GABA in plants: just a metabolite?

ABA and defoliation improve phenolic composition of wine grapes while ABA reduces must free amino acid content and modifies its profile

Grape (Vitis vinifera L.) ripening modulation through exogenous growth regulators and cultural practices has benefits but also downfalls. Abscisic acid (ABA) applications have shown to induce great increases of anthocyanin synthesis and wine color. In turn, severe defoliation may reduce translocation of sugars into berries delaying ripening. The aim of the study was to investigate the interactive effects of exogenous ABA applications to berries and 75 % vine defoliation on grape ripening and nano vinification composition of Tempranillo fruit-bearing cuttings at bunch closure, 46 days after fruit set. At bunch closure the ABA applications started, and plants were partially defoliated (from 12 of untreated to down to 3 leaves) in a factorial design 2 by 2. After 48 h of treatment application, ABA levels in berries increased 10-fold, and concomitantly, the indole acetic acid (IAA) in the berries also increased. Grape anthocyanin content was increased by ABA for berries with the same total soluble solids (TSS), and this was translated to an increase in total polyphenol index (A280) of nano vinifications. Another effect of ABA application was a decrease in free amino acids in the berry must. In addition, the profile of amino acids was shifted to higher proportion of GABA and Glu in detriment of Gln, which implies a GABA shunt activation. Defoliation delayed berry development and induced changes in composition, but only titratable acidity was reduced for berries with the same TSS. Nano vinifications from defoliated plants had higher color attributes (free anthocyanins, flavonols, A360, A620, A420/520 and A620/520). When these two treatments were combined, berries had the highest anthocyanin content while amino acids attributed as aromatic precursors were reduced in must. Results suggest that grape and wine quality attributes such as acidity and color intensity are not necessarily related to ripening speed. The impacts of ABA on berry nitrogen metabolism, deserve further investigation.

Defining seedling stage-specific metabolic adaptations to salinity in landrace Pokkali and cultivated rice IR64

Understanding the biochemical basis of salinity tolerance in naturally evolved landraces cultivated in seawater along coastal India is key to improving elite rice (Oryza sativa L.) genotypes. We conducted a detailed time-course metabolome profiling of two contrasting genotypes: the salt-sensitive IR64 and the salt-tolerant wild rice Pokkali. Principal component analysis revealed distinct metabolic profiles under control and stress, with salinity inducing significant, time-dependent reprogramming. The genotypes showed clear metabolic distinctions between early and prolonged stress phases, highlighting osmotic vs. ionic responses. Pokkali accumulated protective metabolites like proline and glutathione, while IR64 showed elevated tricarboxylic acid cycle intermediates. Differential buildup of phytohormone precursors-azelaic acid, phenylalanine, and tryptophan-suggested their roles in salinity response. Pokkali rapidly restored cellular homeostasis via rapid accumulation of trehalose (4.3×), tryptophan (6.2×), proline (2.2×), glutamate (3.2×), and hydroxyproline (3.3×). Glutamate, a central amino acid metabolism regulator, accumulated prominently in Pokkali, whereas IR64 exhibited higher γ-aminobutyric acid (GABA) (9×) and phenylalanine (4×), indicating cellular stress damage. Exogenous proline application and GABA biosynthesis inhibition confirmed their contrasting roles in stress response and genotype-specific salinity tolerance. Our extensive metabolic dataset and salt-tolerance biomarkers offer valuable insights for developing resilient rice cultivars for saline environments.

γ-Aminobutyric acid modulates terpene biosynthesis through the ATG8a-mediated pathway

Terpenes play crucial roles in plant growth, development, and stress responses. The biosynthesis of terpenes is influenced by abiotic stress factors, such as drought, temperature, or light. However, the molecular network underlying how terpenes are regulated in response to environmental stimuli remains largely unknown. Here, we identified the autophagy protein SgATG8a as a key mediator of GABA-regulated terpene production and drought tolerance in Sindora glabra. SgATG8a, evolutionarily related to the animal GABA receptor-associated protein (GABARAP) subfamily, localizes in both the nucleus and cytoplasm. Exogenous GABA treatment not only increased the expression level of terpene synthase genes (SgTPSs) but also led to enhanced accumulation of six main terpene components in Sindora glabra. In addition, GABA alleviated the photosynthesis damage and enhanced leaf biomass under drought conditions. Consistently, overexpression of SgATG8a in Arabidopsis increased terpene synthase gene (SgTPS) expression, leading to the enhanced production of four major terpenes and improved the tolerance of transgenic plants to drought stress by regulating reactive oxygen species (ROS) scavenging systems. Moreover, the transcription factors SgWRKY13 and SgERF4 were identified as interacting partners of SgATG8a, activating SgTPS3 expression. Lectin receptor-like kinase (LecRK1) is involved in the GABA-mediated pathway by interacting with the SgWRKY13/SgERF4-SgATG8a proteins, and the LecRK1-SgWRKY13/SgERF4 phosphorylation module fine-tunes the transcription of the downstream SgTPS3 gene. Taken together, these findings reveal a novel role for GABA in regulating terpene biosynthesis and drought tolerance, providing insights into the molecular mechanism underlying GABA-mediated terpene production.

Propionic Acid Signalling Modulates Stomatal Opening and Drives Energy Metabolism to Enhance Drought Resistance in Wheat (Triticum aestivum L.)

Drought stress caused by global climate change severely imperils crop productivity and increases environmental deterioration. Wheat (Triticum aestivum L.) is an important worldwide food crop. Drought resistance in wheat encompasses functional gene transcription, metabolism, hormone signalling, and protein modifications. However, the underlying mechanisms by which these regulatory responses are coordinated remain unknown. Herein, we report a drought-resistance network in which wheat triggers a dynamic metabolic flux conversion from propionic acid (PA) to the tricarboxylic acid (TCA) cycle through beta-oxidation of fatty acids and stimulates crosstalk of various hormonal signals. It is also possible that P300/CREB regulates histone acetylation to confer drought resistance in wheat. Exogenous PA drives the TCA cycle and glycolysis and promotes stomatal closure through hormones crosstalk. From Aegilops tauschii Cosson (the diploid progenitor of common wheat) to wheat, this novel PA function serves as a survival strategy against environmental changes, and was validated in wheat field experiments. Our results highlight a new survival strategy that triggers the comprehensive and systemic effects of functional genes, metabolomics, hormone signalling, and protein modification on drought resistance to provide novel insights into improving the agroecological environment.

Integrative analysis of transcriptome and metabolome reveals molecular mechanisms of dynamic change of storage substances during dehydration and drying process in peanuts (Arachis hypogaea L.)

Various substances in seeds occurred many transformations during the drying process, which is key to long-term storage, but the mechanism is unclear. In this study, seeds of the peanut (Arachis hypogaea L.) variety "Silihong" were selected as the experimental materials. Transcriptome and metabolome analyses of the peanut kernels at day 0 (S0d), day 1 (S1d), day 3 (S3d), day 5 (S5d), and day 7 (S7d) of drying were performed to search for the genes that controlled the storage compounds. A total of 165 differentially expressed metabolites (DAMs) and 15,010 differentially expressed genes (DEGs) in the five stages of seed drying were identified. S3d was the key period during which the content of most of the metabolites changed significantly. The contents of most amino acids(87%) and their derivatives decreased significantly, and most of the lipids(68%), sugars(67%) and flavonoids(87%) accumulated to their peak at S3d. A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the DEGs were primarily enriched in four aspects, including amino acid biosynthesis and metabolism, lipid biosynthesis and metabolism, sucrose and starch metabolism, and flavonoid biosynthesis. Crucial genes that potentially regulate the storage substances were identified, including PAL, FAD2, SUS, LOX, and PFK. Overall, this study provides valuable insights into the molecular regulation of storage compounds in peanut seeds and may help to assess edible peanuts that have enhanced nutritional and economic values.

Exogenous γ-aminobutyric acid mitigates drought-induced impairments in Thymus daenensis Celak by regulating physiological traits, antioxidant enzymes and essential oil constituents

Drought stress is one of the most significant environmental challenges, leading to various changes in the physiological processes of plants. Gamma-aminobutyric acid (GABA) is an essential biomolecule that plays a critical role in regulating growth and stress signaling. The current study aims to investigate the effects of GABA on antioxidant enzyme activity and the essential oil composition of Thymus daenensis Celak under different levels of water deficit stress. We examined three different levels of soil moisture (90%, 60%, and 30% of field capacity) alongside three GABA foliar treatments (0 mM, 25 mM, 50 mM, and 75 mM). The results showed that applying 25 mM GABA under severe stress conditions (at 30% of field capacity) significantly increased the activity levels of ascorbate peroxidase, guaiacol peroxidase, and superoxide dismutase enzymes by 95.5%, 78.45%, and 38%, respectively. Additionally, applying GABA at various levels during different water stress treatments led to significant improvements in the chlorophyll, carotenoid, and proline content in leaf tissues. Specifically, the application of 25, 50, and 75 mM GABA enhanced the proline content in T. daenensis by 53.9%, 26.8%, and 11%, respectively, compared to the control group (non-application of GABA). Essential oil analysis revealed the following ranges: thymol was present in the range of 38.07-45.18%, cymene in the range of 5.13-14.10%, caryophyllene in the range of 4.3-23.01%, and cineole in the range of 2-4.15%. The highest amount of thymol was obtained in the absence of GABA at 30% field capacity, while the greatest amount of cymene was also observed without GABA at 90% field capacity. Additionally, the maximum concentration of caryophyllene was found when 50 mM GABA was applied at 90% field capacity, and the maximum level of cineole was detected with 75 mM GABA at 90% field capacity. In conclusion, the exogenous application of GABA demonstrated favorable efficacy, particularly at a concentration of 25 mM. This treatment resulted in a significant enhancement of the plant's defense mechanisms and created favorable conditions that notably impacted the quality of the essential oil produced by T. daenensis.

