Functional divergence in the glutathione transferase superfamily in plants. Identification of two classes with putative functions in redox homeostasis in Arabidopsis thaliana

PbNAC3 coordinates AsA generation and ABA biosynthesis to improve salt tolerance in pear

In plants, dehydroascorbate reductase (DHAR) is one of the key enzymes in AsA generation during the AsA-GSH cycle, which helps maintain the normal metabolic level of AsA. However, the molecular mechanism of DHAR's response to salt stress is still unknown. Our experiments show a ping-pong mechanism, in which DHA is combined with free reductase DHAR, and free reductase DHAR is combined with GSH in the form of sulfenylation to promote AsA generation in response to salt stress. This mechanism is inhibited by H2O2-mediated sulfenylation modification. The overexpression of PbDHAR3 in pear callus and Arabidopsis plants alleviated salt-induced damage, while its silencing decreased salt tolerance in Pyrus betulaefolia. PbNAC3 can activate the expression of PbDHAR3 by directly binding to the promoter. The overexpression of PbNAC3 in pear callus improved salt tolerance, while silencing it reduced tolerance in P. betulaefolia. Overexpression of PbNAC3 in Arabidopsis plants is able to adjust the trade-off between plant growth and salt stress. Higher expression levels of NCEDs or PYLs, and higher ABA content were observed under salt treatment. Further experiments demonstrate that PbNAC3 activates PbNCED5 through interaction with cis-regulatory elements. Overall, our results show that PbNAC3 plays a critical role in salt stress response by targeting the promoters of PbDHAR3 and PbNCED5, promoting AsA generation and ABA biosynthesis. This study will deepen our understanding of the mechanisms underlying the trade-offs between plant growth and stress tolerance and assist the development of stress-resistant, high-yield crops.

DNA Demethylase ROS1 Interferes with DNA Methylation and Activates Stress Response Genes in Plants Infected with Beet Severe Curly Top Virus

DNA methylation is one mechanism of epigenetic regulation in plants. Small interfering RNAs (siRNAs) targeted endogenous genes and caused the promoters to be hypermethylated, namely RNA-directed DNA methylation (RdDM). Repressor of silencing 1 (ROS1) is an active DNA demethylase involved in the regulation of DNA methylation. This study indicates that ROS1-mediated DNA demethylation plays important roles in regulating the expression of these stress response genes and in response to biotic stresses. Further experiments confirmed that the expression level of the ROS1 gene was significantly upregulated in A. thaliana plants infected with beet severe curly top virus (BSCTV). Moreover, the DNA sequencing results demonstrated that ROS1 interferes with DNA methylation of repeat regions in the promoters of ACD6, GSTF14, and ACO3 in A. thaliana plants infected with BSCTV. These findings reveal the epigenetic mechanisms by which ROS1 regulates the expression of the stress response genes, thereby improving the adaptability of plants to biotic stresses.

Chemoproteomic Profiling Reveals Chlorogenic Acid as a Covalent Inhibitor of Arabidopsis Dehydroascorbate Reductase 1

Chlorogenic acid (CA) is an abundant plant secondary metabolite with promising allelopathic effects on weed growth. However, the molecular targets and mechanism of action of CA in plants remain elusive. Here, we report the employment of a clickable photoaffinity probe in identifying the protein targets of CA in Arabidopsis seedling proteomes. CA specifically binds Arabidopsis dehydroascorbate reductase 1 (AtDHAR1), an enzyme responsible for ascorbate regeneration in plants, by covalent alkylating Cys20 within the catalytic center, thereby inhibiting its activity. In vivo application of CA reduced the pool size and redox state of ascorbate, leading to H2O2 accumulation in Arabidopsis seedlings. In agreement with these results, CA significantly induced the upregulation of antioxidant enzymes and downregulation of proteins involved in water transport and photosynthesis, as evidenced by quantitative proteomics. Taken together, this study revealed DHAR1 as a functional target underlying CA's allelopathic activity in plants, which opens new opportunities for the development of novel herbicides from naturally existing resources.

Oxidative post-translational modifications of plant antioxidant systems under environmental stress

Plants are often subject to environmental challenges posed by abiotic and biotic stresses, which are increasing under the current climate change conditions, provoking a loss in crop yield worldwide. Plants must cope with adverse situations such as increasing temperatures, air pollution or loss of agricultural land due to salinity, drought, contamination, and pathogen attacks, among others. Plants under stress conditions increase the production of reactive oxygen-, nitrogen-, and sulphur species (ROS/RNS/RSS), whose concentrations must be tightly regulated. The enzymatic antioxidant system and metabolites are in charge of their control to avoid their deleterious effects on cellular components, allowing their participation in signalling events. As signalling molecules, reactive species are involved in plant responses to the environment through post-translational modifications (PTMs) of proteins, which, in turn, may regulate the structure, function, and location of the antioxidant proteins by oxidative/nitrosative/persulfure modifications of different amino acid residues. In this review, we examine the different effects of these post-translational modifications, which are emerging as a fine-tuned point of control of the antioxidant systems involved in plant responses to climate change, a growing threat to crop production.

Genome-wide identification and expression analysis of the glutathione transferase gene family and its response to abiotic stress in rye (Secale cereale)

BACKGROUND

Glutathione S-transferases (GSTs) are a crucial class of plant enzymes, playing pivotal roles in plant growth, development, and stress responses. However, studies on the functions and regulatory mechanisms of GSTs in plants remain relatively limited.

RESULTS

This study aimed to comprehensively identify and analyze GST proteins in rye. A total of 171 rye GST genes were identified and classified into four subfamilies, Tau, Phi, Theta, and Zeta, based on their sequence similarity and structural features. Notably, genes classified under the Tau subfamily were the most abundant at 118, while only one gene was under the Theta subfamily. Subsequent phylogenetic and collinearity analysis revealed 29 tandem duplications and 6 segmental duplication events. There were 13 collinear genes between rye and wheat, maize, and rice, demonstrating the expansion and evolution of the GST gene family. An analysis of the expression profiles of 20 representative ScGST genes in different tissues and under various environmental stresses was performed to further understand the functions and expression patterns of ScGST genes. The results showed that these genes exhibited the highest expression levels in stems, followed by fruits and leaves.

CONCLUSIONS

This study provides a comprehensive identity, classification, and analysis of rye GST genes, which offer valuable insights into the functionality and regulatory mechanisms of the GST gene family in rye. Especially, ScGST39 was identified as a candidate gene because it was significantly upregulated under multiple stress conditions, indicating its potential crucial role in plant stress tolerance mechanisms.

Overlooked and misunderstood: can glutathione conjugates be clues to understanding plant glutathione transferases?

Plant glutathione transferases (GSTs) constitute a large and diverse family of enzymes that are involved in plant stress response, metabolism and defence, yet their physiological functions remain largely elusive. Consistent with the traditional view on GSTs across organisms as detoxification enzymes, in vitro most plant GSTs catalyse glutathionylation, conjugation of the tripeptide glutathione (GSH; γ-Glu-Cys-Gly) onto reactive molecules. However, when it comes to elucidating GST functions, it remains a key challenge that the endogenous plant glutathione conjugates (GS-conjugates) that would result from such glutathionylation reactions are rarely reported. Furthermore, GSTs often display high substrate promiscuity, and their proposed substrates are prone to spontaneous chemical reactions with GSH; hence, single-gene knockouts rarely provide clear chemotypes or phenotypes. In a few cases, GS-conjugates are demonstrated to be biosynthetic intermediates that are rapidly further metabolized towards a pathway end product, explaining their low abundance and rare detection. In this review, we summarize the current knowledge of plant GST functions and how and possibly why evolution has resulted in a broad and extensive expansion of the plant GST family. Finally, we demonstrate that endogenous GS-conjugates are more prevalent in plants than assumed and suggest they are overlooked as clues towards the identification of plant GST functions. This article is part of the theme issue 'The evolution of plant metabolism'.

