Methylglyoxal detoxification by a DJ-1 family protein provides dual abiotic and biotic stress tolerance in transgenic plants

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.

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.

Saccharomyces cerevisiae DJ-1 paralogs maintain genome integrity through glycation repair of nucleic acids and proteins

Reactive carbonyl species (RCS) such as methylglyoxal and glyoxal are potent glycolytic intermediates that extensively damage cellular biomolecules leading to genetic aberration and protein misfolding. Hence, RCS levels are crucial indicators in the progression of various pathological diseases. Besides the glyoxalase system, emerging studies report highly conserved DJ-1 superfamily proteins as critical regulators of RCS. DJ-1 superfamily proteins, including the human DJ-1, a genetic determinant of Parkinson's disease, possess diverse physiological functions paramount for combating multiple stressors. Although S. cerevisiae retains four DJ-1 orthologs (Hsp31, Hsp32, Hsp33, and Hsp34), their physiological relevance and collective requirement remain obscure. Here, we report for the first time that the yeast DJ-1 orthologs function as novel enzymes involved in the preferential scavenge of glyoxal and methylglyoxal, toxic metabolites, and genotoxic agents. Their collective loss stimulates chronic glycation of the proteome, and nucleic acids, inducing spectrum of genetic mutations and reduced mRNA translational efficiency. Furthermore, the Hsp31 paralogs efficiently repair severely glycated macromolecules derived from carbonyl modifications. Also, their absence elevates DNA damage response, making cells vulnerable to various genotoxins. Interestingly, yeast DJ-1 orthologs preserve functional mitochondrial content, maintain ATP levels, and redistribute into mitochondria to alleviate the glycation damage of macromolecules. Together, our study uncovers a novel glycation repair pathway in S. cerevisiae and a possible neuroprotective mechanism of how hDJ-1 confers mitochondrial health during glycation toxicity.

Role of lactoyl-glutathione lyase of Salmonella in the colonization of plants under salinity stress

Salmonella, a foodborne human pathogen, can colonize the members of the kingdom Plantae. However, the basis of the persistence of Salmonella in plants is largely unknown. Plants encounter various biotic and abiotic stress agents in soil. We conjectured that methylglyoxal (MG), one of the common metabolites that accumulate in plants during both biotic and abiotic stress, plays a role in regulating the plant-Salmonella interaction. The interaction of Salmonella Typhimurium with plants under salinity stress was investigated. It was observed that wild-type Salmonella Typhimurium can efficiently colonize the root, but mutant bacteria lacking MG detoxifying enzyme, lactoyl-glutathione lyase (Lgl), showed lower colonization in roots exclusively under salinity stress. This colonization defect is due to the poor viability of the mutated bacterial strains under these conditions. This is the first report to prove the role of MG-detoxification genes in the colonization of stressed plants and highlights the possible involvement of metabolic genes in the evolution of the plant-associated life of Salmonella.

A glutathione-independent DJ-1/PfpI domain-containing tomato glyoxalaseIII2, SlGLYIII2, confers enhanced tolerance under salt and osmotic stresses

In plants, glyoxalase enzymes are activated under stress conditions to mitigate the toxic effects of hyperaccumulated methylglyoxal (MG), a highly reactive carbonyl compound. Until recently, a glutathione-dependent bi-enzymatic pathway involving glyoxalase I (GLYI) and glyoxalase II (GLYII) was considered the primary MG-detoxification system. Recently, a new glutathione-independent glyoxalase III (GLYIII) mediated direct route was also reported in plants. However, the physiological significance of this new pathway remains to be elucidated across plant species. This study identified the full complement of 22 glyoxalases in tomato. Based on their strong induction under multiple abiotic stresses, SlGLYI4, SlGLYII2 and SlGLYIII2 were selected candidates for further functional characterisation. Stress-inducible overexpression of both glutathione-dependent (SlGLYI4 + SlGLYII2) and independent (SlGLYIII2) pathways led to enhanced tolerance in both sets of transgenic plants under abiotic stresses. However, SlGLYIII2 overexpression (OE) plants outperformed the SlGLYI4 + SlGLYII2 OE counterparts for their stress tolerance under abiotic stresses. Further, knockdown of SlGLYIII2 resulted in plants with exacerbated stress responses than those silenced for both SlGLYI4 and SlGLYII2. The superior performance of SlGLYIII2 OE tomato plants for better growth and yield under salt and osmotic treatments could be attributed to better GSH/GSSG ratio, lower reactive oxygen species levels, and enhanced antioxidant potential, indicating a prominent role of GLYIII MG-detoxification pathway in abiotic stress mitigation in this species.

