What signals the glyoxalase pathway in plants?

Molecular characterization of a phytomelatonin receptor and its overexpression as a 'one-stop' solution to nullify the toxic effects of hazardous inorganic agro-pollutants

Inorganic toxicants like arsenic, copper, lead, nickel and fluoride are notorious agro-pollutants, impeding plant-productivity due to high bioaccumulation. Consumption of such contaminated plant-parts causes irreversible health hazards. We identified a G-protein coupled receptor, serving as melatonin receptor (MelR) in Nicotiana tabacum (NtMelR), that relayed downstream-signaling after binding melatonin, a potent growth regulator and antioxidant. Using inhibitors against G-protein-α and NADPH oxidase (NOX), and by supplementing epidermal strips with exogenous melatonin and H2O2, we established that NtMelR acted upstream of reactive oxygen species (ROS) production in guard cells. Transgenic lines of N. benthamiana overexpressing NtMelR maintained constitutive melatonin-signaling via MelR, leading to efficient stomatal closure for preventing desiccation during oxidative stress. Melatonin biosynthesis was stimulated in the transgenic lines, exposed to different agro-pollutant stress, providing a steady-abundance of ligand for NtMelR binding and activating the defence machinery, comprising of enzymatic-antioxidants like superoxide dismutase, catalase, peroxidases and glyoxalases. Due to increased antioxidant capacity, the transgenics exhibited less molecular injuries (electrolyte leakage, methylglyoxal accumulation and NOX activity), generated less ROS and bioaccumulated significantly lower levels of toxicants. Unlike the wild-type counterparts, the transgenics maintained high relative water content, photosynthetic efficiency, could flower abundantly and even produce seeds. Overall, we established that overexpression of NtMelR is a single-window strategy to generate multiple-stress tolerant genotypes.

Role of methylglyoxal and glyoxalase in the regulation of plant response to heavy metal stress

KEY MESSAGE

Methylglyoxal and glyoxalase function a significant role in plant response to heavy metal stress. We update and discuss the most recent developments of methylglyoxal and glyoxalase in regulating plant response to heavy metal stress. Methylglyoxal (MG), a by-product of several metabolic processes, is created by both enzymatic and non-enzymatic mechanisms. It plays an important role in plant growth and development, signal transduction, and response to heavy metal stress (HMS). Changes in MG content and glyoxalase (GLY) activity under HMS imply that they may be potential biomarkers of plant stress resistance. In this review, we summarize recent advances in research on the mechanisms of MG and GLY in the regulation of plant responses to HMS. It has been discovered that appropriate concentrations of MG assist plants in maintaining a balance between growth and development and survival defense, therefore shielding them from heavy metal harm. MG and GLY regulate plant physiological processes by remodeling cellular redox homeostasis, regulating stomatal movement, and crosstalking with other signaling molecules (including abscisic acid, gibberellic acid, jasmonic acid, cytokinin, salicylic acid, melatonin, ethylene, hydrogen sulfide, and nitric oxide). We also discuss the involvement of MG and GLY in the regulation of plant responses to HMS at the transcriptional, translational, and metabolic levels. Lastly, considering the current state of research, we present a perspective on the future direction of MG research to elucidate the MG anti-stress mechanism and offer a theoretical foundation and useful advice for the remediation of heavy metal-contaminated environments in the future.

A glutathione-independent DJ-1/Pfp1 domain containing glyoxalase III, OsDJ-1C, functions in abiotic stress adaptation in rice

MAIN CONCLUSION

Overexpression of OsDJ-1C in rice improves root architecture, photosynthesis, yield and abiotic stress tolerance through modulating methylglyoxal levels, antioxidant defense, and redox homeostasis. Exposure to abiotic stresses leads to elevated methylglyoxal (MG) levels in plants, impacting seed germination and root growth. In response, the activation of NADPH-dependent aldo-keto reductase and glutathione (GSH)-dependent glyoxalase enzymes helps to regulate MG levels and reduce its toxic effects. However, detoxification may not be carried out effectively due to the limitation of GSH and NADPH in plants under stress. Recently, a novel enzyme called glyoxalase III (GLY III) has been discovered which can detoxify MG in a single step without needing GSH. To understand the physiological importance of this pathway in rice, we overexpressed the gene encoding GLYIII enzyme (OsDJ-1C) in rice. It was observed that OsDJ-1C overexpression in rice regulated MG levels under stress conditions thus, linked well with plants' abiotic stress tolerance potential. The OsDJ-1C overexpression lines displayed better root architecture, improved photosynthesis, and reduced yield penalty compared to the WT plants under salinity, and drought stress conditions. These plants demonstrated an improved GSH/GSSG ratio, reduced level of reactive oxygen species, increased antioxidant capacity, and higher anti-glycation activity thereby indicating that the GLYIII mediated MG detoxification plays a significant role in plants' ability to reduce the impact of abiotic stress. Furthermore, these findings imply the potential of OsDJ-1C in crop improvement programs.

