γ-Aminobutyric acid (GABA) improves pesticide detoxification in plants

High-nitrogen-induced γ-aminobutyric acid triggers host immunity and pathogen oxidative stress tolerance in tomato and Ralstonia solanacearum interaction

Soil nitrogen (N) significantly influences the interaction between plants and pathogens, yet its impact on host defenses and pathogen strategies via alterations in plant metabolism remains unclear. Through metabolic and genetic studies, this research demonstrates that high-N-input exacerbates tomato bacterial wilt by altering γ-aminobutyric acid (GABA) metabolism of host plants. Under high-N conditions, the nitrate sensor NIN-like protein 7 (SlNLP7) promotes the glutamate decarboxylase 2/4 (SlGAD2/4) transcription and GABA synthesis by directly binding to the promoters of SlGAD2/4. The tomato plants with enhanced GABA levels showed stronger immune responses but remained susceptible to Ralstonia solanacearum. This led to the discovery that GABA produced by the host actually heightens the pathogen's virulence. We identified the R. solanacearum LysR-type transcriptional regulator OxyR protein, which senses host-derived GABA and, upon interaction, triggers a response involving protein dimerization that enhances the pathogen's oxidative stress tolerance by activating the expression of catalase (katE/katGa). These findings reveal GABA's dual role in activating host immunity and enhancing pathogen tolerance to oxidative stress, highlighting the complex relationship between tomato plants and R. solanacearum, influenced by soil N status.

Advances in Plant GABA Research: Biological Functions, Synthesis Mechanisms and Regulatory Pathways

The γ-aminobutyric acid (GABA) is a widely distributed neurotransmitter in living organisms, known for its inhibitory role in animals. GABA exerts calming effects on the mind, lowers blood pressure in animals, and enhances stress resistance during the growth and development of plants. Enhancing GABA content in plants has become a focal point of current research. In plants, GABA is synthesized through two metabolic pathways, the GABA shunt and the polyamine degradation pathway, with the GABA shunt being the primary route. Extensive studies have investigated the regulatory mechanisms governing GABA synthesis. At the genetic level, GABA production and degradation can be modulated by gene overexpression, signaling molecule-induced expression, transcription factor regulation, and RNA interference. Additionally, at the level of transporter proteins, increased activity of GABA transporters and proline transporters enhances the transport of glutamate and GABA. The activity of glutamate decarboxylase, a key enzyme in GABA synthesis, along with various external factors, also influences GABA synthesis. This paper summarizes the biological functions, metabolic pathways, and regulatory mechanisms of GABA, providing a theoretical foundation for further research on GABA in plants.

Deciphering the role of nitric oxide in mitigation of systemic fungicide induced growth inhibition and oxidative damage in wheat

Consento (CON) poses a significant environmental hazard as a systemic fungicide, adversely affecting the health of non-target organisms. Nitric oxide (NO), a signaling molecule, is known to play a crucial role in plant physiology and abiotic stress tolerance. However, whether NO plays any role to enhance fungicide CON tolerance in wheat seedlings is yet unclear. Therefore, we conducted a hydroponic experiment i) to investigate the morpho-physio-biochemical changes of wheat seedlings to fungicide CON stress, and ii) to examine the effects of NO and fungicide CON treatments on oxidative damage, antioxidant system, secondary metabolism and detoxification of systemic fungicide in wheat seedlings. The results showed that CON fungicide at the highest (4X) concentration significantly decreased wheat seedlings fresh weight (46.89%), shoot length (40.26%), root length (56.11%) and total chlorophyll contents (67.44%) in a dose response relationship. Moreover, CON significantly increased hydrogen peroxide, malondialdehyde, catalase, ascorbate peroxidase, glutathione-S-transferase, and peroxidase activities while decreased reduced glutathione (GSH) content. This ultimately impaired the redox homeostasis of cells, leading to oxidative damage in cell membrane. Under fungicide treatment, the addition of NO reduced the fungicide phytotoxicity, with an increase of over 60% in seedling growth. The NO application mitigated CON phytotoxicity as reflected by significantly increased chlorophyll pigments (69.88%) and decreased oxidative damage in wheat leaves. Indeed, the NO alleviatory effect was able to increase the tolerance of seedlings to fungicide, which resulted increments in antioxidant and detoxification enzymes activity, with the enhanced GSH level (78.54%). Interestingly, NO alleviated CON phytotoxicity through the phenylpropanoid pathway by enhancing the activity of secondary metabolism enzymes such as phenylalanine ammonia-lyase (47.28%), polyphenol oxidase (9%), and associated metabolites such as phenolic acids (77.62%), flavonoids (34.33%) in wheat leaves. Our study has provided evidence that NO plays a key role in the metabolism and detoxification of systemic fungicide in wheat through enhanced activity of antioxidants, detoxifications and secondary metabolic enzymes.

