Heterologous expression of ZjOMT from Zoysia japonica in Escherichia coli confers aluminum resistance through melatonin production

Therapeutic applications of melatonin in disorders related to the gastrointestinal tract and control of appetite

Most animals have large amounts of the special substance melatonin, which is controlled by the light/dark cycle in the suprachiasmatic nucleus. According to what is now understood, the gastrointestinal tract (GIT) and other areas of the body are sites of melatonin production. According to recent studies, the GIT and adjacent organs depend critically on a massive amount of melatonin. Not unexpectedly, melatonin's many biological properties, such as its antioxidant, anti-inflammatory, pro-apoptotic, anti-proliferative, anti-metastasis, and antiangiogenic properties, have drawn the attention of researchers more and more. Because melatonin is an antioxidant, it produces a lot of secretions in the GIT's mucus and saliva, which shields cells from damage and promotes the development of certain GIT-related disorders. Melatonin's ability to alter cellular behavior in the GIT and other associated organs, such as the liver and pancreas, is another way that it functions. This behavior alters the secretory and metabolic activities of these cells. In this review, we attempted to shed fresh light on the many roles that melatonin plays in the various regions of the gastrointestinal tract by focusing on its activities for the first time.

Biosynthesis of melatonin from L-tryptophan by an engineered microbial cell factory

BACKGROUND

The demand for melatonin is increasing due to its health-promoting bioactivities such as antioxidant and sleep benefits. Although melatonin is present in various organisms, its low content and high extraction cost make it unsustainable. Biosynthesis is a promising alternative method for melatonin production. However, the ectopic production of melatonin in microorganisms is very difficult due to the low or insoluble expression of melatonin synthesis genes. Hence, we aim to explore the biosynthesis of melatonin using Escherichia coli as a cell factory and ways to simultaneously coordinated express genes from different melatonin synthesis pathways.

RESULTS

In this study, the mXcP4H gene from Xanthomonas campestris, as well as the HsAADC, HsAANAT and HIOMT genes from human melatonin synthesis pathway were optimized and introduced into E. coli via a multi-monocistronic vector. The obtained strain BL7992 successfully synthesized 1.13 mg/L melatonin by utilizing L-tryptophan (L-Trp) as a substrate in a shake flask. It was determined that the rate-limiting enzyme for melatonin synthesis is the arylalkylamine N-acetyltransferase, which is encoded by the HsAANAT gene. Targeted metabolomics analysis of L-Trp revealed that the majority of L-Trp flowed to the indole pathway in BL7992, and knockout of the tnaA gene may be beneficial for increasing melatonin production.

CONCLUSIONS

A metabolic engineering approach was adopted and melatonin was successfully synthesized from low-cost L-Trp in E. coli. This study provides a rapid and economical strategy for the synthesis of melatonin.

Harnessing the power of exogenous factors to enhance plant resistance to aluminum toxicity; a critical review

Aluminum (Al) is the most prevalent element in the earth crust and is toxic to plants in acidic soils. However, plants can address Al toxicity through external exclusion (which prevents Al from entering roots) and internal detoxification (which counterbalances the toxic-Al absorbed by roots). Nowadays, certain categories of exogenously added regulatory factors (EARF), such as nutritional elements, organic acids, amino acids, phytohormones, or biochar, etc. play a critical role in reducing the bioavailability/toxicity of Al in plants. Numerous studies suggest that regulating factors against Al toxicity mediate the expression of Al-responsive genes and transcription factors, thereby regulating the secretion of organic acids, alkalizing rhizosphere pH, modulating cell wall (CW) modifications, improving antioxidant defense systems, and promoting the compartmentalization of non-toxic Al within intracellular. This review primarily discusses recent and older published papers to demonstrate the basic concepts of Al phytotoxicity. Furthermore, we provide a comprehensive explanation of the crucial roles of EARF-induced responses against Al toxicity in plants. This information may serve as a foundation for improving plant resistance to Al and enhancing the growth of susceptible species in acidic soils. And this review holds significant theoretical significance for EARF to improve the quality of acidic soils cultivated land, increase crop yield and quality, and ensure food security.