Proteomic and Metabolomic Analysis of the Quercus ilex-Phytophthora cinnamomi Pathosystem Reveals a Population-Specific Response, Independent of Co-Occurrence of Drought

Holm oak (Quercus ilex) is considered to be one of the major structural elements of Mediterranean forests and the agrosilvopastoral Spanish "dehesa", making it an outstanding example of ecological and socioeconomic sustainability in forest ecosystems. The exotic Phytophthora cinnamomi is one of the most aggressive pathogens of woody species and, together with drought, is considered to be one of the main drivers of holm oak decline. The effect of and response to P. cinnamomi inoculation were studied in the offspring of mother trees from two Andalusian populations, Cordoba and Huelva. At the two locations, acorns collected from both symptomatic (damaged) and asymptomatic (apparently healthy) trees were sampled. Damage symptoms, mortality, and chlorophyll fluorescence were evaluated in seedlings inoculated under humid and drought conditions. The effect and response depended on the population and were more apparent in Huelva than in Cordoba. An integrated proteomic and metabolomic analysis revealed the involvement of different metabolic pathways in response to the pathogen in both populations, including amino acid metabolism pathways in Huelva, and terpenoid and flavonoid biosynthesis in Cordoba. However, no differential response was observed between seedlings inoculated under humid and drought conditions. A protective mechanism of the photosynthetic apparatus was activated in response to defective photosynthetic activity in inoculated plants, which seemed to be more efficient in the Cordoba population. In addition, enzymes and metabolites of the phenylpropanoid and flavonoid biosynthesis pathways may have conferred higher resistance in the Cordoba population. Some enzymes are proposed as markers of resilience, among which glyoxalase I, glutathione reductase, thioredoxin reductase, and cinnamyl alcohol dehydrogenase are candidates.

Methylglyoxal metabolism is altered during defence response in pigeonpea (Cajanus cajan (L.) Millsp.) against the spotted pod borer (Maruca vitrata)

Pigeonpea (Cajanus cajan ) production can be affected by the spotted pod borer (Maruca vitrata ). Here, we identified biochemical changes in plant parts of pigeonpea after M. vitrata infestation. Two pigeonpea genotypes (AL 1747, moderately resistant; and MN 1, susceptible) were compared for glyoxalase and non-glyoxalase enzyme systems responsible for methylglyoxal (MG) detoxification, γ-glutamylcysteine synthetase (γ-GCS), glutathione-S-transferase (GST) and glutathione content in leaves, flowers and pods under control and insect-infested conditions. MN 1 had major damage due to M. vitrata infestation compared to AL 1747. Lower accumulation of MG in AL 1747 was due to higher activities of enzymes of GSH-dependent (glyoxylase I, glyoxylase II), GSH-independent (glyoxalase III) pathway, and enzyme of non-glyoxalase pathway (methylglyoxal reductase, MGR), which convert MG to lactate. Decreased glyoxylase enzymes and MGR activities in MN 1 resulted in higher accumulation of MG. Higher lactate dehydrogenase (LDH) activity in AL 1747 indicates utilisation of MG detoxification pathway. Higher glutathione content in AL 1747 genotype might be responsible for efficient working of MG detoxification pathway under insect infestation. Higher activity of γ-GCS in AL 1747 maintains the glutathione pool, necessary for the functioning of glyoxylase pathway to carry out the detoxification of MG. Higher activities of GST and GPX in AL 1747 might be responsible for detoxification of toxic products that accumulates following insect infestation, and elevated activities of glyoxylase and non-glyoxylase enzyme systems in AL 1747 after infestation might be responsible for reducing reactive cabanoyl stress. Our investigation will help the future development of resistant cultivars.

Nitric oxide (NO) modulates low temperature-stress signaling via S-nitrosation, a NO PTM, inducing ethylene biosynthesis inhibition leading to enhanced post-harvest shelf-life of agricultural produce