Glyoxalase I activity affects Arabidopsis sensitivity to ammonium nutrition

Elevated methylglyoxal levels contribute to ammonium-induced growth disorders in Arabidopsis thaliana. Methylglyoxal detoxification pathway limitation, mainly the glyoxalase I activity, leads to enhanced sensitivity of plants to ammonium nutrition. Ammonium applied to plants as the exclusive source of nitrogen often triggers multiple phenotypic effects, with severe growth inhibition being the most prominent symptom. Glycolytic flux increase, leading to overproduction of its toxic by-product methylglyoxal (MG), is one of the major metabolic consequences of long-term ammonium nutrition. This study aimed to evaluate the influence of MG metabolism on ammonium-dependent growth restriction in Arabidopsis thaliana plants. As the level of MG in plant cells is maintained by the glyoxalase (GLX) system, we analyzed MG-related metabolism in plants with a dysfunctional glyoxalase pathway. We report that MG detoxification, based on glutathione-dependent glyoxalases, is crucial for plants exposed to ammonium nutrition, and its essential role in ammonium sensitivity relays on glyoxalase I (GLXI) activity. Our results indicated that the accumulation of MG-derived advanced glycation end products significantly contributes to the incidence of ammonium toxicity symptoms. Using A. thaliana frostbite1 as a model plant that overcomes growth repression on ammonium, we have shown that its resistance to enhanced MG levels is based on increased GLXI activity and tolerance to elevated MG-derived advanced glycation end-product (MAGE) levels. Furthermore, our results show that glyoxalase pathway activity strongly affects cellular antioxidative systems. Under stress conditions, the disruption of the MG detoxification pathway limits the functioning of antioxidant defense. However, under optimal growth conditions, a defect in the MG detoxification route results in the activation of antioxidative systems.

Double DJ-1 domain containing Arabidopsis DJ-1D is a robust macromolecule deglycase

Plants, being sessile, are prone to genotoxin-induced macromolecule damage. Among the inevitable damaging agents are reactive carbonyls that induce glycation of DNA, RNA and proteins to result in the build-up of advanced glycated end-products. However, it is unclear how plants repair glycated macromolecules. DJ-1/PARK7 members are a highly conserved family of moonlighting proteins having double domains in higher plants and single domains in other phyla. Here we show that Arabidopsis DJ-1D offers robust tolerance to endogenous and exogenous stresses through its ability to repair glycated DNA, RNA and proteins. DJ-1D also reduced the formation of reactive carbonyls through its efficient methylglyoxalase activity. Strikingly, full-length double domain-containing DJ-1D suppressed the formation of advanced glycated end-products in yeast and plants. DJ-1D also efficiently repaired glycated nucleic acids and nucleotides in vitro and mitochondrial DNA in vivo under stress, indicating the existence of a new DNA repair pathway in plants. We propose that multi-stress responding plant DJ-1 members, often present in multiple copies among plants, probably contributed to the adaptation to a variety of endogenous and exogenous stresses.

