The cysteine2/histidine2-type transcription factor ZINC FINGER OF ARABIDOPSIS THALIANA 6-activated C-REPEAT-BINDING FACTOR pathway is essential for melatonin-mediated freezing stress resistance in Arabidopsis

Overexpression of EgrZFP6 from Eucalyptus grandis increases ROS levels by downregulating photosynthesis in plants

In plants, abiotic stressors are frequently encountered during growth and development. To counteract these challenges, zinc finger proteins play a critical role as transcriptional regulators. The EgrZFP6 gene, which codes for a zinc finger protein of the C2H2 type, was shown to be considerably elevated in the leaves of Eucalyptus grandis seedlings in the current study when they were subjected to a variety of abiotic stimuli, including heat, salinity, cold, and drought. Analysis conducted later showed that in EgrZFP6 transgenic Arabidopsis thaliana, EgrZFP6 was essential for causing hyponastic leaves and controlling the stress response. Furthermore, the transgenic plants showed elevated levels of reactive oxygen species (ROS), such as superoxide and hydrogen peroxide (H2O2). Additionally, in EgrZFP6-overexpressing plants, transcriptome sequencing analysis demonstrated a considerable downregulation of many genes involved in photosynthesis, decreasing electron transport efficiency and perhaps promoting the buildup of ROS. Auxin levels were higher and auxin signal transduction was compromised in the transgenic plants. Stress-related genes were also upregulated in Arabidopsis as a result of EgrZFP6 overexpression. It is hypothesized that EgrZFP6 can downregulate photosynthesis, which would cause the production of ROS in chloroplasts. As a result, this protein may alter plant stress responses and leaf morphology via a retrograde mechanism driven by ROS. These results highlight the significance of zinc finger proteins in this sophisticated process and advance our understanding of the complex link between gene regulation, ROS signaling, and plant stress responses.

Transcriptome analysis reveals the promoting effects of exogenous melatonin on the selenium uptake in grape under selenium stress

Introduction

Exogenous melatonin (MT) can promote horticultural crops growth under stress conditions.

Methods

In this study, the effects of exogenous MT on the accumulation of selenium (Se) in grape were studied under Se stress.

Results and discussion

Under Se stress, exogenous MT increased the biomass, content of photosynthetic pigments and antioxidant enzyme activity of grapevines. Compared with Se treatment, MT increased the root biomass, shoot biomass, chlorophyll a content, chlorophyll b content, carotenoids, superoxide dismutase activity, and peroxidase activity by 18.11%, 7.71%, 25.70%, 25.00%, 25.93%, 5.73%, and 9.41%, respectively. Additionally, MT increased the contents of gibberellin, auxin, and MT in grapevines under Se stress, while it decreased the content of abscisic acid. MT increased the contents of total Se, organic Se and inorganic Se in grapevines. Compared with Se treatment, MT increased the contents of total Se in the roots and shoots by 48.82% and 135.66%, respectively. A transcriptome sequencing analysis revealed that MT primarily regulated the cellular, metabolic, and bioregulatory processes of grapevine under Se stress, and the differentially expressed genes (DEGs) were primarily enriched in pathways, such as aminoacyl-tRNA biosynthesis, spliceosome, and flavonoid biosynthesis. These involved nine DEGs and nine metabolic pathways in total. Moreover, a field experiment showed that MT increased the content of Se in grapes and improved their quality. Therefore, MT can alleviate the stress of Se in grapevines and promote their growth and the accumulation of Se.

Melatonin Increases Root Cell Wall Phosphorus Reutilization via an NO Dependent Pathway in Rice (Oryza sativa)

Melatonin (MT) has been implicated in the plant response to phosphorus (P) stress; however, the precise molecular mechanisms involved remain unclear. This study investigated whether MT controls internal P distribution and root cell wall P remobilization in rice. Rice was treated with varying MT and P levels and analyzed using biochemical and molecular techniques to study phosphorus utilization. The results demonstrated that low P levels lead to a rapid increase in endogenous MT levels in rice roots. Furthermore, the exogenous application of MT significantly improved rice tolerance to P deficiency, as evidenced by the increased biomass and reduced proportion of roots to shoots under P-deficient conditions. MT application also mitigated the decrease in P content regardless in both the roots and shoots. Mechanistically, MT accelerated the reutilization of P, particularly in the root pectin fraction, leading to increased soluble P liberation. In addition, MT enhanced the expression of OsPT8, a gene involved in root-to-shoot P translocation. Furthermore, we observed that MT induced the production of nitric oxide (NO) in P-deficient rice roots and that the mitigating effect of MT on P deficiency was compromised in the presence of the NO inhibitor, c-PTIO, implying that NO is involved in the MT-facilitated mitigation of P deficiency in rice. Overall, our findings highlight the potential of MT as a promising strategy for enhancing rice tolerance to P deficiency and improving P use efficiency in agricultural practices.

Transcriptomic Identification of Potential C2H2 Zinc Finger Protein Transcription Factors in Pinus massoniana in Response to Biotic and Abiotic Stresses

Biotic and abiotic stresses have already seriously restricted the growth and development of Pinus massoniana, thereby influencing the quality and yield of its wood and turpentine. Recent studies have shown that C2H2 zinc finger protein transcription factors play an important role in biotic and abiotic stress response. However, the members and expression patterns of C2H2 TFs in response to stresses in P. massoniana have not been performed. In this paper, 57 C2H2 zinc finger proteins of P. massoniana were identified and divided into five subgroups according to a phylogenetic analysis. In addition, six Q-type PmC2H2-ZFPs containing the plant-specific motif 'QALGGH' were selected for further study under different stresses. The findings demonstrated that PmC2H2-ZFPs exhibit responsiveness towards various abiotic stresses, including drought, NaCl, ABA, PEG, H2O2, etc., as well as biotic stress caused by the pine wood nematode. In addition, PmC2H2-4 and PmC2H2-20 were nuclear localization proteins, and PmC2H2-20 was a transcriptional activator. PmC2H2-20 was selected as a potential transcriptional regulator in response to various stresses in P. massoniana. These findings laid a foundation for further study on the role of PmC2H2-ZFPs in stress tolerance.

MrERF039 transcription factor plays an active role in the cold response of Medicago ruthenica as a sugar molecular switch

Cold stress severely restricts plant development, causing significant agricultural losses. We found a critical transcription factor network in Medicago ruthenica was involved in plant adaptation to low-temperature. APETALA2/ethylene responsive factor (AP2/ERF) transcription factor MrERF039 was transcriptionally induced by cold stress in M. ruthenica. Overexpression of MrERF039 significantly increased the glucose and maltose content, thereby improving the tolerance of M. ruthenica. MrERF039 could bind to the DRE cis-acting element in the MrCAS15A promoter. Additionally, the methyl group of the 14th amino acid in MrERF039 was required for binding. Transcriptome analysis showed that MrERF039 acted as a sugar molecular switch, regulating numerous sugar transporters and sugar metabolism-related genes. In addition, we found that MrERF039 could directly regulate β-amylase gene, UDP glycosyltransferase gene, and C2H2 zinc finger protein gene expression. In conclusion, these findings suggest that high expression of MrERF039 can significantly improve the cold tolerance of M. ruthenica root tissues during cold acclimation. Our results provide a new theoretical basis and candidate genes for breeding new legume forage varieties with high resistance.

Genome-wide identification, characterization and expression of C2H2 zinc finger gene family in Opisthopappus species under salt stress

BACKGROUND

The C2H2 zinc finger protein family plays important roles in plants. However, precisely how C2H2s function in Opisthopappus (Opisthopappus taihangensis and Opisthopappus longilobus) remains unclear.