Impact of NPK fertilization on the metabolomic profile and nutritional quality of Portulaca oleracea L. using nuclear magnetic resonance analysis

Purslane is a plant with high nutritional content that is mainly produced in the central part of Mexico. The nutritional content of purslane depends on various factors such as climatic and soil conditions, phenology, and fertilization. This article describes the 1H NMR metabolomics profiling of purslane in relation to fertilization at two harvest stages: C1 and C2 (27 and 42 days after emergence). During the first stage, 30 metabolites were identified including free amino acids and organic acids. In the second stage, 35 metabolites were identified, with higher concentrations of carbohydrates and nucleosides being observed. Multivariate analysis revealed differences in the metabolome between harvests C1 and C2. Notably, higher abundances of fructose, galactose, α-glucose, β-glucose, myo-inositol, sucrose, and nucleosides such as adenosine and uridine were observed in C2. Discriminant analysis further demonstrated variations in metabolites among plants treated with different doses of nitrogen, phosphorus, and potassium at the two harvest stages studied. Plants treated with the highest dose of nitrogen (300 kg N ha-1) exhibited maximum levels of metabolites, while low nitrogen-treated plants (0 kg N ha-1) displayed an inverse trend. Amino acids such as alanine, asparagine, GABA, glutamine, histidine, isoleucine, leucine, phenylalanine, proline, threonine, tyrosine, and valine were found to be the most abundant in plants treated with N300. In contrast, untreated plants showed higher levels of citric acid and malic acid. Our results highlight the effectiveness of 1H NMR as a methodology for understanding the role of fertilization and nutrient content in optimizing the crop production of purslane.

Aluminum resistance in plants: A critical review focusing on STOP1

Aluminum (Al) toxicity poses a significant challenge for plant production on acidic soils, which constitute approximately 30% of the world's ice-free land. To combat Al toxicity, plants have evolved both external and internal detoxification mechanisms. The zinc-finger transcription factor STOP1 (SENSITIVE TO PROTON RHIZOTOXICITY 1) plays a critical and conserved role in Al resistance by inducing genes involved in both external exclusion and internal detoxification mechanisms. Recent studies have uncovered multiple layers of post-transcriptional regulation of STOP1 and have elucidated mechanisms by which plants sense Al and activate signaling cascades that regulate STOP1 function. This review offers a comprehensive overview of the mechanisms through which STOP1 and its homologs confer Al resistance in plants, with a particular focus on Arabidopsis thaliana and rice. Additionally, we discuss recent advances and future perspectives in understanding the post-transcriptional regulation of STOP1, as well as the Al sensing and signaling pathways upstream of STOP1.

Exogenous ALA applied on different plant parts promotes tomato fruit quality and GABA synthesis

Introduction

Tomato fruit are rich in γ-aminobutyric acid (GABA), which lowers blood pressure and improves sleep. An increase in GABA content is important for enhancing the nutritional quality of tomato fruit.

Methods

To investigate the effects of 5-aminolevulinic acid (ALA) on fruit quality and GABA synthesis in greenhouse tomatoes, the tomato cultivar (Solanum lycopersicum cv. '184') was used as an experimental material. During the fruit-setting period, root drenching with 0, 10, and 50 mg·L-1 ALA, foliar spraying with 0, 50, and 100 mg·L-1 ALA, and fruit surface spraying with 0, 100, and 200 mg·L-1 ALA were applied. The study investigated the application of exogenous ALA to different parts of the plant to determine the optimal ALA concentrations for each application site (10 mg·L-1 for root application, 100 mg·L-1 for foliar application, and 100 mg·L-1 for fruit surface application). Using the selected optimal ALA concentrations, tomatoes were used to study the effects of exogenous ALA application at different sites on fruit quality and GABA synthesis of greenhouse tomatoes.

Results and discussion

The results demonstrated that exogenous ALA application to different parts of greenhouse-grown tomato plants substantially increased single-fruit weight by 42.37%-76.24%, soluble sugar content by 78.51%-94.52%, soluble solids by 9.09%-41.71%, soluble protein by 82.71%-241.05%, and ascorbic acid content by 1.31%-5.06% in mature tomatoes. And it reduced the organic acid content of the fruit by 12.81%-33.61%. Moreover, ALA applied at different parts of plants substantially enhanced the free amino acid content by 11.22%-16.50%, among them, umami amino acid content by 7.26%-20.13%. Besides, GABA content in mature tomato fruits was increased by 214.58%-433.32 across the different application parts. Exogenous ALA application at different sites regulates the activity of glutamate acid decarboxylase (GAD) and increases the content of glutamate for GABA synthesis pathway during tomato fruit development, thereby affecting the GABA content. In summary, exogenous ALA applied at different parts of tomato plants regulates the metabolism of amino acids and enhances the biosynthesis of GABA, which promotes the nutrient quality of the fruit.

Modulation of polar auxin transport identifies the molecular determinants of source-sink carbon relationships and sink strength in poplar

Source-to-sink carbon (C) allocation driven by the sink strength, i.e., the ability of a sink organ to import C, plays a central role in tissue growth and biomass productivity. However, molecular drivers of sink strength have not been thoroughly characterized in trees. Auxin, as a major plant phytohormone, regulates the mobilization of photoassimilates in source tissues and elevates the translocation of carbohydrates toward sink organs, including roots. In this study, we used an 'auxin-stimulated carbon sink' approach to understand the molecular processes involved in the long-distance source-sink C allocation in poplar. Poplar cuttings were foliar sprayed with polar auxin transport modulators, including auxin enhancers (AE) (i.e., IBA and IAA) and auxin inhibitor (AI) (i.e., NPA), followed by a comprehensive analysis of leaf, stem and root tissues using biomass evaluation, phenotyping, C isotope labeling, metabolomics and transcriptomics approaches. Auxin modulators altered root dry weight and branching pattern, and AE increased photosynthetically fixed C allocation from leaf to root tissues. The transcriptome analysis identified highly expressed genes in root tissue under AE condition including transcripts encoding polygalacturonase and β-amylase that could increase the sink size and activity. Metabolic analyses showed a shift in overall metabolism including an altered relative abundance levels of galactinol, and an opposite trend in citrate levels in root tissue under AE and AI conditions. In conclusion, we postulate a model suggesting that the source-sink C relationships in poplar could be fueled by mobile sugar alcohols, starch metabolism-derived sugars and TCA-cycle intermediates as key molecular drivers of sink strength.

Increasing nitrogen use efficiency in agronomically important plants: An insight into gene characteristics on a genome-wide scale in barley

Nitrogen (N) is a critical element for plant growth and development. Hence, improving nitrogen use efficiency (NUE) is vital for reducing costs and the environmental impact of agricultural practices. Understanding the genetic control of N metabolism is crucial to improve NUE, especially in agronomically important plants, such as barley (Hordeum vulgare). Using bioinformatics and functional genomics tools, we identified and characterized sixteen barley nitrogen metabolism-related gene families (HvNMGs) on a genome-wide scale, analysing gene features and evolution. These genes, located on six of seven barley chromosomes, are highly conserved in plants (including barley, rice, and Arabidopsis), as shown by phylogenetic analysis. We further explored the evolutionary relationships of NMGs through a genome-to-genome synteny analysis, which indicated higher conservation of NMGs between barley and other monocots, suggesting that these orthologous pairs predate species divergence. Protein-protein interaction analyses revealed that all of the HvNMGs show interactions, mainly with each other. The H. vulgare miRNAs target sites (hvu-miR) prediction identified six hvu-miR in 4 HvNMGs (HvGABA-T2, HvALDH10-1, HvALDH10-2 and HvARGAH), indicating their potential involvement in stress responses. The expression patterns analysis of publicly available RNA-seq data revealed that HvNMGs are expressed in all developmental stages of barley, and they respond to different stress conditions, indicating their essential role in plant growth, development and stress response. The organ-specific expression analysis, conducted using qPCR, of HvNMGs revealed higher expression of HvNiR and HvNRs in the leaf and significantly higher expression of HvARGAH and HvALDH10 in the spike than in other tissues, showing that some of the genes may be particularly important in some tissues than others. This data provides a foundation for understanding HvNMG function and could be used to improve barley yield by enhancing NUE - an important goal for both crop productivity and environmental sustainability.

