Melatonin synthesis enzymes interact with ascorbate peroxidase to protect against oxidative stress in cassava

Melatonin Improves Oxidative Stress Injury in Retinopathy of Prematurity by Targeting miR-23a-3p/Nrf2

PURPOSE

Melatonin has promising protective effects for retinopathy. However, its roles in retinopathy of prematurity (ROP) and the underlying mechanisms remain unknown. We aimed to explore its roles and mechanisms in a ROP model.

METHODS

Hematoxylin and eosin staining were used to observe the morphology of the retina. Immunofluorescence was used to detect positive (Nrf2+ and VEGF+) cells. Immunohistochemistry was used to detect the level of nuclear expression of PCNA in retinal tissue. Transmission electron microscope (TEM) was used to observe the morphology and structure of pigment cells. qRT-PCR was used to assay the expression of miR-23a-3p, Nrf2, and HO-1. Western blotting was used to detect the expression of Nrf2, HO-1, β-actin, and Lamin B1.

RESULTS

Melatonin or miR-23a-3p antagomir treatment could ameliorate the Oxygen-induced pathological changes, increased the expression of Nrf2 and HO-1, SOD, and GSH-Px, and decreased the expression of VEGF, miR-23a-3p, MDA and the apoptosis in the ROP model. Further target prediction and luciferase reporter assays confirmed the targeted binding relationship between miR-23a-3p and Nrf2.

CONCLUSION

Our study showed that melatonin could ameliorate H2O2-induced apoptosis and oxidative stress injury in RGC cells by mediating miR-23a-3p/Nrf2 signaling pathway, thereby improving retinal degeneration.

Ascorbic acid: a metabolite switch for designing stress-smart crops

Plant growth and productivity are continually being challenged by a diverse array of abiotic stresses, including: water scarcity, extreme temperatures, heavy metal exposure, and soil salinity. A common theme in these stresses is the overproduction of reactive oxygen species (ROS), which disrupts cellular redox homeostasis causing oxidative damage. Ascorbic acid (AsA), commonly known as vitamin C, is an essential nutrient for humans, and also plays a crucial role in the plant kingdom. AsA is synthesized by plants through the d-mannose/l-galactose pathway that functions as a powerful antioxidant and protects plant cells from ROS generated during photosynthesis. AsA controls several key physiological processes, including: photosynthesis, respiration, and carbohydrate metabolism, either by acting as a co-factor for metabolic enzymes or by regulating cellular redox-status. AsA's multi-functionality uniquely positions it to integrate and recalibrate redox-responsive transcriptional/metabolic circuits and essential biological processes, in accordance to developmental and environmental cues. In recognition of this, we present a systematic overview of current evidence highlighting AsA as a central metabolite-switch in plants. Further, a comprehensive overview of genetic manipulation of genes involved in AsA metabolism has been provided along with the bottlenecks and future research directions, that could serve as a framework for designing "stress-smart" crops in future.

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 mediated tolerance to benzalkonium chloride phytotoxicity through improved growth, photochemical reactions, and antioxidant system in wild-type and snat2 mutant Arabidopsis lines

Melatonin (Mel) is a phytohormone that plays a crucial role in various plant processes, including stress response. Despite numerous studies on the role of Mel in stress resistance, its significance in plants exposed to benzalkonium chloride (BAC) pollution remains unexplored. BAC, a common antiseptic, poses a threat to terrestrial plants due to its widespread use and inefficient removal, leading to elevated concentrations in the environment. This study investigated the impact of BAC (0.5 mg L-1) pollution on wild-type Col-0 and snat2 knockout mutant Arabidopsis lines, revealing reduced growth, altered water relations, and gas exchange parameters. On the other hand, exogenous Mel (100 μM) treatments mitigated BAC-induced phytotoxicity and increased the growth rate by 1.8-fold in Col-0 and 2-fold in snat2 plants. snat2 mutant seedlings had a suppressed carbon assimilation rate (A) under normal conditions, but BAC contamination led to further A repression by 71% and 48% in Col-0 and snat2 leaves, respectively. However, Mel treatment on stressed plants was successful in improving Fv/Fm and increased the total photosynthesis efficiency by regulating photochemical reactions. Excessive H2O2 accumulation in the guard cells of plants exposed to BAC pollution was detected by confocal microscopy. Mel treatments triggered almost all antioxidant enzyme activities (except POX) in both Arabidopsis lines under stress. This enhanced antioxidant activity, facilitated by foliar Mel application, contributed to the alleviation of oxidative damage, regulation of photosynthesis reactions, and promotion of plant growth in Arabidopsis. In addition to corroborating results observed in many agricultural plants regarding the development of tolerance to environmental stresses, this study provides novel insights into the action mechanisms of Mel under the emerging pollutant benzalkonium chloride.

