Sulfation pathways in plants

Metabolism Interaction Between Bacillus cereus SESY and Brassica napus Contributes to Enhance Host Selenium Absorption and Accumulation

The use of beneficial bacteria to enhance selenium absorption in crops has been widely studied. However, it is unclear how the interaction between bacteria and plants affects selenium absorption in crops. Here, pot experiments and Murashige and Skoog medium (MS) experiments were performed. Transcriptomic analyses were used to reveal the interaction between Bacillus cereus SESY and Brassica napus. The results indicated that B. cereus SESY can significantly increase the biomass and selenium content of B. napus. The genes related to the colonization, IAA synthesis, and l-cysteine synthesis and metabolism of B. cereus SESY were significantly stimulated by B. napus through transcriptional regulation. Further verification results showed that l-cysteine increased selenium content in B. napus roots and shoots by 62.9% and 88.4%, respectively. B. cereus SESY and l-cysteine consistently regulated the relative expression level of genes involved in plant hormone, amino acid metabolism, selenium absorption, and Se enzymatic and nonenzymatic metabolic pathway of B. napus. These genes were significantly correlated with selenium content and biomass of B. napus (p < 0.05). Overall, IAA biosynthesis, and l-cysteine biosynthesis and metabolism in B. cereus SESY stimulated by interactions triggered molecular and metabolic responses of B. napus, underpinning host selenium absorption and accumulation.

Sulfonation of IAA in Urtica eliminates its DR5 auxin activity

KEY MESSAGE

N-Sulfonated IAA was discovered as a novel auxin metabolite in Urtica where it is biosynthesized de novo utilizing inorganic sulfate. It showed no auxin activity in DR5::GUS assay, implying possible inactivation/storage mechanism. A novel auxin derivative, N-sulfoindole-3-acetic acid (IAA-N-SO3H, SIAA), was discovered in stinging nettle (Urtica dioica) among 116 sulfonated metabolites putatively identified by a semi-targeted UHPLC-QqTOF-MS analysis of 23 plant/algae/fungi species. These sulfometabolites were detected based on the presence of a neutral loss of sulfur trioxide, as indicated by the m/z difference of 79.9568 Da in the MS2 spectra. The structure of newly discovered SIAA was confirmed by synthesizing its standard and comparing retention time, m/z and MS2 spectrum with those of SIAA found in Urtica. To study its natural occurrence, 73 species in total were further analyzed by UHPLC-QqTOF-MS or targeted UHPLC-MS/MS method with a limit of detection of 244 fmol/g dry weight. However, SIAA was only detected in Urtica at a concentration of 13.906 ± 9.603 nmol/g dry weight. Its concentration was > 30 times higher than that of indole-3-acetic acid (IAA), and the SIAA/IAA ratio was further increased under different light conditions, especially in continuous blue light. In addition to SIAA, structurally similar metabolites, N-sulfoindole-3-lactic acid, 4-(sulfooxy)phenyllactic acid and 4-(sulfooxy)phenylacetic acid, were detected in Urtica for the first time. SIAA was biosynthesized from inorganic sulfate in seedlings, as confirmed by the incorporation of exogenous 34S-ammonium sulfate (1 mM and 10 mM). SIAA exhibited no auxin activity, as demonstrated by both the Arabidopsis DR5::GUS assay and the Arabidopsis phenotype analysis. Sulfonation of IAA may therefore be a mechanism for IAA deactivation and/or storage in Urtica, similar to sulfonation of the jasmonates in Arabidopsis.

Bioengineered heparin: Advances in production technology

Heparin, a highly sulfated glycosaminoglycan, is considered an indispensable anticoagulant with diverse therapeutic applications and has been a mainstay in medical practice for nearly a century. Its potential extends beyond anticoagulation, showing promise in treating inflammation, cancer, and infectious diseases such as COVID-19. However, its current sourcing from animal tissues poses challenges due to variable structures and adulterations, impacting treatment efficacy and safety. Recent advancements in metabolic engineering and synthetic biology offer alternatives through bioengineered heparin production, albeit with challenges such as controlling molecular weight and sulfonation patterns. This review offers comprehensive insight into recent advancements, encompassing: (i) the metabolic engineering strategies in prokaryotic systems for heparin production; (ii) strides made in the development of bioengineered heparin; and (iii) groundbreaking approaches driving production enhancements in eukaryotic systems. Additionally, it explores the potential of recombinant Chinese hamster ovary cells in heparin synthesis, discussing recent progress, challenges, and future prospects, thereby opening up new avenues in biomedical research.