Genome-wide identification and expression analysis of the GAD family reveal their involved in embryogenesis and hormones responses in Dimocarpus longan Lour

Glutamate decarboxylase (GAD) is involved in GABA metabolism and plays an essential regulatory role in plant growth, abiotic stresses, and hormone response. This study investigated the expression mechanism of the GAD family during longan early somatic embryogenesis (SE) and identified 6 GAD genes based on the longan genome. Homology analysis indicated that DlGAD genes had a closer relationship with dicotyledonous plants. The analysis of cis-acting elements in the promoter region suggests that the GAD genes were associated with various stress responses and hormones. RNA sequencing (RNA-Seq) and the qRT-PCR data indicated that most DlGAD genes were highly expressed in the incomplete compact pro-embryogenic cultures (ICpEC) and upregulated in longan embryogenic callus (EC) after treatments with 2,4-D, high temperature (35 °C), IAA, and ABA. Moreover, the RNA-Seq analysis also revealed that DlGADs exhibit different expression patterns in various tissues and organs. The subcellular localization results showed that DlGAD5 was localized in the cytoplasm, suggesting that it played a role in the cytoplasm. Transient overexpression of DlGAD5 enhanced the expression levels of DlGADs and increased the activity of glutamate decarboxylase in longan embryogenic callus (EC), while the content of glutamic acid decreased. Thus, the DlGAD gene can play an important role in the early somatic embryogenesis of longan by responding to hormones such as IAA and ABA. DlGAD5 can affect the growth and development of longan by stimulating the expression of the DlGAD gene family, thereby increasing the GAD activity in the early SE of longan, participating in hormone synthesis and signaling pathways.

Role of Neurotransmitters (Biomediators) in Plant Responses to Stress

Plants possess a complex signaling system that enables them to sense and adapt to various environmental stressors, including abiotic factors like extreme temperatures, drought, salinity, and toxic heavy metals. While the roles of hormones and signaling molecules in plant stress responses are well established, the involvement of neurotransmitters-traditionally linked to animal nervous systems-in plant stress physiology is a relatively underexplored area. Recent findings indicate that neurotransmitters such as gamma-aminobutyric acid, glutamate, serotonin, and dopamine play crucial roles in several physiological processes within plants. They regulate ion channels, adjust stomatal movements, modulate the production of reactive oxygen species, and influence gene expression. Evidence suggests that these neurotransmitters enhance antioxidant defense mechanisms and regulate stress-responsive pathways vital for plant stress tolerance. Additionally, under stressful conditions, neurotransmitters have been shown to impact plant growth, development, and reproductive activities. This review aims to illuminate the emerging understanding of neurotransmitters as key biomediators in plant responses to abiotic stress.

γ-Aminobutyric acid mediated by MdCBF3- MdGAD1 mitigates low temperature damage in apple

Low temperatures can seriously affect apple yield and can also cause chilling injury to apple fruit. γ-aminobutyric acid (GABA) plays an important role in improving plant stress resistance. Some studies have reported that GABA can improve cold resistance in plants, only through exogenous treatment; however, the molecular mechanism of its resistance to low temperature is still unknown. This result suggested that exogenous GABA treatment of both apple seedlings and fruit could improve the resistance of apple to low temperatures. MdGAD1, a key gene involved in GABA synthesis, was overexpressed in tomato plants and apple callus to improve their cold tolerance. Both yeast one-hybrid and luciferase assay showed that MdCBF3 could bind to the MdGAD1 promoter to activate its expression and promote GABA synthesis. These results revealed a molecular mechanism utilizing the MdCBF3-MdGAD1 regulatory module that can enhance cold resistance by increasing endogenous GABA synthesis in apple.

CsGAT1 modulates GABA metabolism and positively regulates cold resistance in tea plants

Tea plants (Camellia sinensis) are perennial woody economic crops that are often exposed to a range of abiotic stresses, especially low temperatures, during development. γ-Aminobutyric acid (GABA) is a nonprotein amino acid widely distributed in plants that is involved in the low-temperature response of plants. Here, we found that CsGAT1 was upregulated in tea leaves subjected to low-temperature stress according to transcriptomic data. Heterologous expression of CsGAT1 in a yeast mutant revealed that it specifically transports GABA. Subcellular localization assays revealed that CsGAT1 was located on the plasma membrane. The organizational localization experiments revealed that the expression level of CsGAT1 was relatively high in the old leaves and roots and relatively low in the flowers. Testing of different cold-tolerant tea germplasm resources revealed that cultivars with relatively low cold resistance presented relatively low CsGAT1 expression and GABA levels. In addition, Arabidopsis plants overexpressing CsGAT1 presented high levels of GABA accumulation and significant low-temperature resistance. In summary, we believe that CsGAT1 regulates the ability of tea plants to resist low-temperature stress by changing the concentration of GABA inside and outside the cell. This study provides a theoretical basis for breeding new tea cultivars with strong resistance to low-temperature stress during production.

Enhanced photorespiratory and TCA pathways by elevated CO2 to manage ammonium nutrition in tomato leaves

Plants grown under exclusive ammonium (NH4+) nutrition have high carbon (C) demand to sustain proper nitrogen (N) assimilation and energy required for plant growth, generally impaired when compared to nitrate (NO3-) nutrition. Thereby, the increment of the atmospheric carbon dioxide (CO2) concentration, in the context of climate change, will potentially allow plants to better face ammonium nutrition. In this work, tomato (Solanum lycopersicum L.) plants were grown under ammonium or nitrate nutrition in conditions of ambient (aCO2, 400 ppm) or elevated CO2 (eCO2, 800 ppm) atmosphere. Elevated CO2 increased photosynthesis rate and tomato shoot growth regardless of the N source. In the case of NH4+-fed leaves the positive effect of elevated CO2 occurred despite of the high tissue NH4+ accumulation. Under eCO2 ammonium nutrition triggered, among others, the modulation of genes related to C provision pathways (including carbonic anhydrase and glyoxylate cycle), antioxidant response and cell membranes protection. The enhanced photosynthate production at eCO2 facilitated C skeleton provision through the TCA cycle and anaplerotic pathways to promote amino acid synthesis. Moreover, photorespiratory activity was stimulated by eCO2 and contributed to yield serine as additional sink for NH4+ excess. Overall, these changes denote a connection between the respiratory and the photorespiratory pathways linked to ammonium nutrition. This metabolic strategy may allow crops to grow efficiently using ammonium as fertilizer in a future climate change scenario, while mitigating N losses.

Relationship between the GABA Pathway and Signaling of Other Regulatory Molecules

GABA (gamma-aminobutyric acid) is an amino acid whose numerous regulatory functions have been identified in animal organisms. More and more research indicate that in plants, this molecule is also involved in controlling basic growth and development processes. As recent studies have shown, GABA plays an essential role in triggering plant resistance to unfavorable environmental factors, which is particularly important in the era of changing climate. The main sources of GABA in plant cells are glutamic acid, converted in the GABA shunt pathway, and polyamines subjected to oxidative degradation. The action of GABA is often related to the activity of other messengers, including phytohormones, polyamines, NO, H2O2, or melatonin. GABA can function as an upstream or downstream element in the signaling pathways of other regulators, acting synergistically or antagonistically with them to control cellular processes. Understanding the role of GABA and its interactions with other signaling molecules may be important for developing crop varieties with characteristics that enable adaptation to a changing environment.

Progresses in biosynthesis pathway, regulation mechanism and potential application of 2-acetyl-1-pyrroline in fragrant rice

The formation of rice aroma is a complex process that is influenced by genetic and environmental factors. More than 500 fragrance compounds have been documented in fragrant rice, among which 2-AP dominates the aroma of rice. This paper introduced the identification of OsBadh2 in the biosynthesis of 2-AP in rice. Then, non-enzymatic and enzymatic pathways of the 2-AP biosynthesis have been comprehensively investigated. In detail, 2-AP biosynthesis-associated enzyme, such as OsBADH2, OsP5CS, OsGAD, OsGAPDH, OsProDH, OsOAT, OsODC and OsDAO, have been summarized, while MG and fatty acids are also implicated in modulating the biosynthesis of 2-AP by providing the acetyl groups. Moreover, extensive collections of traditional fragrant rice varieties have been collated, together with the OsBadh2 haplotypes of 312 fragrant rice germplasm in China. And finally, genetic engineering of OsBadh2 and other genes in the 2-AP biosynthesis to develop fragrant rice are discussed.

Pterostilbene-loaded PLGA nanoparticles alter phenylpropanoid and oxylipin metabolism in Solanum lycopersicum L. leaves

Due to the fast-changing global climate, conventional agricultural systems have to deal with more unpredictable and harsh environmental conditions leading to compromise food production. The application of phytonanotechnology can ensure safer and more sustainable crop production, allowing the target-specific delivery of bioactive molecules with great and partially explored positive effects for agriculture, such as an increase in crop production and plant pathogen reduction. In this study, the effect of free pterostilbene (PTB) and poly(lactic-co-glycolic) acid (PLGA) nanoparticles (NPs) loaded with pterostilbene was investigated on Solanum lycopersicum L. metabolism. An untargeted NMR-based metabolomics approach was used to examine primary and secondary metabolism whereas a targeted HPLC-MS/MS-based approach was used to explore the impact on defense response subjected to anti-oxidant effect of PTB, such as free fatty acids, oxylipins and them impact on hormone biosynthesis, in particular salicylic and jasmonic acid. In tomato leaves after treatment with PTB and PLGA NPs loaded with PTB (NPs + PTB), both NPs + PTB and free PTB treatments increased GABA levels in tomato leaves. In addition, a decrease of quercetin-3-glucoside associated with the increase in caffeic acid was observed suggesting a shift in secondary metabolism towards the biosynthesis of phenylpropanoids and other phenolic compounds. An increase of behenic acid (C22:0) and a remodulation of oxylipin metabolism deriving from the linoleic acid (i.e. 9-HpODE, 13-HpODE and 9-oxo-ODE) and linolenic acid (9-HOTrE and 9-oxoOTrE) after treatment with PLGA NPs and PLGA NPs + PTB were also found as a part of mechanisms of plant redox modulation. To the best of our knowledge, this is the first study showing the role of PLGA nanoparticles loaded with pterostilbene in modulating leaf metabolome and physiology in terms of secondary metabolites, fatty acids, oxylipins and hormones. In perspective, PLGA NPs loaded with PTB could be used to reshape the metabolic profile to allow plant to react more quickly to stresses.

