Improving nutritional quality and fungal tolerance in soya bean and grass pea by expressing an oxalate decarboxylase

Plant synthetic biology as a tool to help eliminate hidden hunger

Agricultural systems are under increasing pressure from declining environmental conditions, a growing population, and changes in consumer preferences, resulting in widespread malnutrition-related illnesses. Improving plant nutritional content through biotechnology techniques such as synthetic biology is a promising strategy to help combat hidden hunger caused by the lack of affordable and healthy foods in human diets. Production of compounds usually found in animal-rich diets, such as vitamin D or omega-3 fatty acids, has been recently demonstrated in planta. Here, we review recent biotechnological approaches to biofortifying plants with vitamins, minerals, and other metabolites, and summarise synthetic biology advances that offer the opportunity to build on these early biofortification efforts.

Recent Advances of Oxalate Decarboxylase: Biochemical Characteristics, Catalysis Mechanisms, and Gene Expression and Regulation

Oxalate decarboxylase (OXDC) is a typical Mn2+/Mn3+ dependent metal enzyme and splits oxalate to formate and CO2 without any organic cofactors. Fungi and bacteria are the main organisms expressing the OXDC gene, but with a significantly different mechanism of gene expression and regulation. Many articles reported its potential applications in the clinical treatment of hyperoxaluria, low-oxalate food processing, degradation of oxalate salt deposits, oxalate acid diagnostics, biocontrol, biodemulsifier, and electrochemical oxidation. However, some questions still remain to be clarified about the role of substrate binding and/or protein environment in modulating the redox properties of enzyme-bound Mn(II)/Mn(III), the nature of dioxygen involved in the catalytic mechanism, and how OXDC acquires Mn(II) /Mn(III). This review mainly summarizes its biochemical and structure characteristics, gene expression and regulation, and catalysis mechanism. We also deep-mined oxalate decarboxylase gene data from National Center for Biotechnology Information to give some insights to explore new OXDC with diverse biochemical properties.

Role of oxalic acid in fungal and bacterial metabolism and its biotechnological potential

Oxalic acid and oxalates are secondary metabolites secreted to the surrounding environment by fungi, bacteria, and plants. Oxalates are linked to a variety of processes in soil, e.g. nutrient availability, weathering of minerals, or precipitation of metal oxalates. Oxalates are also mentioned among low-molecular weight compounds involved indirectly in the degradation of the lignocellulose complex by fungi, which are considered to be the most effective degraders of wood. The active regulation of the oxalic acid concentration is linked with enzymatic activities; hence, the biochemistry of microbial biosynthesis and degradation of oxalic acid has also been presented. The potential of microorganisms for oxalotrophy and the ability of microbial enzymes to degrade oxalates are important factors that can be used in the prevention of kidney stone, as a diagnostic tool for determination of oxalic acid content, as an antifungal factor against plant pathogenic fungi, or even in efforts to improve the quality of edible plants. The potential role of fungi and their interaction with bacteria in the oxalate-carbonate pathway are regarded as an effective way for the transfer of atmospheric carbon dioxide into calcium carbonate as a carbon reservoir.

Identification of genes associated to β -N oxalyl- L-α, β-diaminopropionic acid and their role in mitigating salt stress in a low-neurotoxin cultivar of Lathyrus sativus

Grass pea has the potential to become a miracle crop if the stigma attached to it as a toxic plant is ignored. In light of the following, we conducted transcriptome analyses on the high and low ODAP-containing cultivars i.e., Nirmal and Bidhan respectively in both normal and salt stress conditions. In this study, genes that work upstream and downstream to β-ODAP have been found. Among these genes, AAO3 and ACL5 were related to ABA and polyamine biosynthesis, showing the relevance of ABA and polyamines in boosting the β-ODAP content in Nirmal. Elevated β-ODAP levels in salt stress-treated Bidhan may have evolved tolerance by positively regulating the expression of genes involved in phenylpropanoid and jasmonic acid biosynthesis. Although the concentration of β-ODAP in Bidhan increased under salt stress, it was lower than in stress-treated Nirmal. Despite this, the expression of stress-related genes that work downstream to β-ODAP was found higher in stress-treated Bidhan. This could be because stress-treated Nirmal has lower GSH, proline, and higher H2O2, resulting in the development of severe oxidative stress. Overall, our research not only identified new genes linked with β-ODAP, but also revealed the molecular mechanism by which a low β-ODAP-containing cultivar developed tolerance against salinity stress.

