Exogenous Serotonin and Melatonin Regulate Dietary Isoflavones Profoundly through Ethylene Biosynthesis in Soybean [Glycine max (L.) Merr.]

Crosstalk between ethylene and melatonin activates isoflavone biosynthesis and antioxidant systems to produce high-quality soybean sprouts

Isoflavone, which are mainly found in soybeans, are a secondary metabolite with a variety of physiological functions. In recent years, increasing the isoflavone content of soybeans has received widespread attention. Although ethephon treatment significantly increased isoflavone content in soybean sprouts, it also had a certain inhibitory effect on the growth of sprouts. Melatonin (MT), as a new type of plant hormone, not only alleviated the damage caused by abiotic stress to plants, but also promoted the synthesis of secondary metabolites. In this study, we aimed to elucidate the mechanism of exogenous MT in regulating the growth and development, and the metabolism of isoflavone in soybean sprouts under ethephon treatment. The results indicated that MT alleviated the adverse effects of ethephon treatment on soybean sprouts by increasing the activities of superoxide dismutase, peroxidase, catalase, and the expression of their corresponding genes, as well as decreased the content of malondialdehyde and hydrogen peroxide. In addition, MT further increased the isoflavone content by up-regulating the expression level of isoflavone synthesis genes and increased the activities of phenylalanine ammonia-lyase and cinnamic acid 4-hydroxylase under ethephon treatment. This study provided technical support and reference value for the production of high-quality soybean sprouts to a certain extent.

Serotonin-Salt-Stress Model-Induced Cell Growth via Promoting an Antioxidant System and Secondary Metabolites in Capsicum annuum Cell Suspension Culture

Capsicum annuum contains potential therapeutic capsaicinoids, and various stress factors influence plant productivity. Serotonin is an indoleamine involved in signaling several stress response mechanisms in plants. However, the influence of serotonin on cell growth and the accumulation of secondary metabolites, mainly capsaicinoids production, is not yet clearly defined under salt stress. In this study, we optimized chili cell suspension cultures to maximize biomass, capsaicinoids, and phenolic compounds production using response surface methodology with two variables (serotonin and NaCl) of different concentrations in culture media supplemented with 2,4-dichlorophenoxyacetic acid and Kinetin. The results revealed a significant increase in biomass (14.3 g/L FW), capsaicin (0.93 μg/g FW), and dihydrocapsaicin content (0.32 μg/g FW) in chili cell suspension cultures compared with the control. Among all the phenolic compounds, chlorogenic acid was enhanced (17.4 μg/g FW), compared to control cultures. Serotonin exhibited stress mitigation effects and boosted antioxidant potential in chili suspension cultures. The present results illustrated that the optimized conditions can be used in scale-up studies of capsaicinoids production through the bioreactor.

Metabolic profiling of Citrus maxima L. seedlings in response to cadmium stress using UPLC-QTOF-MS

Cadmium (Cd) pollution significantly reduces agricultural crop yields. In our research, metabolomic changes in Citrus maxima L. subjected to Cd stress were investigated using ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) in tandem with multivariate analytical techniques. This integrative method, coupled with physiological evaluations, aimed to elucidate the core adaptive mechanisms to Cd stress. We found that under Cd stress, C. maxima seedlings exhibited elevated levels of reactive oxygen species, malondialdehyde, and electrolyte leakage. Furthermore, principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) demonstrated distinct a separation of the metabolome among the different treatment groups under Cd stress, indicating dynamic metabolic changes. Metabolic analysis suggested that genes involved are initially induced by Cd treatment, followed by the activation of the flavonoid biosynthesis pathway. This investigation provides new insights into the complex metabolic responses of C. maxima seedlings to Cd exposure.