MdSINA2-MdNAC104 Module Regulates Apple Alkaline Resistance by Affecting γ-Aminobutyric Acid Synthesis and Transport

Soil alkalization is an adverse factor limiting plant growth and yield. As a signaling molecule and secondary metabolite, γ-aminobutyric acid (GABA) responds rapidly to alkaline stress and enhances the alkaline resistance of plants. However, the molecular mechanisms by which the GABA pathway adapts to alkaline stress remain unclear. In this study, a transcription factor, MdNAC104 is identified, from the transcriptome of the alkaline-stressed roots of apple, which effectively reduces GABA levels and negatively regulates alkaline resistance. Nevertheless, applying exogenous GABA compensates the negative regulatory mechanism of overexpressed MdNAC104 on alkaline resistance. Further research confirms that MdNAC104 repressed the GABA biosynthetic gene MdGAD1/3 and the GABA transporter gene MdALMT13 by binding to their promoters. Here, MdGAD1/3 actively regulates alkaline resistance by increasing GABA synthesis, while MdALMT13 promotes GABA accumulation and efflux in roots, resulting in an improved resistance to alkaline stress. This subsequent assays reveal that MdSINA2 interacts with MdNAC104 and positively regulates root GABA content and alkaline resistance by ubiquitinating and degrading MdNAC104 via the 26S proteasome pathway. Thus, the study reveals the regulation of alkaline resistance and GABA homeostasis via the MdSINA2-MdNAC104-MdGAD1/3/MdALMT13 module in apple. These findings provide novel insight into the molecular mechanisms of alkaline resistance in plants.

Regulatory trends in engineering bioactive-phytocompounds

The secondary plant metabolites are of enormous importance because of their extensive medicinal, nutraceutical, and industrial applications. In plants, these secondary metabolites are often found in extremely small amounts, therefore, following the discovery of any prospective metabolite, the main constraining element is the ability to generate enough material for use in both industrial and therapeutic settings. In order to satisfy the rising demand for value-added metabolites, researchers prefer to use different molecular approaches for scalable and sustainable production of these phytocompounds. Here, we discuss the emerging regulatory trends in engineering these bioactive-phytocompounds and provide recommendation on successful employment of these state-of-the-art technologies for translation of these academic researches into novel process and products.

Non-Targeted Metabolomics Analysis of γ-Aminobutyric Acid Enrichment in Germinated Maize Induced by Pulsed Light

Pulsed light is an emerging technique in plant physiology recognized for its ability to enhance germination and accumulate γ-aminobutyric acid in maize. Pulsed light involves exposing plants to brief, high-intensity bursts of light, which can enhance photosynthesis, improve growth, and increase resistance to environmental stresses. Despite its promising potential, the specific metabolic changes leading to γ-aminobutyric acid enrichment in maize induced by pulsed light are not fully understood. This study addresses this gap by quantifying key nutrients and γ-aminobutyric acid-related compounds during maize germination and investigating the underlying mechanisms using non-targeted metabolomics. Our findings indicate that pulsed light significantly promotes maize germination and accelerates the hydrolysis of proteins, sugars, and lipids. This acceleration is likely due to the activation of enzymes involved in these metabolic pathways. Additionally, pulsed light markedly increases the content of glutamic acid and the activity of glutamate decarboxylase, which are crucial for γ-aminobutyric acid synthesis. Moreover, pulsed light significantly reduces the activity of γ-aminobutyric transaminase, thereby inhibiting γ-aminobutyric acid decomposition and resulting in a substantial increase in γ-aminobutyric acid content, with a 27.20% increase observed in germinated maize following pulsed light treatment. Metabolomic analysis further revealed enrichment of metabolic pathways associated with γ-aminobutyric acid, including amino acid metabolism, carbohydrate metabolism, plant hormone signal transduction, energy metabolism, pyrimidine metabolism, and ABC transporters. In conclusion, pulsed light is a robust and efficient method for producing sprouted maize with a high γ-aminobutyric acid content. This technique provides a novel approach for developing sprouted cereal foods with enhanced nutritional profiles, leveraging the physiological benefits of γ-aminobutyric acid, which include stress alleviation and potential health benefits for humans.

Gamma-aminobutyric acid interactions with phytohormones and its role in modulating abiotic and biotic stress in plants

Gamma-aminobutyric acid (GABA), a ubiquitous non-protein 4-carbon amino acid present in both prokaryotic and eukaryotic organisms. It is conventionally recognized as a neurotransmitter in mammals and plays a crucial role in plants. The context of this review centers on the impact of GABA in mitigating abiotic stresses induced by climate change, such as drought, salinity, heat, and heavy metal exposure. Beyond its neurotransmitter role, GABA emerges as a key player in diverse metabolic processes, safeguarding plants against multifaceted abiotic as well as biotic challenges. This comprehensive exploration delves into the GABA biosynthetic pathway, its transport mechanisms, and its intricate interplay with various abiotic stresses. The discussion extends to the nuanced relationship between GABA and phytohormones during abiotic stress acclimation, offering insights into the strategic development of mitigation strategies against these stresses. The delineation of GABA's crosstalk with phytohormones underscores its pivotal role in formulating crucial strategies for abiotic stress alleviation in plants.

β-Aminobutyric acid promotes stress tolerance, physiological adjustments, as well as broad epigenetic changes at DNA and RNA nucleobases in field elms (Ulmus minor)

BACKGROUND

β-Aminobutyric acid (BABA) has been successfully used to prime stress resistance in numerous plant species; however, its effectiveness in forest trees has been poorly explored thus far. This study aimed to investigate the influence of BABA on morphological, physiological, and epigenetic parameters in field elms under various growth conditions. Epigenetic changes were assessed in both DNA and RNA through the use of reversed-phase ultra-performance liquid chromatography (UPLC) coupled with sensitive mass spectrometry.

RESULTS

The presented results confirm the influence of BABA on the development, physiology, and stress tolerance in field elms. However, the most important findings are related to the broad epigenetic changes promoted by this amino acid, which involve both DNA and RNA. Our findings confirm, for the first time, that BABA influences not only well-known epigenetic markers in plants, such as 5-methylcytosine, but also several other non-canonical nucleobases, such as 5-hydroxymethyluracil, 5-formylcytosine, 5-hydroxymethylcytosine, N6-methyladenine, uracil (in DNA) and thymine (in RNA). The significant effect on the levels of N6-methyladenine, the main bacterial epigenetic marker, is particularly noteworthy. In this case, the question arises as to whether this effect is due to epigenetic changes in the microbiome, the plant genome, or both.

CONCLUSIONS

The plant phenotype is the result of complex interactions between the plant's DNA, the microbiome, and the environment. We propose that different types of epigenetic changes in the plant and microbiome may play important roles in the largely unknown memory process that enables plants to adapt faster to changing environmental conditions.

Effect of Palmitoylethanolamide Compared to a Placebo on the Gut Microbiome and Biochemistry in an Overweight Adult Population: A Randomised, Placebo Controlled, Double-Blind Study

This study investigates the effects of palmitoylethanolamide (PEA) on the gut microbiome of overweight adults. Fifty-eight participants (twenty males, thirty-eight females) aged 18-65 years with a BMI range of 30-40 kg/m2 were recruited. Participants were randomised to receive PEA (n = 36) or a placebo (n = 22) for 12 weeks. Microbiota composition, richness, diversity, and metabolic functions, faecal short chain fatty acids and calprotectin, pathology markers, and health-related questionnaires were analysed throughout the 12 weeks of supplementation. PEA supplementation significantly reduced triglyceride levels and IL-2 concentrations. No significant differences were found in the overall microbiota composition between the groups, and microbiota richness and diversity remained consistent for both groups. Functional analysis demonstrated no differences in functional richness and diversity, but specific pathways were modified. PEA supplementation resulted in a decrease in the abundance of pathways related to aromatic compound degradation, NAD interconversion, and L-glutamate degradation, while pathways associated with molybdopterin biosynthesis and O-antigen building blocks exhibited increased abundance. Increased production of O-antigen results in smooth LPS associated with reduced pathogenic stealth and persistence. PEA supplementation may influence specific microbial species, metabolic pathways, and reduce serum triglyceride and IL-2 concentration, shedding light on the intricate relationship between PEA, the microbiome, and host health.