Melatonin: Both a Messenger of Darkness and a Participant in the Cellular Actions of Non-Visible Solar Radiation of Near Infrared Light

Throughout the history of melatonin research, almost exclusive focus has been on nocturnally-generated pineal melatonin production, which accounts for its circadian rhythm in the blood and cerebrospinal fluid; these light/dark melatonin cycles drive the daily and seasonal photoperiodic alterations in organismal physiology. Because pineal melatonin is produced and secreted primarily at night, it is referred to as the chemical expression of darkness. The importance of the other sources of melatonin has almost been ignored. Based on current evidence, there are at least four sources of melatonin in vertebrates that contribute to the whole-body melatonin pool. These include melatonin produced by (1) the pineal gland; (2) extrapineal cells, tissues, and organs; (3) the microbiota of the skin, mouth, nose, digestive tract, and vagina as well as (4) melatonin present in the diet. These multiple sources of melatonin exhibit differentially regulated mechanisms for its synthesis. Visible light striking the retina or an intense physical stimulus can suppress nocturnal pineal melatonin levels; in contrast, there are examples where extrapineal melatonin levels are increased during heavy exercise in daylight, which contains the whole range of NIR radiation. The cumulative impact of all cells producing augmented extrapineal melatonin is sufficient to elevate sweat concentrations, and potentially, if the exposure is sustained, to also increasing the circulating values. The transient increases in sweat and plasma melatonin support the premise that extrapineal melatonin has a production capacity that exceeds by far what can be produced by the pineal gland, and is used to maintain intercellular homeostasis and responds to rapid changes in ROS density. The potential regulatory mechanisms of near infrared light (NIR) on melatonin synthesis are discussed in detail herein. Combined with the discovery of high levels of melanopsin in most fat cells and their response to light further calls into question pineal centric theories. While the regulatory processes related to microbiota-derived melatonin are currently unknown, there does seem to be crosstalk between melatonin derived from the host and that originating from microbiota.

Progress and Challenges in China Turfgrass Abiotic Stress Resistance Research

Turfgrasses are an important vehicle for urban ecology and one of the most important indicators of economy and civilization. The biological characteristics of different turfgrass species affect the productivity and quality of the turf and its potential use in landscapes, slopes, and sports fields. Cultivation and management techniques can assist turfgrasses to meet the challenges of climate change, while the development of molecular breeding will provide a broader platform for the application of turfgrasses. The turfgrass industry of China has developed considerably in the last three decades; however, there is still an objective gap with developed countries. This manuscript reviewed the research progress of turfgrass resistance breeding, analyzed the bottlenecks in the development of turfgrass resistance breeding, and put forward the strategies to cope with the bottlenecks. Our review aims to promote research and utilization of turfgrasses.

Combining protein and metabolic engineering strategies for biosynthesis of melatonin in Escherichia coli

BACKGROUND

Melatonin has attracted substantial attention because of its excellent prospects for both medical applications and crop improvement. The microbial production of melatonin is a safer and more promising alternative to chemical synthesis approaches. Researchers have failed to produce high yields of melatonin in common heterologous hosts due to either the insolubility or low enzyme activity of proteins encoded by gene clusters related to melatonin biosynthesis.

RESULTS

Here, a combinatorial gene pathway for melatonin production was successfully established in Escherichia coli by combining the physostigmine biosynthetic genes from Streptomyces albulus and gene encoding phenylalanine 4-hydroxylase (P4H) from Xanthomonas campestris and caffeic acid 3-O-methyltransferase (COMT) from Oryza sativa. A threefold improvement of melatonin production was achieved by balancing the expression of heterologous proteins and adding 3% glycerol. Further protein engineering and metabolic engineering were conducted to improve the conversion of N-acetylserotonin (NAS) to melatonin. Construction of COMT variant containing C303F and V321T mutations increased the production of melatonin by fivefold. Moreover, the deletion of speD gene increased the supply of S-adenosylmethionine (SAM), an indispensable cofactor of COMT, which doubled the yield of melatonin. In the final engineered strain EcMEL8, the production of NAS and melatonin reached 879.38 ± 71.42 mg/L and 136.17 ± 1.33 mg/L in a shake flask. Finally, in a 2-L bioreactor, EcMEL8 produced 1.06 ± 0.07 g/L NAS and 0.65 ± 0.11 g/L melatonin with tryptophan supplementation.

CONCLUSIONS

This study established a novel combinatorial pathway for melatonin biosynthesis in E. coli and provided alternative strategies for improvement of melatonin production.