QTL mapping and genome-wide association analysis reveal genetic loci and candidate gene for resistance to gray leaf spot in tropical and subtropical maize germplasm

KEY MESSAGE

Using QTL mapping and GWAS, two candidate genes (Zm00001d051039 and Zm00001d051147) were consistently identified across the three different environments and BLUP values. GWAS analysis identified the candidate gene, Zm00001d044845. These genes were subsequently validated to exhibit a significant association with maize gray leaf spot (GLS) resistance. Gray leaf spot (GLS) is a major foliar disease of maize (Zea mays L.) that causes significant yield losses worldwide. Understanding the genetic mechanisms underlying gray leaf spot resistance is crucial for breeding high-yielding and disease-resistant varieties. In this study, eight tropical and subtropical germplasms were crossed with the temperate germplasm Ye107 to develop a nested association mapping (NAM) population comprising 1,653 F2:8 RILs, consisting of eight recombinant inbred line (RIL) subpopulations, using the single-seed descent method. The NAM population was evaluated for GLS resistance in three different environments, and genotyping by sequencing of the NAM population generated 593,719 high-quality single-nucleotide polymorphisms (SNPs). Linkage analysis and genome-wide association studies (GWASs) were conducted to identify candidate genes regulating GLS resistance in maize. Both analyses identified 25 QTLs and 149 SNPs that were significantly associated with GLS resistance. Candidate genes were screened 20 Kb upstream and downstream of the significant SNPs, and three novel candidate genes (Zm00001d051039, Zm00001d051147, and Zm00001d044845) were identified. Zm00001d051039 and Zm00001d051147 were located on chromosome 4 and co-localized in both linkage (qGLS4-1 and qGLS4-2) and GWAS analyses. SNP-138,153,206 was located 0.499 kb downstream of the candidate gene Zm00001d051039, which encodes the protein IN2-1 homolog B, a homolog of glutathione S-transferase (GST). GSTs and protein IN2-1 homolog B scavenge reactive oxygen species under various stress conditions, and GSTs are believed to protect plants from a wide range of biotic and abiotic stresses by detoxifying reactive electrophilic compounds. Zm00001d051147 encodes a probable beta-1,4-xylosyltransferase involved in the biosynthesis of xylan in the cell wall, enhancing resistance. SNP-145,813,215 was located 2.69 kb downstream of the candidate gene. SNP-5,043,412 was consistently identified in three different environments and BLUP values and was located 8.788 kb downstream of the candidate gene Zm00001d044845 on chromosome 9. Zm00001d044845 encodes the U-box domain-containing protein 4 (PUB4), which is involved in regulating plant immunity. qRT-PCR analysis showed that the relative expression levels of the three candidate genes were significantly upregulated in the leaves of the TML139 (resistant) parent, indicating that these three candidate genes could be associated with resistance to GLS. The findings of this study are significant for marker-assisted breeding aimed at enhancing resistance to GLS in maize and lay the foundation for further elucidation of the genetic mechanisms underlying resistance to gray leaf spot in maize and breeding of new disease-resistant varieties.

Overexpression of dehydroascorbate reductase gene IbDHAR1 improves the tolerance to abiotic stress in sweet potato

Dehydroascorbate reductase (DHAR), an indispensable enzyme in the production of ascorbic acid (AsA) in plants, is vital for plant tolerance to various stresses. However, there is limited research on the stress tolerance functions of DHAR genes in sweet potato (Ipomoea batatas [L.] Lam). In this study, the full-length IbDHAR1 gene was cloned from the leaves of sweet potato cultivar Xu 18. The IbDHAR1 protein is speculated to be located in both the cytoplasm and the nucleus. As revealed by qRT-PCR, the relative expression level of IbDHAR1 in the proximal storage roots was much greater than in the other tissues, and could be upregulated by high-temperature, salinity, drought, and abscisic acid (ABA) stress. The results of pot experiments indicated that under high salinity and drought stress conditions, transgenic Arabidopsis and sweet potato plants exhibited decreases in H2O2 and MDA levels. Conversely, the levels of antioxidant enzymes APX, SOD, POD, and ACT, and the content of DHAR increased. Additionally, the ratio of AsA/DHA was greater in transgenic lines than in the wild type. The results showed that overexpression of IbDHAR1 intensified the ascorbic acid-glutathione cycle (AsA-GSH) and promoted the activity of the related antioxidant enzyme systems to improve plant stress tolerance and productivity.

An intronless tau class glutathione transferase detoxifies several herbicides in flufenacet-resistant ryegrass

Resistance to preemergence herbicides, e.g. inhibitors of the biosynthesis of very-long-chain fatty acids (VLCFAs), is evolving in response to increased use of these compounds. Grass weeds such as ryegrasses (Lolium spp.) have accumulated resistance to various herbicide modes of action. Here, an RNA-seq analysis was conducted using 3 ryegrass populations resistant to the VLCFA biosynthesis inhibitor flufenacet to investigate this phenomenon. Besides various transcripts, including putative long noncoding RNAs (lncRNAs), a single putatively functional tau class glutathione transferase (GST) was constitutively differentially expressed. It was further induced by herbicide application. This GST was expressed as a recombinant protein in Escherichia coli along with other GSTs and detoxified flufenacet rapidly in vitro. Detoxification rates of other herbicides tested in vitro were in accordance with cross-resistance patterns previously determined in vivo. A genome-wide GST analysis revealed that the candidate GST was located in a cluster of 3 intronless GSTs. Their intronless nature possibly results from the retroposition of cellular mRNAs followed by tandem duplication and may affect gene expression. The large number of GSTs (≥195) in the genome of rigid ryegrass (Lolium rigidum) compared with other plant organisms is likely a key factor in the ability of this weed to evolve resistance to different herbicide chemistries. However, in the case of flufenacet resistance, a single upregulated GST with high affinity for the substrate flufenacet possibly contributes overproportionally to rapid herbicide detoxification in planta. The regulation of this gene and the role of differentially expressed transcripts, including various putative lncRNAs, require further investigation.

Regulation of nitro-oxidative homeostasis: an effective approach to enhance salinity tolerance in plants

Soil salinity is a major constraint for sustainable agricultural productivity, which together with the incessant climate change may be transformed into a severe threat to the global food security. It is, therefore, a serious concern that needs to be addressed expeditiously. The overproduction and accumulation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the key events occurring during salt stress, consequently employing nitro-oxidative stress and programmed cell death in plants. However, very sporadic studies have been performed concerning different aspects of nitro-oxidative stress in plants under salinity stress. The ability of plants to tolerate salinity is associated with their ability to maintain the cellular redox equilibrium mediated by both non-enzymatic and enzymatic antioxidant defense mechanisms. The present review emphasizes the mechanisms of ROS and RNS generation in plants, providing a detailed evaluation of how redox homeostasis is conserved through their effective removal. The uniqueness of this article stems from its incorporation of expression analyses of candidate genes for different antioxidant enzymes involved in ROS and RNS detoxification across various developmental stages and tissues of rice, utilizing publicly available microarray data. It underscores the utilization of modern biotechnological methods to improve salinity tolerance in crops, employing different antioxidants as markers. The review also explores how various transcription factors contribute to plants' ability to tolerate salinity by either activating or repressing the expression of stress-responsive genes. In summary, the review offers a thorough insight into the nitro-oxidative homeostasis strategy for extenuating salinity stress in plants.

Evolutionary insights into strategy shifts for the safe and effective accumulation of ascorbate in plants

Plants accumulate high concentrations of ascorbate, commonly in their leaves, as a redox buffer. While ascorbate levels have increased during plant evolution, the mechanisms behind this phenomenon are unclear. Moreover, has the increase in ascorbate concentration been achieved without imposing any detrimental effects on the plants? In this review, we focus on potential transitions in two regulatory mechanisms related to ascorbate biosynthesis and the availability of cellular dehydroascorbate (DHA) during plant evolution. The first transition might be that the trigger for the transcriptional induction of VTC2, which encodes the rate-limiting enzyme in ascorbate biosynthesis, has shifted from oxidative stress (in green algae) to light/photosynthesis (in land plants), probably enabling the continuous accumulation of ascorbate under illumination. This could serve as a preventive system against the unpredictable occurrence of oxidative stress. The second transition might be that DHA-degrading enzymes, which protect cells from the highly reactive DHA in green algae and mosses, have been lost in ferns or flowering plants. Instead, flowering plants may have increased glutathione concentrations to reinforce the DHA reduction capacity, possibly allowing ascorbate accumulation and avoiding the toxicity of DHA. These potential transitions may have contributed to strategies for plants' safe and effective accumulation of ascorbate.