Development of packaging films based on UiO-66 MOF loaded melatonin with antioxidation functions for spinach preservation

Spinach tends to deteriorate after harvest due to physiological metabolic activities. As a natural, pollution-free, and environmentally friendly preservative, melatonin (MT) can effectively maintain the quality of fruits and vegetables after harvest and delay senescence. To enhance the preservation effect of MT, this study developed antioxidant films using MT-loaded UiO-66 metal-organic framework (MOF) nanoparticles. This approach effectively extends the shelf life of spinach while preserving its quality. The underlying mechanism involves leveraging the microporous structure and stability of UiO-66 MOF. Experimental results obtained from the packaging films demonstrated significant improvements in both mechanical strength and antioxidant properties when UiO-66 was loaded with MT at a concentration of 0.20 mg/mL and combined with sodium alginate. Freshness preservation experiments also indicated the effective preservation effect of these films on spinach. In conclusion, the results of this study suggest that MT-loaded UiO-66 MOF is a promising active packaging material for spinach preservation.

Elucidating the role of exogenous melatonin in mitigating alkaline stress in soybeans across different growth stages: a transcriptomic and metabolomic approach

BACKGROUND

Soybean (Glycine max), a vital grain and oilseed crop, serves as a primary source of plant protein and oil. Soil salinization poses a significant threat to soybean planting, highlighting the urgency to improve soybean resilience and adaptability to saline stress. Melatonin, recently identified as a key plant growth regulator, plays crucial roles in plant growth, development, and responses to environmental stress. However, the potential of melatonin to mitigate alkali stress in soybeans and the underlying mechanisms remain unclear.

RESULTS

This study investigated the effects of exogenous melatonin on the soybean cultivar Zhonghuang 13 under alkaline stress. We employed physiological, biochemical, transcriptomic, and metabolomic analyses throughout both vegetative and pod-filling growth stages. Our findings demonstrate that melatonin significantly counteracts the detrimental effects of alkaline stress on soybean plants, promoting plant growth, photosynthesis, and antioxidant capacity. Transcriptomic analysis during both growth stages under alkaline stress, with and without melatonin treatment, identified 2,834 and 549 differentially expressed genes, respectively. These genes may play a vital role in regulating plant adaptation to abiotic stress. Notably, analysis of phytohormone biosynthesis pathways revealed altered expression of key genes, particularly in the ARF (auxin response factor), AUX/IAA (auxin/indole-3-acetic acid), and GH3 (Gretchen Hagen 3) families, during the early stress response. Metabolomic analysis during the pod-filling stage identified highly expressed metabolites responding to melatonin application, such as uteolin-7-O-(2''-O-rhamnosyl)rutinoside and Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside, which helped alleviate the damage caused by alkali stress. Furthermore, we identified 183 differentially expressed transcription factors, potentially playing a critical role in regulating plant adaptation to abiotic stress. Among these, the gene SoyZH13_04G073701 is particularly noteworthy as it regulates the key differentially expressed metabolite, the terpene metabolite Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside. WGCNA analysis identified this gene (SoyZH13_04G073701) as a hub gene, positively regulating the crucial differentially expressed metabolite of terpenoids, Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside. Our findings provide novel insights into how exogenous melatonin alleviates alkali stress in soybeans at different reproductive stages.