RESULTS

In this study, a total of 69 OpC2H2 zinc finger protein genes were identified and clustered into five Groups. Seven tandem and ten fragment repeats were found in OpC2H2s, which underwent robust purifying selection. Of the identified motifs, motif 1 was present in all OpC2H2s and conserved at important binding sites. Most OpC2H2s possessed few introns and exons that could rapidly activate and react when faced with stress. The OpC2H2 promoter sequences mainly contained diverse regulatory elements, such as ARE, ABRE, and LTR. Under salt stress, two up-regulated OpC2H2s (OpC2H2-1 and OpC2H2-14) genes and one down-regulated OpC2H2 gene (OpC2H2-7) might serve as key transcription factors through the ABA and JA signaling pathways to regulate the growth and development of Opisthopappus species.

CONCLUSION

The above results not only help to understand the function of C2H2 gene family but also drive progress in genetic improvement for the salt tolerance of Opisthopappus species.

High-throughput diagnostic markers for foliar fungal disease resistance and high oleic acid content in groundnut

BACKGROUND

Foliar diseases namely late leaf spot (LLS) and leaf rust (LR) reduce yield and deteriorate fodder quality in groundnut. Also the high oleic acid content has emerged as one of the most important traits for industries and consumers due to its increased shelf life and health benefits.

RESULTS

Genetic mapping combined with pooled sequencing approaches identified candidate resistance genes (LLSR1 and LLSR2 for LLS and LR1 for LR) for both foliar fungal diseases. The LLS-A02 locus housed LLSR1 gene for LLS resistance, while, LLS-A03 housed LLSR2 and LR1 genes for LLS and LR resistance, respectively. A total of 49 KASPs markers were developed from the genomic regions of important disease resistance genes, such as NBS-LRR, purple acid phosphatase, pentatricopeptide repeat-containing protein, and serine/threonine-protein phosphatase. Among the 49 KASP markers, 41 KASPs were validated successfully on a validation panel of contrasting germplasm and breeding lines. Of the 41 validated KASPs, 39 KASPs were designed for rust and LLS resistance, while two KASPs were developed using fatty acid desaturase (FAD) genes to control high oleic acid levels. These validated KASP markers have been extensively used by various groundnut breeding programs across the world which led to development of thousands of advanced breeding lines and few of them also released for commercial cultivation.

CONCLUSION

In this study, high-throughput and cost-effective KASP assays were developed, validated and successfully deployed to improve the resistance against foliar fungal diseases and oleic acid in groundnut. So far deployment of allele-specific and KASP diagnostic markers facilitated development and release of two rust- and LLS-resistant varieties and five high-oleic acid groundnut varieties in India. These validated markers provide opportunities for routine deployment in groundnut breeding programs.

Melatonin as a master regulatory hormone for genetic responses to biotic and abiotic stresses in model plant Arabidopsis thaliana: a comprehensive review

Melatonin is a naturally occurring biologically active amine produced by plants, animals and microbes. This review explores the biosynthesis of melatonin in plants, with a particular focus on its diverse roles in Arabidopsis thaliana , a model species. Melatonin affects abiotic and biotic stress resistance in A. thaliana . Exogenous and endogenous melatonin is addressed in association with various conditions, including cold stress, high light stress, intense heat and infection with Botrytis cinerea or Pseudomonas , as well as in seed germination and lateral root formation. Furthermore, melatonin confers stress resistance in Arabidopsis by initiating the antioxidant system, remedying photosynthesis suppression, regulating transcription factors involved with stress resistance (CBF, DREB, ZAT, CAMTA, WRKY33, MYC2, TGA) and other stress-related hormones (abscisic acid, auxin, ethylene, jasmonic acid and salicylic acid). This article additionally addresses other precursors, metabolic components, expression of genes (COR , CBF , SNAT , ASMT , PIN , PR1 , PDF1.2 and HSFA ) and proteins (JAZ, NPR1) associated with melatonin and reducing both biological and environmental stressors. Furthermore, the future perspective of melatonin rich agri-crops is explored to enhance plant tolerance to abiotic and biotic stresses, maximise crop productivity and enhance nutritional worth, which may help improve food security.

Jasmonate: A Hormone of Primary Importance for Temperature Stress Response in Plants

Temperature is a critical environmental factor that plays a vital role in plant growth and development. Temperatures below or above the optimum ranges lead to cold or heat stress, respectively. Temperature stress retards plant growth and development, and it reduces crop yields. Jasmonates (JAs) are a class of oxylipin phytohormones that play various roles in growth, development, and stress response. In recent years, studies have demonstrated that cold and heat stress affect JA biosynthesis and signaling, and JA plays an important role in the response to temperature stress. Recent studies have provided a large body of information elucidating the mechanisms underlying JA-mediated temperature stress response. In the present review, we present recent advances in understanding the role of JA in the response to cold and heat stress, and how JA interacts with other phytohormones during this process.

Interactive effect of silicon and zinc on cadmium toxicity alleviation in wheat plants

Silicon (Si) and Zinc (Zn) have been frequently used to alleviate cadmium (Cd) toxicity, which are feasible strategies for crop safety production. However, the mechanisms underlying the interaction of Si and Zn on alleviating Cd toxicity are not well understood. A hydroponic system was adopted to evaluate morphological, physiological-biochemical responses, and related gene expression of wheat seedlings to Si (1 mM) and Zn (50 µM) addition under Cd stress (10 µM). Cd induced obvious inhibition of wheat growth by disturbing photosynthesis and chlorophyll synthesis, provoking generation of reactive oxygen species (ROS) and interfering ion homeostasis. Cd concentration was decreased by 68.3%, 43.1% and 73.3% in shoot, and 78.9%, 44.1% and 85.8% in root by Si, Zn, and combination of Si with Zn, relative to Cd only, respectively. Si and Zn effectively ameliorated Cd toxicity and enhanced wheat growth; but single Si or combination of Si with Zn had more efficient ability on alleviating Cd stress than only Zn, indicating Si and Zn have synergistic effect on Cd toxicity; Interaction of them alleviated oxidative stress by reducing ROS content, improving AsA-GSH cycle and antioxidant enzymes activities, and regulating Cd into vacuole through PC-Cd complexes transported by HMA3 transporter. Our results suggest that fertilizers including Si and Zn should be made to reduce Cd content, which will beneficial for food production and safety.

Phytomelatonin: A key regulator of redox and phytohormones signaling against biotic/abiotic stresses

Plants being sessile in nature, are exposed to unwarranted threats as a result of constantly changing environmental conditions. These adverse factors can have negative impacts on their growth, development, and yield. Hormones are key signaling molecules enabling cells to respond rapidly to different external and internal stimuli. In plants, melatonin (MT) plays a critical role in the integration of various environmental signals and activation of stress-response networks to develop defense mechanisms and plant resilience. Additionally, melatonin can tackle the stress-induced alteration of cellular redox equilibrium by regulating the expression of redox hemostasis-related genes and proteins. The purpose of this article is to compile and summarize the scientific research pertaining to MT's effects on plants' resilience to biotic and abiotic stresses. Here, we have summarized that MT exerts a synergistic effect with other phytohormones, for instance, ethylene, jasmonic acid, and salicylic acid, and activates plant defense-related genes against phytopathogens. Furthermore, MT interacts with secondary messengers like Ca²⁺, nitric oxide, and reactive oxygen species to regulate the redox network. This interaction triggers different transcription factors to alleviate stress-related responses in plants. Hence, the critical synergic role of MT with diverse plant hormones and secondary messengers demonstrates phytomelatonin's importance in influencing multiple mechanisms to contribute to plant resilience against harsh environmental factors.

The Classification, Molecular Structure and Biological Biosynthesis of Flavonoids, and Their Roles in Biotic and Abiotic Stresses

With the climate constantly changing, plants suffer more frequently from various abiotic and biotic stresses. However, they have evolved biosynthetic machinery to survive in stressful environmental conditions. Flavonoids are involved in a variety of biological activities in plants, which can protect plants from different biotic (plant-parasitic nematodes, fungi and bacteria) and abiotic stresses (salt stress, drought stress, UV, higher and lower temperatures). Flavonoids contain several subgroups, including anthocyanidins, flavonols, flavones, flavanols, flavanones, chalcones, dihydrochalcones and dihydroflavonols, which are widely distributed in various plants. As the pathway of flavonoid biosynthesis has been well studied, many researchers have applied transgenic technologies in order to explore the molecular mechanism of genes associated with flavonoid biosynthesis; as such, many transgenic plants have shown a higher stress tolerance through the regulation of flavonoid content. In the present review, the classification, molecular structure and biological biosynthesis of flavonoids were summarized, and the roles of flavonoids under various forms of biotic and abiotic stress in plants were also included. In addition, the effect of applying genes associated with flavonoid biosynthesis on the enhancement of plant tolerance under various biotic and abiotic stresses was also discussed.