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.

Multiomics Explore the Detoxification Mechanism of Nanoselenium and Melatonin on Bensulfuron Methyl in Wheat Plants

Combining nanoselenium (nano-Se) and melatonin (MT) was more effective than treatment alone against abiotic stress. However, their combined application mitigated the toxic effects of bensulfuron methyl, and enhanced wheat growth and metabolism has not been studied. Metabolomics and proteomics revealed that combining nano-Se and MT markedly activated phenylpropanoid biosynthesis pathways, elevating the flavonoid (quercetin by 33.5 and 39.8%) and phenolic acid (vanillic acid by 38.8 and 48.7%) levels in leaves and roots of wheat plants. Interstingly, beneficial rhizosphere bacteria in their combination increased (Oxalobacteraceae, Nocardioidaceae, and Xanthomonadaceae), which positively correlated with the enhancement of soil urease and fluorescein diacetate enzyme activity (27.0 and 26.9%) and the allelopathic substance levels. To summarize, nano-Se and MT mitigate the adverse effects of bensulfuron methyl by facilitating interactions between the phenylpropane metabolism of the plant and the beneficial microbial community. The findings provide a theoretical basis for using nano-Se and MT to remediate herbicide-contaminated soil.

Integrating transcriptome and metabolome to explore the growth-promoting mechanisms of GABA in blueberry plantlets

Tissue culture technology is the main method for the commercial propagation of blueberry plants, but blueberry plantlets grow slowly and have long growth cycles under in vitro propagation, resulting in low propagation efficiency. In addition, the long culturing time can also result in reduced nutrient content in the culture medium, and the accumulation of toxic and harmful substances that can lead to weak growth for the plantlets or browning and vitrification, which ultimately can seriously reduce the quality of the plantlets. Gamma-aminobutyric acid (GABA) is a four-carbon non-protein amino acid that can improve plant resistance to various stresses and promote plant growth, but the effects of its application and mechanism in tissue culture are still unclear. In this study, the effects of GABA on the growth of in vitro blueberry plantlets were analyzed following the treatment of the plantlets with GABA. In addition, the GABA-treated plantlets were also subjected to a comparative transcriptomic and metabolomic analysis. The exogenous application of GABA significantly promoted growth and improved the quality of the blueberry plantlets. In total, 2,626 differentially expressed genes (DEGs) and 377 differentially accumulated metabolites (DAMs) were detected by comparison of the control and GABA-treated plantlets. Most of the DEGs and DAMs were involved in carbohydrate metabolism and biosynthesis of secondary metabolites. The comprehensive analysis results indicated that GABA may promote the growth of blueberry plantlets by promoting carbon metabolism and nitrogen assimilation, as well as increasing the accumulation of secondary metabolites such as flavonoids, steroids and terpenes.

Exogenous tannic acid relieves imidacloprid-induced oxidative stress in tea tree by activating antioxidant responses and the flavonoid biosynthetic pathway

Pesticide stress on plants is receiving increased scrutiny due to its effect on plant secondary metabolism and nutritional quality. Tannic acid (TA) is a natural polyphenolic compound showing excellent antioxidant properties and is involved in alleviating stress. The present study thoroughly investigated the effects and mechanism of exogenous TA on relieving imidacloprid (IMI) stress in tea plants. Our research found that TA(10 mg/L) activated the antioxidant defense system, enhanced the antioxidant ability, reduced the accumulation of ROS and membrane peroxidation, and notably promoted tea plant tolerance to imidacloprid stress. Additionally, TA boosted photosynthetic capacity, strengthened the accumulation of nutrients. regulated detoxification metabolism, and accelerated the digestion and metabolism of imidacloprid in tea plants. Furthermore, TA induced significant changes in 90 important metabolites in tea, targeting 17 metabolic pathways through extensively targeted metabolomics. Specifically, TA activated the flavonoid biosynthetic pathway, resulting in a 1.3- to 3.1-fold increase in the levels of 17 compounds and a 1.5- to 63.8-fold increase in the transcript level of related genes, such as ANR, LAR and CHS in this pathway. As a potential tea health activator, TA alleviates the oxidative damage caused by imidacloprid and improves the yield and quality of tea under pesticide stress.

Review on Pesticide Abiotic Stress over Crop Health and Intervention by Various Biostimulants

Plants are essential for life on earth, and agricultural crops are a primary food source for humans. For the One Health future, crop health is crucial for safe, high-quality agricultural products and the development of future green commodities. However, the overuse of pesticides in modern agriculture raises concerns about their adverse effects on crop resistance and product quality. Recently, biostimulants, including microecological bacteria agents and nanoparticles, have garnered worldwide interest for their ability to sustain plant health and enhance crop resistance. This review analyzed the effects and mechanisms of pesticide stress on crop health. It also investigated the regulation of biostimulants on crop health and the multiomics mechanism, combining research on nanoselenium activating various crop health aspects conducted by the authors' research group. The paper helps readers understand the impact of pesticides on crop health and the positive influence of various biostimulants, especially nanomaterials and small molecules, on crop health.