Ethephon promotes isoflavone accumulation in germinating soybeans by its acceleration of isoflavone biosynthetic pathway

Soybeans have medicinal value and are an oil crop with medicinal and food properties. The present work investigated two aspects of isoflavone accumulation in soybean. First, germination conditions for exogenous-ethephon-mediated accumulation of isoflavone were optimised through response surface methodology. Second, various influences of ethephon on the growth of germinating soybeans and isoflavone metabolism were investigated. The findings of the research led to the conclusion that exogenous ethephon treatment effectively facilitated the enrichment of isoflavones in soybeans during germination. Optimal germination conditions were obtained through a response surface optimization test, which yielded the following criteria: a germination time of 4.2 d, an ethephon concentration of 102.6 μM, and a germination temperature of 30.2 °C. The maximum isoflavone content was 544.53 μg/sprout FW. Relative to the control, the addition of ethephon significantly inhibited sprout growth. Exogenous ethephon treatment led to the phenomenon that peroxidase, superoxide dismutase, and catalase activities and their gene expression increased significantly in germinating soybeans. Meanwhile, the expression of genes related to ethylene synthetase increase under the effect of ethephon promoting ethylene synthesis. Ethylene multiplied the total flavonoid content of soybean sprouts relying on the increase in activity and gene expression of crucial isoflavone biosynthesis-related enzymes (phenylalanine ammonia-lyase and 4-coumarate coenzyme A ligase) during germination.

Genome-wide identification of MATE, functional analysis and molecular dynamics of DcMATE21 involved in anthocyanin accumulation in Daucus carota

Anthocyanins are a subclass of flavonoids that are synthesized in the endoplasmic reticulum and then transported to the vacuole in plants. Multidrug and toxic compound extrusion transporters (MATE) is a family of membrane transporters that transport ions and secondary metabolites, such as anthocyanins, in plants. Although various studies on MATE transporters have been carried out on different plant species, this is the first comprehensive report to mine the Daucus carota genome to identify the MATE gene family. Our study identified 45 DcMATEs through genome-wide analysis and detected five segmental and six tandem duplications from the genome. The chromosome distribution, phylogenetic analysis, and cis-regulatory elements revealed the structural diversity and numerous functions associated with the DcMATEs. In addition, we analyzed RNA-seq data obtained from the European Nucleotide Archive to screen for the expression of DcMATEs involved in anthocyanin biosynthesis. Among the identified DcMATEs, DcMATE21 correlated with anthocyanin content in the different D. carota varieties. In addition, the expression of DcMATE21 and anthocyanin biosynthesis genes was correlated under abscisic acid, methyl jasmonate, sodium nitroprusside, salicylic acid, and phenylalanine treatments, which were substantiated by anthocyanin accumulation in the in vitro cultures. Further molecular membrane dynamics of DcMATE21 with anthocyanin (cyanidin-3-glucoside) identified the binding pocket, showing extensive H-bond interactions with 10 crucial amino acids present in the transmembrane helix of 7, 8, and 10 of DcMATE21. The current investigation, using RNA-seq, in vitro cultures, and molecular dynamics studies revealed the involvement of DcMATE21 in anthocyanin accumulation in vitro cultures of D. carota.

Melatonin-mediated development and abiotic stress tolerance in plants

Melatonin is a multifunctional molecule that has been widely discovered in most plants. An increasing number of studies have shown that melatonin plays essential roles in plant growth and stress tolerance. It has been extensively applied to alleviate the harmful effects of abiotic stresses. In view of its role in regulating aspects of plant growth and development, we ponder and summarize the scientific discoveries about seed germination, root development, flowering, fruit maturation, and senescence. Under abiotic and biotic stresses, melatonin brings together many pathways to increase access to treatments for the symptoms of plants and to counteract the negative effects. It has the capacity to tackle regulation of the redox, plant hormone networks, and endogenous melatonin. Furthermore, the expression levels of several genes and the contents of diverse secondary metabolites, such as polyphenols, terpenoids, and alkaloids, were significantly altered. In this review, we intend to examine the actions of melatonin in plants from a broader perspective, explore the range of its physiological functions, and analyze the relationship between melatonin and other metabolites and metabolic pathways.