Exogenous melatonin enhances tomato heat resistance by regulating photosynthetic electron flux and maintaining ROS homeostasis

Heat stress reduces plant growth and reproduction and increases agricultural risks. As a natural compound, melatonin modulates broad aspects of the responses of plants to various biotic and abiotic stresses. However, regulation of the photosynthetic electron transfer, reactive oxygen species (ROS) homeostasis and the redox state of redox-sensitive proteins in the tolerance to heat stress induced by melatonin remain largely unknown. The oxygen evolution complex activity on the electron-donating side of photosystem II (PSII) is inhibited, and the electron transfer process from QA to QB on the electron-accepting side of PSII is inhibited. In this case, heat stress decreased the chlorophyll content, carbon assimilation rate, PSII activity, and the proportion of light absorbed by tomato seedlings during electron transfer. The ROS burst led to the breakdown of the PSII core protein. However, exogenous melatonin increased the net photosynthetic rate by 11.3% compared with heat stress, substantially reducing the restriction of photosynthetic systems induced by heat stress. Additionally, melatonin reduces the oxidative damage to PSII by balancing electron transfer on the donor, reactive center, and acceptor sides. Melatonin was used under heat stress to increase the activity of the antioxidant enzyme and preserve ROS equilibrium. In addition, redox proteomics also showed that melatonin controls the redox levels of proteins involved in photosynthesis, and stress and defense processes, which enhances the expression of oxidative genes. In conclusion, melatonin via controlling the photosynthetic electron transport and antioxidant, melatonin increased tomato heat stress tolerance and aided plant growth.

Phytomelatonin: A master regulator for plant oxidative stress management

Phytomelatonin is the multifunctional molecule that governs a range of developmental processes in plants subjected to a plethora of environmental cues. It acts as an antioxidant molecule to regulate the oxidative burst through reactive oxygen species (ROS) scavenging. Moreover, it also activates stress-responsive genes followed by alleviating oxidation. Phytomelatonin also stimulates antioxidant enzymes that further regulate redox homeostasis in plants under adverse conditions. This multifunctional molecule also regulates different physiological processes of plants in terms of leaf senescence, seed germination, lateral root growth, photosynthesis, etc. Due to its versatile nature, it is regarded as a master regulator of plant cell physiology and it holds a crucial position in molecular signaling as well. Phytomelatonin mediated oxidative stress management occurs through a series of antioxidative defense systems, both enzymatic as well as non-enzymatic, along with the formation of an array of secondary defensive metabolites that counteract the stresses. These phytomelatonin-derived antioxidants reduce the lipid peroxidation and improve membrane integrity of the cells subjected to stress. Here in, the data from transcriptomic and omics approaches are summarized which help to identify the gene regulatory mechanisms involved in the regulation of redox homeostasis and oxidative stress management. Further, we also recap the signaling cascade underlying phytomelatonin interactions with both ROS and reactive nitrogen species (RNS)and their crosstalk. The discoveries related to phytomelatonin have shown that this regulatory master molecule is critical for plant cell physiology. The current review is focussed the role of phytomelatonin as a multifunctional molecule in plant stress management.

Functions of Melatonin during Postharvest of Horticultural Crops

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

Melatonin biosynthesis and signal transduction in plants in response to environmental conditions

Melatonin, the most widely distributed hormone in nature, plays important roles in plants. Many physiological processes in plants are linked to melatonin, including seed germination, anisotropic cell growth, and senescence. Compared with animals, different plants possess diverse melatonin biosynthetic pathways and regulatory networks. Whereas melatonin biosynthesis in animals is known to be regulated by ambient signals, little is known about how melatonin biosynthesis in plants responds to environmental signals. Plants are affected by numerous environmental factors, such as light, temperature, moisture, carbon dioxide, soil conditions, and nutrient availability at all stages of development and in different tissues. Melatonin content exhibits dynamic changes that affect plant growth and development. Melatonin plays various species-specific roles in plant responses to different environmental conditions. However, much remains to be learned, as not all environmental factors have been studied, and little is known about the mechanisms by which these factors influence melatonin biosynthesis. In this review, we provide a detailed, systematic description of melatonin biosynthesis and signaling and of the roles of melatonin in plant responses to different environmental factors, providing a reference for in-depth research on this important issue.

Exogenous melatonin promotes the growth of alfalfa (Medicago sativa L.) under NaCl stress through multiple pathways

Salinity is one of the most common factors affecting alfalfa (Medicago sativa L.), and NaCl is one of the main factors of salinity stress which can cause heavy losses in agricultural production in the world. The application of exogenous melatonin (MT) plays a major role in numerous plants against various stress environments. The effects of exogenous MT on the NaCl tolerance of alfalfa treated with the control, 100 µmol L^-1 MT, 150 mmol L^-1 NaCl, or 150 mmol L^-1 NaCl+ 100 µmol L^-1 MT were investigated. The results showed that MT increased growth parameters, inhibited chlorophyll degradation and promoted photosynthetic gas exchange parameters (photosynthetic rate, conductance to H₂O, and transpiration rate) and stomatal opening under NaCl stress. Osmotic regulation substances such as soluble sugar, proline and glycine betaine were the highest in the NaCl treatment and the second in the NaCl+MT treatment. Nitrogen, phosphorus, potassium, calcium and magnesium were reduced and sodium was increased by NaCl, whereas these levels were reversed by the NaCl+MT treatment. MT inhibited cell membrane imperfection, lipid peroxidation and reactive oxygen species (ROS) accumulation caused by NaCl stress. MT up-regulated the gene expression and activity of antioxidant enzymes and increased the content of antioxidant non-enzyme substances to scavenge excessive ROS in NaCl-treated plants. In addition, all indicators interacted with each other to a certain extent and could be grouped according to the relative values. All variables were divided into PC 1 (89.2 %) and PC 2 (4 %). They were clustered into two categories with opposite effects, and most of them were significant variables. Hence, these findings reveal that exogenous MT alleviates the inhibitory effects of NaCl stress on photosynthesis, stomata opening, osmotic adjustment, ion balance and redox homeostasis, enhancing tolerance and growth of alfalfa. Furthermore, it suggests that MT could be implemented to improve the NaCl tolerance of alfalfa.

Genome-Wide Analysis of C2H2 Zinc Finger Gene Family and Its Response to Cold and Drought Stress in Sorghum [Sorghum bicolor (L.) Moench]

C2H2 zinc finger protein (C2H2-ZFP) is one of the most important transcription factor families in higher plants. In this study, a total of 145 C2H2-ZFPs was identified in Sorghum bicolor and randomly distributed on 10 chromosomes. Based on the phylogenetic tree, these zinc finger gene family members were divided into 11 clades, and the gene structure and motif composition of SbC2H2-ZFPs in the same clade were similar. SbC2H2-ZFP members located in the same clade contained similar intron/exon and motif patterns. Thirty-three tandem duplicated SbC2H2-ZFPs and 24 pairs of segmental duplicated genes were identified. Moreover, synteny analysis showed that sorghum had more collinear regions with monocotyledonous plants such as maize and rice than did dicotyledons such as soybean and Arabidopsis. Furthermore, we used quantitative RT-PCR (qRT-PCR) to analyze the expression of C2H2-ZFPs in different organs and demonstrated that the genes responded to cold and drought. For example, Sobic.008G088842 might be activated by cold but is inhibited in drought in the stems and leaves. This work not only revealed an important expanded C2H2-ZFP gene family in Sorghum bicolor but also provides a research basis for determining the role of C2H2-ZFPs in sorghum development and abiotic stress resistance.