Detoxification mechanism of herbicide in Polypogon fugax and its influence on rhizosphere enzyme activities

The excessive use of chemical herbicides has resulted in evolution of herbicide-resistant weeds. Cytochrome P450 monooxygenases (P450s) are vital detoxification enzymes for herbicide-resistant weeds. Herein, we confirmed a resistant (R) Polypogon fugax population showing resistance to quizalofop-p-ethyl, acetolactate synthase (ALS)-inhibiting herbicide pyroxsulam, and several other ACCase (acetyl-CoA carboxylase)-inhibiting herbicides. Molecular analysis revealed no target-site gene mutations in the R population. Foliar spraying with malathion clearly reversed the quizalofop-p-ethyl phytotoxicity. Higher level of quizalofop-p-ethyl degradation was confirmed in the R population using HPLC analysis. Subsequently, RNA-Seq transcriptome analysis indicated that the overexpression of CYP89A2 gene appeared to be responsible for reducing quizalofop-p-ethyl phytotoxicity. The molecular docking results supported a metabolic effect of CYP89A2 protein on most herbicides tested. Furthermore, we found that low doses of herbicides stimulated the rhizosphere enzyme activities in P. fugax and the increase of rhizosphere dehydrogenase of R population may be related to its resistance mechanism. In summary, our research has shown that metabolic herbicide resistance mediated by CYP89A2, contributes to quizalofop-p-ethyl resistance in P. fugax.

γ-Aminobutyric acid plays a key role in alleviating Glomerella leaf spot in apples

The fungal disease Glomerella leaf spot (GLS) seriously impacts apple production. As a nonprotein amino acid, γ-aminobutyric acid (GABA) is widely involved in biotic and abiotic stresses. However, it is not clear whether GABA is involved in a plant's response to GLS, nor is its molecular mechanism understood. Here, we found that exogenous GABA could significantly alleviate GLS, reduce lesion lengths, and increase antioxidant capacity. MdGAD1 was identified as a possible key gene for GABA synthesis in apple. Further analysis indicated that MdGAD1 promoted antioxidant capacity to improve apple GLS resistance in transgenic apple calli and leaves. Yeast one-hybrid analysis identified the transcription factor MdWRKY33 upstream of MdGAD1. Electrophoretic mobility shift assay, β-glucuronidase activity, and luciferase activity further supported that MdWRKY33 bound directly to the promoter of MdGAD1. The content of GABA and the transcription level of MdGAD1 in the MdWRKY33 transgenic calli were higher than that of the wild type. When MdWRKY33 transgenic calli and leaves were inoculated with GLS, MdWKRY33 positively regulated resistance to GLS. These results explained the positive regulatory effects of GABA on apple GLS and provided insight into the metabolic regulatory network of GABA.

Exogenous γ-aminobutyric acid (GABA) alleviates nitrogen deficiency by mediating nitrate uptake and assimilation in Andrographis paniculata seedlings

γ-Aminobutyric acid (GABA) plays significant metabolic and signaling roles in plant stress responses. Recent studies have proposed that GABA alleviates plant nitrogen (N) deficient stress; however, the mechanism by which GABA mediates plant N deficiency adaptation remains not yet well understood. Herein we found in a medicinal plant Andrographis paniculata that 5 mmol L^-1 exogenous GABA promoted plant growth under N deficient (1 mmol L^-1 NO₃^-) condition, with remarkably increments in total N and NO₃^- concentrations in plants. GABA increased N assimilation and protein synthesis by up-regulating the activities and expression of N metabolic enzymes. GABA also increased the accumulation of α-ketoglutarate and malate, which could facilitate the assimilation of NO₃^-. Inhibition of NR by Na₂WO₄ counteracted the promoting effects of GABA on plant growth, and the effects of GABA were not affected by L-DABA and 3-MP, the inhibitors of GABA transaminase (GABA-T) and glutamate decarboxylase (GAD), respectively. These results suggested that the nutritional role of GABA was excluded in promoting plant growth under low N condition. The results of ¹⁵N isotopic tracing and NRTs transcription indicated that exogenous GABA could up-regulate NRT2.4 and NRT3.2 to increase plant NO₃^- uptake under N deficient condition. Interestingly, primidone, an inhibitor of GABA receptor, impeded the effects of GABA on plant growth and N accumulation. Thus, our results revealed that exogenous GABA acted as a signal to up-regulate NRTs via its receptor to increase NO₃^- uptake, and subsequently promoted NO₃^- assimilation to alleviate N deficiency in A. paniculata.