Glyoxalase III enhances salinity tolerance through reactive oxygen species scavenging and reduced glycation

Methylglyoxal (MG) is a metabolically generated highly cytotoxic compound that accumulates in all living organisms, from Escherichia coli to humans, under stress conditions. To detoxify MG, nature has evolved reduced glutathione (GSH)-dependent glyoxalase and NADPH-dependent aldo-keto reductase systems. But both GSH and NADPH have been reported to be limiting in plants under stress conditions, and thus detoxification might not be performed efficiently. Recently, glyoxalase III (GLY III)-like enzyme activity has been reported from various species, which can detoxify MG without any cofactor. In the present study, we have tested whether an E. coli gene, hchA, encoding a functional GLY III, could provide abiotic stress tolerance to living systems. Overexpression of this gene showed improved tolerance in E. coli and Saccharomyces cerevisiae cells against salinity, dicarbonyl, and oxidative stresses. Ectopic expression of the E. coli GLY III gene (EcGLY-III) in transgenic tobacco plants confers tolerance against salinity at both seedling and reproductive stages as indicated by their height, weight, membrane stability index, and total yield potential. Transgenic plants showed significantly increased glyoxalase and antioxidant enzyme activity that resisted the accumulation of excess MG and reactive oxygen species (ROS) during stress. Moreover, transgenic plants showed more anti-glycation activity to inhibit the formation of advanced glycation end product (AGE) that might prevent transgenic plants from stress-induced senescence. Taken together, all these observations indicate that overexpression of EcGLYIII confers salinity stress tolerance in plants and should be explored further for the generation of stress-tolerant plants.

Transcriptional Response of Candida auris to the Mrr1 Inducers Methylglyoxal and Benomyl

Candida auris is an urgent threat to human health due to its rapid spread in health care settings and its repeated development of multidrug resistance. Diseases that increase risk for C. auris infection, such as diabetes, kidney failure, or immunocompromising conditions, are associated with elevated levels of methylglyoxal (MG), a reactive dicarbonyl compound derived from several metabolic processes. In other Candida species, expression of MG reductase enzymes that catabolize and detoxify MG are controlled by Mrr1, a multidrug resistance-associated transcription factor, and MG induces Mrr1 activity. Here, we used transcriptomics and genetic assays to determine that C. aurisMRR1a contributes to MG resistance, and that the main Mrr1a targets are an MG reductase and MDR1, which encodes a drug efflux protein. The C. auris Mrr1a regulon is smaller than Mrr1 regulons described in other species. In addition to MG, benomyl (BEN), a known Mrr1 stimulus, induces C. auris Mrr1 activity, and characterization of the MRR1a-dependent and -independent transcriptional responses revealed substantial overlap in genes that were differentially expressed in response to each compound. Additionally, we found that an MRR1 allele specific to one C. auris phylogenetic clade, clade III, encodes a hyperactive Mrr1 variant, and this activity correlated with higher MG resistance. C. aurisMRR1a alleles were functional in Candida lusitaniae and were inducible by BEN, but not by MG, suggesting that the two Mrr1 inducers act via different mechanisms. Together, the data presented in this work contribute to the understanding of Mrr1 activity and MG resistance in C. auris.

IMPORTANCECandida auris is a fungal pathogen that has spread since its identification in 2009 and is of concern due to its high incidence of resistance against multiple classes of antifungal drugs. In other Candida species, the transcription factor Mrr1 plays a major role in resistance against azole antifungals and other toxins. More recently, Mrr1 has been recognized to contribute to resistance to methylglyoxal (MG), a toxic metabolic product that is often elevated in different disease states. MG can activate Mrr1 and its induction of Mdr1 which can protect against diverse challenges. The significance of this work lies in showing that MG is also an inducer of Mrr1 in C. auris, and that one of the major pathogenic C. auris lineages has an activating Mrr1 mutation that confers protection against MG.