CONCLUSIONS

Integrating transcriptomic and metabolomic approaches, our study elucidates the mechanisms by which exogenous melatonin ameliorates the inhibitory effects of alkaline stress on soybean growth and development. This occurs through modulation of biosynthesis pathways for key compounds, including terpenes, flavonoids, and phenolics. Our findings provide initial mechanistic insights into how melatonin mitigates alkaline stress in soybeans, offering a foundation for molecular breeding strategies to enhance salt-alkali tolerance in this crop.

Ascorbate peroxidase in fruits and modulation of its activity by reactive species

Ascorbate peroxidase (APX) is one of the enzymes of the ascorbate-glutathione cycle and is the key enzyme that breaks down H2O2 with the aid of ascorbate as an electron source. APX is present in all photosynthetic eukaryotes from algae to higher plants and, at the cellular level, it is localized in all subcellular compartments where H2O2 is generated, including the apoplast, cytosol, plastids, mitochondria, and peroxisomes, either in soluble form or attached to the organelle membranes. APX activity can be modulated by various post-translational modifications including tyrosine nitration, S-nitrosation, persulfidation, and S-sulfenylation. This allows the connection of H2O2 metabolism with other relevant signaling molecules such as NO and H2S, thus building a complex coordination system. In both climacteric and non-climacteric fruits, APX plays a key role during the ripening process and during post-harvest, since it participates in the regulation of both H2O2 and ascorbate levels affecting fruit quality. Currently, the exogenous application of molecules such as NO, H2S, H2O2, and, more recently, melatonin is seen as a new alternative to maintain and extend the shelf life and quality of fruits because they can modulate APX activity as well as other antioxidant systems. Therefore, these molecules are being considered as new biotechnological tools to improve crop quality in the horticultural industry.

Cassava phosphatase PP2C1 modulates thermotolerance via fine-tuning dephosphorylation of antioxidant enzymes

Global warming is an adverse environmental factor that threatens crop yields and food security. 2C-type protein phosphatases (PP2Cs), as core protein phosphatase components, play important roles in plant hormone signaling to cope with various environmental stresses. However, the function and underlying mechanism of PP2Cs in the heat stress response remain elusive in tropical crops. Here, we report that MePP2C1 negatively regulated thermotolerance in cassava (Manihot esculenta Crantz), accompanied by the modulation of reactive oxygen species (ROS) accumulation and the underlying antioxidant enzyme activities of catalase (CAT) and ascorbate peroxidase (APX). Further investigation found that MePP2C1 directly interacted with and dephosphorylated MeCAT1 and MeAPX2 at serine (S) 112 and S160 residues, respectively. Moreover, in vitro and in vivo assays showed that protein phosphorylation of MeCAT1S112 and MeAPX2S160 was essential for their enzyme activities, and MePP2C1 negatively regulated thermotolerance and redox homeostasis by dephosphorylating MeCAT1S112 and MeAPX2S160. Taken together, this study illustrates the direct relationship between MePP2C1-mediated protein dephosphorylation of MeCAT1 and MeAPX2 and ROS accumulation in thermotolerance to provide insights for adapting to global warming via fine-tuning thermotolerance of the tropical crop cassava.

Endogenous melatonin involved in plant salt response by impacting auxin signaling

KEY MESSAGE

The study on melatonin biosynthesis mutant snat1snat2 revealed that endogenous melatonin plays an important role in salt responsiveness by mediating auxin signaling. Melatonin is a pleiotropic signaling molecule, which, besides being involved in multiple growth and developmental processes, also mediates environmental stress responses. However, whether and how endogenous melatonin is involved in salt response has not been determined. In this study, we elucidated the involvement of endogenous melatonin in salt response by investigatiing the impact of salt stress on a double mutant of Arabidopsis (snat1snat2) defective in melatonin biosynthesis genes SNAT1 and SNAT2. This mutant was found to exhibit salt sensitivity, manifested by unhealthy growth, ion imbalance and ROS accumulation under salt stress. Transcriptomic profiles of snat1snat2 revealed that the expression of a large number of salt-responsive genes was affected by SNAT defect, and these genes were closely related to the synthesis of auxin and several signaling pathways. In addition, the salt-sensitive growth phenotype of snat1snat2 was alleviated by the application of exogenous auxin. Our results show that endogenous melatonin may be essential for plant salt tolerance, a function that could be correlated with diverse activity in mediating auxin signaling.

