different traits, including the secondary metabolites production. However, the effect and mechanism of endophytic bacteria in the mushrooms fruit body on mycelia are still not clear. In this study, we investigated the effect of endophytic bacterial metabolites on the quality of Lyophyllum decastes mycelia. Soluble sugars, starch, protein, free amino acids, 5'-Nucleotides, EUC, and organic acids contents of mycelia were analyzed. We found that endophytic bacterial metabolites significantly increased the contents of soluble sugars, starch, protein, free amino acids, organic acids, and EUC. The present study thus suggests that endophytic bacteria could promote the quality of Lyophyllum decastes by improving non-volatile taste components of mycelia.

Exogenous Melatonin Enhances Rice Plant Resistance Against Xanthomonas oryzae pv. oryzae

Rice bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae, is one of the most serious diseases of rice. In this study we found that exogenous melatonin can increase rice resistance to BB. Treatment of rice plants with exogenous melatonin (20 µg/ml) increased nitrate reductase, nitric oxide synthase, and peroxidase activity, enabling high intracellular concentrations of melatonin, nitric oxide, and H₂O₂. The expression of NPR1, a key regulator in the salicylic acid signaling pathway, was upregulated more than 10-fold when the plants were challenged with melatonin. Similarly, the messenger RNA level of PDF1.2, a jasmonic acid-induced defense marker, was 15 times higher in the treated plants than in the control plants. Moreover, three pathogenesis-related proteins, PR1b, PR8a, and PR9, were upregulated 20-fold in the presence of melatonin. The application of melatonin (100 µg/ml) to soil-grown rice reduced the incidence of BB by 86.21%. Taken together, these results not only provide a better understanding of melatonin-mediated innate immunity to X. oryzae pv. oryzae in rice but also represent a promising cultivation strategy to protect rice against X. oryzae pv. oryzae infection.

Rhizosphere Microbiome Assembly and Its Impact on Plant Growth

Microorganisms colonizing the plant rhizosphere provide a number of beneficial functions for their host. Although an increasing number of investigations clarified the great functional capabilities of rhizosphere microbial communities, the understanding of the precise mechanisms underlying the impact of rhizosphere microbiome assemblies is still limited. Also, not much is known about the various beneficial functions of the rhizosphere microbiome. In this review, we summarize the current knowledge of biotic and abiotic factors that shape the rhizosphere microbiome as well as the rhizosphere microbiome traits that are beneficial to plants growth and disease-resistance. We give particular emphasis on the impact of plant root metabolites on rhizosphere microbiome assemblies and on how the microbiome contributes to plant growth, yield, and disease-resistance. Finally, we introduce a new perspective and a novel method showing how a synthetic microbial community construction provides an effective approach to unravel the plant-microbes and microbes-microbes interplays.

Microorganisms: Producers of Melatonin in Fermented Foods and Beverages

Melatonin has recently been detected in fermented beverages and foods, in which microorganism metabolism is highly important. The existing literature knowledge discusses the direction for future studies in this review. Evidence shows that many species of microorganisms could synthesize melatonin. However, the actual concentrations of melatonin in fermented foods and beverages range from picograms per milliliter to nanograms per milliliter. Different types of microorganisms, different raw materials, different culture environments, the presence or absence of precursors, high or low alcohol content, and different detection methods are all possible reasons for the huge difference of melatonin levels. Thus far, there have been relatively few studies on the melatonin synthesis pathway microorganisms. Thus, referring to the synthetic pathway of plants and animals, the putative melatonin biosynthesis pathway of microorganisms is presented. It will be significant to discuss whether all species of microorganisms have the capacity to synthesize melatonin and what the biological functions of melatonin are in microorganisms. Melatonin plays a lot of important roles in microorganisms, particularly in enhancing the tolerance of environment stress. Also, the loss of melatonin concentration in commercially available fermented foods and beverages is a ubiquitous trend, and how to solve this problem is a new field to be further explored.

Exogenous Melatonin Application Enhances Rhizophagus irregularis Symbiosis and Induces the Antioxidant Response of Medicago truncatula Under Lead Stress

Melatonin is a new kind of plant growth regulator. The aim of this study was to figure out the effect of melatonin on arbuscular mycorrhizal (AM) symbiosis and heavy metal tolerance. A three-factor experiment was conducted to determine the effect of melatonin application on the growth, AM symbiosis, and stress tolerance of Medicago truncatula. A two-factor (AM inoculation and Pb stress) experiment was conducted to determine the effect of AM fungus on melatonin accumulation under Pb stress. AM plants under Pb stress had a higher melatonin accumulation than non-mycorrhizal (NM) plants under Pb stress. Acetylserotonin methyltransferase (ASMT) is the enzymatic reaction of the last step in melatonin synthesis. The accumulation of melatonin may be related to the expression of MtASMT. Melatonin application increased the relative expression of MtPT4 and AM colonization in AM plants. Melatonin application decreased Pb uptake with and without AM inoculation. Both melatonin application and AM inoculation improved M. truncatula growth and increased antioxidant response with Pb stress. These results indicated that melatonin application has positive effects on AM symbiosis and Pb stress tolerance under Pb stress. AM inoculation improve melatonin synthesis capacity under Pb stress. Melatonin application may improve AM plant growth by enhancing AM symbiosis, stimulating antioxidant response, and inhibiting Pb uptake.

Microbial Engineering for Production of N-Functionalized Amino Acids and Amines

N-functionalized amines play important roles in nature and occur, for example, in the antibiotic vancomycin, the immunosuppressant cyclosporine, the cytostatic actinomycin, the siderophore aerobactin, the cyanogenic glucoside linamarin, and the polyamine spermidine. In the pharmaceutical and fine-chemical industries N-functionalized amines are used as building blocks for the preparation of bioactive molecules. Processes based on fermentation and on enzyme catalysis have been developed to provide sustainable manufacturing routes to N-alkylated, N-hydroxylated, N-acylated, or other N-functionalized amines including polyamines. Metabolic engineering for provision of precursor metabolites is combined with heterologous N-functionalizing enzymes such as imine or ketimine reductases, opine or amino acid dehydrogenases, N-hydroxylases, N-acyltransferase, or polyamine synthetases. Recent progress and applications of fermentative processes using metabolically engineered bacteria and yeasts along with the employed enzymes are reviewed and the perspectives on developing new fermentative processes based on insight from enzyme catalysis are discussed.