Plant hormones and neurotransmitter interactions mediate antioxidant defenses under induced oxidative stress in plants

Due to global climate change, abiotic stresses are affecting plant growth, productivity, and the quality of cultivated crops. Stressful conditions disrupt physiological activities and suppress defensive mechanisms, resulting in stress-sensitive plants. Consequently, plants implement various endogenous strategies, including plant hormone biosynthesis (e.g., abscisic acid, jasmonic acid, salicylic acid, brassinosteroids, indole-3-acetic acid, cytokinins, ethylene, gibberellic acid, and strigolactones) to withstand stress conditions. Combined or single abiotic stress disrupts the normal transportation of solutes, causes electron leakage, and triggers reactive oxygen species (ROS) production, creating oxidative stress in plants. Several enzymatic and non-enzymatic defense systems marshal a plant's antioxidant defenses. While stress responses and the protective role of the antioxidant defense system have been well-documented in recent investigations, the interrelationships among plant hormones, plant neurotransmitters (NTs, such as serotonin, melatonin, dopamine, acetylcholine, and γ-aminobutyric acid), and antioxidant defenses are not well explained. Thus, this review discusses recent advances in plant hormones, transgenic and metabolic developments, and the potential interaction of plant hormones with NTs in plant stress response and tolerance mechanisms. Furthermore, we discuss current challenges and future directions (transgenic breeding and genome editing) for metabolic improvement in plants using modern molecular tools. The interaction of plant hormones and NTs involved in regulating antioxidant defense systems, molecular hormone networks, and abiotic-induced oxidative stress tolerance in plants are also discussed.

Genome-wide identification, characterization of Serotonin N-acetyltransferase and deciphering its importance under development, biotic and abiotic stress in soybean

Serotonin N-acetyltransferase (SNAT) is the penultimate enzyme involved in plant melatonin biosynthesis. Identifying its expression under development and stress will reveal the regulatory role in the soybean. To identify and characterize SNAT, we employed genome-wide analysis, gene structure, cis-acting elements, expression, and enzyme activity. We identified seven putative genes by genome-wide analysis and found chloroplast signal peptides in three GmSNATs. To elucidate GmSNATs role, expression datasets of more than a hundred samples related to circadian rhythm, developmental stages, and stress conditions were analysed. Notably, the expression of GmSNAT1 did not show significant expression during biotic and abiotic stress. The GmSNAT1 sequence showed 67.8 and 72.2 % similarities with OsSNAT and AtSNAT, respectively. The Km and Vmax of the purified recombinant GmSNAT1 were 657 μM and 3780 pmol/min/mg, respectively. To further understand the GmSNAT1 role, we supplemented different concentrations of serotonin and melatonin to in-vitro cultures and seed priming. These studies revealed that the GmSNAT1 expression was significantly up-regulated at higher concentrations of serotonin and down-regulated at higher melatonin concentrations. We speculate that a high concentration of melatonin during abiotic, biotic stress, and in-vitro cultures are responsible for regulating GmSNAT1 expression, which may regulate them at the enzyme level during stress in soybean.

Exogenous melatonin stimulated isoflavone biosynthesis in NaCl-stressed germinating soybean (Glycine max L.)

Melatonin (MT) has gained increasing attention due to its pleiotropic effects. In this study, the function of exogenous MT on the response to NaCl stress and isoflavone biosynthesis in germinating soybeans was investigated. Results showed the exogenous MT (100 μM) application neutralised the negative effects of NaCl stress (60 mM), induced sprout growth, biomass and fluorescence intensity of intracellular free calcium, decreased malondialdehyde, H2O2 content and fluorescence intensity of O2•-, and enhanced superoxide dismutase, catalase and peroxidas activities of germinating soybeans. Meanwhile, total flavonoids and different forms of isoflavone content were enhanced by MT application, not only companied by the up-regulated relative gene expression of cinnamic acid 4-hydroxylase chalcone reductase, chalcone isomerase 1A, isoflavone reductase and isoflavone synthase 1 that involved in isoflavone biosynthesis, but also increased activities of phenylalanine ammonia lyase and 4-coumarate coenzyme A ligase. Given the evidence from the present study, it's proposed that the exogenous MT could relieve NaCl stress and stimulate isoflavone biosynthesis in germinating soybeans.