Exogenous Melatonin Improves Cold Tolerance of Strawberry (Fragaria × ananassa Duch.) through Modulation of DREB/CBF-COR Pathway and Antioxidant Defense System

The strawberry (Fragaria × ananassa Duch.) is an important fruit crop cultivated worldwide for its unique taste and nutritional properties. One of the major risks associated with strawberry production is cold damage. Recently, melatonin has emerged as a multifunctional signaling molecule that influences plant growth and development and reduces adverse consequences of cold stress. The present study was conducted to investigate the defensive role of melatonin and its potential interrelation with abscisic acid (ABA) in strawberry plants under cold stress. The results demonstrate that melatonin application conferred improved cold tolerance on strawberry seedlings by reducing malondialdehyde and hydrogen peroxide contents under cold stress. Conversely, pretreatment of strawberry plants with 100 μM melatonin increased soluble sugar contents and different antioxidant enzyme activities (ascorbate peroxidase, catalase, and peroxidase) and non-enzymatic antioxidant (ascorbate and glutathione) activities under cold stress. Furthermore, exogenous melatonin treatment stimulated the expression of the DREB/CBF—COR pathways’ downstream genes. Interestingly, ABA treatment did not change the expression of the DREB/CBF—COR pathway. These findings imply that the DREB/CBF-COR pathway confers cold tolerance on strawberry seedlings through exogenous melatonin application. Taken together, our results reveal that melatonin (100 μM) pretreatment protects strawberry plants from the damages induced by cold stress through enhanced antioxidant defense potential and modulating the DREB/CBF—COR pathway.

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

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

Jasmonate and Melatonin Act Synergistically to Potentiate Cold Tolerance in Tomato Plants

Both jasmonic acid (JA) and melatonin (MT) have been demonstrated to play positive roles in cold tolerance, however, whether and how they crosstalk in the cold responses in plants remain elusive. Here, we report that JA and MT act synergistically in the cold tolerance in tomato plants (Solanum lycopersicum). It was found that JA and MT were both substantially accumulated in response to cold stress and foliar applications of methyl jasmonate (MeJA) and MT promoted cold tolerance as evidenced by increased Fv/Fm, decreased relative electrolyte leakage (EL) and declined H₂O₂ accumulation in tomato plants. Inhibition of MT biosynthesis attenuated MeJA-induced cold tolerance, while inhibition of JA biosynthesis reduced MT accumulation in tomato plants under cold conditions. Furthermore, qRT-PCR analysis showed that the expressions of two MT biosynthetic genes, SlSNAT and SlAMST, were strongly induced by MeJA, whereas suppression of SlMYC2, a master JA signaling regulator, abated the expressions of SlSNAT and SlAMST under cold stress. Additionally, suppression of SlMYC2 reduced MT accumulation, decreased Fv/Fm and increased EL in cold-stressed tomato plants. Interestingly, exogenous MT promoted JA accumulation, while inhibition of MT biosynthesis significantly reduced JA accumulation in tomato plants under the cold condition. Taken together, these results suggest that JA and MT act cooperatively in cold tolerance and form a positive feedback loop, amplifying the cold responses of tomato plants. Our findings might be translated into the development of cold-resistant tomato cultivars by genetically manipulating JA and MT pathways.

Melatonin-induced physiology and transcriptome changes in banana seedlings under salt stress conditions

Soil salinization poses a serious threat to the ecological environment and agricultural production and is one of the most common abiotic stresses in global agricultural production. As a salt-sensitive plant, the growth, development, and production of bananas (Musa acuminata L.) are restricted by salt stress. Melatonin is known to improve the resistance of plants to stress. The study analyzed the effects of 100 μM melatonin on physiological and transcriptome changes in banana varieties (AAA group cv. Cavendish) under 60 mmol/l of NaCl salt stress situation. The phenotypic results showed that the application of exogenous melatonin could maintain banana plants' health growth and alleviate the damage caused by salt stress. The physiological data show that the application of exogenous melatonin can enhance salt tolerance of banana seedlings by increasing the content of proline content and soluble protein, slowing down the degradation of chlorophyll, reducing membrane permeability and recovery of relative water content, increasing the accumulation of MDA, and enhancing antioxidant defense activity. Transcriptome sequencing showed that melatonin-induced salt tolerance of banana seedlings involved biological processes, molecular functions, and cellular components. We also found that differentially expressed genes (DEGs) are involved in a variety of metabolic pathways, including amino sugar and nucleotide sugar metabolism, phenylalanine metabolism, cyanoamino acid metabolism, starch and sucrose metabolism, and linoleic acid metabolism. These major metabolism and biosynthesis may be involved in the potential mechanism of melatonin under salt stress. Furthermore, some members of the transcription factor family, such as MYB, NAC, bHLH, and WRKY, might contribute to melatonin alleviating salt stress tolerance of the banana plant. The result laid a basis for further clarifying the salt stress resistance mechanism of bananas mediated by exogenous melatonin and provides theoretical bases to utilize melatonin to improve banana salt tolerance in the future.

Melatonin in Plant Defense against Abiotic Stress

Abiotic stress adversely affects plant growth and metabolism and as such reduces plant productivity. Recognized as a major contributor in the production of reactive oxygen species (ROS), it hinders the growth of plants through induction of oxidative stress. Biostimulants such as melatonin have a multifunctional role, acting as a defense strategy in minimizing the effects of oxidative stress. Melatonin plays important role in plant processes ranging from seed germination to senescence, besides performing the function of a biostimulant in improving the plant’s productivity. In addition to its important role in the signaling cascade, melatonin acts as an antioxidant that helps in scavenging ROS, generated as part of different stresses among plants. The current study was undertaken to elaborate the synthesis and regulation of melatonin in plants, besides emphasizing its function under various abiotic stress namely, salt, temperature, herbicides, heavy metals, and drought. Additionally, a special consideration was put on the crosstalk of melatonin with phytohormones to overcome plant abiotic stress.

Exogenous melatonin induces drought stress tolerance by promoting plant growth and antioxidant defence system of soybean plants

Melatonin is an indolamine bioactive molecule that regulates a wide range of physiological processes during plant growth and enhances abiotic stress tolerance. Here we examined the putative role of exogenous melatonin application (foliar or root zone) in improving drought stress tolerance in soybean seedlings. Pre-treatment of soybean seedlings with melatonin (50 and 100 µM) was found to significantly mitigate the negative effects of drought stress on plant growth-related parameters and chlorophyll content. The beneficial impacts against drought were more pronounced by melatonin application in the rhizosphere than in foliar treatments. The melatonin-induced enhanced tolerance could be attributed to improved photosynthetic activity, reduction of abscisic acid and drought-induced oxidative damage by lowering the accumulation of reactive oxygen species and malondialdehyde. Interestingly, the contents of jasmonic acid and salicylic acid were significantly higher following melatonin treatment in the root zone than in foliar treatment compared with the control. The activity of major antioxidant enzymes such as superoxide dismutase, catalase, polyphenol oxidase, peroxidase and ascorbate peroxidase was stimulated by melatonin application. In addition, melatonin counteracted the drought-induced increase in proline and sugar content. These findings revealed that modifying the endogenous plant hormone content and antioxidant enzymes by melatonin application improved drought tolerance in soybean seedlings. Our findings provide evidence for the stronger physiological role of melatonin in the root zone than in leaves, which may be useful in the large-scale field level application during drought.