Coping with salinity stress: segmental group 7 chromosome introgressions from halophytic Thinopyrum species greatly enhance tolerance of recipient durum wheat

Increased soil salinization, tightly related to global warming and drought and exacerbated by intensified irrigation supply, implies highly detrimental effects on staple food crops such as wheat. The situation is particularly alarming for durum wheat (DW), better adapted to arid/semi-arid environments yet more sensitive to salt stress than bread wheat (BW). To enhance DW salinity tolerance, we resorted to chromosomally engineered materials with introgressions from allied halophytic Thinopyrum species. "Primary" recombinant lines (RLs), having portions of their 7AL arms distally replaced by 7el1L Th. ponticum segments, and "secondary" RLs, harboring Th. elongatum 7EL insertions "nested" into 7el1L segments, in addition to near-isogenic lines lacking any alien segment (CLs), cv. Om Rabia (OR) as salt tolerant control, and BW introgression lines with either most of 7el1 or the complete 7E chromosome substitution as additional CLs, were subjected to moderate (100 mM) and intense (200 mM) salt (NaCl) stress at early growth stages. The applied stress altered cell cycle progression, determining a general increase of cells in G1 and a reduction in S phase. Assessment of morpho-physiological and biochemical traits overall showed that the presence of Thinopyrum spp. segments was associated with considerably increased salinity tolerance versus its absence. For relative water content, Na+ accumulation and K+ retention in roots and leaves, oxidative stress indicators (malondialdehyde and hydrogen peroxide) and antioxidant enzyme activities, the observed differences between stressed and unstressed RLs versus CLs was of similar magnitude in "primary" and "secondary" types, suggesting that tolerance factors might reside in defined 7el1L shared portion(s). Nonetheless, the incremental contribution of 7EL segments emerged in various instances, greatly mitigating the effects of salt stress on root and leaf growth and on the quantity of photosynthetic pigments, boosting accumulation of compatible solutes and minimizing the decrease of a powerful antioxidant like ascorbate. The seemingly synergistic effect of 7el1L + 7EL segments/genes made "secondary" RLs able to often exceed cv. OR and equal or better perform than BW lines. Thus, transfer of a suite of genes from halophytic germplasm by use of fine chromosome engineering strategies may well be the way forward to enhance salinity tolerance of glycophytes, even the sensitive DW.

Glutathione and peroxisome redox homeostasis

Despite intensive research on peroxisome biochemistry, the role of glutathione in peroxisomal redox homeostasis has remained a matter of speculation for many years, and only recently has this issue started to be experimentally addressed. Here, we summarize and compare data from several organisms on the peroxisome-glutathione topic. It is clear from this comparison that the repertoire of glutathione-utilizing enzymes in peroxisomes of different organisms varies widely. In addition, the available data suggest that the kinetic connectivity between the cytosolic and peroxisomal pools of glutathione may also be different in different organisms, with some possessing a peroxisomal membrane that is promptly permeable to glutathione whereas in others this may not be the case. However, regardless of the differences, the picture that emerges from all these data is that glutathione is a crucial component of the antioxidative system that operates inside peroxisomes in all organisms.

Comparative Transcriptomic and Proteomic Analyses Provide New Insights into the Tolerance to Cyclic Dehydration in a Lichen Phycobiont

Desiccation tolerance (DT) is relatively frequent in non-vascular plants and green algae. However, it is poorly understood how successive dehydration/rehydration (D/R) cycles shape their transcriptomes and proteomes. Here, we report a comprehensive analysis of adjustments on both transcript and protein profiles in response to successive D/R cycles in Coccomyxa simplex (Csol), isolated from the lichen Solorina saccata. A total of 1833 transcripts and 2332 proteins were differentially abundant as a consequence of D/R; however, only 315 of these transcripts/proteins showed similar trends. Variations in both transcriptomes and proteomes along D/R cycles together with functional analyses revealed an extensive decrease in transcript and protein levels during dehydration, most of them involved in gene expression, metabolism, substance transport, signalling and folding catalysis, among other cellular functions. At the same time, a series of protective transcripts/proteins, such as those related to antioxidant defence, polyol metabolism and autophagy, was upregulated during dehydration. Overall, our results show a transient decrease in most cellular functions as a result of drying and a gradual reactivation of specific cell processes to accommodate the hydration status along successive D/R cycles. This study provides new insights into key mechanisms involved in the DT of Csol and probably other dehydration-tolerant microalgae. In addition, functionally characterising the high number of genes/proteins of unknown functions found in this study may lead to the discovery of new DT mechanisms.

Glutathione Transferases Are Involved in the Genotype-Specific Salt-Stress Response of Tomato Plants

Glutathione transferases (GSTs) are one of the most versatile multigenic enzyme superfamilies. In our experiments, the involvement of the genotype-specific induction of GST genes and glutathione- or redox-related genes in pathways regulating salt-stress tolerance was examined in tomato cultivars (Solanum lycopersicum Moneymaker, Mobil, and Elán F1). The growth of the Mobil plants was adversely affected during salt stress (100 mM of NaCl), which might be the result of lowered glutathione and ascorbate levels, a more positive glutathione redox potential (EGSH), and reduced glutathione reductase (GR) and GST activities. In contrast, the Moneymaker and Elán F1 cultivars were able to restore their growth and exhibited higher GR and inducible GST activities, as well as elevated, non-enzymatic antioxidant levels, indicating their enhanced salt tolerance. Furthermore, the expression patterns of GR, selected GST, and transcription factor genes differed significantly among the three cultivars, highlighting the distinct regulatory mechanisms of the tomato genotypes during salt stress. The correlations between EGSH and gene expression data revealed several robust, cultivar-specific associations, underscoring the complexity of the stress response mechanism in tomatoes. Our results support the cultivar-specific roles of distinct GST genes during the salt-stress response, which, along with WRKY3, WRKY72, DREB1, and DREB2, are important players in shaping the redox status and the development of a more efficient stress tolerance in tomatoes.

Identification of Omega-class glutathione transferases in helminths of the Taeniidae family

Glutathione transferase enzymes (GSTs) are believed to be a major detoxification system in helminth parasites and have been associated with immunomodulation of the host response. Echinococcus granulosus sensu lato (s.l.) is a cestode parasite known to express at least five different GSTs, but no Omega-class enzymes have been reported in this parasite or in any other cestode. Herein we report the identification of a new member of the GST superfamily in E. granulosus s.l., which is phylogenetically related to the Omega-class: EgrGSTO. Through mass spectrometry, we showed that the 237 amino acids protein EgrGSTO is expressed by the parasite. Moreover, we identified homologues of EgrGSTO in other eight members of the Taeniidae family, including E. canadensis, E. multilocularis, E. oligarthrus, Hydatigera taeniaeformis, Taenia asiatica, T. multiceps, T. saginata and T. solium. A manual sequence inspection and rational modification yielded eight Taeniidae's GSTO sequences, each one encoding for a 237 aa polypeptide showing 80.2% overall identity. To the best of our knowledge, this is the first description of genes encoding for Omega-class GSTs in worms belonging to the Taeniidae family -that at least in E. granulosus s.l. is expressed as a protein- suggesting the gene encodes for a functional protein.

Species-specific dynamics of specialized metabolism in germinating sorghum grain revealed by temporal and tissue-resolved transcriptomics and metabolomics

Seed germination is crucial for plant productivity, and the biochemical changes during germination affect seedling survival, plant health and yield. While the general metabolism of germination is extensively studied, the role of specialized metabolism is less investigated. We therefore analyzed the metabolism of the defense compound dhurrin during sorghum (Sorghum bicolor) grain germination and early seedling development. Dhurrin is a cyanogenic glucoside, which is catabolized into different bioactive compounds at other stages of plant development, but its fate and role during germination is unknown. We dissected sorghum grain into three different tissues and investigated dhurrin biosynthesis and catabolism at the transcriptomic, metabolomic and biochemical level. We further analyzed transcriptional signature differences of cyanogenic glucoside metabolism between sorghum and barley (Hordeum vulgare), which produces similar specialized metabolites. We found that dhurrin is de novo biosynthesized and catabolized in the growing embryonic axis as well as the scutellum and aleurone layer, two tissues otherwise mainly acknowledged for their involvement in release and transport of general metabolites from the endosperm to the embryonic axis. In contrast, genes encoding cyanogenic glucoside biosynthesis in barley are exclusively expressed in the embryonic axis. Glutathione transferase enzymes (GSTs) are involved in dhurrin catabolism and the tissue-resolved analysis of GST expression identified new pathway candidate genes and conserved GSTs as potentially important in cereal germination. Our study demonstrates a highly dynamic tissue- and species-specific specialized metabolism during cereal grain germination, highlighting the importance of tissue-resolved analyses and identification of specific roles of specialized metabolites in fundamental plant processes.

