Cyclic GMP mediates abscisic acid-stimulated isoflavone synthesis in soybean sprouts

cGMP functions as an important messenger involved in SlSAMS1-regulated salt stress tolerance in tomato

Salt stress adversely affects the growth, development, and yield of tomato (Solanum lycopersicum). SAM Synthetase (SAMS), which is responsible for the biosynthesis of S-adenosylmethionine (SAM, a precursor of polyamine biosynthesis), participates in plant response to abiotic stress. However, the regulatory mechanism of SAMS-mediated salt stress tolerance remains elusive. In this study, we characterized a SAMS homologue SlSAMS1 in tomato. We found that SlSAMS1 is highly expressed in tomato roots, and its expression can be induced by salt stress. Crucially, overexpression of SlSAMS1 in tomato enhances salt stress tolerance. Through metabolomic profiling, we identified some differentially accumulated metabolites, especially, a secondary messenger guanosine 3',5'-cyclic monophosphate (cGMP) which may play a key role in SlSAMS1-regulated salt tolerance. A series of physiological and biochemical data suggest that cGMP alleviates salt stress-induced growth inhibition, and potentially acts downstream of the polyamine-nitric oxide (PA-NO) signaling pathway to trigger H2O2 signaling in response to salt stress. Taken together, the study reveals that SlSAMS1 regulates tomato salt tolerance via the PA-NO-cGMP-H2O2 signal module. Our findings elucidate the regulatory pathway of SlSAMS1-induced plant response to salt stress and indicate a pivotal role of cGMP in salt tolerance.

Widely targeted metabolomics analysis characterizes the phenolic compounds profiles in mung bean sprouts under sucrose treatment

Phenolic compounds are one of the wholesome substances of mung bean sprouts, showing numerous health-promoting functions. Here, effects of sucrose on phenolic compounds profiles of mung bean sprouts were investigated. Results showed that the content and composition of phenolic compounds were significantly altered by 1‰ and 5‰ sucrose, respectively. The antioxidant capacity was significantly improved by sucrose. Based on metabolomics, 251 metabolites were detected, of which 106 were phenolic compounds. Correlation analysis showed 21 phenolics were positively correlated with antioxidant capacity. The changes in phenolic composition and antioxidant capacity after sucrose treatment were mainly due to the enrichment of phenolic biosynthesis pathways. Moreover, the gene expression and enzyme activity analysis of key phenolic biosynthetic genes contributed to elucidate the phenolic profile under sucrose treatment. In summary, mung bean sprouts are promising sources of dietary phenolic compounds and sucrose treatment is a good process to produce phenolic-rich mung bean sprouts.

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.

Occurrence of isoflavones in soybean sprouts and strategies to enhance their content: A review

Sprouting is a common strategy to enhance the nutritional value of seeds. Here, all the reports regarding the occurrence of isoflavones in soybean sprouts have been covered for the first time. Isoflavones were detected with concentrations ranging from 1 × 10-2 to 1 × 101  g/kg in soybean sprouts. Isoflavone concentration depends on the cultivar, germination time, part of the sprout, light, and temperature. Aglycon isoflavones increased during germination, especially in the hypocotyl, while 6″-O-malonyl-7-O-β-glucoside isoflavones decreased in the hypocotyl and increased in the cotyledon and root. Cooking reduced total isoflavone content. Regarding the strategies to enhance isoflavone contents, fermentation with Aspergillus sojae and external irradiation with UV-A or far-infrared were the methods that caused the greatest increases in aglycon, 7-O-β-glucoside, and total isoflavones. However, the largest increases in 6″-O-malonyl-7-O-β-glucoside and 6″-O-acetyl-7-O-β-glucosides isoflavones were detected after treatment with chitohexaose and calcium chloride, respectively. PRACTICAL APPLICATION: Soybean sprouts are widely consumed and provide essential proteins, antioxidants, and minerals. They are rich in isoflavones, which exhibit numerous health benefits, and have been studied as alternative therapies for a range of hormone-dependent conditions, such as cancer, menopausal symptoms, cardiovascular disease, and osteoporosis. Despite numerous reports being published to date regarding the occurrence of isoflavones in soybean sprouts, the publications in this field are highly dispersed, and a review has not yet been published. This review aims to (1) highlight the particular isoflavones that have been detected in soybean sprouts and their concentrations, (2) compared the effects of temperature, light, cooking and soybean cultivar affect the isoflavone levels on the different parts of the sprout, and (3) discuss the efficacy of the methods to enhance isoflavone contents. This review will provide a better understanding of the current state of this field of research by comparing the general trends and the different treatments for soybean sprouts.