Identification and characterization of the Bicupin domain family and functional analysis of GhBCD11 in response to verticillium wilt in cotton

Bicupin domain protein (BCD) family, an important component of Cupin domain superfamily, plays important roles in oxalic acid (OA) degradation and stress responses in high plants. However, no studies have been reported on the Cupin domain family in cotton up till now. In our study, a total 110 proteins including Cupin domain were identified from the upland cotton (Gossypium hirsutum). Among them, 17 proteins contained Bicupin domain. Subsequently, we found that V. dahliae produces OA leading to cotton leaf wilting. RT-qPCR analysis of GhBCDs revealed that OA and V. dahliae Vd080 significantly enhanced the expression of GhBCD11. The Virus-induced gene silencing and overexpression analysis showed that GhBCD11 positively regulates plant resistance to V. dahliae. Subcellular localization showed GhBCD11 located on the plasma membrane. The analysis of expression pattern showed that GhBCD11 can be induced via hormone-mediated signal pathway including salicylic acid (SA), ethephon (ET), methyl jasmonate (JA) and abscisic acid (ABA). In addition, we identified an interaction between 60 S ribosomal protein GhRPL12-3 and GhBCD11 by yeast double hybridization. Overall, this is the first study, where we identified Cupin domain family in cotton, clarified the role of GhBCD11 in cotton for resistance to V. dahliae and found an interaction between GhRPL12-3 and GhBCD11.

NM, Jebakani K. S, Selvaraj S, Pramitha J. L, Selvaraj R, Petchiammal K. I, Kather Sheriff S, Thinakaran J, Rathinamoorthy S, Kumar P. R. Genetic manipulation of anti-nutritional factors in major crops for a sustainable diet in future

The consumption of healthy food, in order to strengthen the immune system, is now a major focus of people worldwide and is essential to tackle the emerging pandemic concerns. Moreover, research in this area paves the way for diversification of human diets by incorporating underutilized crops which are highly nutritious and climate-resilient in nature. However, although the consumption of healthy foods increases nutritional uptake, the bioavailability of nutrients and their absorption from foods also play an essential role in curbing malnutrition in developing countries. This has led to a focus on anti-nutrients that interfere with the digestion and absorption of nutrients and proteins from foods. Anti-nutritional factors in crops, such as phytic acid, gossypol, goitrogens, glucosinolates, lectins, oxalic acid, saponins, raffinose, tannins, enzyme inhibitors, alkaloids, β-N-oxalyl amino alanine (BOAA), and hydrogen cyanide (HCN), are synthesized in crop metabolic pathways and are interconnected with other essential growth regulation factors. Hence, breeding with the aim of completely eliminating anti-nutrition factors tends to compromise desirable features such as yield and seed size. However, advanced techniques, such as integrated multi-omics, RNAi, gene editing, and genomics-assisted breeding, aim to breed crops in which negative traits are minimized and to provide new strategies to handle these traits in crop improvement programs. There is also a need to emphasize individual crop-based approaches in upcoming research programs to achieve smart foods with minimum constraints in future. This review focuses on progress in molecular breeding and prospects for additional approaches to improve nutrient bioavailability in major crops.

Biotechnological detoxification: an unchanging source-sink balance strategy for crop improvement

The wide occurrence of natural phytotoxins renders many crops unfit for human consumption. To overcome this problem and produce detoxified crop varieties, we propose the use of biotechnological strategies that can enhance the harvest index without the need to increase crop biomass or alter whole plant architecture.

Oxalate in Plants: Metabolism, Function, Regulation, and Application

Characterized by strong acidity, chelating ability, and reducing ability, oxalic acid, a low molecular weight dicarboxylic organic acid, plays important roles in the regulation of plant growth and development, the response to both biotic and abiotic stresses such as plant defense and heavy metals detoxification, and food quality. The metabolism of oxalic acid has been well-studied in microorganisms, fungi, and animals but remains less understood in plants. However, excessive accumulation of oxalic acid is detrimental to plants. Therefore, the level of oxalic acid has to be precisely controlled in plant tissues. In this review, we summarize the metabolism, function, and regulation of oxalic acid in plants, and we discuss solutions such as agricultural practices and plant biotechnology to manipulate oxalic acid metabolism to regulate plant responses to both external stimuli and internal developmental cues.

Tomato Oxalyl-CoA Synthetase Degrades Oxalate and Affects Fruit Quality

Acyl activating enzyme 3 (AAE3) encodes oxalyl-CoA synthetase involved in oxalate degradation. In this study, we investigated the role of AAE3 (SlAAE3) in the fruit quality of tomato (Solanum lycopersicum). The purified recombinant SlAAE3 protein from Escherichia coli exhibited a high activity toward oxalate, with a K _m of 223.8 ± 20.03 μm and V _max of 7.908 ± 0.606 μmol mg^-1 protein min^-1. Transient expression of SlAAE3-green fluorescent protein (GFP) fusion proteins suggests that SlAAE3 is a soluble protein without specific subcellular localization. The expression of SlAAE3 is both tissue- and development-dependent, and increased during fruit ripping. The Slaae3 knockout mutants had improved fruit quality as evidenced by the increased sugar-acid ratio and mineral nutrient content. To find the mechanism by which SlAAE3 affects fruit quality, transcriptome, and metabolome were employed on SlAAE3 over-expressed line and wide type fruits. The transcriptomic and metabolic profiles indicated that SlAAE3 in fruits mainly functions at 20 days post-anthesis (20 DPA) and mature green (MG) stages, resulting in up-regulation of amino acid derivatives, nucleotides, and derivatives, but down-regulation of lipid compounds. However, differentially expressed genes (DEGs) were mainly enriched at redox pathways. Taken together, both in vivo and in vitro results suggest that SlAAE3-encoded protein acts as an oxalyl-CoA synthetase, which also participates in redox metabolism. These data provide a further understanding of the mechanism by which SlAAE3 participates in tomato fruit quality.