Recent Advances in Understanding Mechanisms of Plant Tolerance and Response to Aluminum Toxicity

Aluminum (Al) toxicity is a major environmental stress that inhibits plant growth and development. There has been impressive progress in recent years that has greatly increased our understanding of the nature of Al toxicity and its mechanisms of tolerance. This review describes the transcription factors (TFs) and plant hormones involved in the adaptation to Al stress. In particular, it discusses strategies to confer plant resistance to Al stress, such as transgenic breeding, as well as small molecules and plant growth-promoting rhizobacteria (PGPRs) to alleviate Al toxicity. This paper provides a theoretical basis for the enhancement of plant production in acidic soils.

Role of Melatonin in Plant Tolerance to Soil Stressors: Salinity, pH and Heavy Metals

Melatonin (MT) is a pleiotropic molecule with diverse and numerous actions both in plants and animals. In plants, MT acts as an excellent promotor of tolerance against abiotic stress situations such as drought, cold, heat, salinity, and chemical pollutants. In all these situations, MT has a stimulating effect on plants, fomenting many changes in biochemical processes and stress-related gene expression. Melatonin plays vital roles as an antioxidant and can work as a free radical scavenger to protect plants from oxidative stress by stabilization cell redox status; however, MT can alleviate the toxic oxygen and nitrogen species. Beyond this, MT stimulates the antioxidant enzymes and augments antioxidants, as well as activates the ascorbate–glutathione (AsA–GSH) cycle to scavenge excess reactive oxygen species (ROS). In this review, we examine the recent data on the capacity of MT to alleviate the effects of common abiotic soil stressors, such as salinity, alkalinity, acidity, and the presence of heavy metals, reinforcing the general metabolism of plants and counteracting harmful agents. An exhaustive analysis of the latest advances in this regard is presented, and possible future applications of MT are discussed.

Melatonin Represses Oil and Anthocyanin Accumulation in Seeds

Previous studies have clearly demonstrated that the putative phytohormone melatonin functions directly in many aspects of plant growth and development. In Arabidopsis (Arabidopsis thaliana), the role of melatonin in seed oil and anthocyanin accumulation, and corresponding underlying mechanisms, remain unclear. Here, we found that serotonin N-acetyltransferase1 (SNAT1) and caffeic acid O-methyltransferase (COMT) genes were ubiquitously and highly expressed and essential for melatonin biosynthesis in Arabidopsis developing seeds. We demonstrated that blocking endogenous melatonin biosynthesis by knocking out SNAT1 and/or COMT significantly increased oil and anthocyanin content of mature seeds. In contrast, enhancement of melatonin signaling by exogenous application of melatonin led to a significant decrease in levels of seed oil and anthocyanins. Further gene expression analysis through RNA sequencing and reverse-transcription quantitative PCR demonstrated that the expression of a series of important genes involved in fatty acid and anthocyanin accumulation was significantly altered in snat1-1 comt-1 developing seeds during seed maturation. We also discovered that SNAT1 and COMT significantly regulated the accumulation of both mucilage and proanthocyanidins in mature seeds. These results not only help us understand the function of melatonin and provide valuable insights into the complicated regulatory network controlling oil and anthocyanin accumulation in seeds, but also divulge promising gene targets for improvement of both oil and flavonoids in seeds of oil-producing crops and plants.

Plasma membrane proteomic analysis by TMT-PRM provides insight into mechanisms of aluminum resistance in tamba black soybean roots tips

Aluminum (Al) toxicity in acid soil is a worldwide agricultural problem that inhibits crop growth and productivity. However, the signal pathways associated with Al tolerance in plants remain largely unclear. In this study, tandem mass tag (TMT)-based quantitative proteomic methods were used to identify the differentially expressed plasma membrane (PM) proteins in Tamba black soybean (TBS) root tips under Al stress. Data are available via ProteomeXchange with identifier PXD017160. In addition, parallel reaction monitoring (PRM) was used to verify the protein quantitative data. The results showed that 907 PM proteins were identified in Al-treated plants. Among them, compared to untreated plants, 90 proteins were differentially expressed (DEPs) with 46 up-regulated and 44 down-regulated (fold change > 1.3 or < 0.77, p < 0.05). Functional enrichment based on GO, KEGG and protein domain revealed that the DEPs were associated with membrane trafficking and transporters, modifying cell wall composition, defense response and signal transduction. In conclusion, our results highlight the involvement of GmMATE13, GmMATE75, GmMATE87 and H⁺-ATPase in Al-induced citrate secretion in PM of TBS roots, and ABC transporters and Ca²⁺ have been implicated in internal detoxification and signaling of Al, respectively. Importantly, our data provides six receptor-like protein kinases (RLKs) as candidate proteins for further investigating Al signal transmembrane mechanisms.