Effects of Melatonin on Morphological Characteristics, Mineral Nutrition, Nitrogen Metabolism, and Energy Status in Alfalfa Under High-Nitrate Stress

Melatonin is an indoleamine small molecular substance that has been shown to play an important role in the growth, development, and stress response of plants. The effects of melatonin on the morphological characteristics, mineral nutrition, nitrogen metabolism, and energy status in alfalfa (Medicago sativa L.) under high-nitrate stress were studied. The alfalfa plants were treated with water (CK), 200 mmol L^-1 nitrates (HN), or 200 mmol L^-1 nitrates + 0.1 mmol L^-1 melatonin (HN+MT), and then were sampled for measurements on days 0 and 10, respectively. The results showed that the HN treatment resulted in a decrease in the morphological characteristics (such as shoot height, leaf length, leaf width, leaf area, and biomass), phosphorus, soluble protein (SP), nitrogen-related enzymes activities and gene relative expression, adenosine triphosphate (ATP), and energy charge (EC). It also caused an increase in nitrogen, sodium, potassium, calcium, nitrate-nitrogen ( NO 3 - -N), ammonium-nitrogen ( NH 4 + -N), adenosine diphosphate (ADP), and adenosine monophosphate (AMP). However, these parameters were conversely changed in the HN+MT treatment. Besides, these parameters were closely related to each other, and were divided into two principal components. It reveals that melatonin plays an important role in modulating the morphology, mineral nutrition, nitrogen metabolism and energy status, thereby alleviating the adverse effects of high-nitrate stress and improving the growth of alfalfa.

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.

Melatonin elevated Sclerotinia sclerotiorum resistance via modulation of ATP and glucosinolate biosynthesis in Brassica rapa ssp. pekinensis

Sclerotinia stem rot is a common disease found in Brassica rapa that is caused by the necrotic plant pathogen Sclerotinia sclerotiorum. Melatonin (MT) has known biological activity and effectively relieved this type of Sclerotinia stem rot in B. rapa. To better understand the mechanisms behind MT-induced S. sclerotiorum resistance in B. rapa, we performed both proteomic and metabolomic analysis. Our results showed that during S. sclerotiorum infection, thiamine synthesis was activated and defended against it. In infected leaves, ribosomal synthesis-related proteins responded positively to MT treatment. Integrated proteomic and metabolomic analysis showed that amino acid metabolism was activated by MT treatment. After MT treatment, adenosine-triphosphate (ATP) content and the activity of antioxidant enzymes were both increased in B. rapa infected leaves. Cysteine synthase, sulfur transfer-related proteins, and glucosinolate (GS) were all increased after MT treatment in infected B. rapa leaves. Taken together, these results indicated that B. rapa leaves promoted thiamine formation to defend against S. sclerotiorum infection. Moreover, MT helped further induce antioxidant activation in B. rapa in an ATP-dependent manner and stimulating GS biosynthesis to well inhibit the S. sclerotiorum infection. SIGNIFICANCE: Melatonin (MT) has biological activity and effectively relieved the Sclerotinia stem rot of Brassica rapa caused by the necrotic plant pathogen Sclerotinia sclerotiorum. In order to reveal the molecular mechanisms of MT-induced S. sclerotiorum resistance in B. rapa, comprehensive proteomic and metabolomic analyses were conducted. The integration analysis of omic-data illustrated that the modulation of ATP and glucosinolate biosynthesis induced by MT administration helped to defend the infection of S. sclerotiorum in B. rapa. Our results will provide insights into MT-induced anti-fungal mechanism and therapeutic strategies to mitigate Sclerotinia stem rot of B. rapa, thereby increasing plant yield and decreasing economic losses.

Comparative physiological and full-length transcriptome analyses reveal the molecular mechanism of melatonin-mediated salt tolerance in okra (Abelmoschus esculentus L.)

BACKGROUND

Melatonin, a multifunctional signal molecule, has been reported to play crucial roles in growth and development and stress responses in various plant species. Okra (Abelmoschus esculentus L.) is a food crop with extremely high values of nutrition and healthcare. Recent reports have revealed the protective role of melatonin in alleviating salt stress. However, little is known about its regulatory mechanisms in response to salt stress in okra.

RESULTS

In this study, we explored whether exogenous melatonin pretreatment could alleviate salt stress (300 mM NaCl) of okra plants. Results showed that exogenous application of melatonin (50 μM) significantly enhanced plant tolerance to salt stress, as demonstrated by the plant resistant phenotype, as well as by the higher levels of the net photosynthetic rate, chlorophyll fluorescence and chlorophyll content in comparison with nontreated salt-stressed plants. Additionally, melatonin pretreatment remarkably decreased the levels of lipid peroxidation and H₂O₂ content and scavenged O₂^•- in melatonin-pretreated plants, which may be attributed to the higher levels of enzyme activities including POD and GR. Moreover, a combination of third- (PacBio) and second-generation (Illumina) sequencing technologies was applied to sequence full-length transcriptomes of okra. A total of 121,360 unigenes was obtained, and the size of transcript lengths ranged from 500 to 6000 bp. Illumina RNA-seq analysis showed that: Comparing with control, 1776, 1063 and 1074 differential expression genes (DEGs) were identified from the three treatments (NaCl, MT50 and MT + NaCl, respectively). These genes were enriched in more than 10 GO terms and 34 KEGG pathways. Nitrogen metabolism, sulfur metabolism, and alanine, aspartate and glutamate metabolism were significantly enriched in all three treatments. Many transcription factors including MYB, WRKY, NAC etc., were also identified as DEGs.

CONCLUSIONS

Our preliminary results suggested that melatonin pretreatment enhanced salt tolerance of okra plants for the first time. These data provide the first set of full-length isoforms in okra and more comprehensive insights into the molecular mechanism of melatonin responses to salt stress.

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.

Melatonin Enhanced the Tolerance of Arabidopsis thaliana to High Light Through Improving Anti-oxidative System and Photosynthesis

Land plants live in a crisis-filled environment and the fluctuation of sunlight intensity often causes damage to photosynthetic apparatus. Phyto-melatonin is an effective bioactive molecule that helps plants to resist various biotic and abiotic stresses. In order to explore the role of melatonin under high light stress, we investigated the effects of melatonin on anti-oxidative system and photosynthesis of Arabidopsis thaliana under high light. Results showed that exogenous melatonin increased photosynthetic rate and protected photosynthetic proteins under high light. This was mainly owing to the fact that exogenous melatonin effectively decreased the accumulation of reactive oxygen species and protected integrity of membrane and photosynthetic pigments, and reduced cell death. Taken together, our study promoted more comprehensive understanding in the protective effects of exogenous melatonin under high light.

Melatonin Mitigates the Infection of Colletotrichum gloeosporioides via Modulation of the Chitinase Gene and Antioxidant Activity in Capsicum annuum L

Anthracnose, caused by Colletotrichum gloeosporioides, is one of the most damaging pepper (Capsicum annum L.) disease. Melatonin induces transcription of defense-related genes that enhance resistance to pathogens and mediate physiological activities in plants. To study whether the melatonin-mediated pathogen resistance is associated with chitinase gene (CaChiIII2), pepper plants and Arabidopsis seeds were treated with melatonin, then CaChiIII2 activation, hydrogen peroxide (H₂O₂) levels, and antioxidant enzymes activity during plant–pathogen interactions were investigated. Melatonin pretreatment uncoupled the knockdown of CaChiIII2 and transiently activated its expression level in both control and CaChiIII2-silenced pepper plants and enhanced plant resistance. Suppression of CaChiIII2 in pepper plants showed a significant decreased in the induction of defense-related genes and resistance to pathogens compared with control plants. Moreover, melatonin efficiently enabled plants to maintain intracellular H₂O₂ concentrations at steady-state levels and enhanced the activities of antioxidant enzymes, which possibly improved disease resistance. The activation of the chitinase gene CaChiIII2 in transgenic Arabidopsis lines was elevated under C. gloeosporioides infection and exhibited resistance through decreasing H₂O₂ biosynthesis and maintaining H₂O₂ at a steady-state level. Whereas melatonin primed CaChiIII2-overexpressed (OE) and wild-type (WT) Arabidopsis seedlings displayed a remarkable increase in root-length compared to the unprimed WT plants. Using an array of CaChiIII2 knockdown and OE, we found that melatonin efficiently induced CaChiIII2 and other pathogenesis-related genes expressions, responsible for the innate immunity response of pepper against anthracnose disease.