Effector-mediated plant-virus-vector interactions

Hemipterans (such as aphids, whiteflies, and leafhoppers) are some of the most devastating insect pests due to the numerous plant pathogens they transmit as vectors, which are primarily viral. Over the past decade, tremendous progress has been made in broadening our understanding of plant-virus-vector interactions, yet on the molecular level, viruses and vectors have typically been studied in isolation of each other until recently. From that work, it is clear that both hemipteran vectors and viruses use effectors to manipulate host physiology and successfully colonize a plant and that co-evolutionary dynamics have resulted in effective host immune responses, as well as diverse mechanisms of counterattack by both challengers. In this review, we focus on advances in effector-mediated plant-virus-vector interactions and the underlying mechanisms. We propose that molecular synergisms in vector-virus interactions occur in cases where both the virus and vector benefit from the interaction (mutualism). To support this view, we show that mutualisms are common in virus-vector interactions and that virus and vector effectors target conserved mechanisms of plant immunity, including plant transcription factors, and plant protein degradation pathways. Finally, we outline ways to identify true effector synergisms in the future and propose future research directions concerning the roles effectors play in plant-virus-vector interactions.

Glycation damage to organelles and their DNA increases during maize seedling development

Shoot development in maize begins when meristematic, non-pigmented cells at leaf base stop dividing and proceeds toward the expanded green cells of the leaf blade. During this transition, promitochondria and proplastids develop into mature organelles and their DNA becomes fragmented. Changes in glycation damage during organelle development were measured for protein and DNA, as well as the glycating agent methyl glyoxal and the glycation-defense protein DJ-1 (known as Park7 in humans). Maize seedlings were grown under normal, non-stressful conditions. Nonetheless, we found that glycation damage, as well as defenses against glycation, follow the same developmental pattern we found previously for reactive oxygen species (ROS): as damage increases, damage-defense measures decrease. In addition, light-grown leaves had more glycation and less DJ-1 compared to dark-grown leaves. The demise of maize organellar DNA during development may therefore be attributed to both oxidative and glycation damage that is not repaired. The coordination between oxidative and glycation damage, as well as damage-response from the nucleus is also discussed.

A continuous spectrophotometric assay for glutathione-independent glyoxalases

We developed a novel continuous assay to quantitatively characterize the catalytic activity of type III methylglyoxalases, a family of enzymes that detoxify methylglyoxal. This assay is based on spectrophotometric detection of hemithioacetal which forms in the reversible reaction of methylglyoxal with dithiothreitol. Due to rapid interconversion between hemithioacetal and methylglyoxal and the known equilibrium constant, hemithioacetal can be quantified spectrophotometrically at 286 nm and used as a reporter for methylglyoxal. When the concentration of methylglyoxal decreases due to catalytic conversion by methylglyoxalases, the concentration of hemithioacetal concomitantly decreases due to its spontaneous decomposition driven by the shift in equilibrium position. Therefore, the rate of total methylglyoxal consumption is the sum of the rate of hemithioacetal decomposition determined spectrophotometrically and the rate of change of methylglyoxal calculated from known concentrations of hemithioacetal. Varying concentrations of dithiothreitol and methylglyoxal creates a broad range of free methylglyoxal in solution that is crucial for the reliable determination of Michaelis constants. We demonstrate the utility of this assay using several recombinant glyoxalases for which kinetic parameters have been determined. This cost-effective and simple assay offers advantages over the existing discontinuous methods and will be useful for quantitative characterization of catalytic activities of type III methylglyoxalases.

Functional characterization and expression profiling of glyoxalase III genes in date palm grown under abiotic stresses

Methylglyoxal (MG), a by-product of various metabolic processes, including glycolysis, is a highly reactive cytotoxic metabolite. The level of MG in the cell is maintained at a non-toxic level via MG detoxification pathways such as the universal glyoxalase system, including glyoxalase I/II/III enzymes. Glyoxalase III (DJ-1) can breakdown MG to d-lactate in a single step without reducing glutathione (GSH). Elucidating the function of the DJ-1 gene family may provide further knowledge about its role in plants under abiotic stresses. Here, we characterize four glyoxalase III genes (PdDJ-1B1, PdDJ-1B2, PdDJ-1C, and PdDJ-1D) encoding the conserved DJ-1 domain in the genome of the date palm, a crop with high drought and salinity tolerance. The expression level of the PdDJ-1 genes increased in date palm leaves upon salinity treatment. In addition, overexpression of PdDJ-1 genes in Escherichia coli and the complementation in yeast hsp31Δ knockout mutant cells enhanced their growth rate and reduced the accumulation of reactive oxygen species (ROS) under MG and oxidative stress conditions as shown by the flow cytometry assay. Subcellular localization using confocal microscopy revealed the accumulation of PdDJ-1B1, PdDJ-1C, and PdDJ-1D in the chloroplast, whereas PdDJ-1B2 was localized to the cytosol. Remarkably, constitutive expression of the PdDJ-1C gene in Arabidopsis thaliana Columbia (Col-0) resulted in the generation of non-viable albino plants implying that PdDJ-1C plays a critical function in chloroplast development. These findings suggest that PdDJ-1 protein has an important function in MG-detoxification and maintaining the redox balance in date palm plants under abiotic stress conditions.