Genes encoding cytochrome P450 monooxygenases and glutathione S-transferases associated with herbicide resistance evolved before the origin of land plants

Cytochrome P450 (CYP) monooxygenases and glutathione S-transferases (GST) are enzymes that catalyse chemical modifications of a range of organic compounds. Herbicide resistance has been associated with higher levels of CYP and GST gene expression in some herbicide-resistant weed populations compared to sensitive populations of the same species. By comparing the protein sequences of 9 representative species of the Archaeplastida-the lineage which includes red algae, glaucophyte algae, chlorophyte algae, and streptophytes-and generating phylogenetic trees, we identified the CYP and GST proteins that existed in the common ancestor of the Archaeplastida. All CYP clans and all but one land plant GST classes present in land plants evolved before the divergence of streptophyte algae and land plants from their last common ancestor. We also demonstrate that there are more genes encoding CYP and GST proteins in land plants than in algae. The larger numbers of genes among land plants largely results from gene duplications in CYP clans 71, 72, and 85 and in the GST phi and tau classes [1,2]. Enzymes that either metabolise herbicides or confer herbicide resistance belong to CYP clans 71 and 72 and the GST phi and tau classes. Most CYP proteins that have been shown to confer herbicide resistance are members of the CYP81 family from clan 71. These results demonstrate that the clan and class diversity in extant plant CYP and GST proteins had evolved before the divergence of land plants and streptophyte algae from a last common ancestor estimated to be between 515 and 474 million years ago. Then, early in embryophyte evolution during the Palaeozoic, gene duplication in four of the twelve CYP clans, and in two of the fourteen GST classes, led to the large numbers of CYP and GST proteins found in extant land plants. It is among the genes of CYP clans 71 and 72 and GST classes phi and tau that alleles conferring herbicide resistance evolved in the last fifty years.

Signaling and Detoxification Strategies in Plant-Microbes Symbiosis under Heavy Metal Stress: A Mechanistic Understanding

Plants typically interact with a variety of microorganisms, including bacteria, mycorrhizal fungi, and other organisms, in their above- and below-ground parts. In the biosphere, the interactions of plants with diverse microbes enable them to acquire a wide range of symbiotic advantages, resulting in enhanced plant growth and development and stress tolerance to toxic metals (TMs). Recent studies have shown that certain microorganisms can reduce the accumulation of TMs in plants through various mechanisms and can reduce the bioavailability of TMs in soil. However, relevant progress is lacking in summarization. This review mechanistically summarizes the common mediating pathways, detoxification strategies, and homeostatic mechanisms based on the research progress of the joint prevention and control of TMs by arbuscular mycorrhizal fungi (AMF)-plant and Rhizobium-plant interactions. Given the importance of tripartite mutualism in the plant-microbe system, it is necessary to further explore key signaling molecules to understand the role of plant-microbe mutualism in improving plant tolerance under heavy metal stress in the contaminated soil environments. It is hoped that our findings will be useful in studying plant stress tolerance under a broad range of environmental conditions and will help in developing new technologies for ensuring crop health and performance in future.

Transcriptional response of a target plant to benzoxazinoid and diterpene allelochemicals highlights commonalities in detoxification

BACKGROUND

Plants growing in proximity to other plants are exposed to a variety of metabolites that these neighbors release into the environment. Some species produce allelochemicals to inhibit growth of neighboring plants, which in turn have evolved ways to detoxify these compounds.

RESULTS

In order to understand how the allelochemical-receiving target plants respond to chemically diverse compounds, we performed whole-genome transcriptome analysis of Arabidopsis thaliana exposed to either the benzoxazinoid derivative 2-amino- 3H-phenoxazin-3-one (APO) or momilactone B. These two allelochemicals belong to two very different compound classes, benzoxazinoids and diterpenes, respectively, produced by different Poaceae crop species.

CONCLUSIONS

Despite their distinct chemical nature, we observed similar molecular responses of A. thaliana to these allelochemicals. In particular, many of the same or closely related genes belonging to the three-phase detoxification pathway were upregulated in both treatments. Further, we observed an overlap between genes upregulated by allelochemicals and those involved in herbicide detoxification. Our findings highlight the overlap in the transcriptional response of a target plant to natural and synthetic phytotoxic compounds and illustrate how herbicide resistance could arise via pathways involved in plant-plant interaction.

An Anthocyanin-Related Glutathione S-Transferase, MrGST1, Plays an Essential Role in Fruit Coloration in Chinese Bayberry (Morella rubra)

Chinese bayberry (Morella rubra) is a fruit tree economically important in China and accumulates abundant amounts of anthocyanins in fruit as it ripens. Owing to the fact that all anthocyanin containing fruit tissues in Chinese bayberry are edible and anthocyanins can provide various health benefits in human body, the mechanisms underpinning anthocyanin accumulation in this fruit are worthy of investigation. It has been known that in plants anthocyanins are synthesized in the cytoplasmic surface of the endoplasmic reticulum and subsequently transported into the vacuole for storage, and glutathione S-transferases (GSTs) have been verified to be involved in this process. But the characterization and functionalization of the GST counterpart in Chinese bayberry is not available. The GST anthocyanin transporter MrGST1 was discovered to be related with anthocyanin accumulation in fruit from distinct developmental stages of "Biqi," a staple cultivar that accumulates over 1 mg/g anthocyanins in ripe fruit. The expression of MrGST1 was well associated with anthocyanin accumulation either in fruit collected at six developmental stages or in ripe fruit from 12 cultivars. MrGST1 was found to be responsible for the transport of anthocyanins but not proanthocyanidins when the Arabidopsis tt19 mutant was functionally complemented. Transient ectopic expression of MrGST1 in combination with MrMYB1.1 and MrbHLH1 dramatically boosted pigmentation in Nicotiana tabacum leaves in contrast to MrMYB1.1 and MrbHLH1. The promoter of MrGST1 comprised eight MYB binding sites (MBSs) according to cis-element analysis. Data from yeast one-hybrid assay and dual-luciferase tests demonstrated that MrMYB1.1 exerted considerable transactivation effect on the MrGST1 promoter by recognizing the MBS4, the fourth MBS from the ATG start site. Our results together provided molecular evidence for the contribution of MrGST1 in regulating anthocyanin accumulation in Chinese bayberry fruit.

Over-Expression of Dehydroascorbate Reductase Improves Salt Tolerance, Environmental Adaptability and Productivity in Oryza sativa

Abiotic stress induces reactive oxygen species (ROS) generation in plants, and high ROS levels can cause partial or severe oxidative damage to cellular components that regulate the redox status. Here, we developed salt-tolerant transgenic rice plants that overexpressed the dehydroascorbate reductase gene (OsDHAR1) under the control of a stress-inducible sweet potato promoter (SWPA2). OsDHAR1-expressing transgenic plants exhibited improved environmental adaptability compared to wild-type plants, owing to enhanced ascorbate levels, redox homeostasis, photosynthetic ability, and membrane stability through cross-activation of ascorbate-glutathione cycle enzymes under paddy-field conditions, which enhanced various agronomic traits, including root development, panicle number, spikelet number per panicle, and total grain yield. dhar2-knockdown plants were susceptible to salt stress, and owing to poor seed maturation, exhibited reduced biomass (root growth) and grain yield under paddy field conditions. Microarray revealed that transgenic plants highly expressed genes associated with cell growth, plant growth, leaf senescence, root development, ROS and heavy metal detoxification systems, lipid metabolism, isoflavone and ascorbate recycling, and photosynthesis. We identified the genetic source of functional genomics‒based molecular breeding in crop plants and provided new insights into the physiological processes underlying environmental adaptability, which will enable improvement of stress tolerance and crop species productivity in response to climate change.

Functional Characterization of MtrGSTF7, a Glutathione S-Transferase Essential for Anthocyanin Accumulation in Medicago truncatula

Flavonoids are essential compounds widespread in plants and exert many functions such as defence, definition of organ colour and protection against stresses. In Medicago truncatula, flavonoid biosynthesis and accumulation is finely regulated in terms of tissue specificity and induction by external factors, such as cold and other stresses. Among flavonoids, anthocyanin precursors are synthesised in the cytoplasm, transported to the tonoplast, then imported into the vacuole for further modifications and storage. In the present work, we functionally characterised MtrGSTF7, a phi-class glutathione S-transferase involved in anthocyanin transport to the tonoplast. The mtrgstf7 mutant completely lost the ability to accumulate anthocyanins in leaves both under control and anthocyanin inductive conditions. On the contrary, this mutant showed an increase in the levels of soluble proanthocyanidins (Pas) in their seeds with respect to the wild type. By complementation and expression data analysis, we showed that, differently from A. thaliana and similarly to V. vinifera, transport of anthocyanin and proanthocyanidins is likely carried out by different GSTs belonging to the phi-class. Such functional diversification likely results from the plant need to finely tune the accumulation of diverse classes of flavonoids according to the target organs and developmental stages.