Melatonin as a key regulator in seed germination under abiotic stress

Seed germination (SG) is the first stage in a plant's life and has an immense importance in sustaining crop production. Abiotic stresses reduce SG by increasing the deterioration of seed quality, and reducing germination potential, and seed vigor. Thus, to achieve a sustainable level of crop yield, it is important to improve SG under abiotic stress conditions. Melatonin (MEL) is an important biomolecule that interplays in developmental processes and regulates many adaptive responses in plants, especially under abiotic stresses. Thus, this review specifically summarizes and discusses the mechanistic basis of MEL-mediated SG under abiotic stresses. MEL regulates SG by regulating some stress-specific responses and some common responses. For instance, MEL induced stress specific responses include the regulation of ionic homeostasis, and hydrolysis of storage proteins under salinity stress, regulation of C-repeat binding factors signaling under cold stress, starch metabolism under high temperature and heavy metal stress, and activation of aquaporins and accumulation of osmolytes under drought stress. On other hand, MEL mediated regulation of gibberellins biosynthesis and abscisic acid catabolism, redox homeostasis, and Ca2+ signaling are amongst the common responses. Nonetheless factors such as endogenous MEL contents, plant species, and growth conditions also influence above-mentioned responses. In conclusion, MEL regulates SG under abiotic stress conditions by interacting with different physiological mechanisms.

Prolong the postharvest shelf life of spinach through the antioxidative ability of melatonin

Spinach is also known as Persian cuisine, it is rich in nutrients such as protein, vitamin C and minerals, and has high nutritional value. In this study, Spinach was treated with melatonin in order to prolong its shelf life. Melatonin has strong antioxidant effects as an endogenous free radical scavenger. The spinach was sprayed with 0.10, 0.20 and 0.30 mg/mL melatonin solution after harvesting, and distilled water was used as control for low temperature storage at 4 °C. The results showed that melatonin spraying Spinach delayed the degradation of chlorophyll, especially the treatment of 0.20 mg/mL melatonin was the most effective. The content of soluble sugar and soluble protein in spinach tissue was kept high, the accumulation of malondialdehyde (MDA) was reduced, and the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were increased. These findings suggested that melatonin treatment may be a useful technique to prolong the postharvest life of spinach and improve its quality.

The self-association of cytoplasmic malate dehydrogenase 1 promotes malate biosynthesis and confers disease resistance in cassava

Malate dehydrogenase (MDH) as an essential metabolic enzyme is widely involved in plant developmental processes. However, the direct relationship between its structural basis and in vivo roles especially in plant immunity remains elusive. In this study, we found that cytoplasmic cassava (Manihot esculenta, Me) MDH1 was essential for plant disease resistance against cassava bacterial blight (CBB). Further investigation revealed that MeMDH1 positively modulated cassava disease resistance, accompanying the regulation of salicylic acid (SA) accumulation and pathogensis-related protein 1 (MePR1) expression. Notably, the metabolic product of MeMDH1 (malate) also improved disease resistance in cassava, and its application rescued the disease susceptibility and decreased immune responses of MeMDH1-silenced plants, indicating that malate was responsible for MeMDH1-mediated disease resistance. Interestingly, MeMDH1 relied on Cys330 residues to form homodimer, which was directly related with MeMDH1 enzyme activity and the corresponding malate biosynthesis. The crucial role of Cys330 residue in MeMDH1 was further confirmed by in vivo functional comparison between overexpression of MeMDH1 and MeMDH1C330A in cassava disease resistance. Taken together, this study highlights that MeMDH1 confers improved plant disease resistance through protein self-association to promote malate biosynthesis, extending the knowledge of the relationship between its structure and cassava disease resistance.