BdGUCD1 and Cyclic GMP Are Required for Responses of Brachypodium distachyon to Fusarium pseudograminearum in the Mechanism Involving Jasmonate

Guanosine 3′,5′-cyclic monophosphate (cGMP) is an important signaling molecule in plants. cGMP and guanylyl cyclases (GCs), enzymes that catalyze the synthesis of cGMP from GTP, are involved in several physiological processes and responses to environmental factors, including pathogen infections. Using in vitro analysis, we demonstrated that recombinant BdGUCD1 is a protein with high guanylyl cyclase activity and lower adenylyl cyclase activity. In Brachypodium distachyon, infection by Fusarium pseudograminearum leads to changes in BdGUCD1 mRNA levels, as well as differences in endogenous cGMP levels. These observed changes may be related to alarm reactions induced by pathogen infection. As fluctuations in stress phytohormones after infection have been previously described, we performed experiments to determine the relationship between cyclic nucleotides and phytohormones. The results revealed that inhibition of cellular cGMP changes disrupts stress phytohormone content and responses to pathogen. The observations made here allow us to conclude that cGMP is an important element involved in the processes triggered as a result of infection and changes in its levels affect jasmonic acid. Therefore, stimuli-induced transient elevation of cGMP in plants may play beneficial roles in priming an optimized response, likely by triggering the mechanisms of feedback control.

Integrative analysis of the pharmaceutical active ingredient and transcriptome of the aerial parts of Glycyrrhiza uralensis under salt stress reveals liquiritin accumulation via ABA-mediated signaling

The aerial parts of Glycyrrhiza uralensis supply substantial raw material for the extraction of active pharmaceutical ingredients comprehensively utilized in many industries. Our previous study indicated that salt stress increased the content of active ingredients. However, the regulatory mechanism remains unclear. In this study, RNA-sequencing (RNA-seq) of the aerial parts of G. uralensis treated with 150 mM NaCl for 0, 2, 6, and 12 h was performed to identify the key genes and metabolic pathways regulating pharmacological active component accumulation. The main active component detection showed that liquiritin was the major ingredient and exhibited more than a ten-fold significant increase in the 6 h NaCl treatment. Temporal expression analysis of the obtained 4245 differentially expressed genes (DEGs) obtained by RNA-seq revealed two screened profiles that included the significant up-regulated DEGs (UDEGs) at different treatment points. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of these UDEGs identified phenylpropanoid metabolism and flavonoid biosynthesis as the most significantly enriched pathways in 2 h treated materials. Interestingly, the carotenoid biosynthesis pathway that is related to ABA synthesis was also discovered, and the ABA content was significantly promoted after 6 h NaCl treatment. Following ABA stimulation, the content of liquiritin demonstrated a significant and immediate increase after 2 h treatment, with the corresponding consistent expression of genes involved in the pathways of ABA signal transduction and flavonoid biosynthesis, but not in the pathway of glycyrrhizic acid biosynthesis. Our study concludes that salt stress might promote liquiritin accumulation through the ABA-mediated signaling pathway, and provides effective reference for genetic improvement and comprehensive utilization of G. uralensis.

Iron toxicity-induced regulation of key secondary metabolic processes associated with the quality and resistance of Panax ginseng and Panax quinquefolius

Panax ginseng and Panax quinquefolius can survive for long periods of time in iron toxicity-stressed environments, which cause rusty roots and reduced productivity. To reveal the proteomic changes in these two Panax species in response to iron toxicity stress, plants of these two species were divided into a control group and an iron toxicity-stress group. An isobaric tags for relative and absolute quantitation (iTRAQ) proteomics approach was used to explore the changes in protein accumulation and the potential mechanisms underlying the response to iron toxicity stress in the two Panax species. Proteomic analyses revealed approximately 725 differentially expressed proteins (DEPs) in the iron toxicity-stress and control groups, including 233 and 492 proteins whose expression was upregulated and downregulated, respectively. The expression of DEPs related to photosynthesis was significantly downregulated, and DEPs whose expression was significantly upregulated were associated with redox reactions. Many upregulated DEPs were also involved in pathways such as those involving phenylpropanoid, flavonoid, isoflavone and ginsenoside synthesis. The abundance of some ginsenoside monomers (Rg1 and Rb3) also significantly increased in P. ginseng and P. quinquefolius. Moreover, P. quinquefolius contained 455 DEPs whose expression was higher than that in P. ginseng, including many proteins related to the regulation of ion homeostasis, indicating that P. quinquefolius is more resistant to iron toxicity stress than P. ginseng is.