Physiological, Biochemical and Molecular Response of Different Winter Wheat Varieties under Drought Stress at Germination and Seedling Growth Stage

Due to climate change in recent years, there has been an increasing water deficit during the winter wheat sowing period. This study evaluated six Croatian winter wheat varieties’ physiological, biochemical, and molecular responses under two drought stress levels at the germination/seedling growth stage. Lipid peroxidation was mainly induced under both drought stress treatments, while the antioxidative response was variety-specific. The most significant role in the antioxidative response had glutathione along with the ascorbate-glutathione pathway. Under drought stress, wheat seedlings responded in proline accumulation that was correlated with the P5CS gene expression. Expression of genes encoding dehydrins (DHN5, WZY2) was highly induced under the drought stress in all varieties, while genes encoding transcription factors were differentially regulated. Expression of DREB1 was upregulated under severe drought stress in most varieties, while the expression of WRKY2 was downregulated or revealed control levels. Different mechanisms were shown to contribute to the drought tolerance in different varieties, which was mainly associated with osmotic adjustment and dehydrins expression. Identifying different mechanisms in drought stress response would advance our understanding of the complex strategies contributing to wheat tolerance to drought in the early growth stage and could contribute to variety selection useful for developing new drought-tolerant varieties.

Genome-Wide Identification, Evolution and Expression Analysis of the Glutathione S-Transferase Supergene Family in Euphorbiaceae

Euphorbiaceae, a family of plants mainly grown in the tropics and subtropics, is also widely distributed all over the world and is well known for being rich in rubber, oil, medicinal materials, starch, wood and other economically important plant products. Glutathione S-transferases (GSTs) constitute a family of proteins encoded by a large supergene family and are widely expressed in animals, bacteria, fungi and plants, but with few reports of them in Euphorbiaceae plants. These proteins participate in and regulate the detoxification and oxidative stress response of heterogeneous organisms, resistance to stress, growth and development, signal transduction and other related processes. In this study, we identified and analyzed the whole genomes of four species of Euphorbiaceae, namely Ricinus communis, Jatropha curcas, Hevea brasiliensis, and Manihot esculenta, which have high economic and practical value. A total of 244 GST genes were identified. Based on their sequence characteristics and conserved domain types, the GST supergene family in Euphorbiaceae was classified into 10 subfamilies. The GST supergene families of Euphorbiaceae and Arabidopsis have been found to be highly conserved in evolution, and tandem repeats and translocations in these genes have made the greatest contributions to gene amplification here and have experienced strong purification selection. An evolutionary analysis showed that Euphorbiaceae GST genes have also evolved into new subtribes (GSTO, EF1BG, MAPEG), which may play a specific role in Euphorbiaceae. An analysis of expression patterns of the GST supergene family in Euphorbiaceae revealed the functions of these GSTs in different tissues, including resistance to stress and participation in herbicide detoxification. In addition, an interaction analysis was performed to determine the GST gene regulatory mechanism. The results of this study have laid a foundation for further analysis of the functions of the GST supergene family in Euphorbiaceae, especially in stress and herbicide detoxification. The results have also provided new ideas for the study of the regulatory mechanism of the GST supergene family, and have provided a reference for follow-up genetics and breeding work.

Crosstalk between the redox signalling and the detoxification: GSTs under redox control?

Reactive oxygen species (ROS), antioxidants and their reduction-oxidation (redox) states all contribute to the redox homeostasis, but glutathione is considered to be the master regulator of it. We aimed to understand the relationship between the redox potential and the diverse glutathione transferase (GST) enzyme family by comparing the stress responses of two tomato cultivars (Solanum lycopersicum 'Moneymaker' and 'Ailsa Craig'). Four-week-old plants were treated by two concentrations of mannitol, NaCl and salicylic acid. The lower H₂O₂ and malondialdehyde contents indicated higher stress tolerance of 'Moneymaker'. The redox status of roots was characterized by measuring the reduced and oxidized form of ascorbate and glutathione spectrophotometrically after 24 h. The redox potential of 'Ailsa Craig' was more oxidized compared to 'Moneymaker' even under control conditions and became more positive due to treatments. High-throughput quantitative real-time PCR revealed that besides overall higher expression levels, SlGSTs were activated more efficiently in 'Moneymaker' due to stresses, resulting in generally higher GST and glutathione peroxidase activities compared to 'Ailsa Craig'. The expression level of SlGSTs correlated differently, however Pearson's correlation analysis showed usually strong positive correlation between SlGST transcription and glutathione redox potential. The possible redox regulation of SlGST expressions was discussed.

CRISPR/Cas9 and Transgene Verification of Gene Involvement in Unfolded Protein Response and Recombinant Protein Production in Barley Grain

The use of plants as heterologous hosts to produce recombinant proteins has some intriguing advantages. There is, however, the potential of overloading the endoplasmic reticulum (ER) capacity when producing recombinant proteins in the seeds. This leads to an ER-stress condition and accumulating of unfolded proteins. The unfolded protein response (UPR) is activated to alleviate the ER-stress. With the aim to increase the yield of human epidermal growth factor (EGF) and mouse leukemia inhibitory factor (mLIF) in barley, we selected genes reported to have increased expression during ER-induced stress. The selected genes were calreticulin (CRT), protein disulfide isomerase (PDI), isopentenyl diphosphate isomerase (IPI), glutathione-s-transferase (GST), HSP70, HSP26, and HSP16.9. These were knocked out using CRISPR/Cas9 or overexpressed by conventional transgenesis. The generated homozygous barley lines were crossed with barley plants expressing EGF or mLIF and the offspring plants analyzed for EGF and mLIF protein accumulation in the mature grain. All manipulated genes had an impact on the expression of UPR genes when plantlets were subjected to tunicamycin (TN). The PDI knockout plant showed decreased protein body formation, with protein evenly distributed in the cells of the endosperm. The two genes, GST and IPI, were found to have a positive effect on recombinant protein production. mLIF expression was increased in a F2 homozygous GST knockout mutant background as compared to a F2 GST wild-type offspring. The overexpression of IPI in a F1 cross showed a significant increase in EGF expression. We demonstrate that manipulation of UPR related genes can have a positive effect on recombinant protein accumulation.

Silicon induces metallochaperone-driven cadmium binding to the cell wall and restores redox status through elevated glutathione in Cd-stressed sugar beet

Cadmium (Cd) is toxic; however, whether silicon (Si) alleviates Cd toxicity was never studied in sugar beet. The study was conducted on 2-week-old sugar beet cultivated in the presence or absence of Cd (10 μM CdSO₄ ) and Si (1 mM Na₂ SiO₃ ) in hydroponic conditions. The morphological impairment and cellular damages observed in sugar beet upon Cd toxicity were entirely reversed due to Si. Si substantially restored the energy-providing ability, absorbed energy flux, and electron transport toward PSII, which might be correlated with the upregulation of BvIRT1 and ferric chelate reductase activity leading to the restoration of Fe status in Cd-stressed sugar beet. Although Si caused a reduction of shoot Cd, the root Cd substantially increased under Cd stress, a significant part of which was retained in the cell wall rather than in the root vacuole. While the concentration of phytochelatin and the expression of BvPCS3 (PHYTOCHELATIN SYNTHASE 3) showed no changes upon Si exposure, Si induced the expression of BvHIPP32 (HEAVY METAL-ASSOCIATED ISOPRENYLATED PLANT PROTEIN 32) in the Cd-exposed root. The BvHIPP32 and AtHIPP32 metallochaperone proteins are localized in the cell wall and they share similar sequence alignment, physiochemical properties, secondary structure, cellular localization, motif locations, domain association, and metal-binding site (cd00371) linked to the metallochaperone-like protein. It suggests that Si reduces the Cd level in shoot by retaining the excess Cd in the cell wall of roots due to the induction of BvHIPP32 gene. Also, Si stimulates glutathione-related antioxidants along with the BvGST23 expression, inferring an ascorbate-glutathione ROS detoxification pathway in Cd-exposed plants.

The Cd-induced morphological and photosynthetic disruption is related to the reduced Fe status and increased oxidative injuries in sugar beet

Cadmium (Cd) toxicity is a form of soil contamination that causes losses in plant growth and yield. Understanding the effects of Cd-induced changes in physiological and cellular processes will help scientists develop better scientific strategies for sugar beet plant improvement. Cd toxicity triggered a substantial decrease in morphological parameters and total soluble protein in sugar beets, as well as membrane damage and cell death. Furthermore, the SPAD score and photosynthetic OJIP parameters in leaves were severely affected due to Cd stress. This was correlated with the decreased FCR activity and BvIRT1 expression in roots, suggesting the adverse effect of Cd in Fe acquisition in sugar beet. Our findings also revealed that BvHMA3 and BvNRAMP3 were upregulated in Cd-exposed roots, indicating that these genes might be involved in Cd uptake in sugar beet. In silico analysis of BvHMA3 and BvNRAMP3 proteins showed close partnerships with several Arabidopsis genes mainly linked to metal tolerance protein, cation diffusion facilitator, vacuolar metal transporter, and vacuolar Fe transporter. Subsequently, Cd-exposed sugar beet showed severe sensitivity to oxidative damages resulted in elevated H₂O₂ and O₂^.- without possessed efficient antioxidant defense. Finally, growth retardation in Cd-exposed sugar beets is linked to photosynthetic inefficiency caused by low Fe levels and oxidative stress in cells. These results may be used to improve Cd-sensitive sugar beet plants by breeding or transgenic programs.