Low temperature (cold) stress is one of the major abiotic stress conditions affecting crop productivity worldwide. Nitric oxide (NO) is a dynamic signaling molecule that interacts with various stress regulators and provides abiotic stress tolerance. Stress enhanced NO contributes to S-nitrosothiol accumulation which causes oxidation of the -SH group in proteins leading to S-nitrosation, a post-translational modification. Cold stress induced in vivo S-nitrosation of > 240 proteins majorly belonging to stress/signaling/redox (myrosinase, SOD, GST, CS, DHAR), photosynthesis (RuBisCO, PRK), metabolism (FBA, GAPDH, TPI, SBPase), and cell wall modification (Beta-xylosidases, alpha-l-arabinogalactan) in different crop plants indicated role of NO in these important cellular and metabolic pathways. NO mediated regulation of a transcription factor CBF (C-repeat Binding Factor, a transcription factor) at transcriptional and post-translational level was shown in Solanum lycopersicum seedlings. NO donor priming enhances seed germination, breaks dormancy and provides tolerance to stress in crops. Its role in averting stress, promoting seed germination, and delaying senescence paved the way for use of NO and NO releasing compounds to prevent crop loss and increase the shelf-life of fruits and vegetables. An alternative to energy consuming and expensive cold storage led to development of a storage device called "shelf-life enhancer" that delays senescence and increases shelf-life at ambient temperature (25-27 °C) using NO donor. The present review summarizes NO research in plants and exploration of NO for its translational potential to improve agricultural yield and post-harvest crop loss.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01371-z.

Exogenous Allantoin Confers Rapeseed (Brassica campestris) Tolerance to Simulated Drought by Improving Antioxidant Metabolism and Physiology

Allantoin is an emerging plant metabolite, but its role in conferring drought-induced oxidative stress is still elusive. Therefore, an experiment was devised to explore the role of allantoin (0.5 and 1.0 mM; foliar spray) in rapeseed (Brassica campestris cv. BARI Sarisha-17) under drought. Seedlings at fifteen days of age were subjected to drought, maintaining soil moisture levels at 50% and 25% field capacities, while well-irrigated plants served as the control group. Drought-stressed plants exhibited increased levels of lipid peroxidation and hydrogen peroxide, electrolyte leakage, and impaired glyoxalase systems. Thus, the growth, biomass, and yield attributes of rapeseed were significantly impaired under drought. However, the allantoin-supplemented plants showed a notable increase in their contents of ascorbate and glutathione and decreased dehydroascorbate and glutathione disulfide contents under drought. Moreover, the activity of antioxidant enzymes such as ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase were accelerated with the allantoin spray and the glyoxalase system was also enhanced under drought. Moreover, the improvement in water balance with reduction in proline and potassium ion contents was also observed when allantoin was applied to the plants. Overall, the beneficial effects of allantoin supplementation resulted in the improved plant growth, biomass, and yield of rapeseed under drought conditions. These findings suggest that allantoin acts as an efficient metabolite in mitigating the oxidative stress caused by reactive oxygen species by enhancing antioxidant defense mechanisms and the glyoxalase system.

Insight into the physiological and biochemical mechanisms of biostimulating effect of Ascophyllum nodosum and Moringa oleifera extracts to minimize cadmium-induced oxidative stress in rice

Cadmium (Cd) is a serious threat for environmental sustainability as it can be taken up quickly by plants and transported to the food chain of living organisms. It alters plants' metabolic and physiological activities and causes yield loss, thereby, enhancing plant tolerance to Cd stress is of utmost essential. Therefore, an experiment was executed to investigate the potential role of Ascophyllum nodosum extract (ANE) and moringa (Moringa oleifera) leaf extract (MLE) to confer Cd tolerance in rice (Oryza sativa cv. BRRI dhan89). Thirty-five-day-old seedling was subjected to Cd stress (50 mg kg-1 CdCl2) alone and in a combination of ANE (0.25%) or MLE (0.5%) in a semi-controlled net house. Exposure to Cd resulted in accelerated production of reactive oxygen species, enhanced lipid peroxidation, and disrupted antioxidant defense and glyoxalase system, thus retarded plant growth, biomass production, and yield attributes of rice. On the contrary, the supplementation of ANE or MLE enhanced the contents of ascorbate and glutathione, and the activities of antioxidant enzymes such as ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase. Moreover, supplementation of ANE and MLE enhanced the activities of glyoxalase I and glyoxalase II which prevented the overgeneration of methylglyoxal in Cd stressed rice plants. Thus, because of ANE and MLE addition Cd-induced rice plants showed a noticeable declination in membrane lipid peroxidation, hydrogen peroxide generation, and electrolyte leakage, whereas improved water balance. Furthermore, the growth and yield attributes of Cd-affected rice plants were improved with the supplementation of ANE and MLE. All the studied parameters indicates the potential role of ANE and MLE in mitigating Cd stress in rice plants through improving the physiological attributes, modulating antioxidant defense and glyoxalase system.