Melatonin improves rice salinity stress tolerance by NADPH oxidase-dependent control of the plasma membrane K+ transporters and K+ homeostasis

This study aimed to reveal the mechanistic basis of the melatonin-mediated amelioration of salinity stress in plants. Electrophysiological experiments revealed that melatonin decreased salt-induced K⁺ efflux (a critical determinant of plant salt tolerance) in a dose- and time-dependent manner and reduced sensitivity of the plasma membrane K⁺ -permeable channels to hydroxyl radicals. These beneficial effects of melatonin were abolished by NADPH oxidase blocker DPI. Transcriptome analyses revealed that melatonin induced 585 (448 up- and 137 down-regulated) and 59 (54 up- and 5 down-regulated) differentially expressed genes (DEGs) in the root tip and mature zone, respectively. The most noticeable changes in the root tip were melatonin-induced increase in the expression of several DEGs encoding respiratory burst NADPH oxidases (OsRBOHA and OsRBOHF), calcineurin B-like/calcineurin B-like-interacting protein kinase (OsCBL/OsCIPK), and calcium-dependent protein kinase (OsCDPK) under salt stress. Melatonin also enhanced the expression of potassium transporter genes (OsAKT1, OsHAK1, and OsHAK5). Taken together, these results indicate that melatonin improves salt tolerance in rice by enabling K⁺ retention in roots, and that the latter process is conferred by melatonin scavenging of hydroxyl radicals and a concurrent OsRBOHF-dependent ROS signalling required to activate stress-responsive genes and increase the expression of K⁺ uptake transporters in the root tip.

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.

Understanding salt tolerance mechanism using transcriptome profiling and de novo assembly of wild tomato Solanum chilense

Soil salinity affects the plant growth and productivity detrimentally, but Solanum chilense, a wild relative of cultivated tomato (Solanum lycopersicum L.), is known to have exceptional salt tolerance. It has precise adaptations against direct exposure to salt stress conditions. Hence, a better understanding of the mechanism to salinity stress tolerance by S. chilense can be accomplished by comprehensive gene expression studies. In this study 1-month-old seedlings of S. chilense and S. lycopersicum were subjected to salinity stress through application of sodium chloride (NaCl) solution. Through RNA-sequencing here we have studied the differences in the gene expression patterns. A total of 386 million clean reads were obtained through RNAseq analysis using the Illumina HiSeq 2000 platform. Clean reads were further assembled de novo into a transcriptome dataset comprising of 514,747 unigenes with N50 length of 578 bp and were further aligned to the public databases. Genebank non-redundant (Nr), Viridiplantae, Gene Ontology (GO), KOG, and KEGG databases classification suggested enrichment of these unigenes in 30 GO categories, 26 KOG, and 127 pathways, respectively. Out of 265,158 genes that were differentially expressed in response to salt treatment, 134,566 and 130,592 genes were significantly up and down-regulated, respectively. Upon placing all the differentially expressed genes (DEG) in known signaling pathways, it was evident that most of the DEGs involved in cytokinin, ethylene, auxin, abscisic acid, gibberellin, and Ca²⁺ mediated signaling pathways were up-regulated. Furthermore, GO enrichment analysis was performed using REVIGO and up-regulation of multiple genes involved in various biological processes in chilense under salinity were identified. Through pathway analysis of DEGs, “Wnt signaling pathway” was identified as a novel pathway for the response to the salinity stress. Moreover, key genes for salinity tolerance, such as genes encoding proline and arginine metabolism, ROS scavenging system, transporters, osmotic regulation, defense and stress response, homeostasis and transcription factors were not only salt-induced but also showed higher expression in S. chilense as compared to S. lycopersicum. Thus indicating that these genes may have an important role in salinity tolerance in S. chilense. Overall, the results of this study improve our understanding on possible molecular mechanisms underlying salt tolerance in plants in general and tomato in particular.

PeSTZ1 confers salt stress tolerance by scavenging the accumulation of ROS through regulating the expression of PeZAT12 and PeAPX2 in Populus

ZINC FINGER OF ARABIDOPSIS THALIANA12 (ZAT12) plays an important role in stress responses, but the transcriptional regulation of ZAT12 in response to abiotic stress remains unclear. In this study, we confirmed that a SALT TOLERANCE ZINC FINGER1 transcription factor from Populus euphratica (PeSTZ1) could regulate the expression of PeZAT12 by dual-luciferase reporter (DLR) assay and electrophoretic mobility shift assay. The expression of PeSTZ1 was rapidly induced by NaCl and hydrogen peroxide (H2O2) treatments. Overexpressing PeSTZ1 in poplar 84K (Populus alba × Populus glandulosa) plant was endowed with a strong tolerance to salt stress. Under salt stress, transgenic poplar exhibited higher expression levels of PeZAT12 and accumulated a larger amount of antioxidant than the wild-type plants. Meanwhile, ASCORBATE PEROXIDASE2 (PeAPX2) can be activated by PeZAT12 and PeSTZ1, promoting the accumulation of cytosolic ascorbate peroxidase (APX) to scavenge reactive oxygen species (ROS) under salt stress. This new regulatory model (PeSTZ1-PeZAT12-PeAPX2) was found in poplar, providing a new idea and insight for the interpretation of poplar resistance. Transgenic poplar reduced the accumulation of ROS, restrained the degradation of chlorophyll and guaranteed the photosynthesis and electron transport system. On the other hand, transgenic poplar slickly adjusted K+/Na+ homeostasis to alleviate salt toxicity in photosynthetic organs of plants under salt stress and then increased biomass accumulation. In summary, PeSTZ1 confers salt stress tolerance by scavenging the accumulation of ROS through regulating the expression of PeZAT12 and PeAPX2 in poplar.

Evidence that melatonin promotes soybean seedlings growth from low-temperature stress by mediating plant mineral elements and genes involved in the antioxidant pathway

Melatonin (MT) regulates several physiological activities in plants. However, information on how MT regulates soybean growth under low-temperature (LT) stress is lacking. To better understand how MT promotes plant growth and development under LT stress, we designed this study to evaluate the role of MT pretreatment on soybean seedlings exposed to LT stress. Our results showed that LT stress increased oxidative damage by increasing reactive oxygen species (ROS) accumulation, which affected the growth and development of soybean seedlings. However, the application of 5 µmol L-1 MT significantly decreased the oxidative damage by increasing plant mineral element concentrations and the transcript abundance of antioxidant related genes, which enhanced the decrease in ROS accumulation. These results collectively suggest the involvement of MT in improving LT stress tolerance of soybean seedlings by mediating plant mineral elements and the expression of genes involved in the antioxidant pathway.

Genome-wide characterization of the C2H2 zinc-finger genes in Cucumis sativus and functional analyses of four CsZFPs in response to stresses

BACKGROUNDS

C2H2-type zinc finger protein (ZFPs) form a relatively large family of transcriptional regulators in plants, and play many roles in plant growth, development, and stress response. However, the comprehensive analysis of C2H2 ZFPs in cucumber (CsZFPs) and their regulation function in cucumber are still lacking.

RESULTS

In the current study, the whole genome identification and characterization of CsZFPs, including the gene structure, genome localization, phylogenetic relationship, and gene expression were performed. Functional analysis of 4 selected genes by transient transformation were also conducted. A total of 129 full-length CsZFPs were identified, which could be classified into four groups according to the phylogenetic analysis. The 129 CsZFPs unequally distributed on 7 chromosomes. Promoter cis-element analysis showed that the CsZFPs might involve in the regulation of phytohormone and/or abiotic stress response, and 93 CsZFPs were predicted to be targeted by one to 20 miRNAs. Moreover, the subcellular localization analysis indicated that 10 tested CsZFPs located in the nucleus and the transcriptome profiling analysis of CsZFPs demonstrated that these genes are involved in root and floral development, pollination and fruit spine. Furthermore, the transient overexpression of Csa1G085390 and Csa7G071440 into Nicotiana benthamiana plants revealed that they could decrease and induce leave necrosis in response to pathogen attack, respectively, and they could enhance salt and drought stresses through the initial induction of H2O2. In addition, Csa4G642460 and Csa6G303740 could induce cell death after 5 days transformation.