Identification and characterization of the key enzyme in the biosynthesis of the neurotoxin β-ODAP in grass pea

Grass pea (Lathyrus sativus L.) is a grain legume commonly grown in Asia and Africa for food and forage. It is a highly nutritious and robust crop, capable of surviving both droughts and floods. However, it produces a neurotoxic compound, β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), which can cause a severe neurological disorder when consumed as a primary diet component. While the catalytic activity associated with β-ODAP formation was demonstrated more than 50 years ago, the enzyme responsible for this activity has not been identified. Here, we report on the identity, activity, 3D structure, and phylogenesis of this enzyme—β-ODAP synthase (BOS). We show that BOS belongs to the benzylalcohol O-acetyltransferase, anthocyanin O-hydroxycinnamoyltransferase, anthranilate N-hydroxycinnamoyl/benzoyltransferase, deacetylvindoline 4-O-acetyltransferase superfamily of acyltransferases and is structurally similar to hydroxycinnamoyl transferase. Using molecular docking, we propose a mechanism for its catalytic activity, and using heterologous expression in tobacco leaves (Nicotiana benthamiana), we demonstrate that expression of BOS in the presence of its substrates is sufficient for β-ODAP production in vivo. The identification of BOS may pave the way toward engineering β-ODAP–free grass pea cultivars, which are safe for human and animal consumption.

N-Acetylglucosamine Sensing and Metabolic Engineering for Attenuating Human and Plant Pathogens

During evolution, both human and plant pathogens have evolved to utilize a diverse range of carbon sources. N-acetylglucosamine (GlcNAc), an amino sugar, is one of the major carbon sources utilized by several human and phytopathogens. GlcNAc regulates the expression of many virulence genes of pathogens. In fact, GlcNAc catabolism is also involved in the regulation of virulence and pathogenesis of various human pathogens, including Candida albicans, Vibrio cholerae, Leishmania donovani, Mycobacterium, and phytopathogens such as Magnaporthe oryzae. Moreover, GlcNAc is also a well-known structural component of many bacterial and fungal pathogen cell walls, suggesting its possible role in cell signaling. Over the last few decades, many studies have been performed to study GlcNAc sensing, signaling, and metabolism to better understand the GlcNAc roles in pathogenesis in order to identify new drug targets. In this review, we provide recent insights into GlcNAc-mediated cell signaling and pathogenesis. Further, we describe how the GlcNAc metabolic pathway can be targeted to reduce the pathogens’ virulence in order to control the disease prevalence and crop productivity.

WRKY genes provide novel insights into their role against Ralstonia solanacearum infection in cultivated peanut (Arachis hypogaea L.)

As one of the most important and largest transcription factors, WRKY plays a critical role in plant disease resistance. However, little is known regarding the functions of the WRKY family in cultivated peanuts (Arachis hypogaea L.). In this study, a total of 174 WRKY genes (AhWRKY) were identified from the genome of cultivated peanuts. Phylogenetic analysis revealed that AhWRKY proteins could be divided into four groups, including 35 (20.12%) in group I, 107 (61.49%) in group II, 31 (17.82%) in group III, and 1 (0.57%) in group IV. This division is further supported by the conserved motif compositions and intron/exon structures. All AhWRKY genes were unevenly located on all 20 chromosomes, among which 132 pairs of fragment duplication and seven pairs of tandem duplications existed. Eighteen miRNAs were found to be targeting 50 AhWRKY genes. Most AhWRKY genes from some groups showed tissue-specific expression. AhWRKY46, AhWRKY94, AhWRKY156, AhWRKY68, AhWRKY41, AhWRKY128, AhWRKY104, AhWRKY19, AhWRKY62, AhWRKY155, AhWRKY170, AhWRKY78, AhWRKY34, AhWRKY12, AhWRKY95, and AhWRKY76 were upregulated in ganhua18 and kainong313 genotypes after Ralstonia solanacearum infection. Ten AhWRKY genes (AhWRKY34, AhWRKY76, AhWRKY78, AhWRKY120, AhWRKY153, AhWRKY155, AhWRKY159, AhWRKY160, AhWRKY161, and AhWRKY162) from group III displayed different expression patterns in R. solanacearum sensitive and resistant peanut genotypes infected with the R. solanacearum. Two AhWRKY genes (AhWRKY76 and AhWRKY77) from group III obtained the LRR domain. AhWRKY77 downregulated in both genotypes; AhWRKY76 showed lower-higher expression in ganhua18 and higher expression in kainong313. Both AhWRKY76 and AhWRKY77 are targeted by ahy-miR3512, which may have an important function in peanut disease resistance. This study identified candidate WRKY genes with possible roles in peanut resistance against R. solanacearum infection. These findings not only contribute to our understanding of the novel role of WRKY family genes but also provide valuable information for disease resistance in A. hypogaea.