Tracing the Evolution of Plant Glyoxalase III Enzymes for Structural and Functional Divergence

Glyoxalase pathway is the primary route for metabolism of methylglyoxal (MG), a toxic ubiquitous metabolite that affects redox homeostasis. It neutralizes MG using Glyoxalase I and Glyoxalase II (GLYI and GLYII) enzymes in the presence of reduced glutathione. In addition, there also exists a shorter route for the MG detoxification in the form of Glyoxalase III (GLYIII) enzymes, which can convert MG into D-lactate in a single-step without involving glutathione. GLYIII proteins in different systems demonstrate diverse functional capacities and play a vital role in oxidative stress response. To gain insight into their evolutionary patterns, here we studied the evolution of GLYIII enzymes across prokaryotes and eukaryotes, with special emphasis on plants. GLYIII proteins are characterized by the presence of DJ-1_PfpI domains thereby, belonging to the DJ-1_PfpI protein superfamily. Our analysis delineated evolution of double DJ-1_PfpI domains in plant GLYIII. Based on sequence and structural characteristics, plant GLYIII enzymes could be categorized into three different clusters, which followed different evolutionary trajectories. Importantly, GLYIII proteins from monocots and dicots group separately in each cluster and the each of the two domains of these proteins also cluster differentially. Overall, our findings suggested that GLYIII proteins have undergone significant evolutionary changes in plants, which is likely to confer diversity and flexibility in their functions.

Dissecting the molecular responses of lentil to individual and combined drought and heat stresses by comparative transcriptomic analysis

Lentil cultivation could be challenged by combined heat and drought stress in semi-arid regions. We used RNA-seq approach to profile transcriptome changes of Lens culinaris exposed to individual and combined heat and drought stresses. It was determined that most of the differentially expressed genes observed in response to combined stress, could not be identified by analysis of transcriptome exposed to corresponding individual stresses. Interestingly, this study results revealed that the expression of ribosome generation and protein biosynthesis and starch degradation pathways related genes were uniquely up-regulated under the combined stress. Although multiple genes related to antioxidant activity were up-regulated in response to all stresses, variation in types and expression levels of these genes under the combined stress were higher than that of individual stresses. Using this comparative approach, for the first time, we reported up-regulation of several TF, CDPK, CYP, and antioxidant genes in response to combined stress in plants.

Quantification of Methylglyoxal Levels in Cowpea Leaves in Response to Cowpea Aphid Infestation

Aphids are a serious pest of crops across the world. Aphids feed by inserting their flexible hypodermal needlelike mouthparts, or stylets, into their host plant tissues. They navigate their way to the phloem where they feed on its sap causing little mechanical damage to the plant. Additionally, while feeding, aphids secrete proteinaceous effectors in their saliva to alter plant metabolism and disrupt plant defenses to gain an advantage over the plant. Even with these arsenals to overcome plant responses, plants have evolved ways to detect and counter with defense responses to curtail aphid infestation. One of such response of cowpea to cowpea aphid infestation, is accumulation of the metabolite methylglyoxal. Methylglyoxal is an α,β-dicarbonyl ketoaldehyde that is toxic at high concentrations. Methylglyoxal levels increase modestly after exposure to a number of different abiotic and biotic stresses and has been shown to act as an emerging defense signaling molecule at low levels. Here we describe a protocol to measure methylglyoxal in cowpea leaves after cowpea aphid infestation, by utilizing a perchloric acid extraction process. The extracted supernatant was neutralized with potassium carbonate, and methylglyoxal was quantified through its reaction with N-acetyl-L-cysteine to form N-α-acetyl-S-(1-hydroxy-2-oxo-prop-1-yl)cysteine, a product that is quantified spectrophotometrically.