Glutathione system enhancement for cardiac protection: pharmacological options against oxidative stress and ferroptosis

The glutathione (GSH) system is considered to be one of the most powerful endogenous antioxidant systems in the cardiovascular system due to its key contribution to detoxifying xenobiotics and scavenging overreactive oxygen species (ROS). Numerous investigations have suggested that disruption of the GSH system is a critical element in the pathogenesis of myocardial injury. Meanwhile, a newly proposed type of cell death, ferroptosis, has been demonstrated to be closely related to the GSH system, which affects the process and outcome of myocardial injury. Moreover, in facing various pathological challenges, the mammalian heart, which possesses high levels of mitochondria and weak antioxidant capacity, is susceptible to oxidant production and oxidative damage. Therefore, targeted enhancement of the GSH system along with prevention of ferroptosis in the myocardium is a promising therapeutic strategy. In this review, we first systematically describe the physiological functions and anabolism of the GSH system, as well as its effects on cardiac injury. Then, we discuss the relationship between the GSH system and ferroptosis in myocardial injury. Moreover, a comprehensive summary of the activation strategies of the GSH system is presented, where we mainly identify several promising herbal monomers, which may provide valuable guidelines for the exploration of new therapeutic approaches.

Recent advances and mechanistic insights on Melatonin-mediated salt stress signaling in plants

Salinity stress is one of the major abiotic constraints that limit plant growth and yield, which thereby is a serious concern to world food security. It adversely affects crop production by inducing hyperosmotic stress and ionic toxicity as well as secondary stresses such as oxidative stress, all of which disturb optimum physiology and metabolism. Nonetheless, various strategies have been employed to improve salt tolerance in crop plants, among which the application of Melatonin (Mel) could also be used as it has demonstrated promising results. The ongoing experimental evidence revealed that Mel is a pleiotropic signaling molecule, which besides being involved in various growth and developmental processes also mediates environmental stress responses. The current review systematically discusses and summarizes how Mel mediates the response of plants under salt stress and could optimize the balance between plant growth performances and stress responses. Specifically, it covers the latest advances of Mel in fine-tuning the signaling in plants. Furthermore, it highlights plant-built tolerance of salt stress by manifesting the biosynthesis of Mel, its cross talks with nitric oxide (NO), and Mel as a multifaceted antioxidant molecule.

Interactions of melatonin, reactive oxygen species, and nitric oxide during fruit ripening: an update and prospective view

Fruit ripening is a physiological process that involves a complex network of signaling molecules that act as switches to activate or deactivate certain metabolic pathways at different levels, not only by regulating gene and protein expression but also through post-translational modifications of the involved proteins. Ethylene is the distinctive molecule that regulates the ripening of fruits, which can be classified as climacteric or non-climacteric according to whether or not, respectively, they are dependent on this phytohormone. However, in recent years it has been found that other molecules with signaling potential also exert regulatory roles, not only individually but also as a result of interactions among them. These observations imply the existence of mutual and hierarchical regulations that sometimes make it difficult to identify the initial triggering event. Among these 'new' molecules, hydrogen peroxide, nitric oxide, and melatonin have been highlighted as prominent. This review provides a comprehensive outline of the relevance of these molecules in the fruit ripening process and the complex network of the known interactions among them.

PP2C1 fine-tunes melatonin biosynthesis and phytomelatonin receptor PMTR1 binding to melatonin in cassava

Melatonin is an important molecule in both animals and plants, regulating circadian rhythms and stress responses. Therefore, the improvement of melatonin accumulation not only strengthens the function of melatonin but also improves stress resistance in crops. Although melatonin biosynthetic enzymes have been identified through reverse genetics previously, an investigation of melatonin level-related genes through forward genetics in plants has yet to be performed. In this study, a genome-wide association study using cassava natural population of 298 genetic resources identified melatonin accumulation 1 (MA1), which regulates the natural variation of melatonin levels in cassava. We found that MA1 encodes type 2C protein phosphatase 1 (PP2C1), which serves as a negative regulator of melatonin levels in cassava. MePP2C1 physically interacts with MeRAV1/2 and MeWRKY20 and dephosphorylates them at serine (S) 35 residue, S34 residue, and S176 residue, respectively, thereby hindering their transcriptional activation on downstream melatonin biosynthetic genes. Notably, MePP2C1 interacts with phytomelatonin receptor MePMTR1 and dephosphorylates it at S11 residue, repressing its binding to melatonin. In summary, this study demonstrates that MePP2C1 as MA1 plays dual roles in negatively regulating both melatonin accumulation and signaling, extending the understanding of the molecular mechanism underlying melatonin accumulation and signaling through forward genetics in plants.