Role of exogenous melatonin involved in phenolic acid metabolism of germinated hulless barley under NaCl stress

In this study, the effects of exogenous MT on phenolic acids biosynthesis and the response to NaCl stress in germinating barley were investigated to explicate the role and molecular mechanism of MT in the regulation of phenolic acids and biomass under salt stress. Results showed that exogenous MT increased the gene expression and activities of phenylalanine ammonia lyase and cinnamate 4-hydroxylase involved in phenols biosynthesis. As a result, phenolic acids contents significantly increased, and ferulic acid, p-coumaric acid and p-hydroxybenzoic acid were mostly induced by exogenous MT treatment. Meanwhile, exogenous MT application reduced the damage of NaCl stress, including promotion sprout growth, biomass and Ca²⁺ influs, malonaldehyde and H₂O₂ content reduction, increases of peroxidase, superoxide dismutase and catalase activities in barley seedlings. These results indicated that exogenous MT was essential for inducing phenolic acids accumulation and alleviated the inhibition of NaCl stress on barley seedlings.

Distinct GmASMTs are involved in regulating transcription factors and signalling cross-talk across embryo development, biotic, and abiotic stress in soybean

N-Acetylserotonin O-methyltransferase (ASMT) is the final enzyme involved in melatonin biosynthesis. Identifying the expression of ASMT will reveal the regulatory role in the development and stress conditions in soybean. To identify and characterize ASMT in soybean (GmASMT), we employed genome-wide analysis, gene structure, cis-acting elements, gene expression, co-expression network analysis, and enzyme assay. We found seven pairs of segmental and tandem duplication pairs among the 44 identified GmASMTs by genome-wide analysis. Notably, co-expression network analysis reported that distinct GmASMTs are involved in various stress response. For example, GmASMT3, GmASMT44, GmASMT17, and GmASMT7 are involved in embryo development, heat, drought, aphid, and soybean cyst nematode infections, respectively. These distinct networks of GmASMTs were associated with transcription factors (NAC, MYB, WRKY, and ERF), stress signalling, isoflavone and secondary metabolites, calcium, and calmodulin proteins involved in stress regulation. Further, GmASMTs demonstrated auxin-like activities by regulating the genes involved in auxin transporter (WAT1 and NRT1/PTR) and auxin-responsive protein during developmental and biotic stress. The current study identified the key regulatory role of GmASMTs during development and stress. Hence GmASMT could be the primary target in genetic engineering for crop improvement under changing environmental conditions.

Salt Stress-Induced Anthocyanin Biosynthesis Genes and MATE Transporter Involved in Anthocyanin Accumulation in Daucus carota Cell Culture

Anthocyanins biosynthesis is a well-studied biosynthesis pathway in Daucus carota. However, the scale-up production at the bioreactor level and transporter involved in accumulation is poorly understood. To increase anthocyanin content and elucidate the molecular mechanism involved in accumulation, we examined D. carota cell culture in flask and bioreactor for 18 days under salt stress (20.0 mM NH₄NO₃/37.6 mM KNO₃) at 3 day intervals. The expression of anthocyanin biosynthesis and putative MATE (multidrug and toxic compound extrusion) transporter expression was analyzed by qRT-PCR. It was observed that there was a significant enhancement of anthocyanin in the bioreactor compared to the control culture. A correlation was observed between the expression of MATE and the anthocyanin biosynthesis genes (CHS, C4H, LDOX, and UFGT) on the 9th day in a bioreactor, where maximum anthocyanin accumulation and expression was detected. We hypothesize the involvement of MATE in transporting anthocyanin to tonoplast in D. carota culture under salt stress.