The Tomato Transcription Factor SlNAC063 Is Required for Aluminum Tolerance by Regulating SlAAE3-1 Expression

Aluminum (Al) toxicity constitutes one of the major limiting factors of plant growth and development on acid soils, which comprises approximately 50% of potentially arable lands worldwide. When suffering Al toxicity, plants reprogram the transcription of genes, which activates physiological and metabolic pathways to deal with the toxicity. Here, we report the role of a NAM, ATAF1, 2 and CUC2 (NAC) transcription factor (TF) in tomato Al tolerance. Among 53 NAC TFs in tomatoes, SlNAC063 was most abundantly expressed in root apex and significantly induced by Al stress. Furthermore, the expression of SlNAC063 was not induced by other metals. Meanwhile, the SlNAC063 protein was localized at the nucleus and has transcriptional activation potentials in yeast. By constructing CRISPR/Cas9 knockout mutants, we found that slnac063 mutants displayed increased sensitivity to Al compared to wild-type plants. However, the mutants accumulated even less Al than wild-type (WT) plants, suggesting that internal tolerance mechanisms but not external exclusion mechanisms are implicated in SlNAC063-mediated Al tolerance in tomatoes. Further comparative RNA-sequencing analysis revealed that only 45 Al-responsive genes were positively regulated by SlNAC063, although the expression of thousands of genes (1,557 upregulated and 636 downregulated) was found to be affected in slnac063 mutants in the absence of Al stress. The kyoto encyclopedia of genes and genomes (KEGG) pathway analysis revealed that SlNAC063-mediated Al-responsive genes were enriched in "phenylpropanoid metabolism," "fatty acid metabolism," and "dicarboxylate metabolism," indicating that SlNAC063 regulates metabolisms in response to Al stress. Quantitative real-time (RT)-PCR analysis showed that the expression of SlAAE3-1 was repressed by SlNAC063 in the absence of Al. However, the expression of SlAAE3-1 was dependent on SlNAC063 in the presence of Al stress. Taken together, our results demonstrate that a NAC TF SlNAC063 is involved in tomato Al tolerance by regulating the expression of genes involved in metabolism, and SlNAC063 is required for Al-induced expression of SlAAE3-1.

The identification and characterization of an oxalyl-CoA synthetase from grass pea (Lathyrus sativus L.)

Oxalic acid is a small metabolite that can be found in many plants in which it serves as protection from herbivores, a chelator of metal ions, a regulator of calcium...

Current Perspectives on Reducing the β-ODAP Content and Improving Potential Agronomic Traits in Grass Pea (Lathyrus sativus L.)

Grass pea is well-established as one of the most resilient and versatile crops that can thrive under extreme climatic circumstances such as cold, heat, drought, salt-affected soils, submergence, and excessive rainfall along with resistance to several diseases and pests. However, despite the awareness of its virtues, its cultivation globally has decreased recently owing to the presence of a neurotoxin, β-N-oxalyl-L-α, β-diaminopropionic acid (β-ODAP), in the seedlings and seeds of this legume, which has been reported to cause neurolathyrism, a non-reversible neurological disorder in humans and animals. Significant repositories of Lathyrus germplasm are available across countries that have provided access to a wide range of agro-morphological traits as well as the low β ODAP content. Efforts have been made worldwide to use these germplasms for the genetic enhancement of grass pea to make this food safe for human consumption. Efforts on molecular breeding of this crop are also lagging. However, during the last decade, the research scenario has changed with some efforts being made toward improving this climate resilient pulse in terms of genomic resources. Molecular markers have also been used to evaluate the interspecific diversity as well as the phylogenetic relationship among the species and mapping studies. Intron-targeted amplified polymorphic, genomic simple sequence repeat, resistance genes analogs, and disease resistance markers developed for other legume species have been successfully cross-amplified in grass pea. Transcriptomic studies have recently been undertaken on grass pea by deploying several second-generation sequencing techniques. In addition, a few studies have attempted to unveil the genes and the underlying mechanism conferring biotic and abiotic stress or regulating the pathway of β-ODAP in grass pea. Proteomics has accelerated the identification studies on differential proteomes in response to salinity and low-temperature stress conditions for unveiling the common signaling pathways involved in mitigating these abiotic stresses and in discovering differentially regulated proteins. In grass pea, a metabolomics approach has been used to identify the metabolic processes associated with β-ODAP synthesis. Genome sequencing of grass pea is under way which is expected to be vital for whole-genome re-sequencing and gene annotation toward the identification of genes with novel functions. Recently, a draft genome sequence of grass pea was developed, and some efforts are underway to re-sequence a diverse panel of grass pea comprising 384 germplasm lines. Owing to the scantiness of a successful transformation protocol, research on the application of modern approaches of genome editing like the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) or CRISPR-associated protein 9 (CRISPR/Cas9) system for the engineering of signaling pathways or regulatory mechanisms seeks immediate attention to reduce the β-ODAP content in seeds and to improve the potential agronomic traits in grass pea.