Lipidomic and Metabolomic Analyses Reveal Changes of Lipid and Metabolite Profiles in Rapeseed during Nitrogen Deficiency

Nitrogen is one of the most essential macronutrients for plant growth and its availability in soil is vital for agricultural sustainability and productivity. However, excessive nitrogen application could reduce the nitrogen use efficiency and produce environmental pollution. Here, we systematically determined the response in lipidome and metabolome in rapeseed during nitrogen starvation. Plant growth was severely retarded during nitrogen deficiency, while the levels of most amino acids were significantly decreased. The level of monogalactosyldiacyglycerol (MGDG) in leaves and roots was significantly decreased, while the level of digalactosyldiacylglycerol (DGDG) was significantly decreased in roots, resulting in a significant reduction of the MGDG/DGDG ratio during nitrogen starvation. Meanwhile, the levels of sulfoquinovosyl diacylglycerol, phosphatidylglycerol and glucuronosyl diacylglycerol were reduced to varying extents. Moreover, the levels of metabolites in the tricarboxylic acid cycle, Calvin cycle and energy metabolism were changed during nitrogen deficiency. These findings show that nitrogen deprivation alters the membrane lipid metabolism and carbon metabolism, and our study provides valuable information to further understand the response of rapeseed to nitrogen deficiency at the metabolism level.

γ-Aminobutyric acid (GABA) priming alleviates acid-aluminum toxicity to roots of creeping bentgrass via enhancements in antioxidant defense and organic metabolites remodeling

MAIN CONCLUSION

γ-Aminobutyric acid alleviates acid-aluminum toxicity to roots associated with enhanced antioxidant metabolism as well as accumulation and transportation of citric and malic acids. Aluminum (Al) toxicity has become the main limiting factor for crop growth and development in acidic soils and is further being aggravated worldwide due to continuous industrial pollution. The current study was designed to examine effects of GABA priming on alleviating acid-Al toxicity in terms of root growth, antioxidant defense, citrate and malate metabolisms, and extensive metabolites remodeling in roots under acidic conditions. Thirty-seven-day-old creeping bentgrass (Agrostis stolonifera) plants were used as test materials. Roots priming with or without 0.5 mM GABA for 3 days were cultivated in standard nutrient solution for 15 days as control or subjected to nutrient solution containing 5 mM AlCl3·6H2O for 15 days as acid-Al stress treatment. Roots were sampled for determinations of root characteristics, physiological and biochemical parameters, and metabolomics. GABA priming significantly alleviated acid-Al-induced root growth inhibition and oxidative damage, despite it promoted the accumulation of Al in roots. Analysis of metabolomics showed that GABA priming significantly increased accumulations of organic acids, amino acids, carbohydrates, and other metabolites in roots under acid-Al stress. In addition, GABA priming also significantly up-regulated key genes related to accumulation and transportation of malic and citric acids in roots under acid-Al stress. GABA-regulated metabolites participated in tricarboxylic acid cycle, GABA shunt, antioxidant defense system, and lipid metabolism, which played positive roles in reactive oxygen species scavenging, energy conversion, osmotic adjustment, and Al ion chelation in roots.

Gamma amino butyric acid (GABA) application modulated the morpho-physiological and yield traits of fragrant rice under well-watered and drought conditions

BACKGROUND

Changing climate is causing erratic rainfall and prolonged drought periods, thus posing serious threats to crop productivity. Owing to severity of drought events, it is imperative to take proactive measures to enhance the resilience of drought sensitive crops like rice. Therefore, the present study was carried out to improve the drought stress tolerance in rice through gamma amino butyric acid (GABA) application.

METHODS

The experiment was included four GABA concentrations i.e., 0 mM as control, 1 mM, 1.5 mM, and 2 mM, two water levels i.e., 100% and 50% field capacity (referred as FC100 for well-watered and FC50 for drought conditions, respectively), and two fragrant rice cultivars i.e., Super Basmati and Basmati-515.

RESULTS

The findings unveiled a comprehensive improvement in various parameters with GABA application in fragrant rice under both well-watered (FC100) and water-limited (FC50) conditions, compared to the control. Specifically, GABA induced enhancements were observed in plant height, root length, fresh weight, dry weight, total soluble protein content, and total free amino acid content across both cultivars. Moreover, GABA application significantly improved peroxidase (POD) and catalase (CAT) enzyme activities, alongside elevating anthocyanin levels, while concurrently reducing H2O2 contents in both FC100 and FC50 treatments. Furthermore, the positive impact of GABA extended to morphological traits, with notable increases in panicle length, total tillers and productive tillers per hill, branch and grain numbers per panicle, and 1000-grain weight for Super Basmati and Basmati 515 cultivars under both water regimes, compared to Ck. Similarly, the grain yield increased by 31.01% and 27.32% under FC100 and 36.85% and 27.71% under FC50 in Super Basmati and Basmati-515, respectively, in response to GABA application, compared to Ck. Additionally, principal component analysis (PCA) revealed significant variances attributed to Dim1 and Dim2, with 86.1% and 4.0% of the variance, respectively, across three bi-plots encompassing rice cultivars, water levels, and GABA treatments. Notably, all tested indices, except for H2O2 and non-productive tillers per hill, exhibited positive correlations amongst themselves and with rice yield, further emphasizing the beneficial effects of GABA application on fragrant rice under well-watered and drought conditions.

CONCLUSIONS

GABA significantly improved fragrant rice performance under both well-watered (FC100) and water-limited (FC50) conditions. Moreover, integrating GABA application into rice cultivation practices could not only improve the crop resilience to drought stress but also potentially benefiting the future food and nutritional security globally. However, however; further research is needed to understand the cellular and molecular mechanisms of the functionality of GABA in fragrant rice, particularly under drought conditions.

Exogenous GABA Enhances Copper Stress Resilience in Rice Plants via Antioxidant Defense Mechanisms, Gene Regulation, Mineral Uptake, and Copper Homeostasis

The importance of gamma-aminobutyric acid (GABA) in plants has been highlighted due to its critical role in mitigating metal toxicity, specifically countering the inhibitory effects of copper stress on rice plants. This study involved pre-treating rice plants with 1 mM GABA for one week, followed by exposure to varying concentrations of copper at 50 μM, 100 μM, and 200 μM. Under copper stress, particularly at 100 μM and 200 μM, plant height, biomass, chlorophyll content, relative water content, mineral content, and antioxidant activity decreased significantly compared to control conditions. However, GABA treatment significantly alleviated the adverse effects of copper stress. It increased plant height by 13%, 18%, and 32%; plant biomass by 28%, 52%, and 60%; chlorophyll content by 12%, 30%, and 24%; and relative water content by 10%, 24%, and 26% in comparison to the C50, C100, and C200 treatments. Furthermore, GABA treatment effectively reduced electrolyte leakage by 11%, 34%, and 39%, and the concentration of reactive oxygen species, such as malondialdehyde (MDA), by 9%, 22%, and 27%, hydrogen peroxide (H2O2) by 12%, 38%, and 30%, and superoxide anion content by 8%, 33, and 39% in comparison to C50, C100, and C200 treatments. Additionally, GABA supplementation led to elevated levels of glutathione by 69% and 80%, superoxide dismutase by 22% and 125%, ascorbate peroxidase by 12% and 125%, and catalase by 75% and 100% in the C100+G and C200+G groups as compared to the C100 and C200 treatments. Similarly, GABA application upregulated the expression of GABA shunt pathway-related genes, including gamma-aminobutyric transaminase (OsGABA-T) by 38% and 80% and succinic semialdehyde dehydrogenase (OsSSADH) by 60% and 94% in the C100+G and C200+G groups, respectively, as compared to the C100 and C200 treatments. Conversely, the expression of gamma-aminobutyric acid dehydrogenase (OsGAD) was downregulated. GABA application reduced the absorption of Cu2+ by 54% and 47% in C100+G and C200+G groups as compared to C100, and C200 treatments. Moreover, GABA treatment enhanced the uptake of Ca2+ by 26% and 82%, Mg2+ by 12% and 67%, and K+ by 28% and 128% in the C100+G and C200+G groups as compared to C100, and C200 treatments. These findings underscore the pivotal role of GABA-induced enhancements in various physiological and molecular processes, such as plant growth, chlorophyll content, water content, antioxidant capacity, gene regulation, mineral uptake, and copper sequestration, in enhancing plant tolerance to copper stress. Such mechanistic insights offer promising implications for the advancement of safe and sustainable food production practices.

Emerging Trends in Non-Protein Amino Acids as Potential Priming Agents: Implications for Stress Management Strategies and Unveiling Their Regulatory Functions

Plants endure the repercussions of environmental stress. As the advancement of global climate change continues, it is increasingly crucial to protect against abiotic and biotic stress effects. Some naturally occurring plant compounds can be used effectively to protect the plants. By externally applying priming compounds, plants can be prompted to trigger their defensive mechanisms, resulting in improved immune system effectiveness. This review article examines the possibilities of utilizing exogenous alpha-, beta-, and gamma-aminobutyric acid (AABA, BABA, and GABA), which are non-protein amino acids (NPAAs) that are produced naturally in plants during instances of stress. The article additionally presents a concise overview of the studies' discoveries on this topic, assesses the particular fields in which they might be implemented, and proposes new avenues for future investigation.