AcDCXR Is a Cowpea Aphid Effector With Putative Roles in Altering Host Immunity and Physiology

Cowpea, Vigna unguiculata, is a crop that is essential to semiarid areas of the world like Sub-Sahara Africa. Cowpea is highly susceptible to cowpea aphid, Aphis craccivora, infestation that can lead to major yield losses. Aphids feed on their host plant by inserting their hypodermal needlelike flexible stylets into the plant to reach the phloem sap. During feeding, aphids secrete saliva, containing effector proteins, into the plant to disrupt plant immune responses and alter the physiology of the plant to their own advantage. Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to identify the salivary proteome of the cowpea aphid. About 150 candidate proteins were identified including diacetyl/L-xylulose reductase (DCXR), a novel enzyme previously unidentified in aphid saliva. DCXR is a member of short-chain dehydrogenases/reductases with dual enzymatic functions in carbohydrate and dicarbonyl metabolism. To assess whether cowpea aphid DCXR (AcDCXR) has similar functions, recombinant AcDCXR was purified and assayed enzymatically. For carbohydrate metabolism, the oxidation of xylitol to xylulose was tested. The dicarbonyl reaction involved the reduction of methylglyoxal, an α-β-dicarbonyl ketoaldehyde, known as an abiotic and biotic stress response molecule causing cytotoxicity at high concentrations. To assess whether cowpea aphids induce methylglyoxal in plants, we measured methylglyoxal levels in both cowpea and pea (Pisum sativum) plants and found them elevated transiently after aphid infestation. Agrobacterium-mediated transient overexpression of AcDCXR in pea resulted in an increase of cowpea aphid fecundity. Taken together, our results indicate that AcDCXR is an effector with a putative ability to generate additional sources of energy to the aphid and to alter plant defense responses. In addition, this work identified methylglyoxal as a potential novel aphid defense metabolite adding to the known repertoire of plant defenses against aphid pests.

Uncovering the potential of novel micromonosporae isolated from an extreme hyper-arid Atacama Desert soil

The taxonomic status, biotechnological and ecological potential of several Micromonospora strains isolated from an extreme hyper arid Atacama Desert soil were determined. Initially, a polyphasic study was undertaken to clarify the taxonomic status of five micromonosporae, strains LB4, LB19, LB32^T, LB39^T and LB41, isolated from an extreme hyper-arid soil collected from one of the driest regions of the Atacama Desert. All of the isolates were found to have chemotaxonomic, cultural and morphological properties consistent with their classification in the genus Micromonospora. Isolates LB32^T and LB39^T were distinguished from their nearest phylogenetic neighbours and proposed as new species, namely as Micromonospora arida sp. nov. and Micromonospora inaquosa sp. nov., respectively. Eluted methanol extracts of all of the isolates showed activity against a panel of bacterial and fungal indicator strains, notably against multi-drug resistant Klebsiella pneumoniae ATCC 700603 while isolates LB4 and LB41 showed pronounced anti-tumour activity against HepG2 cells. Draft genomes generated for the isolates revealed a rich source of novel biosynthetic gene clusters, some of which were unique to individual strains thereby opening up the prospect of selecting especially gifted micromonosporae for natural product discovery. Key stress-related genes detected in the genomes of all of the isolates provided an insight into how micromonosporae adapt to the harsh environmental conditions that prevail in extreme hyper-arid Atacama Desert soils.