Organic acids: versatile stress-response roles in plants

Organic acids (OAs) are central to cellular metabolism. Many plant stress responses involve the exudation of OAs at the root-soil interface, which can improve soil mineral acquisition and toxic metal tolerance. Because of their simple structure, the low-molecular-weight OAs are widely studied. We discuss the conventional roles of OAs, and some newly emerging roles in plant stress tolerance. OAs are more versatile in their role in plant stress tolerance and are more efficient chelating agents than other acids, such as amino acids. Root OA exudation is important in soil carbon sequestration. These functions are key processes in combating climate change and helping with more sustainable food production. We briefly review the mechanisms behind enhanced biosynthesis, secretion, and regulation of these activities under different stresses, and provide an outline of the transgenic approaches targeted towards the enhanced production and secretion of OAs. A recurring theme of OAs in plant biology is their role as 'acids' modifying pH, as 'chelators' binding metals, or as 'carbon sources' for microbes. We argue that these multiple functions are key factors for understanding these molecules' important roles in plant stress biology. Finally, we discuss how the functions of OAs in plant stress responses could be used, and identify the important unanswered questions.

An Arabidopsis Oxalyl-CoA Decarboxylase, AtOXC, Is Important for Oxalate Catabolism in Plants

Considering the widespread occurrence of oxalate in nature and its broad impact on a host of organisms, it is surprising that so little is known about the turnover of this important acid. In plants, oxalate oxidase is the most well-studied enzyme capable of degrading oxalate, but not all plants possess this activity. Recently, acyl-activating enzyme 3 (AAE3), encoding an oxalyl-CoA synthetase, was identified in Arabidopsis. This enzyme has been proposed to catalyze the first step in an alternative pathway of oxalate degradation. Since this initial discovery, this enzyme and proposed pathway have been found to be important to other plants and yeast as well. In this study, we identify, in Arabidopsis, an oxalyl-CoA decarboxylase (AtOXC) that is capable of catalyzing the second step in this proposed pathway of oxalate catabolism. This enzyme breaks down oxalyl-CoA, the product of AtAAE3, into formyl-CoA and CO₂. AtOXC:GFP localization suggested that this enzyme functions within the cytosol of the cell. An Atoxc knock-down mutant showed a reduction in the ability to degrade oxalate into CO₂. This reduction in AtOXC activity resulted in an increase in the accumulation of oxalate and the enzyme substrate, oxalyl-CoA. Size exclusion studies suggest that the enzyme functions as a dimer. Computer modeling of the AtOXC enzyme structure identified amino acids of predicted importance in co-factor binding and catalysis. Overall, these results suggest that AtOXC catalyzes the second step in this alternative pathway of oxalate catabolism.

Sclerotinia Stem Rot Resistance in Rapeseed: Recent Progress and Future Prospects

Sclerotinia stem rot (SSR) of rapeseed (Brassica napus), caused by the soil-borne fungus Sclerotinia sclerotiorum, is one of the main diseases seriously affecting the yield and oil quality of infected rapeseed crops. The complexity of the inheritance of resistance and of the interaction mechanisms between rapeseed and S. sclerotiorum limits resistance gene identification and molecular breeding. In this review, the latest progress of research into resistance to SSR in B. napus is summarized from the following three directions: the pathogenesis mechanisms of S. sclerotiorum, the resistance mechanisms of B. napus toward S. sclerotiorum, and rapeseed breeding for resistance to SSR. This review aims to provide a theoretical basis and useful reference for analyzing the mechanism of the interaction between B. napus and S. sclerotiorum, searching for gene loci associated with the resistance response, and for achieving disease-resistance genetic manipulation and molecular design breeding in rapeseed.

Overexpression of the chitinase gene CmCH1 from Coniothyrium minitans renders enhanced resistance to Sclerotinia sclerotiorum in soybean