Role of plant neurotransmitters in salt stress: A critical review

Neurotransmitters are naturally found in many plants, but the molecular processes that govern their actions still need to be better understood. Acetylcholine, γ-Aminobutyric acid, histamine, melatonin, serotonin, and glutamate are the most common neurotransmitters in animals, and they all play a part in the development and information processing. It is worth noting that all these chemicals have been found in plants. Although much emphasis has been placed on understanding how neurotransmitters regulate mood and behaviour in humans, little is known about how they regulate plant growth and development. In this article, the information was reviewed and updated considering current thinking on neurotransmitter signaling in plants' metabolism, growth, development, salt tolerance, and the associated avenues for underlying research. The goal of this study is to advance neurotransmitter signaling research in plant biology, especially in the area of salt stress physiology.

Monitoring Changes in Biochemical and Metabolite Profiles in Garlic Cloves during Storage

Storage is important for the garlic cloves industry because it is critical to enabling a year-round supply. This study aimed to investigate the changes in biochemical and metabolic profiles in garlic cloves in terms of different temperatures and cultivars during storage using nontargeted and targeted metabolomics. The results showed that the storage temperatures and times were important factors affecting the composition and metabolite content of garlic cloves. In detail, the metabolic profiling of garlic cloves changed significantly at 22 °C, which was mainly related to sprouting. Furthermore, γ-glutamyl peptide was converted into the corresponding flavor precursors or free amino acids, leading to the fluctuation in the amount of nutrients in garlic cloves. In contrast, the quality of garlic cloves remained stable for 290 days at 0 °C though metabolism still occurred, which indicated that the slight chemical changes did not impact the quality significantly and low temperature could prolong their dormancy.

Metabolite-mediated adaptation of crops to drought and the acquisition of tolerance

Drought is one of the major and growing threats to agriculture productivity and food security. Metabolites are involved in the regulation of plant responses to various environmental stresses, including drought stress. The complex drought tolerance can be ascribed to several simple metabolic traits. These traits could then be used for detecting the genetic architecture of drought tolerance. Plant metabolomes show dynamic differences when drought occurs during different developmental stages or upon different levels of drought stress. Here, we reviewed the major and most recent findings regarding the metabolite-mediated plant drought response. Recent progress in the development of drought-tolerant agents is also discussed. We provide an updated schematic overview of metabolome-driven solutions for increasing crop drought tolerance and thereby addressing an impending agricultural challenge.

The potassium transporter TaNHX2 interacts with TaGAD1 to promote drought tolerance via modulating stomatal aperture in wheat

Drought is a major global challenge in agriculture that decreases crop production. γ-Aminobutyric acid (GABA) interfaces with drought stress in plants; however, a mechanistic understanding of the interaction between GABA accumulation and drought response remains to be established. Here we showed the potassium/proton exchanger TaNHX2 functions as a positive regulator in drought resistance in wheat by mediating cross-talk between the stomatal aperture and GABA accumulation. TaNHX2 interacted with glutamate decarboxylase TaGAD1, a key enzyme that synthesizes GABA from glutamate. Furthermore, TaNHX2 targeted the C-terminal auto-inhibitory domain of TaGAD1, enhanced its activity, and promoted GABA accumulation under drought stress. Consistent with this, the tanhx2 and tagad1 mutants showed reduced drought tolerance, and transgenic wheat with enhanced TaNHX2 expression had a yield advantage under water deficit without growth penalty. These results shed light on the plant stomatal movement mechanism under drought stress and the TaNHX2-TaGAD1 module may be harnessed for amelioration of negative environmental effects in wheat as well as other crops.

Integrated metabolomics and transcriptomics analysis reveals γ-aminobutyric acid enhances the ozone tolerance of wheat by accumulation of flavonoids

Wheat is susceptible to atmospheric ozone (O3) pollution, thus the increasing O3 is a serious threat to wheat production. γ-aminobutyric acid (GABA) is found to play key roles in the tolerance of plants to stress. However, few studies elaborated the function of GABA in response of wheat to O3. Here, we incorporated metabolome and transcriptome data to provide a more comprehensive insight on the role of GABA in enhancing the O3-tolerance of wheat. In our study, there were 31, 23, and 32 differentially accumulated flavonoids in the carbon-filtered air with GABA, elevated O3 with or without GABA treatments compared to the carbon-filtered air treatment, respectively. Elevated O3 triggered the accumulation of dihydroflavone, flavonols, and flavanols. Exogenous GABA enhanced dihydroflavone and dihydroflavonol, and also altered the expression of genes encoding some key enzymes in the flavonoid synthesis pathway. Additionally, GABA stimulated proline accumulation and antioxidant enzyme activities under elevated O3, resulting in the less accumulation of H2O2 and malondialdehyde. Consequently, GABA alleviated the grain yield loss from 19.6% to 9.6% induced by elevated O3. Our study provided comprehensive insight into the role of GABA in the alleviating the detrimental effects of elevated O3 on wheat, and a new avenue to mitigate O3 damage to the productivity of crops.

"Deciphering the enigmatic role of gamma-aminobutyric acid (GABA) in plants: Synthesis, transport, regulation, signaling, and biological roles in interaction with growth regulators and abiotic stresses."

Gamma-aminobutyric acid (GABA) is an amino acid with a four-carbon structure, widely distributed in various organisms. It exists as a zwitterion, possessing both positive and negative charges, enabling it to interact with other molecules and participate in numerous physiological processes. GABA is widely distributed in various plant cell compartments such as cytoplasm mitochondria, vacuoles, peroxisomes, and plastids. GABA is primarily synthesized from glutamate using glutamate decarboxylase and participates in the GABA shunt within mitochondria, regulating carbon and nitrogen metabolism in plants The transport of GABA is regulated by several intracellular and intercellular transporters such as aluminium-activated malate transporters (ALMTs), GABA transporters (GATs), bidirectional amino acid transporters (BATs), and cationic amino acid transporters (CATs). GABA plays a vital role in cellular transformations, gene expression, cell wall modifications, and signal transduction in plants. Recent research has unveiled the role of GABA as a signaling molecule in plants, regulating stomatal movement and pollen tube growth. This review provides insights into multifaceted impact of GABA on physiological and biochemical traits in plants, including cellular communication, pH regulation, Krebs cycle circumvention, and carbon and nitrogen equilibrium. The review highlights involvement of GABA in improving the antioxidant defense system of plants, mitigating levels of reactive oxygen species under normal and stressed conditions. Moreover, the interplay of GABA with other plant growth regulators (PGRs) have also been explored.

Truncation of the calmodulin binding domain in rice glutamate decarboxylase 4 (OsGAD4) leads to accumulation of γ-aminobutyric acid and confers abiotic stress tolerance in rice seedlings

GABA (Gamma-aminobutyric acid) is a non-protein amino acid widely known as major inhibitory neurotransmitter. It is synthesized from glutamate via the enzyme glutamate decarboxylase (GAD). GAD is ubiquitous in all organisms, but only plant GAD has ability to bind Ca2+/calmodulin (CaM). This kind of binding suppresses the auto-inhibition of Ca2+/calmodulin binding domain (CaMBD) when the active site of GAD is unfolded resulting in stimulated GAD activity. OsGAD4 is one of the five GAD genes in rice genome. It was confirmed that OsGAD4 has ability to bind to Ca2+/CaM. Moreover, it exhibits strongest expression against several stress conditions among the five OsGAD genes. In this study, CRISPR/Cas9-mediated genome editing was performed to trim the coding region of CaMBD from the OsGAD4 gene, to remove its autoinhibitory function. DNA sequence analysis of the genome edited rice plants revealed the truncation of CaMBD (216 bp). Genome edited line (#14-1) produced 11.26 mg GABA/100 g grain, which is almost nine-fold in comparison to wild type. Short deletion in the coding region for CaMBD yielded in mutant (#14-6) with lower GABA content than wild type counterpart. Abiotic stresses like salinity, flooding and drought significantly enhanced GABA accumulation in #14-1 at various time points compared to wild-type and #14-6 under the same stress conditions. Moreover, upregulated mRNA expression in vegetative tissues seems correlated with the stress-responsiveness of OsGAD4 when exposed to the above-mentioned stresses. Stress tolerance of OsGAD4 genome edited lines was evidenced by the higher survival rate indicating the gene may induce tolerance against abiotic stresses in rice. This is the first report on abiotic stress tolerance in rice modulated by endogenous GABA.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01460-1.