Recent Advances in Heterologous Synthesis Paving Way for Future Green-Modular Bioindustries: A Review With Special Reference to Isoflavonoids

Isoflavonoids are well-known plant secondary metabolites that have gained importance in recent time due to their multiple nutraceutical and pharmaceutical applications. In plants, isoflavonoids play a role in plant defense and can confer the host plant a competitive advantage to survive and flourish under environmental challenges. In animals, isoflavonoids have been found to interact with multiple signaling pathways and have demonstrated estrogenic, antioxidant and anti-oncologic activities in vivo. The activity of isoflavonoids in the estrogen pathways is such that the class has also been collectively called phytoestrogens. Over 2,400 isoflavonoids, predominantly from legumes, have been identified so far. The biosynthetic pathways of several key isoflavonoids have been established, and the genes and regulatory components involved in the biosynthesis have been characterized. The biosynthesis and accumulation of isoflavonoids in plants are regulated by multiple complex environmental and genetic factors and interactions. Due to this complexity of secondary metabolism regulation, the export and engineering of isoflavonoid biosynthetic pathways into non-endogenous plants are difficult, and instead, the microorganisms Saccharomyces cerevisiae and Escherichia coli have been adapted and engineered for heterologous isoflavonoid synthesis. However, the current ex-planta production approaches have been limited due to slow enzyme kinetics and traditionally laborious genetic engineering methods and require further optimization and development to address the required titers, reaction rates and yield for commercial application. With recent progress in metabolic engineering and the availability of advanced synthetic biology tools, it is envisaged that highly efficient heterologous hosts will soon be engineered to fulfill the growing market demand.

Exogenous application of phytosulfokine α (PSKα) delays yellowing and preserves nutritional quality of broccoli florets during cold storage

In this study, we tested the exogenous application of phytosulfokine α (PSKα) for delaying the yellowing of broccoli florets during cold storage. Our results showed that the lower yellowing in broccoli florets treated with 150 nM PSKα was probably due to the higher endogenous accumulation of PSKα, leading to the endogenous accumulation of guanosine 3', 5'-cyclic monophosphate (cGMP). Besides, broccoli florets treated with 150 nM PSKα exhibited a higher accumulation of phenols and flavonoids by triggering gene expression and activities of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS). Moreover, the higher expression of L-galactotno-1,4-lactone dehydrogenase (GLDH) gene and the lower expression of ascorbic acid oxidase (AAO) gene in broccoli florets treated with 150 nM PSKα may be the reasons for the higher accumulation of ascorbic acid. In conclusion, the exogenous application of PSKα is a promising strategy in delaying the yellowing and preserving the nutritional quality of broccoli florets during cold storage.

Integrated Analysis of mRNA and microRNA Elucidates the Regulation of Glycyrrhizic Acid Biosynthesis in Glycyrrhiza uralensis Fisch

Licorice (Glycyrrhiza) is a staple Chinese herbal medicine in which the primary bioactive compound is glycyrrhizic acid (GA), which has important pharmacological functions. To date, the structural genes involved in GA biosynthesis have been identified. However, the regulation of these genes in G. uralensis has not been elucidated. In this study, we performed a comprehensive analysis based on the transcriptome and small RNAome by high-throughput sequencing. In total, we identified 18 structural GA genes and 3924 transporter genes. We identified genes encoding 2374 transporters, 1040 transcription factors (TFs), 262 transcriptional regulators (TRs) and 689 protein kinases (PKs), which were coexpressed with at least one structural gene. We also identified 50,970 alternative splicing (AS) events, in which 17 structural genes exhibited AS. Finally, we also determined that miRNAs potentially targeted 4 structural genes, and 318, 8, and 218 miRNAs potentially regulated 150 TFs, 34 TRs, and 88 PKs, respectively, related to GA. Overall, the results of this study helped to elucidate the gene expression and regulation of GA biosynthesis in G. uralensis, provided a theoretical basis for the synthesis of GA via synthetic biology, and laid a foundation for the cultivation of new varieties of licorice with high GA content.

Isoflavone accumulation and the metabolic gene expression in response to persistent UV-B irradiation in soybean sprouts

This study investigated the effects of persistent ultraviolet B (UV-B) irradiation on isoflavone accumulation in soybean sprouts. Three malonyl isoflavones were increased by UV-B. Malonylgenistin specifically accumulated upon UV-B exposure, whereas the other isoflavones were significantly increased under both dark conditions and UV-B exposure. The results of isoflavone accumulation to UV-B irradiation time were observed as following: acetyl glycitin rapidly increased and then gradually decreased; malonyl daidzin and malonyl genistin were highly accumulated within an intermediate period; genistein and daidzin were gradually maximized; daidzin, glycitin, genistein, and malonyl glycitin did not increase; and glycitin, acetyl daidzin, and acetyl genistin exhibited trace amounts. Transcriptional analysis of isoflavonoid biosynthetic genes demonstrated that most metabolic genes were highly activated in response to UV-B 24 and UV-B 36 treatments. In particular, it was found that GmCHS6, GmCHS7, and GmCHS8 genes among the eight known genes encoding chalcone synthase were specifically related to UV-B response.