CONCLUSIONS

The identification and function analysis of CsZFPs demonstrated that some key individual CsZFPs might play essential roles in response to biotic and abiotic stresses. These results could lay the foundation for understanding the role of CsZFPs in cucumber development for future genetic engineering studies.

ROS Homeostasis in Abiotic Stress Tolerance in Plants

Climate change-induced abiotic stress results in crop yield and production losses. These stresses result in changes at the physiological and molecular level that affect the development and growth of the plant. Reactive oxygen species (ROS) is formed at high levels due to abiotic stress within different organelles, leading to cellular damage. Plants have evolved mechanisms to control the production and scavenging of ROS through enzymatic and non-enzymatic antioxidative processes. However, ROS has a dual function in abiotic stresses where, at high levels, they are toxic to cells while the same molecule can function as a signal transducer that activates a local and systemic plant defense response against stress. The effects, perception, signaling, and activation of ROS and their antioxidative responses are elaborated in this review. This review aims to provide a purview of processes involved in ROS homeostasis in plants and to identify genes that are triggered in response to abiotic-induced oxidative stress. This review articulates the importance of these genes and pathways in understanding the mechanism of resistance in plants and the importance of this information in breeding and genetically developing crops for resistance against abiotic stress in plants.

Transcriptomic Profiling of Young Cotyledons Response to Chilling Stress in Two Contrasting Cotton (Gossypium hirsutum L.) Genotypes at the Seedling Stage

Young cotyledons of cotton seedlings are most susceptible to chilling stress. To gain insight into the potential mechanism of cold tolerance of young cotton cotyledons, we conducted physiological and comparative transcriptome analysis of two varieties with contrasting phenotypes. The evaluation of chilling injury of young cotyledons among 74 cotton varieties revealed that H559 was the most tolerant and YM21 was the most sensitive. The physiological analysis found that the ROS scavenging ability was lower, and cell membrane damage was more severe in the cotyledons of YM21 than that of H559 under chilling stress. RNA-seq analysis identified a total of 44,998 expressed genes and 19,982 differentially expressed genes (DEGs) in young cotyledons of the two varieties under chilling stress. Weighted gene coexpression network analysis (WGCNA) of all DEGs revealed four significant modules with close correlation with specific samples. The GO-term enrichment analysis found that lots of genes in H559-specific modules were involved in plant resistance to abiotic stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that pathways such as plant hormone signal transduction, MAPK signaling, and plant–pathogen interaction were related to chilling stress response. A total of 574 transcription factors and 936 hub genes in these modules were identified. Twenty hub genes were selected for qRT-PCR verification, revealing the reliability and accuracy of transcriptome data. These findings will lay a foundation for future research on the molecular mechanism of cold tolerance in cotyledons of cotton.

Cold priming uncouples light- and cold-regulation of gene expression in Arabidopsis thaliana

BACKGROUND

The majority of stress-sensitive genes responds to cold and high light in the same direction, if plants face the stresses for the first time. As shown recently for a small selection of genes of the core environmental stress response cluster, pre-treatment of Arabidopsis thaliana with a 24 h long 4 °C cold stimulus modifies cold regulation of gene expression for up to a week at 20 °C, although the primary cold effects are reverted within the first 24 h. Such memory-based regulation is called priming. Here, we analyse the effect of 24 h cold priming on cold regulation of gene expression on a transcriptome-wide scale and investigate if and how cold priming affects light regulation of gene expression.

RESULTS

Cold-priming affected cold and excess light regulation of a small subset of genes. In contrast to the strong gene co-regulation observed upon cold and light stress in non-primed plants, most priming-sensitive genes were regulated in a stressor-specific manner in cold-primed plant. Furthermore, almost as much genes were inversely regulated as co-regulated by a 24 h long 4 °C cold treatment and exposure to heat-filtered high light (800 μmol quanta m- 2 s- 1). Gene ontology enrichment analysis revealed that cold priming preferentially supports expression of genes involved in the defence against plant pathogens upon cold triggering. The regulation took place on the cost of the expression of genes involved in growth regulation and transport. On the contrary, cold priming resulted in stronger expression of genes regulating metabolism and development and weaker expression of defence genes in response to high light triggering. qPCR with independently cultivated and treated replicates confirmed the trends observed in the RNASeq guide experiment.

CONCLUSION

A 24 h long priming cold stimulus activates a several days lasting stress memory that controls cold and light regulation of gene expression and adjusts growth and defence regulation in a stressor-specific manner.

Exogenous Melatonin Improves Salt Tolerance by Mitigating Osmotic, Ion, and Oxidative Stresses in Maize Seedlings

Melatonin has been confirmed extensively for the positive effects on increasing plant tolerance to various abiotic stresses. However, the roles of melatonin in mediating different stresses still need to be explored in different plants species and growth periods. To investigate the role of melatonin in mitigating salt stress, maize (Zea mays L.) seedlings growing in hydroponic solution were treated with 100 mM NaCl combined with or without 1 μM melatonin. Melatonin application had no effects on maize growth under normal condition, while it moderately alleviated the NaCl-induced inhibition of plant growth. The leaf area, biomass, and photosynthesis of melatonin-treated plants were higher than that of without melatonin under NaCl treatment. The osmotic potential was lower, and the osmolyte contents (including sucrose and fructose) were higher in melatonin-treated plants. Meanwhile, the decreases in Na+ content and increases in K+/Na+ ratio were found in shoots of melatonin-applied plant under salt stress. Moreover, both enzymatic and nonenzymatic antioxidant activities were significantly increased in leaves with melatonin application under salt treatment. These results clearly indicate that the exogenous melatonin-enhanced salt tolerance under short-term treatment could be ascribed to three aspects, including osmotic adjustment, ion balance, and alleviation of salt-induced oxidative stress.

Heterologous Expression of a Glycine soja C2H2 Zinc Finger Gene Improves Aluminum Tolerance in Arabidopsis

Aluminum (Al) toxicity limits plant growth and has a major impact on the agricultural productivity in acidic soils. The zinc-finger protein (ZFP) family plays multiple roles in plant development and abiotic stresses. Although previous reports have confirmed the function of these genes, their transcriptional mechanisms in wild soybean (Glycine soja) are unclear. In this study, GsGIS3 was isolated from Al-tolerant wild soybean gene expression profiles to be functionally characterized in Arabidopsis. Laser confocal microscopic observations demonstrated that GsGIS3 is a nuclear protein, containing one C2H2 zinc-finger structure. Our results show that the expression of GsGIS3 was of a much higher level in the stem than in the leaf and root and was upregulated under AlCl3, NaCl or GA3 treatment. Compared to the control, overexpression of GsGIS3 in Arabidopsis improved Al tolerance in transgenic lines with more root growth, higher proline and lower Malondialdehyde (MDA) accumulation under concentrations of AlCl3. Analysis of hematoxylin staining indicated that GsGIS3 enhanced the resistance of transgenic plants to Al toxicity by reducing Al accumulation in Arabidopsis roots. Moreover, GsGIS3 expression in Arabidopsis enhanced the expression of Al-tolerance-related genes. Taken together, our findings indicate that GsGIS3, as a C2H2 ZFP, may enhance tolerance to Al toxicity through positive regulation of Al-tolerance-related genes.