Exogenous Melatonin Improves Seed Germination of Wheat (Triticum aestivum L.) under Salt Stress

Melatonin (MT) can effectively reduce oxidative damage induced by abiotic stresses such as salt in plants. However, the effects of MT on physiological responses and molecular regulation during wheat germination remains largely elusive. In this study, the response of wheat seeds to MT under salt stress during germination was investigated at physiological and transcriptome levels. Our results revealed that application of MT significantly reduced the negative influence of salt stress on wheat seed germination. The oxidative load was reduced by inducing high activities of antioxidant enzymes. In parallel, the content of gibberellin A3 (GA3) and jasmonic acid (JA) increased in MT-treated seedling. RNA-seq analysis demonstrated that MT alters oxidoreductase activity and phytohormone-dependent signal transduction pathways under salt stress. Weighted correlation network analysis (WGCNA) revealed that MT participates in enhanced energy metabolism and protected seeds via maintained cell morphology under salt stress during wheat seed germination. Our findings provide a conceptual basis of the MT-mediated regulatory mechanism in plant adaptation to salt stress, and identify the potential candidate genes for salt-tolerant wheat molecular breeding.

LSD3 mediates the oxidative stress response through fine-tuning APX2 activity and the NF-YC15-GSTs module in cassava

Reactive oxygen species (ROS) overproduction leads to oxidative damage under almost all stress conditions. Lesion-Simulating Disease (LSD), a zinc finger protein, is an important negative regulator of ROS accumulation and cell death in plants. However, the in vivo role of LSD in cassava (Manihot esculenta) and the underlying molecular mechanisms remain elusive. Here, we found that MeLSD3 is essential for the oxidative stress response in cassava. MeLSD3 physically interacted with ascorbate peroxidase 2 (MeAPX2), thereby promoting its enzymatic activity. In addition, MeLSD3 also interacted with the nuclear factor YC15 (MeNF-YC15), which also interacted with nuclear factor YA2/4 (MeNF-YA2/4) and nuclear factor YB18 (MeNF-YB18) to form an MeNF-YC15-MeNF-YA2/4-MeNF-YB18 complex. Notably, MeLSD3 positively modulated the transcriptional activation of the MeNF-YC15-MeNF-YA2/4-MeNF-YB18 complex by interacting with the CCAAT boxes of the promoters of glutathione S-transferases U37/U39 (MeGST-U37/U39), activating their transcription. When one or both of MeLSD3 and the MeNF-YC15-MeNF-YA2/4-MeNF-YB18 complex were co-silenced, cassava showed decreased oxidative stress resistance, while overexpression of MeGST-U37/U39 alleviated the oxidative stress-sensitive phenotype of these silenced plants. This study illustrates the dual roles of MeLSD3 in promoting MeAPX2 activity and MeNF-YC15-MeGST-U37/U39 regulation, which underlie the oxidative stress response in cassava.

Fine-tuning of pathogenesis-related protein 1 (PR1) activity by the melatonin biosynthetic enzyme ASMT2 in defense response to cassava bacterial blight