Pathogenic fungi represent one of the major biotic stresses for soybean production across the world. Sclerotinia sclerotiorum, the causal agent of Sclerotinia stem rot, is a devastating fungal pathogen that is responsible for significant yield losses in soybean. In this study, the chitinase gene CmCH1, from the mycoparasitic fungus Coniothyrium minitans, which infects a range of ascomycetous sclerotia, including S. sclerotiorum and S. minor, was introduced into soybean. Transgenic plants expressing CmCH1 showed higher resistance to S. sclerotiorum infection, with significantly reduced lesion sizes in both detached stem and leaf assays, compared to the non-transformed control. Increased hydrogen peroxide content and activities of defense-responsive enzymes, such as peroxidase, superoxide dismutase, phenylalanine ammonia lyase, and polyphenoloxidase were also observed at the infection sites in the transgenic plants inoculated with S. sclerotiorum. Consistent with the role of chitinases in inducing downstream defense responses by the release of elicitors, several defense-related genes, such as GmNPR2, GmSGT-1, GmRAR1, GmPR1, GmPR3, GmPR12, GmPAL, GmAOS, GmPPO, were also significantly upregulated in the CmCH1-expressing soybean after inoculation. Collectively, our results demonstrate that overexpression of CmCH1 led to increased accumulation of H2O2 and up-regulation of defense-related genes and enzymes, and thus enhanced resistance to S. sclerotiorum infection while showing no detrimental effects on growth and development of soybean plants.

A convenient and robust protocol for preparation of ODAP-free Lathyrus sativus protein

The present study aimed to develop a protocol for easy removal of β-ODAP neurotoxin by converting it into its isomer α-ODAP (reported to be less toxic) followed by its separation from the protein fraction in pH dependent manner. Use of β-mercaptoethanol prevented aggregate formation and increased solubility of the prepared Lathyrus sativus protein. Validation of ODAP removal by paper chromatography and mass spectrometry indicated the robustness of the protocol. Removal of ODAP and presence of high antioxidants and homoarginine content can enable Lathyrus sativus to be an alternate source of protein, as well as have other health benefits, including benefits for patients with cardiovascular diseases.

Grass pea (Lathyrus sativus L.): orphan crop, nutraceutical or just plain food?

Although grass pea is an environmentally successful robust legume with major traits of interest for food and nutrition security, the genetic potential of this orphan crop has long been neglected. Grass pea (Lathyrus sativus L.) is a Neolithic plant that has survived millennia of cultivation and has spread over three continents. It is a robust legume crop that is considered one of the most resilient to climate changes and to be survival food during drought-triggered famines. The hardy penetrating root system allows the cultivation of grass pea in various soil types, including marginal ones. As an efficient nitrogen fixer, it meets its own nitrogen requirements and positively benefits subsequent crops. However, already in ancient India and Greece, overconsumption of the seeds and a crippling neurological disorder, later coined neurolathyrism, had been linked. Overemphasis of their suspected toxic properties has led to disregard the plant's exceptionally positive agronomic properties and dietary advantages. In normal socio-economic and environmental situations, in which grass pea is part of a balanced diet, neurolathyrism is virtually non-existent. The etiology of neurolathyrism has been oversimplified and the deficiency in methionine in the diet has been overlooked. In view of the global climate change, this very adaptable and nutritious orphan crop deserves more attention. Grass pea can become a wonder crop if the double stigma on its reputation as a toxic plant and as food of the poor can be disregarded. Additionally, recent research has exposed the potential of grass pea as a health-promoting nutraceutical. Development of varieties with an improved balance in essential amino acids and diet may be relevant to enhance the nutritional value without jeopardizing the multiple stress tolerance of this promising crop.

Mechanisms of plant protection against two oxalate-producing fungal pathogens by oxalotrophic strains of Stenotrophomonas spp

Oxalotrophic Stenotrophomonas isolated from tomato rhizosphere are able to protect plants against oxalate-producing pathogens by a combination of actions including induction of plant defence signalling callose deposition and the strengthening of plant cell walls and probably the degradation of oxalic acid. Oxalic acid plays a pivotal role in the virulence of the necrotrophic fungi Botrytis cinerea and Sclerotinia sclerotiorum. In this work, we isolated two oxalotrophic strains (OxA and OxB) belonging to the bacterial genus Stenotrophomonas from the rhizosphere of tomato plants. Both strains were capable to colonise endophytically Arabidopsis plants and protect them from the damage caused by high doses of oxalic acid. Furthermore, OxA and OxB protected Arabidopsis from S. sclerotiorum and B. cinerea infections. Bacterial inoculation induced the production of phenolic compounds and the expression of PR-1. Besides, both isolates exerted a protective effect against fungal pathogens in Arabidopsis mutants affected in the synthesis pathway of salicylic acid (sid2-2) and jasmonate perception (coi1). Callose deposition induced by OxA and OxB was required for protection against phytopathogens. Moreover, B. cinerea and S. sclerotiorum mycelial growth was reduced in culture media containing cell wall polysaccharides from leaves inoculated with each bacterial strain. These findings suggest that cell walls from Arabidopsis leaves colonised by these bacteria would be less susceptible to pathogen attack. Our results indicate that these oxalotrophic bacteria can protect plants against oxalate-producing pathogens by a combination of actions and show their potential for use as biological control agents against fungal diseases.