What Antarctic Plants Can Tell Us about Climate Changes: Temperature as a Driver for Metabolic Reprogramming

Global warming is strongly affecting the maritime Antarctica climate and the consequent melting of perennial snow and ice covers resulted in increased colonization by plants. Colobanthus quitensis is a vascular plant highly adapted to the harsh environmental conditions of Antarctic Peninsula and understanding how the plant is responding to global warming is a new challenging target for modern cell physiology. To this aim, we performed differential proteomic analysis on C. quitensis plants grown in natural conditions compared to plants grown for one year inside open top chambers (OTCs) which determine an increase of about 4 °C at midday, mimicking the effect of global warming. A thorough analysis of the up- and downregulated proteins highlighted an extensive metabolism reprogramming leading to enhanced photoprotection and oxidative stress control as well as reduced content of cell wall components. Overall, OTCs growth seems to be advantageous for C. quitensis plants which could benefit from a better CO₂ diffusion into the mesophyll and a reduced ROS-mediated photodamage.

Glutathione-S-transferases genes-promising predictors of hepatic dysfunction

One of the most commonly known genes involved in chronic diffuse liver diseases pathogenesis are genes that encodes the synthesis of glutathione-S-transferase (GST), known as the second phase enzyme detoxification system that protects against endogenous oxidative stress and exogenous toxins, through catalisation of glutathione sulfuric groups conjugation and decontamination of lipid and deoxyribonucleic acid oxidation products. The group of GST enzymes consists of cytosolic, mitochondrial and microsomal fractions. Recently, eight classes of soluble cytoplasmic isoforms of GST enzymes are widely known: α-, ζ-, θ-, κ-, μ-, π-, σ-, and ω-. The GSTs gene family in the Human Gene Nomenclature Committee, online database recorded over 20 functional genes. The level of GSTs expression is considered to be a crucial factor in determining the sensitivity of cells to a broad spectrum of toxins. Nevertheless, human GSTs genes have multiple and frequent polymorphisms that include the complete absence of the GSTM1 or the GSTT1 gene. Current review supports the position that genetic polymorphism of GST genes is involved in the pathogenesis of various liver diseases, particularly non-alcoholic fatty liver disease, hepatitis and liver cirrhosis of different etiology and hepatocellular carcinoma. Certain GST allelic variants were proven to be associated with susceptibility to hepatological pathology, and correlations with the natural course of the diseases were subsequently postulated.

Pyroxasulfone-Resistant Annual Ryegrass (Lolium rigidum) Has Enhanced Capacity for Glutathione Transferase-Mediated Pyroxasulfone Conjugation

The herbicide pyroxasulfone was widely introduced in 2012, and cases of evolved resistance in weeds such as annual ryegrass (Lolium rigidum Gaud.) and tall waterhemp [Amaranthus tuberculatus (Moq.) Sauer] have started to emerge. Pyroxasulfone is detoxified by tolerant crops, and by annual ryegrass that has been recurrently selected with pyroxasulfone, in a pathway that is hypothesized to involve glutathione conjugation. In the current study, it was confirmed that pyroxasulfone is conjugated to glutathione in vitro by glutathione transferases (GSTs) purified from susceptible and resistant annual ryegrass populations and from a tolerant crop species, wheat. The extent of conjugation corresponded to the pyroxasulfone resistance level. Pyroxasulfone-conjugating activity was higher in radicles, roots, and seeds compared to coleoptiles or expanded leaves. Among the GSTs purified from annual ryegrass radicles and seeds, an orthologue of Brachypodium distachyon GSTF13 was >20-fold more abundant in the pyroxasulfone-resistant population, suggesting that this protein could be responsible for pyroxasulfone conjugation.

Gene expression and morphological responses of Lolium perenne L. exposed to cadmium (Cd2+) and mercury (Hg2+)

Soil contamination with heavy metals is a major problem worldwide, due to the increasing impact mainly caused by anthropogenic activities. This research evaluated the phytoremediation capacity of, Lolium perenne for heavy metals such as cadmium (Cd²⁺) and mercury (Hg²⁺), and the effects of these metals on morphology, biomass production, and the changes on gene expression. Seeds of L. perenne were exposed to six concentrations of Cd²⁺ and Hg²⁺ in the range of 0 to 25 mg L⁻¹, and two mixtures of Cd²⁺–Hg². The Non-Observed Effect Level (NOEL) was established with dose response curves and the expression of specific genes was evaluated applying a commercially available quantitative reverse transcription (RT-qPCR) assay. There was no significant effect when exposing the seeds to Hg²⁺, for Cd²⁺ the maximum concentration was established in 0.1 mg L⁻¹, and for the two concentrations of mixtures, there was a negative effect. An increase of expression of genes that regulate antioxidant activity and stress was found when the plant was exposed to heavy metals. Given the high tolerance to metals analyzed that was reflected both, the development of the plant and in its molecular response, these results highlight that L. perenne is a plant with phytoremediator potential.

Comparative Analysis of the Glutathione S-Transferase Gene Family of Four Triticeae Species and Transcriptome Analysis of GST Genes in Common Wheat Responding to Salt Stress

Glutathione S-transferases (GSTs) are ancient proteins encoded by a large gene family in plants, which play multiple roles in plant growth and development. However, there has been little study on the GST genes of common wheat (Triticum aestivum) and its relatives (Triticum durum, Triticum urartu, and Aegilops tauschii), which are four important species of Triticeae. Here, a genome-wide comprehensive analysis of this gene family was performed on the genomes of common wheat and its relatives. A total of 346 GST genes in T. aestivum, 226 in T. durum, 104 in T. urartu, and 105 in Ae. tauschii were identified, and all members were divided into ten classes. Transcriptome analysis was used to identify GST genes that respond to salt stress in common wheat, which revealed that the reaction of GST genes is not sensitive to low and moderate salt concentrations but is sensitive to severe concentrations of the stressor, and the GST genes related to salt stress mainly come from the Tau and Phi classes. Six GST genes which respond to different salt concentrations were selected and validated by a qRT-PCR assay. These findings will not only provide helpful information about the function of GST genes in Triticeae species but also offer insights for the future application of salt stress resistance breeding in common wheat.

Biochemical aspects of seeds from Cannabis sativa L. plants grown in a mountain environment

Cannabis sativa L. (hemp) is a versatile plant which can adapt to various environmental conditions. Hempseeds provide high quality lipids, mainly represented by polyunsaturated acids, and highly digestible proteins rich of essential aminoacids. Hempseed composition can vary according to plant genotype, but other factors such as agronomic and climatic conditions can affect the presence of nutraceutic compounds. In this research, seeds from two cultivars of C. sativa (Futura 75 and Finola) grown in a mountain environment of the Italian Alps were analyzed. The main purpose of this study was to investigate changes in the protein profile of seeds obtained from such environments, using two methods (sequential and total proteins) for protein extraction and two analytical approaches SDS-PAGE and 2D-gel electrophoresis, followed by protein identification by mass spectrometry. The fatty acids profile and carotenoids content were also analysed. Mountain environments mainly affected fatty acid and protein profiles of Finola seeds. These changes were not predictable by the sole comparison of certified seeds from Futura 75 and Finola cultivars. The fatty acid profile confirmed a high PUFA content in both cultivars from mountain area, while protein analysis revealed a decrease in the protein content of Finola seeds from the experimental fields.

Cysteine modifications (oxPTM) and protein sulphenylation-mediated sulfenome expression in plants: evolutionary conserved signaling networks?

Plant resilience to oxidative stress possibly operates through the restoration of intracellular redox milieu and the activity of various posttranslationally modified proteins. Among various modes of redox regulation operative in plants cys oxPTMs are brought about by the activity of reactive oxygen species (ROS), reactive nitrogen species (RNS), and hydrogen peroxide. Cysteine oxPTMs are capable of transducing ROS-mediated long-distance hormone signaling (ABA, JA, SA) in plants. S-sulphenylation is an intermediary modification en route to other oxidative states of cysteine. In silico analysis have revealed evolutionary conservation of certain S-sulphenylated proteins across human and plants. Further analysis of protein sulphenylation in plants should be extended to the functional follow-up studies followed by site-specific characterization and case-by-case validation of protein activity. The repertoire of physiological methods (fluorescent conjugates (dimedone) and yeast AP-1 (YAP1)-based genetic probes) in the recent past has been successful in the detection of sulphenylated proteins and other cysteine-based modifications in plants. In view of a better understanding of the sulfur-based redoxome it is necessary to update our timely progress on the methodological advancements for the detection of cysteine-based oxPTM. This substantiative information can extend our investigations on plant-environment interaction thus improving crop manipulation strategies. The simulation-based computational approach has emerged as a new method to determine the directive mechanism of cysteine oxidation in plants. Thus, sulfenome analysis in various plant systems might reflect as a pinnacle of plant redox biology in the future.