Melatonin is widely involved in plant disease resistance through modulation of immune responses. Pathogenesis-related (PR) proteins play important roles in plant immune responses. However, the direct association between melatonin biosynthetic enzyme and PR protein remains elusive in plants. In this study, we found that N-acetylserotonin O-methyltransferase 2 (MeASMT2) physically interacted with MePR1 in vitro and in vivo, thereby promoting the anti-bacterial activity of MePR1 against Xanthomonas axonopodis pv. manihotis (Xam). Consistently, MeASMT2 improved the effect of MePR1 on positively regulating cassava disease resistance. In addition, we found that type 2C protein phosphatase 1 (MePP2C1) interacted with MeASMT2 to interfere with MePR1-MeASMT2 interaction, so as to inhibiting the effect of MeASMT2 and MePR1 on positively regulating cassava disease resistance. In contrast to the increased transcripts of MeASMT2 and MePR1 in response to Xam infection, the transcript of MePP2C1 was decreased upon Xam infection. Therefore, disease activated MeASMT2 was released from disease inhibited MePP2C1, so as to improving the anti-bacterial activity of MePR1, resulting in improved immune response. In summary, this study illustrates the dynamic modulation of the MePP2C1-MeASMT2-MePR1 module on cassava defense response against cassava bacterial blight (CBB), extending the understanding of the correlation between melatonin biosynthetic enzyme and PR in plants.

Melatonin and Carbohydrate Metabolism in Plant Cells

Melatonin, a multifunctional molecule that is present in all living organisms studied, is synthesized in plant cells in several intercellular organelles including in the chloroplasts and in mitochondria. In plants, melatonin has a relevant role as a modulatory agent which improves their tolerance response to biotic and abiotic stress. The role of melatonin in stress conditions on the primary metabolism of plant carbohydrates is reviewed in the present work. Thus, the modulatory actions of melatonin on the various biosynthetic and degradation pathways involving simple carbohydrates (mono- and disaccharides), polymers (starch), and derivatives (polyalcohols) in plants are evaluated. The possible applications of the use of melatonin in crop improvement and postharvest products are examined.

Recent Developments in Enzymatic Antioxidant Defence Mechanism in Plants with Special Reference to Abiotic Stress

The stationary life of plants has led to the evolution of a complex gridded antioxidant defence system constituting numerous enzymatic components, playing a crucial role in overcoming various stress conditions. Mainly, these plant enzymes are superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferases (GST), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR), which work as part of the antioxidant defence system. These enzymes together form a complex set of mechanisms to minimise, buffer, and scavenge the reactive oxygen species (ROS) efficiently. The present review is aimed at articulating the current understanding of each of these enzymatic components, with special attention on the role of each enzyme in response to the various environmental, especially abiotic stresses, their molecular characterisation, and reaction mechanisms. The role of the enzymatic defence system for plant health and development, their significance, and cross-talk mechanisms are discussed in detail. Additionally, the application of antioxidant enzymes in developing stress-tolerant transgenic plants are also discussed.

Lighting the way: advances in transcriptional regulation and integrative crosstalk of melatonin biosynthetic enzymes in cassava

The role of melatonin biosynthetic enzymes has been well studied. However, the transcriptional regulation of melatonin biosynthetic enzymes and their integrative crosstalk with other signaling pathways remain elusive. Here, we summarize recent progress in the functional analysis of melatonin biosynthetic enzymes and the major sites of melatonin synthesis in plants. We focus on the dual roles of melatonin biosynthetic enzymes in melatonin biosynthesis and in the crosstalk between melatonin and autophagy, antioxidant signaling, and stress responses in cassava. We highlight the transcriptional regulation and integrative protein complex of melatonin biosynthetic enzymes, and then raise the challenge of uncovering their precise regulation and crosstalk.

Melatonin in business with abiotic stresses in plants

Melatonin (MEL) is the potential biostimulator molecule, governing multiple range of growth and developmental processes in plants, particularly under different environmental constrains. Mainly, its role is considered as an antioxidant molecule that copes with oxidative stress through scavenging of reactive oxygen species and modulation of stress related genes. It also enhances the antioxidant enzyme activities and thus helps in regulating the redox hemostasis in plants. Apart from its broad range of antioxidant functions, it is involved in the regulation of various physiological processes such as germination, lateral root growth and senescence in plants. Moreover this multifunctional molecule takes much interest due to its recent identification and characterization of receptorCandidate G-protein-Coupled Receptor 2/Phytomelatonin receptor(CAND2/PMTR1) in Arabidopsis thaliana. In this compiled work, different aspects of melatonin in plants such as melatonin biosynthesis and detection in plants, signaling pathway, modulation of stress related genes and physiological role of melatonin under different environmental stresses have been dissected in detail.