Metabolic and proteomic mechanism of benzo[a]pyrene degradation by Brevibacillus brevis

Benzo[a]pyrene (BaP) is a model compound of polycyclic aromatic hydrocarbons. The relationship between its toxicity and some target biomolecules has been investigated. To reveal the interactions of BaP biodegradation and metabolic network, BaP intermediates, proteome, carbon metabolism and ion transport were analyzed. The results show that 76% BaP was degraded by Brevibacillus brevis within 7 d through the cleavage of aromatic rings with the production of 1-naphthol and 2-naphthol. During this process, the expression of xylose isomerase was induced for xylose metabolism, whereas, α-cyclodextrin could no longer be metabolized. Lactic acid, acetic acid and oxalic acid at 0.1-1.2 mg dm^-3 were released stemming from their enhanced biosynthesis in the pathways of pyruvate metabolism and citrate cycle, while 5-7 mg dm^-3 of PO₄^3- were transported for energy metabolism. The relative abundance of 43 proteins was significantly increased for pyruvate metabolism, citrate cycle, amino acid metabolism, purine metabolism, ribosome metabolism and protein synthesis.

Manipulation of oxalate metabolism in plants for improving food quality and productivity

Oxalic acid is a naturally occurring metabolite in plants and a common constituent of all plant-derived human diets. Oxalic acid has diverse unrelated roles in plant metabolism, including pH regulation in association with nitrogen metabolism, metal ion homeostasis and calcium storage. In plants, oxalic acid is also a pathogenesis factor and is secreted by various fungi during host infection. Unlike those of plants, fungi and bacteria, the human genome does not contain any oxalate-degrading genes, and therefore, the consumption of large amounts of plant-derived oxalate is considered detrimental to human health. In this review, we discuss recent biotechnological approaches that have been used to reduce the oxalate content of plant tissues.

Enhanced resistance to sclerotinia stem rot in transgenic soybean that overexpresses a wheat oxalate oxidase

Sclerotinia stem rot (SSR), caused by the oxalate-secreting necrotrophic fungal pathogen Sclerotinia sclerotiorum, is one of the devastating diseases that causes significant yield loss in soybean (Glycine max). Until now, effective control of the pathogen is greatly limited by a lack of strong resistance in available commercial soybean cultivars. In this study, transgenic soybean plants overexpressing an oxalic acid (OA)-degrading oxalate oxidase gene OXO from wheat were generated and evaluated for their resistance to S. sclerotiorum. Integration and expression of the transgene were confirmed by Southern and western blot analyses. As compared with non-transformed (NT) control plants, the transgenic lines with increased oxalate oxidase activity displayed significantly reduced lesion sizes, i.e., by 58.71-82.73% reduction of lesion length in a detached stem assay (T3 and T4 generations) and 76.67-82.0% reduction of lesion area in a detached leaf assay (T4 generation). The transgenic plants also showed increased tolerance to the externally applied OA (60 mM) relative to the NT controls. Consecutive resistance evaluation further confirmed an enhanced and stable resistance to S. sclerotiorum in the T3 and T4 transgenic lines. Similarly, decreased OA content and increased hydrogen peroxide (H2O2) levels were also observed in the transgenic leaves after S. sclerotiorum inoculation. Quantitative real-time polymerase chain reaction analysis revealed that the expression level of OXO reached a peak at 1 h and 4 h after inoculation with S. sclerotiorum. In parallel, a significant up-regulation of the hypersensitive response-related genes GmNPR1-1, GmNPR1-2, GmSGT1, and GmRAR occurred, eventually induced by increased release of H2O2 at the infection sites. Interestingly, other defense-related genes such as salicylic acid-dependent genes (GmPR1, GmPR2, GmPR3, GmPR5, GmPR12 and GmPAL), and ethylene/jasmonic acid-dependent genes (GmAOS, GmPPO) also exhibited higher expression levels in the transgenic plants than in the NT controls. Our results demonstrated that overexpression of OXO enhances SSR resistance by degrading OA secreted by S. sclerotiorum and increasing H2O2 levels, and eliciting defense responses mediated by multiple signaling pathways.

Mechanisms of Broad Host Range Necrotrophic Pathogenesis in Sclerotinia sclerotiorum

Among necrotrophic fungi, Sclerotinia sclerotiorum is remarkable for its extremely broad host range and for its aggressive host tissue colonization. With full genome sequencing, transcriptomic analyses and the increasing pace of functional gene characterization, the factors underlying the basis of this broad host range necrotrophic pathogenesis are now being elucidated at a greater pace. Among these, genes have been characterized that are required for infection via compound appressoria in addition to genes associated with colonization that regulate oxalic acid (OA) production and OA catabolism. Moreover, virulence-related secretory proteins have been identified, among which are candidates for manipulating host activities apoplastically and cytoplasmically. Coupled with these mechanistic studies, cytological observations of the colonization process have blurred the heretofore clear-cut biotroph versus necrotroph boundary. In this review, we reexamine the cytology of S. sclerotiorum infection and put more recent molecular and genomic data into the context of this cytology. We propose a two-phase infection model in which the pathogen first evades, counteracts and subverts host basal defense reactions prior to killing and degrading host cells. Spatially, the pathogen may achieve this via the production of compatibility factors/effectors in compound appressoria, bulbous subcuticular hyphae, and primary invasive hyphae. By examining the nuances of this interaction, we hope to illuminate new classes of factors as targets to improve our understanding of broad host range necrotrophic pathogens and provide the basis for understanding corresponding host resistance.