Bifunctional Chloroplastic DJ-1B from Arabidopsis thaliana is an Oxidation-Robust Holdase and a Glyoxalase Sensitive to H₂O₂

Members of the DJ-1 protein family are multifunctional enzymes whose loss increases the susceptibility of the cell to oxidative stress. However, little is known about the function of the plant DJ-1 homologs. Therefore, we analyzed the effect of oxidation on the structure and function of chloroplastic AtDJ-1B and studied the phenotype of T-DNA lines lacking the protein. In vitro oxidation of AtDJ-1B with H₂O₂ lowers its glyoxalase activity, but has no effect on its holdase chaperone function. Remarkably, upon oxidation, the thermostability of AtDJ-1B increases with no significant alteration of the overall secondary structure. Moreover, we found that AtDJ-1B transcript levels are invariable, and loss of AtDJ-1B does not affect plant viability, growth and stress response. All in all, two discrete functions of AtDJ-1B respond differently to H₂O₂, and AtDJ-1B is not essential for plant development under stress.

Methylglyoxal - a signaling molecule in plant abiotic stress responses

Abiotic stresses are the most common harmful factors, adversely affecting all aspects of plants' life. Plants have to elicit appropriate responses against multifaceted effects of abiotic stresses by reprogramming various cellular processes. Signaling molecules play vital roles in sensing environmental stimuli to modulate gene expression, metabolism and physiological processes in plants to cope with the adverse effects. Methylglyoxal (MG), a dicarbonyl compound, is known to accumulate in cells as a byproduct of various metabolic pathways, including glycolysis. Several works in recent years have demonstrated that MG could play signaling roles via Ca²⁺, reactive oxygen species (ROS), K⁺ and abscisic acid. Recently, global gene expression profiling has shown that MG could induce signaling cascades, and an overlap between MG-responsive and stress-responsive signaling events might exist in plants. Once overaccumulated in cells, MG can provoke detrimental effects by generating ROS, forming advanced glycation end products and inactivating antioxidant systems. Plants are also equipped with MG-detoxifying glyoxalase system to save cellular organelles from MG toxicity. Since MG has regulatory functions in plant growth and development, and glyoxalase system is an integral component of abiotic stress adaptation, an in-depth understanding on MG metabolism and glyoxalase system will help decipher mechanisms underlying plant responses to abiotic stresses. Here, we provide a comprehensive update on the current knowledge of MG production and detoxification in plants, and highlight the putative functions of glyoxalase system in mediating plant defense against abiotic stresses. We particularly emphasize on the dual roles of MG and its connection with glutathione-related redox regulation, which is crucial for plant defense and adaptive responses under changing environmental conditions.

Genome-wide dissection and expression profiling of unique glyoxalase III genes in soybean reveal the differential pattern of transcriptional regulation

Reactive carbonyl species, such as methylglyoxal and glyoxal are very toxic in nature and can inactivate various cellular macromolecules such as DNA, RNA, and protein by forming advanced glycation end products. Conventional glyoxalase pathway with two enzymes- glyoxalase I and glyoxalase II, detoxify MG into D-lactate with the help of reduced glutathione. However, DJ-1/PfpI domain(s) containing DJ-1/ Hsp31 proteins do the same in a single step, and thus termed as "glyoxalase III". A comprehensive genome-wide analysis of soybean identified eleven putative glyoxalase III proteins with DJ-1/PfpI domain encoded by seven genes. Most of these proteins are predicted to be mitochondria and chloroplast localized. In spite of similar function, a differential evolution pattern was observed between Hsp31 and DJ-1 proteins. Expression of GmDJ-1A, GmDJ-1B, and GmDJ-1D2 transcripts was found to be constitutive in different tissues and developmental stages. Transcript profiling revealed the strong substrate-specific upregulation of GmDJ-1 genes in response to exogenous methylglyoxal exposure. Out of seven genes, GmDJ-1D1 and GmDJ-1D2 showed maximum upregulation against salinity, dehydration, and oxidative stresses. Moreover, GmDJ-1D2 showed functional glyoxalase III enzyme activity by utilizing MG as a substrate. Overall, this study identifies some novel tissue-specific and abiotic stress-responsive GmDJ-1 genes that could be investigated further.