Identification of novel seed longevity genes related to oxidative stress and seed coat by genome-wide association studies and reverse genetics

Seed longevity is a polygenic trait of relevance for agriculture and for understanding the effect of environment on the ageing of biological systems. In order to identify novel longevity genes, we have phenotyped the natural variation of 270 ecotypes of the model plant, Arabidopsis thaliana, for natural ageing and for three accelerated ageing methods. Genome-wide analysis, using publicly available single-nucleotide polymorphisms (SNPs) data sets, identified multiple genomic regions associated with variation in seed longevity. Reverse genetics of 20 candidate genes in Columbia ecotype resulted in seven genes positive for seed longevity (PSAD1, SSLEA, SSTPR, DHAR1, CYP86A8, MYB47 and SPCH) and five negative ones (RBOHD, RBOHE, RBOHF, KNAT7 and SEP3). In this uniform genetic background, natural and accelerated ageing methods provided similar results for seed-longevity in knock-out mutants. The NADPH oxidases (RBOHs), the dehydroascorbate reductase (DHAR1) and the photosystem I subunit (PSAD1) highlight the important role of oxidative stress on seed ageing. The cytochrome P-450 hydroxylase, CYP86A8, and the transcription factors, MYB47, KNAT7 and SEP3, support the protecting role of the seed coat during seed ageing.

Plant Chloroplast Stress Response: Insights from Thiol Redox Proteomics

Significance: Plant chloroplasts generate reactive oxygen species (ROS) during photosynthesis, especially under stresses. The sulfhydryl groups of protein cysteine residues are susceptible to redox modifications, which regulate protein structure and function, and thus different signaling and metabolic processes. The ROS-governed protein thiol redox switches play important roles in chloroplasts. Recent Advances: Various high-throughput thiol redox proteomic approaches have been developed, and they have enabled the improved understanding of redox regulatory mechanisms in chloroplasts. For example, the thioredoxin-modulated antioxidant enzymes help to maintain cellular ROS homeostasis. The light- and dark-dependent redox regulation of photosynthetic electron transport, the Calvin/Benson cycle, and starch biosynthesis ensures metabolic coordination and efficient energy utilization. In addition, redox cascades link the light with the dynamic changes of metabolites in nitrate and sulfur assimilation, shikimate pathway, and biosynthesis of fatty acid hormone as well as purine, pyrimidine, and thiamine. Importantly, redox regulation of tetrapyrrole and chlorophyll biosynthesis is critical to balance the photodynamic tetrapyrrole intermediates and prevent oxidative damage. Moreover, redox regulation of diverse elongation factors, chaperones, and kinases plays an important role in the modulation of gene expression, protein conformation, and posttranslational modification that contribute to photosystem II (PSII) repair, state transition, and signaling in chloroplasts. Critical Issues: This review focuses on recent advances in plant thiol redox proteomics and redox protein networks toward understanding plant chloroplast signaling, metabolism, and stress responses. Future Directions: Using redox proteomics integrated with biochemical and molecular genetic approaches, detailed studies of cysteine residues, their redox states, cross talk with other modifications, and the functional implications will yield a holistic understanding of chloroplast stress responses.

The pivotal function of dehydroascorbate reductase in glutathione homeostasis in plants

Under natural conditions, plants are exposed to various abiotic and biotic stresses that trigger rapid changes in the production and removal of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2). The ascorbate-glutathione pathway has been recognized to be a key player in H2O2 metabolism, in which reduced glutathione (GSH) regenerates ascorbate by reducing dehydroascorbate (DHA), either chemically or via DHA reductase (DHAR), an enzyme belonging to the glutathione S-transferase (GST) superfamily. Thus, DHAR has been considered to be important in maintaining the ascorbate pool and its redox state. Although some GSTs and peroxiredoxins may contribute to GSH oxidation, analysis of Arabidopsis dhar mutants has identified the key role of DHAR in coupling H2O2 to GSH oxidation. The reaction of DHAR has been proposed to proceed by a ping-pong mechanism, in which binding of DHA to the free reduced form of the enzyme is followed by binding of GSH. Information from crystal structures has shed light on the formation of sulfenic acid at the catalytic cysteine of DHAR that occurs with the reduction of DHA. In this review, we discuss the molecular properties of DHAR and its importance in coupling the ascorbate and glutathione pools with H2O2 metabolism, together with its functions in plant defense, growth, and development.

Mercury Phytoremediation with Lolium perenne-Mycorrhizae in Contaminated Soils

The symbiotic association between the roots of a plant and the mycelium of some fungi is identified as mycorrhizae. Symbiosis helps the plant to obtain nutrients from the soil more efficiently, and may favor the phytoremediation capacity of plants such as Lolium perenne, in soils contaminated with mercury. In this study, the morphological and molecular response was evaluated, as well as the variation in mercury accumulation in the different structures of L. perenne when associated with arbuscular mycorrhizal fungi. Association tests were performed to determine the optimal concentration of the biological inoculant and it was found that the best results were given with the proportion of one part of inoculant in three parts of soil (w/w ratio). The differential expression of the glutathione-S-transferase GST gene was evaluated through real-time PCR and the concentration of heavy metals inside and outside the plant was evaluated with inductively coupled plasma atomic emission spectroscopy (ICP). It was found that the plants that were inoculated with mycorrhizae developed longer stems and shorter roots; in the same way, the GST gene had greater expression in the stem than in the root, largely because the roots help the filtration of nutrients to the stem, retaining metals and detoxifying by GST-catalyzed glutathione.

Expression of Heterologous OsDHAR Gene Improves Glutathione (GSH)-Dependent Antioxidant System and Maintenance of Cellular Redox Status in Synechococcus elongatus PCC 7942

An excess of reactive oxygen species (ROS) can cause severe oxidative damage to cellular components in photosynthetic cells. Antioxidant systems, such as the glutathione (GSH) pools, regulate redox status in cells to guard against such damage. Dehydroascorbate reductase (DHAR, EC 1.8.5.1) catalyzes the glutathione-dependent reduction of oxidized ascorbate (dehydroascorbate) and contains a redox active site and glutathione binding-site. The DHAR gene is important in biological and abiotic stress responses involving reduction of the oxidative damage caused by ROS. In this study, transgenic Synechococcus elongatus PCC 7942 (TA) was constructed by cloning the Oryza sativa L. japonica DHAR (OsDHAR) gene controlled by an isopropyl β-D-1-thiogalactopyranoside (IPTG)-inducible promoter (Ptrc) into the cyanobacterium to study the functional activities of OsDHAR under oxidative stress caused by hydrogen peroxide exposure. OsDHAR expression increased the growth of S. elongatus PCC 7942 under oxidative stress by reducing the levels of hydroperoxides and malondialdehyde (MDA) and mitigating the loss of chlorophyll. DHAR and glutathione S-transferase activity were higher than in the wild-type S. elongatus PCC 7942 (WT). Additionally, overexpression of OsDHAR in S. elongatus PCC 7942 greatly increased the glutathione (GSH)/glutathione disulfide (GSSG) ratio in the presence or absence of hydrogen peroxide. These results strongly suggest that DHAR attenuates deleterious oxidative effects via the glutathione (GSH)-dependent antioxidant system in cyanobacterial cells. The expression of heterologous OsDHAR in S. elongatus PCC 7942 protected cells from oxidative damage through a GSH-dependent antioxidant system via GSH-dependent reactions at the redox active site and GSH binding site residues during oxidative stress.

Transcriptome analysis reveals the defense mechanism of cotton against Verticillium dahliae in the presence of the biocontrol fungus Chaetomium globosum CEF-082

BACKGROUND

Verticillium wilt of cotton is a serious soil-borne disease that causes a substantial reduction in cotton yields. A previous study showed that the endophytic fungus Chaetomium globosum CEF-082 could control Verticillium wilt of cotton, and induce a defense response in cotton plants. However, the comprehensive molecular mechanism governing this response is not yet clear.