Melatonin enhances drought resistance by regulating leaf stomatal behaviour, root growth and catalase activity in two contrasting rapeseed (Brassica napus L.) genotypes

Two contrasting rapeseed (Brassica napus L.) genotypes, Qinyou 8 (drought-sensitive) and Q2 (drought-tolerant), were studied under drought stress with or without pretreatment with melatonin to (i) explore whether melatonin enhances drought resistance by regulating root growth and (ii) determine the relationship between the belowground and aboveground responses to melatonin under drought stress. Results show that the light-saturated rate of photosynthesis (P_n), stomatal conductance (g_s), water use efficiency (WUE) and chlorophyll content were decreased by drought for Qinyou 8, whereas drought only decreased P_n and chlorophyll content for Q2. Drought decreased actual photochemical efficiency in saturated light (F_v'/F_m'), actual photochemical efficiency (PhiPSⅡ), quenching of photochemical efficiency (qL) and electron transport rate (ETR) in Qinyou 8. However drought only decreased F_v'/F_m' and qL in Q2. Drought increased malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents in the roots of both genotypes. Melatonin had no significant additional effects on root guaiacol peroxidase (POD) and superoxide dismutase (SOD) activities, but enhanced root catalase (CAT) activity of droughted plants further. Melatonin promoted taproot and lateral root growth under drought stress. Melatonin also promoted stomatal opening resulting in enhanced photosynthesis in the two genotypes. The two mechanisms induced by melatonin synergistically enhance drought resistance of rapeseed as indicated by enhanced gas exchange parameters under melatonin pretreatment. The findings provide evidence for a physiological role of melatonin in improving drought resistance, especially in belowground parts.

Melatonin Mitigates Chilling-Induced Oxidative Stress and Photosynthesis Inhibition in Tomato Plants

Melatonin has been demonstrated to play a variety of roles in plants. Of particular importance is its role as a potent antioxidative agent. In the present study, we generated melatonin-deficient tomato plants using virus-induced gene silencing (VIGS) approach and melatonin-rich tomato plants by foliar application of melatonin. These tomato plants were used to assess the effect of melatonin on chilling-induced oxidative stress and chilling-induced photosynthesis inhibition. We found that melatonin deficiency increased accumulation of reactive oxygen species (ROS) and aggravated lipid peroxidation in chilling-stressed tomato leaves, while exogenous application of melatonin had the opposite effect. Under chilling stress, melatonin-deficient tomato plants showed impaired antioxidant capacity as evidenced by lower activities of antioxidant enzymes and decreased rations of reduced glutathione (GSH)/oxidized glutathione (GSSG) and reduced ascorbate (AsA)/oxidized ascorbate (DHA), compared with melatonin-rich tomato plants. Furthermore, suppression of melatonin biosynthesis led to more photosynthesis inhibition under the chilling condition and compromised the capability of subsequent photosynthesis recovery in tomato plants. In addition, melatonin-deficient tomato plants displayed less activity of an important Calvin-Benson cycle enzyme sedoheptulose-1,7-bisphosphatase (SBPase) than melatonin-rich tomato plants under chilling stress. Collectively, our data indicate that melatonin is critical for antioxidant capacity and redox balance and is in favor of photosynthesis in tomato plants under chilling stress.

Is Phytomelatonin a New Plant Hormone?

Melatonin (N-acetyl-5-methoxytryptamine) is of particular importance as a chronobiological hormone in mammals, acting as a signal of darkness that provides information to the brain and peripheral organs. It is an endogenous synchronizer for both endocrine (i.e., via neurotransmitter release) and other physiological rhythms. In this work we will try to add to the series of scientific events and discoveries made in plants that, surprisingly, confirm the great similarity of action of melatonin in animals and plants. The most relevant milestones on the 25 years of phytomelatonin studies are presented, from its discovery in 1995 to the discovery of its receptor in plants in 2018, suggesting it should be regarded as a new plant hormone.

Role of Melatonin to Enhance Phytoremediation Capacity

Phytoremediation is a green technology that aims to take up pollutants from soil or water. Metals are one of the targets of these techniques due to their high toxicity in biological systems, including plants and animals. Their elimination or, at least, decrease will help keep them from being incorporated in the trophic chain and thus reaching animal and human food. The metal removal efficiency of plants is closely related to their growth rate, tolerance, and their adaptability to different environments. Melatonin (N-acetyl-5-methoxytryptamine) is a ubiquitous molecule present in animals, plants, fungi, and bacteria. In plants, it plays an important role related to antioxidant activity, but also as an important redox network regulator. Thus, melatonin has been defined as a biostimulator of plant growth, especially under environmental stress conditions, whether abiotic (water deficit and waterlogging, extreme temperature, UV radiation, salinity, alkalinity, specific mineral deficit/excess, metals and other toxic compounds, etc.) or biotic (bacteria, fungi, and viruses). Exogenous melatonin treated plants have been seen to have a high tolerance to stressors, minimizing possible harmful effects through the control of reactive oxygen species (ROS) levels and activating antioxidative responses. Furthermore, important gene expression changes in stress specific transcription factors have been demonstrated. Melatonin is capable of mobilizing toxic metals, through phytochelatins, transporting this, while sequestration adds to the biostimulator effect of melatonin on plants, improving plant tolerance against toxic pollutants. Furthermore, melatonin improves the uptake of nitrogen (N), phosphorus (P), and sulfur (S) in stress situations, enhancing cell metabolism. In light of the above, the application of melatonin seems to be a useful option for clearing toxic pollutants from the environment by improving phytoremediation. Interestingly, a variety of stressors induce melatonin biosynthesis in plants, and the study of this endogenous response in hyperaccumulator plants may be even more interesting as a natural response of the phytoremediation of diverse plants.

PeSTZ1, a C2H2-type zinc finger transcription factor from Populus euphratica, enhances freezing tolerance through modulation of ROS scavenging by directly regulating PeAPX2

In the present study, PeSTZ1, a cysteine-2/histidine-2-type zinc finger transcription factor, was isolated from the desert poplar, Populus euphratica, which serves as a model stress adaptation system for trees. PeSTZ1 was preferentially expressed in the young stems and was significantly up-regulated during chilling and freezing treatments. PeSTZ1 was localized to the nucleus and bound specifically to the PeAPX2 promoter. To examine the potential functions of PeSTZ1, we overexpressed it in poplar 84K hybrids (Populus alba × Populus glandulosa), which are known to be stress-sensitive. Upon exposure to freezing stress, transgenic poplars maintained higher photosynthetic activity and dissipated more excess light energy (in the form of heat) than wild-type poplars. Thus, PeSTZ1 functions as a transcription activator to enhance freezing tolerance without sacrificing growth. Under freezing stress, PeSTZ1 acts upstream of ASCORBATE PEROXIDASE2 (PeAPX2) and directly regulates its expression by binding to its promoter. Activated PeAPX2 promotes cytosolic APX that scavenges reactive oxygen species (ROS) under cold stress. PeSTZ1 may operate in parallel with C-REPEAT-BINDING FACTORS to regulate COLD-REGULATED gene expression. Moreover, PeSTZ1 up-regulation reduces malondialdehyde and ROS accumulation by activating the antioxidant system. Taken together, these results suggested that overexpressing PeSTZ1 in 84K poplar enhances freezing tolerance through the modulation of ROS scavenging via the direct regulation of PeAPX2 expression.

The bZIP gene family in watermelon: genome-wide identification and expression analysis under cold stress and root-knot nematode infection

The basic leucine zipper (bZIP) family transcription factors play crucial roles in regulating plant development and stress response. In this study, we identified 62 ClabZIP genes from watermelon genome, which were unevenly distributed across the 11 chromosomes. These ClabZIP proteins could be classified into 13 groups based on the phylogenetic relationships, and members in the same group showed similar compositions of conserved motifs and gene structures. Transcriptome analysis revealed that a number of ClabZIP genes have important roles in the melatonin (MT) induction of cold tolerance. In addition, some ClabZIP genes were induced or repressed under red light (RL) or root-knot nematode infection according to the transcriptome data, and the expression patterns of several ClabZIP genes were further verified by quantitative real-time PCR, revealing their possible roles in RL induction of watermelon defense against nematode infection. Our results provide new insights into the functions of different ClabZIP genes in watermelon and their roles in response to cold stress and nematode infection.