Exogenous γ-aminobutyric acid and Bacillus pumilus reduce arsenic uptake and toxicity in rice

In this study, the addition of γ-aminobutyric acid (GABA), Bacillus pumilus, or both, was found to enhance rice growth and yield while significantly decreasing arsenic (As) accumulation in Oryza sativa rice tissues. GABA emerged as a regulator of iron (Fe) homeostasis, acting as a signaling modulator that influenced phytosiderophore secretions in the plant. Meanwhile, B. pumilus directly increased Fe levels through siderophore production, promoting the development of Fe-rich rice plants. Subsequently, Fe competed with As uptake at the root surface, leading to decreased As levels and translocation to the grains. Furthermore, the addition of GABA and B. pumilus optimized rice indole-3 acetic acid (IAA) contents, thereby adjusting cell metabolite balance under As stress. This adjustment results in low malondialdehyde (MDA) contents in the leaves and roots during the early and late vegetative phases, effectively reducing oxidative stress. When added to As-contaminated soil, GABA and B. pumilus effectively maintained endogenous GABA levels and exhibited low ROS generation, similar to normal soil. Concurrently, GABA and B. pumilus significantly downregulated the activity of OsLsi1, OsLsi2, and OsABCC1 in roots, reducing As uptake through roots, shoots, and grains, respectively. These findings suggest that GABA and B. pumilus additions impede As translocation through grains, ultimately enhancing rice productivity under As stress.

Identification and function analysis of GABA branch three gene families in the cotton related to abiotic stresses

γ -aminobutyric acid (GABA) is closely related to the growth, development and stress resistance of plants. Combined with the previous study of GABA to promote the cotton against abiotic stresses, the characteristics and expression patterns of GABA branch gene family laid the foundation for further explaining its role in cotton stress mechanism. Members of GAD, GAB-T and SSADH (three gene families of GABA branch) were identified from the Gossypium hirsutum, Gossypium barbadense, Gossypium arboreum and Gossypium raimondii genome. The GABA branch genes were 10 GAD genes, 4 GABA-T genes and 2 SSADH genes. The promoter sequences of genes mainly contains response-related elements such as light, hormone and environment.Phylogenetic analysis shows that GAD indicating that even in the same species, the homologous sequences in the family. The GABA-T gene of each cotton genus was in sum the family had gene loss in the process of dicotyledon evolution. SSADH families Gossypium hirsutum, Gossypium barbadense, Gossypium arboreum and Gossypium raimondii were closely related to the dicot plants.GABA gene is involved in the regulation of salt stress and high temperature in Gossypium hirsutum.GABA attenuated part of the abiotic stress damage by increasing leaf protective enzyme activity and reducing reactive oxygen species production.This lays the foundation for a thorough analysis of the mechanism of GABA in cotton stress resistance.

The complexed crystal structure of dihydropyrimidinase reveals a potential interactive link with the neurotransmitter γ-aminobutyric acid (GABA)

Dihydropyrimidinase (DHPase) plays a crucial role in pyrimidine degradation, showcasing a broad substrate specificity that extends beyond pyrimidine catabolism, hinting at additional roles for this ancient enzyme. In this study, we solved the crystal structure of Pseudomonas aeruginosa DHPase (PaDHPase) complexed with the neurotransmitter γ-aminobutyric acid (GABA) at a resolution of 1.97 Å (PDB ID 8WQ9). Our structural analysis revealed two GABA binding sites in each monomer of PaDHPase. Interactions between PaDHPase and GABA molecules, involving residues within a contact distance of <4 Å, were examined. In silico analyses via PISA and PLIP software revealed hydrogen bonds formed between the side chain of Cys318 and GABA 1, as well as the main chains of Ser333, Ile335, and Asn337 with GABA 2. Comparative structural analysis between GABA-bound and unbound states unveiled significant conformational changes at the active site, particularly within dynamic loop I, supporting the conclusion that PaDHPase binds GABA through the loop-out mechanism. Building upon this molecular evidence, we discuss and propose a working model. The study expands the GABA interactome by identifying DHPase as a novel GABA-interacting protein and provides structural insight into the interaction between a dimetal center in the protein's active site and GABA. Further investigations are warranted to explore potential interactions of GABA with other DHPase-like proteins and to understand whether DHPase may have additional regulatory and physiological roles in the cell, extending beyond pyrimidine catabolism.

Effect of drought stress on wheat (Triticum durum) growth and metabolism: insight from GABA shunt, reactive oxygen species and dehydrin genes expression

Activation of γ-aminobutyric acid (GABA) shunt pathway and upregulation of dehydrins are involved in metabolic homeostasis and protective mechanisms against drought stress. Seed germination percentage, seedling growth, levels of GABA, alanine, glutamate, malondialdehyde (MDA), and the expression of glutamate decarboxylase (GAD ) and dehydrin (dhn and wcor ) genes were examined in post-germination and seedlings of four durum wheat (Triticum durum L.) cultivars in response to water holding capacity levels (80%, 50%, and 20%). Data showed a significant decrease in seed germination percentage, seedling length, fresh and dry weight, and water content as water holding capacity level was decreased. Levels of GABA, alanine, glutamate, and MDA were significantly increased with a negative correlation in post-germination and seedling stages as water holding capacity level was decreased. Prolonged exposure to drought stress increased the GAD expression that activated GABA shunt pathway especially at seedlings growth stage to maintain carbon/nitrogen balance, amino acids and carbohydrates metabolism, and plant growth regulation under drought stress. The mRNA transcripts of dhn and wcor significantly increased as water availability decreased in all wheat cultivars during the post-germination stage presumably to enhance plant tolerance to drought stress by cell membrane protection, cryoprotection of enzymes, and prevention of reactive oxygen species (ROS) accumulation. This study showed that the four durum wheat cultivars responded differently to drought stress especially during the seedling growth stage which might be connected with ROS scavenging systems and the activation of antioxidant enzymes that were associated with activation of GABA shunt pathway and the production of GABA in durum seedlings.

Heat tolerance of a tropical-subtropical rainforest tree species Polyscias elegans: time-dependent dynamic responses of physiological thermostability and biochemistry

Heat stress interrupts physiological thermostability and triggers biochemical responses that are essential for plant survival. However, there is limited knowledge on the speed plants adjust to heat in hours and days, and which adjustments are crucial. Tropical-subtropical rainforest tree species (Polyscias elegans) were heated at 40°C for 5 d, before returning to 25°C for 13 d of recovery. Leaf heat tolerance was quantified using the temperature at which minimal chl a fluorescence sharply rose (Tcrit ). Tcrit , metabolites, heat shock protein (HSP) abundance and membrane lipid fatty acid (FA) composition were quantified. Tcrit increased by 4°C (48-52°C) within 2 h of 40°C exposure, along with rapid accumulation of metabolites and HSPs. By contrast, it took > 2 d for FA composition to change. At least 2 d were required for Tcrit , HSP90, HSP70 and FAs to return to prestress levels. The results highlight the multi-faceted response of P. elegans to heat stress, and how this response varies over the scale of hours to days, culminating in an increased level of photosynthetic heat tolerance. These responses are important for survival of plants when confronted with heat waves amidst ongoing global climate change.

The metabolic profiles of Eugenia astringens and E. uniflora (Myrtaceae) sensitive seeds affect desiccation

Myrtaceae species are abundant in tropical Atlantic rainforests, but 41% of the 5500 species of this family are of extreme conservation concern. Eugenia astringens and E. uniflora are native Brazilian Myrtaceae species that occur in the same habitats and produce desiccation-sensitive (DS) seeds. We hypothesized that their seed desiccation-sensitivity degree is associated with specific metabolic signatures. To test it, we analyzed the germination and metabolic profiles of fresh and desiccated seeds. The water content (WC) at which at least half of the seeds survived desiccation was lower in E. astringens (0.17 g H2 O g-1 DW) than in E. uniflora (0.41 g H2 O g-1 DW). We identified 103 annotated metabolites from 3261 peaks in both species, which differed in their relative contents between E. astringens and E. uniflora seeds. The main differences in seed metabolic profiles include several protective molecules in the group of carbohydrates and organic acids and amino acid contents. The relative contents of monosaccharides and disaccharides, malic and quinic acids, amino acids and saturated fatty acids may have taken part in the distinct DS behaviour of E. astringens and E. uniflora seeds. Our study provides evidence of the relationship between desiccation sensitivity, seed viability and metabolic profile of tropical seeds by comparing two closely related Eugenia species with different DS degrees.

Biosynthesis of Gamma-Aminobutyric Acid (GABA) by Lactiplantibacillus plantarum in Fermented Food Production

In recent decades, given the important role of gamma-aminobutyric acid (GABA) in human health, scientists have paid great attention to the enrichment of this chemical compound in food using various methods, including microbial fermentation. Moreover, GABA or GABA-rich products have been successfully commercialized as food additives or functional dietary supplements. Several microorganisms can produce GABA, including bacteria, fungi, and yeasts. Among GABA-producing microorganisms, lactic acid bacteria (LAB) are commonly used in the production of many fermented foods. Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) is a LAB species that has a long history of natural occurrence and safe use in a wide variety of fermented foods and beverages. Within this species, some strains possess not only good pro-technological properties but also the ability to produce various bioactive compounds, including GABA. The present review aims, after a preliminary excursus on the function and biosynthesis of GABA, to provide an overview of the current uses of microorganisms and, in particular, of L. plantarum in the production of GABA, with a detailed focus on fermented foods. The results of the studies reported in this review highlight that the selection of new probiotic strains of L. plantarum with the ability to synthesize GABA may offer concrete opportunities for the design of new functional foods.