Sclerotinia sclerotiorum: An Evaluation of Virulence Theories

Oxalic acid production in Sclerotinia sclerotiorum has long been associated with virulence. Research involving UV-induced, genetically undefined mutants that concomitantly lost oxalate accumulation, sclerotial formation, and pathogenicity supported the conclusion that oxalate is an essential pathogenicity determinant of S. sclerotiorum. However, recent investigations showed that genetically defined mutants that lost oxalic acid production but accumulated fumaric acid could cause disease on many plants and substantiated the conclusion that acidic pH, not oxalic acid per se, is the necessary condition for disease development. Critical evaluation of available evidence showed that the UV-induced mutants harbored previously unrecognized confounding genetic defects in saprophytic growth and pH responsiveness, warranting reevaluation of the conclusions about virulence based on the UV-induced mutants. Furthermore, analyses of the evidence suggested a hypothesis for the existence of an unrecognized regulator responsive to acidic pH. Identifying the unknown pH regulator would offer a new avenue for investigating pH sensing/regulation in S. sclerotiorum and novel targets for intervention in disease control strategies.

Enhanced resistance to rice blast and sheath blight in rice (oryza sativa L.) by expressing the oxalate decarboxylase protein Bacisubin from Bacillus subtilis

Oxalate decarboxylase (OxDC), catalyzing the degradation of oxalic acid, is widely distributed in varieties of organisms. In this study, an oxalate decarboxylase gene from Bacillus subtilis strain BS-916, Bacisubin, was transformed into rice variety Nipponbare to generate transgenic rice with increased OxDC activity. Pathogenicity test revealed that the transgenic rice showed enhanced resistance to rice blast and sheath blight. Further RNA-seq analysis between Nipponbare WT (wild type) and transgenic rice identified 1764 DEGs (Differentially expressed genes) including 723 up-regulated unigenes and 1041 down-regulated unigenes. Five GO terms including single-organism process and oxidation-reduction process were significantly enriched in the up-regulated genes. Interestingly, five genes encoding glutaredoxin and one gene encoding MADS box were up- and down-regulated in the transgenic rice, respectively. Collectively, our study advances the understanding of OxDC in resistance to rice disease and its possible mechanisms. Our results also suggest that OxDC would be an effective antifungal protein preventing fungal infection in transgenic rice.

Genetic Engineering: A Possible Strategy for Protein-Energy Malnutrition Regulation

Protein-energy malnutrition (PEM) has adversely affected the generations of developing countries. It is a syndrome that in severity causes death. PEM generally affects infants of 1-5 age group. This manifestation is maintained till adulthood in the form of poor brain and body development. The developing nations are continuously making an effort to curb PEM. However, it is still a prime concern as it was in its early years of occurrence. Transgenic crops with high protein and enhanced nutrient content have been successfully developed. Present article reviews the studies documenting genetic engineering-mediated improvement in the pulses, cereals, legumes, fruits and other crop plants in terms of nutritional value, stress tolerance, longevity and productivity. Such genetically engineered crops can be used as a possible remedial tool to eradicate PEM.

Genetically modified (GM) crops: milestones and new advances in crop improvement

New advances in crop genetic engineering can significantly pace up the development of genetically improved varieties with enhanced yield, nutrition and tolerance to biotic and abiotic stresses. Genetically modified (GM) crops can act as powerful complement to the crops produced by laborious and time consuming conventional breeding methods to meet the worldwide demand for quality foods. GM crops can help fight malnutrition due to enhanced yield, nutritional quality and increased resistance to various biotic and abiotic stresses. However, several biosafety issues and public concerns are associated with cultivation of GM crops developed by transgenesis, i.e., introduction of genes from distantly related organism. To meet these concerns, researchers have developed alternative concepts of cisgenesis and intragenesis which involve transformation of plants with genetic material derived from the species itself or from closely related species capable of sexual hybridization, respectively. Recombinase technology aimed at site-specific integration of transgene can help to overcome limitations of traditional genetic engineering methods based on random integration of multiple copy of transgene into plant genome leading to gene silencing and unpredictable expression pattern. Besides, recently developed technology of genome editing using engineered nucleases, permit the modification or mutation of genes of interest without involving foreign DNA, and as a result, plants developed with this technology might be considered as non-transgenic genetically altered plants. This would open the doors for the development and commercialization of transgenic plants with superior phenotypes even in countries where GM crops are poorly accepted. This review is an attempt to summarize various past achievements of GM technology in crop improvement, recent progress and new advances in the field to develop improved varieties aimed for better consumer acceptance.