The involvement of hydrogen sulphide in melatonin-induced tolerance to arsenic toxicity in pepper (Capsicum annuum L.) plants by regulating sequestration and subcellular distribution of arsenic, and antioxidant defense system

Melatonin (MT) and hydrogen sulphide (H₂S) are recognised as vital biomolecules actively taking part in plant defence systems as free radical scavengers and antioxidants against a myriad of biotic and abiotic stressors. However, it has been yet unknown in plants subjected to arsenic (As) toxicity whether or not H₂S interacts with MT to regulate endogenous antioxidant defence system. Prior to beginning As stress (As-S) treatments, MT (0.10 mM) was applied externally to plants daily for three days. AsS was then started for two weeks with As(V) (0.1 mM as Na₂HAsO₄·7H₂O). The treatment of As reduced plant biomass (24.4%) and chlorophyll a (51.7%), chlorophyll b (25.9%), while it increased subcellular As in roots and leaves, levels of glutathione (GSH), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), methylglyoxal (MG), H₂S and phytochelatins (PCs) in pepper plants. In As-stressed pepper plants, the application of MT increased plant biomass (16.3%), chlorophyll a (52.7%), chlorophyll b (28.2%), antioxidant enzymes' activities, and H₂S accumulation, while it lowered the concentrations of MDA and H₂O₂. In As-treated plants, GSH and phytochelatins (PCs) were increased by MT by regulating As sequestration to make it harmless. The addition of MT increased As accumulation in the vacuoles of roots and caused the soluble fraction of As in vacuoles to become less toxic to vital organelles. MT-induced tolerance to As stress was further enhanced using NaHS, a source of H₂S. Hypotaurine (0.1 mM HT), a H₂S scavenger, was applied to the control and As-stressed plants together with MT and MT + NaHS to determine whether H₂S was implicated in MT-induced increased As-S tolerance. By reducing H₂S generation in pepper plants, HT counteracted the beneficial effects of MT, whereas the addition of NaHS to MT + HT restored the negative effects of HT, proving that H₂S is necessary for the pepper plants As-stress tolerance caused by MT.

Methylglyoxal detoxification pathway - Explored first time for imazethapyr tolerance in lentil (Lens culinaris L.)

Lentil is an important pulses crop but it's short stature and slow growth rate make it vulnerable to weed competition, limiting crop productivity. There is need to identify herbicide tolerant genotypes and their tolerance mechanism. The present investigation was conducted to understand the effect of imazethapyr (IM) treatment on accumulation of methylglyoxal (MG) and its detoxification mechanism in IM-tolerant (LL1397 and LL1612) susceptible (FLIP2004-7L and PL07) genotypes sown under control (weed free), weedy check (weeds were growing with crop) and sprayed with imazethapyr. The enzymes of glyoxalase pathway (glyoxalase I, II and III) and non glyoxalase pathway (methylglyoxal reductase), lactate dehydrogenase (LDH), glutathione content, gamma-glutamyl-cysteine synthetase (γ-GCS) were estimated in lentil genotypes at different days after spray. Higher activities of glyoxalase I, II and III and MGR along with the increased glutathione content (GSH) content in LL1397 and LL1612 under IM treatment as compared to FLIP2004-7L and PL07 might be responsible for lowering MG accumulation and increasing lactate content, which is end product of these pathways. Enhanced LDH activity in LL1397 and LL1612 might be responsible for energy production via TCA cycle that might be responsible for growth and recovery of tolerant genotypes after IM treatment. Higher γ-GCS activity in tolerant genotypes led to increased glutathione content required for glyoxalase pathway. However, decreased activities of glyoxalase enzymes and MGR in susceptible genotypes result in MG accumulation which limit plant growth. This is the first ever study elucidating the role of MG detoxification pathway conferring IM tolerance in lentil.

A Metabolic Profiling Analysis Revealed a Primary Metabolism Reprogramming in Arabidopsis glyI4 Loss-of-Function Mutant

Methylglyoxal (MG) is a cytotoxic compound often produced as a side product of metabolic processes such as glycolysis, lipid peroxidation, and photosynthesis. MG is mainly scavenged by the glyoxalase system, a two-step pathway, in which the coordinate activity of GLYI and GLYII transforms it into D-lactate, releasing GSH. In Arabidopsis thaliana, a member of the GLYI family named GLYI4 has been recently characterized. In glyI4 mutant plants, a general stress phenotype characterized by compromised MG scavenging, accumulation of reactive oxygen species (ROS), stomatal closure, and reduced fitness was observed. In order to shed some light on the impact of gly4 loss-of-function on plant metabolism, we applied a high resolution mass spectrometry-based metabolomic approach to Arabidopsis Col-8 wild type and glyI4 mutant plants. A compound library containing a total of 70 metabolites, differentially synthesized in glyI4 compared to Col-8, was obtained. Pathway analysis of the identified compounds showed that the upregulated pathways are mainly involved in redox reactions and cellular energy maintenance, and those downregulated in plant defense and growth. These results improved our understanding of the impacts of glyI4 loss-of-function on the general reprogramming of the plant's metabolic landscape as a strategy for surviving under adverse physiological conditions.