Enhancing crop resilience by harnessing the synergistic effects of biostimulants against abiotic stress

Plants experience constant exposed to diverse abiotic stresses throughout their growth and development stages. Given the burgeoning world population, abiotic stresses pose significant challenges to food and nutritional security. These stresses are complex and influenced by both genetic networks and environmental factors, often resulting in significant crop losses, which can reach as high as fifty percent. To mitigate the effects of abiotic stresses on crops, various strategies rooted in crop improvement and genomics are being explored. In particular, the utilization of biostimulants, including bio-based compounds derived from plants and beneficial microbes, has garnered considerable attention. Biostimulants offer the potential to reduce reliance on artificial chemical agents while enhancing nutritional efficiency and promoting plant growth under abiotic stress condition. Commonly used biostimulants, which are friendly to ecology and human health, encompass inorganic substances (e.g., zinc oxide and silicon) and natural substances (e.g., seaweed extracts, humic substances, chitosan, exudates, and microbes). Notably, prioritizing environmentally friendly biostimulants is crucial to prevent issues such as soil degradation, air and water pollution. In recent years, several studies have explored the biological role of biostimulants in plant production, focusing particularly on their mechanisms of effectiveness in horticulture. In this context, we conducted a comprehensive review of the existing scientific literature to analyze the current status and future research directions concerning the use of various biostimulants, such as plant-based zinc oxide, silicon, selenium and aminobutyric acid, seaweed extracts, humic acids, and chitosan for enhancing abiotic stress tolerance in crop plants. Furthermore, we correlated the molecular modifications induced by these biostimulants with different physiological pathways and assessed their impact on plant performance in response to abiotic stresses, which can provide valuable insights.

P. Reddy G, Li Z, Chen F, Sun Y, Zhao Z. The nitrogen-dependent GABA pathway of tomato provides resistance to a globally invasive fruit fly

Introduction

The primary metabolism of plants, which is mediated by nitrogen, is closely related to the defense response to insect herbivores.

Methods

An experimental system was established to examine how nitrogen mediated tomato resistance to an insect herbivore, the oriental fruit fly (Bactrocera dorsalis). All tomatoes were randomly assigned to the suitable nitrogen (control, CK) treatment, nitrogen excess (NE) treatment and nitrogen deficiency (ND) treatment.

Results

We found that nitrogen excess significantly increased the aboveground biomass of tomato and increased the pupal biomass of B. dorsalis. Metabolome analysis showed that nitrogen excess promoted the biosynthesis of amino acids in healthy fruits, including γ-aminobutyric acid (GABA), arginine and asparagine. GABA was not a differential metabolite induced by injury by B. dorsalis under nitrogen excess, but it was significantly induced in infested fruits at appropriate nitrogen levels. GABA supplementation not only increased the aboveground biomass of plants but also improved the defensive response of tomato.

Discussion

The biosynthesis of GABA in tomato is a resistance response to feeding by B. dorsalis in appropriate nitrogen, whereas nitrogen excess facilitates the pupal weight of B. dorsalis by inhibiting synthesis of the GABA pathway. This study concluded that excess nitrogen inhibits tomato defenses in plant-insect interactions by inhibiting GABA synthesis, answering some unresolved questions about the nitrogen-dependent GABA resistance pathway to herbivores.

Gamma-Aminobutyric Acid Supplementation Boosts the Phytohormonal Profile in 'Candidatus Liberibacter asiaticus'-Infected Citrus

The devastating citrus disease, Huanglongbing (HLB), is associated with 'Candidatus Liberibacter sp.' and transmitted by citrus psyllids. Unfortunately, HLB has no known sustainable cure yet. Herein, we proposed γ-aminobutyric acid (GABA) as a potential eco-friendly therapeutic solution to HLB. Herein, we used GC/MS-based targeted metabolomics combined with gene expression to investigate the role of GABA in citrus response against HLB and to better understand its relationship(s) with different phytohormones. GABA supplementation via root drench boosts the accumulation of endogenous GABA in the leaves of both healthy and 'Ca. L. asiaticus'-infected trees. GABA accumulation benefits the activation of a multi-layered defensive system via modulating the phytohormone levels and regulating the expression of their biosynthesis genes and some pathogenesis-related proteins (PRs) in both healthy and 'Ca. L. asiaticus'-infected plants. Moreover, our findings showed that GABA application stimulates auxin biosynthesis in 'Ca. L. asiaticus'-infected plants via the activation of the indole-3-pyruvate (I3PA) pathway, not via the tryptamine (TAM)-dependent pathway, to enhance the growth of HLB-affected trees. Likewise, GABA accumulation was associated with the upregulation of SA biosynthesis genes, particularly the PAL-dependent route, resulting in higher SA levels that activated CsPR1, CsPR2, CsPR5, and CsWRKY70, which are prominent to activation of the SA-mediated pathway. Additionally, higher GABA levels were correlated with an enhanced JA profile and linked with both CsPR3 and CsPR4, which activates the JA-mediated pathway. Collectively, our findings suggest that exogenous GABA application might be a promising alternative and eco-friendly strategy that helps citrus trees battle HLB.

Detection of locally adapted genomic regions in wild rice (Oryza rufipogon) using environmental association analysis

Oryza rufipogon is the wild progenitor of cultivated rice Oryza sativa and exhibits high levels of genetic diversity across its distribution, making it a useful resource for the identification of abiotic stress-tolerant varieties and genes that could limit future climate-changed-induced yield losses. To investigate local adaptation in O. rufipogon, we analyzed single nucleotide polymorphism (SNP) data from a panel of 286 samples located across a diverse range of climates. Environmental association analysis (EAA), a genome-wide association study (GWAS)-based method, was used and revealed 15 regions of the genome significantly associated with various climate factors. Genes within these environmentally associated regions have putative functions in abiotic stress response, phytohormone signaling, and the control of flowering time. This provides an insight into potential local adaptation in O. rufipogon and reveals possible locally adaptive genes that may provide opportunities for breeding novel rice varieties with climate change-resilient phenotypes.

Heat hardening enhances metabolite-driven thermoprotection in the Mediterranean mussel Mytilus galloprovincialis

Introduction: Temperature affects organisms' metabolism and ecological performance. Owing to climate change, sea warming constituting a severe source of environmental stress for marine organisms, since it increases at alarming rates. Rapid warming can exceed resilience of marine organisms leading to fitness loss and mortality. However, organisms can improve their thermal tolerance when briefly exposed to sublethal thermal stress (heat hardening), thus generating heat tolerant phenotypes. Methods: We investigated the "stress memory" effect caused by heat hardening on M. galloprovincialis metabolite profile of in order to identify the underlying biochemical mechanisms, which enhance mussels' thermal tolerance. Results: The heat hardening led to accumulation of amino acids (e.g., leucine, isoleucine and valine), including osmolytes and cytoprotective agents with antioxidant and anti-inflammatory properties that can contribute to thermal protection of the mussels. Moreover, proteolysis was inhibited and protein turnover regulated by the heat hardening. Heat stress alters the metabolic profile of heat stressed mussels, benefiting the heat-hardened individuals in increasing their heat tolerance compared to the non-heat-hardened ones. Discussion: These findings provide new insights in the metabolic mechanisms that may reinforce mussels' tolerance against thermal stress providing both natural protection and potential manipulative tools (e.g., in aquaculture) against the devastating climate change effects on marine organisms.

Metabolic pathways engineering for drought or/and heat tolerance in cereals

Drought (D) and heat (H) are the two major abiotic stresses hindering cereal crop growth and productivity, either singly or in combination (D/+H), by imposing various negative impacts on plant physiological and biochemical processes. Consequently, this decreases overall cereal crop production and impacts global food availability and human nutrition. To achieve global food and nutrition security vis-a-vis global climate change, deployment of new strategies for enhancing crop D/+H stress tolerance and higher nutritive value in cereals is imperative. This depends on first gaining a mechanistic understanding of the mechanisms underlying D/+H stress response. Meanwhile, functional genomics has revealed several stress-related genes that have been successfully used in target-gene approach to generate stress-tolerant cultivars and sustain crop productivity over the past decades. However, the fast-changing climate, coupled with the complexity and multigenic nature of D/+H tolerance suggest that single-gene/trait targeting may not suffice in improving such traits. Hence, in this review-cum-perspective, we advance that targeted multiple-gene or metabolic pathway manipulation could represent the most effective approach for improving D/+H stress tolerance. First, we highlight the impact of D/+H stress on cereal crops, and the elaborate plant physiological and molecular responses. We then discuss how key primary metabolism- and secondary metabolism-related metabolic pathways, including carbon metabolism, starch metabolism, phenylpropanoid biosynthesis, γ-aminobutyric acid (GABA) biosynthesis, and phytohormone biosynthesis and signaling can be modified using modern molecular biotechnology approaches such as CRISPR-Cas9 system and synthetic biology (Synbio) to enhance D/+H tolerance in cereal crops. Understandably, several bottlenecks hinder metabolic pathway modification, including those related to feedback regulation, gene functional annotation, complex crosstalk between pathways, and metabolomics data and spatiotemporal gene expressions analyses. Nonetheless, recent advances in molecular biotechnology, genome-editing, single-cell metabolomics, and data annotation and analysis approaches, when integrated, offer unprecedented opportunities for pathway engineering for enhancing crop D/+H stress tolerance and improved yield. Especially, Synbio-based strategies will accelerate the development of climate resilient and nutrient-dense cereals, critical for achieving global food security and combating malnutrition.