RESULTS

To study the signalling mechanism induced by CEF-082, the transcriptome of cotton seedlings pretreated with CEF-082 was sequenced. The results revealed 5638 DEGs at 24 h post inoculation with CEF-082, and 2921 and 2153 DEGs at 12 and 48 h post inoculation with Verticillium dahliae, respectively. At 24 h post inoculation with CEF-082, KEGG enrichment analysis indicated that the DEGs were enriched mainly in the plant-pathogen interaction, MAPK signalling pathway-plant, flavonoid biosynthesis, and phenylpropanoid biosynthesis pathways. There were 1209 DEGs specifically induced only in cotton plants inoculated with V. dahliae in the presence of the biocontrol fungus CEF-082, and not when cotton plants were only inoculated with V. dahliae. GO analysis revealed that these DEGs were enriched mainly in the following terms: ROS metabolic process, H2O2 metabolic process, defense response, superoxide dismutase activity, and antioxidant activity. Moreover, many genes, such as ERF, CNGC, FLS2, MYB, GST and CML, that regulate crucial points in defense-related pathways were identified and may contribute to V. dahliae resistance in cotton. These results provide a basis for understanding the molecular mechanism by which the biocontrol fungus CEF-082 increases the resistance of cotton to Verticillium wilt.

CONCLUSIONS

The results of this study showed that CEF-082 could regulate multiple metabolic pathways in cotton. After treatment with V. dahliae, the defense response of cotton plants preinoculated with CEF-082 was strengthened.

Identification and characterization of the glutathione S-Transferase (GST) family in radish reveals a likely role in anthocyanin biosynthesis and heavy metal stress tolerance

Glutathione S-transferases (GSTs) are a large complex family of enzymes (EC 2.5.1.18) that play vital roles in flavonoid metabolism and plant growth and development and are responsive to heavy metal stress. However, knowledge about GST genes in radish (a vegetable crop with an extraordinary capacity to adapt to heavy metal stresses) is limited. Therefore, it is critical to identify putative candidate GST genes responsible for heavy metal stress tolerance and anthocyanin biosynthesis. In this study, we first identified 82 R. sativus GST (RsGST) genes using various bioinformatic approaches, and their expression profiles were characterized from RNAseq data. These RsGST genes could be grouped into 7 major subclasses: tau (43 members), phi (21 members), tetrachlorohydroquinone dehalogenase (7 members), dehydroascorbat reductase (5 members), zeta (3 members), lambda (2 members) and theta (1 member). In addition, most of the RsGST genes showed organ-specific expression in our study. Moreover, the transcripts of RsGSTF12-1 and RsGSTF12-2, belonging to the phi class, might be candidates encoding anthocyanin transporters in carmine radish, whereas the tau class, consisting of RsGSTU13-1, RsGSTU19, RsGSTU24-1, and RsGSTU3, and theta class, consisting of RsGSTT1-1, might be defend radish against adverse heavy metal stresses. These results will aid in understanding the functions of the GST family related to heavy metal stress and anthocyanin biosynthesis, thereby potentially improving radish breeding programs for high-pigment-content material as well as HM-tolerant material.

iTRAQ-Based Quantitative Proteomic Analysis of the Arabidopsis Mutant opr3-1 in Response to Exogenous MeJA

Jasmonates (JAs) regulate the defense of biotic and abiotic stresses, growth, development, and many other important biological processes in plants. The comprehensive proteomic profiling of plants under JAs treatment provides insights into the regulation mechanism of JAs. Isobaric tags for relative and absolute quantification (iTRAQ)-based quantitative proteomic analysis was performed on the Arabidopsis wild type (Ws) and JA synthesis deficiency mutant opr3-1. The effects of exogenous MeJA treatment on the proteome of opr3-1, which lacks endogenous JAs, were investigated. A total of 3683 proteins were identified and 126 proteins were differentially regulated between different genotypes and treatment groups. The functional classification of these differentially regulated proteins showed that they were involved in metabolic processes, responses to abiotic stress or biotic stress, the defense against pathogens and wounds, photosynthesis, protein synthesis, and developmental processes. Exogenous MeJA treatment induced the up-regulation of a large number of defense-related proteins and photosynthesis-related proteins, it also induced the down-regulation of many ribosomal proteins in opr3-1. These results were further verified by a quantitative real-time PCR (qRT-PCR) analysis of 15 selected genes. Our research provides the basis for further understanding the molecular mechanism of JAs’ regulation of plant defense, photosynthesis, protein synthesis, and development.

Molecular cloning of putative chloroplastic cysteine synthase in Leucaena leucocephala

Cysteine biosynthesis is directed by the successive commitments of serine acetyltransferase, and O-acetylserine (thiol) lyase (OASTL) compounds, which subsequently frame the decameric cysteine synthase complex. The isoforms of OASTL are found in three compartments of the cell: the cytosol, plastid, and mitochondria. In this investigation, we first isolated putative chloroplastic OASTL (Ch-OASTL) from Leucaena leucocephala, and the Ch-OASTL was then expressed in BL21-competent Escherichia coli. The putative Ch-OASTL cDNA clone had 1,543 base pairs with 391 amino acids in its open reading frame and a molecular weight of 41.54 kDa. The purified protein product exhibited cysteine synthesis ability, but not mimosine synthesis activity. However, they both make the common α-aminoacrylate intermediate in their first half reaction scheme with the conventional substrate O-acetyl serine (OAS). Hence, we considered putative Ch-OASTL a cysteine-specific enzyme. Kinetic studies demonstrated that the optimum pH for cysteine synthesis was 7.0, and the optimum temperature was 40 °C. In the cysteine synthesis assay, the K_m and k_cat values were 838 ± 26 µM and 72.83 s^-1 for OAS, respectively, and 60 ± 2 µM and 2.43 s^-1 for Na₂S, respectively. We can infer that putative Ch-OASTL regulatory role is considered a sensor for sulfur constraint conditions, and it acts as a forerunner of various metabolic compound molecules.

Genome-wide identification and expression profiling of glutathione transferase gene family under multiple stresses and hormone treatments in wheat (Triticum aestivum L.)

BACKGROUND

Glutathione transferases (GSTs), the ancient, ubiquitous and multi-functional proteins, play significant roles in development, metabolism as well as abiotic and biotic stress responses in plants. Wheat is one of the most important crops, but the functions of GST genes in wheat were less studied.

RESULTS

A total of 330 TaGST genes were identified from the wheat genome and named according to the nomenclature of rice and Arabidopsis GST genes. They were classified into eight classes based on the phylogenetic relationship among wheat, rice, and Arabidopsis, and their gene structure and conserved motif were similar in the same phylogenetic class. The 43 and 171 gene pairs were identified as tandem and segmental duplication genes respectively, and the Ka/Ks ratios of tandem and segmental duplication TaGST genes were less than 1 except segmental duplication gene pair TaGSTU24/TaGSTU154. The 59 TaGST genes were identified to have syntenic relationships with 28 OsGST genes. The expression profiling involved in 15 tissues and biotic and abiotic stresses suggested the different expression and response patterns of the TaGST genes. Furthermore, the qRT-PCR data showed that GST could response to abiotic stresses and hormones extensively in wheat.

CONCLUSIONS

In this study, a large GST family with 330 members was identified from the wheat genome. Duplication events containing tandem and segmental duplication contributed to the expansion of TaGST family, and duplication genes might undergo extensive purifying selection. The expression profiling and cis-elements in promoter region of 330 TaGST genes implied their roles in growth and development as well as adaption to stressful environments. The qRT-PCR data of 14 TaGST genes revealed that they could respond to different abiotic stresses and hormones, especially salt stress and abscisic acid. In conclusion, this study contributed to the further functional analysis of GST genes family in wheat.

Integrative analysis of hexaploid wheat roots identifies signature components during iron starvation

Iron (Fe) is an essential micronutrient for all organisms. In crop plants, Fe deficiency can decrease crop yield significantly; however, our current understanding of how major crops respond to Fe deficiency remains limited. Herein, the effect of Fe deprivation at both the transcriptomic and metabolic level in hexaploid wheat was investigated. Genome-wide gene expression reprogramming was observed in wheat roots subjected to Fe starvation, with a total of 5854 genes differentially expressed. Homoeologue and subgenome-specific analysis unveiled the induction-biased contribution from the A and B genomes. In general, the predominance of genes coding for nicotianamine synthase, yellow stripe-like transporters, metal transporters, ABC transporters, and zinc-induced facilitator-like protein was noted. Expression of genes related to the Strategy II mode of Fe uptake was also predominant. Our transcriptomic data were in agreement with the GC-MS analysis that showed the enhanced accumulation of various metabolites such as fumarate, malonate, succinate, and xylofuranose, which could be contributing to Fe mobilization. Interestingly, Fe starvation leads to a significant temporal increase of glutathione S-transferase at both the transcriptional level and enzymatic activity level, which indicates the involvement of glutathione in response to Fe stress in wheat roots. Taken together, our result provides new insight into the wheat response to Fe starvation at the molecular level and lays the foundation to design new strategies for the improvement of Fe nutrition in crops.