Inhibition of sulfur assimilation by S-benzyl-L-cysteine: Impacts on growth, photosynthesis, and leaf proteome of maize plants

Sulfur is an essential nutrient for various physiological processes, including protein synthesis and enzyme activation. We aimed to evaluate how S-benzyl-L-cysteine (SBC), an inhibitor of the sulfur assimilation pathway, affects maize plants' growth, photosynthesis, and leaf proteomic profile. Thus, maize plants were grown for 14 days in vermiculite supplemented with SBC. Photosynthesis was assessed using light and CO2 response curves and chlorophyll a fluorescence. Leaf proteome analysis was conducted to evaluate photosynthetic protein biosynthesis, and ROS content was quantified to assess oxidative stress. Applying SBC resulted in a significant decrease in the growth of maize plants. The gas exchange analysis revealed that maize plants exhibited a diminished rate of CO2 assimilation attributable to both stomatal and non-stomatal limitations. Furthermore, SBC suppressed the activity of important elements involved in the photosynthetic electron transport chain (including photosystems I and II, cytochrome b6f, and ATP synthase) and enzymes responsible for the Calvin cycle, some of which have sulfur-containing prosthetic groups. Consequently, the diminished electron flow rate resulted in a substantial increase in the levels of ROS within the leaves. Our research highlights the crucial role of SBC in disrupting maize photosynthesis by limiting L-cysteine and assimilated sulfur availability, which are essential for the synthesis of protein and prosthetic groups and photosynthetic processes, emphasizing the potential of OAS-TL as a new herbicide site of action.

Selenium dynamics in plants: Uptake, transport, toxicity, and sustainable management strategies

Selenium (Se) plays crucial roles in human, animal, and plant physiology, but its varied plant functions remain complex and not fully understood. While Se deficiency affects over a billion people worldwide, excessive Se levels can be toxic, presenting substantial risks to ecosystem health and public safety. The delicate balance between Se's beneficial and harmful effects necessitates a deeper understanding of its speciation dynamics and how different organisms within ecosystems respond to Se. Since humans primarily consume Se through Se-rich foods, exploring Se's behavior, uptake, and transport within agroecosystems is critical to creating effective management strategies. Traditional physicochemical methods for Se remediation are often expensive and potentially harmful to the environment, pushing the need for more sustainable solutions. In recent years, phytotechnologies have gained traction as a promising approach to Se management by harnessing plants' natural abilities to absorb, accumulate, metabolize, and volatilize Se. These strategies range from boosting Se uptake and tolerance in plants to releasing Se as less toxic volatile compounds or utilizing it as a biofortified supplement, opening up diverse possibilities for managing Se, offering sustainable pathways to improve crop nutritional quality, and protecting human health in different environmental contexts. However, closing the gaps in our understanding of Se dynamics within agricultural systems calls for a united front of interdisciplinary collaboration from biology to environmental science, agriculture, and public health, which has a crucial role to play. Phytotechnologies offer a sustainable bridge between Se deficiency and toxicity, but further research is needed to optimize these methods and explore their potential in various agricultural and environmental settings. By shedding light on Se's multifaceted roles and refining management strategies, this review contributes to developing cost-effective and eco-friendly approaches for Se management in agroecosystems. It aims to lead the way toward a healthier and more sustainable future by balancing the need to address Se deficiency and mitigate the risks of Se toxicity.

Withania frutescens (L.) Pauquy, a valuable Mediterranean shrub containing bioactive withanolides

The bushy plant Withania frutescens (L.) Pauquy is well distributed in the West-Mediterranean area, notably in the south of Spain, Algeria and Morocco where is it is used traditionally for the treatment of various human diseases, including diabetes. Unlike the two major species W. somnifera and W. coagulans extensively studied, the genomically close species W. frutescens has been much less investigated. Nevertheless, this shrub species displays a comparable phytochemical profile and marked antioxidant and anti-inflammatory properties, at the origin of reported pharmacological effects and its traditional uses. Here we have analyzed the diversity of biological effects reported with leaves and root extracts of W. frutescens. Hydroalcoholic extracts prepared from the aerial parts of the plant have revealed antihyperglycemic and cell-protective activities along with antimicrobial and anticorrosive effects. The extracts contained diverse polyphenolic compounds and a few alkaloids (calystegines) but most of the observed effects have been attributed to the presence of withanolides which are modified C28 ergostane-type steroids. Our analysis focused in part on specific withanolides found in W. frutescens, in particular an unusual 3-O-sulfated withanolide considered as a potential pro-drug of the major active compound withaferin A (WA) and a lead compound for the development of a potential drug candidate. The mechanism of action of this sulfated WA analogue is discussed. Altogether, our unprecedented extensive analysis of W. frutescens highlighted the pharmacological potential of this atypical medicinal plant. By analogy with the major cultivated Withania species, the market potential of little-known plant is underlined.

Uptake patterns for nitrogen and sulfur source by aquatic plants and various nitrogen acquisition strategies: Affected by mining activities

Understanding the nitrogen and sulfur uptake strategies of mine plants, including sources and preferences for nitrogen forms (ammonium nitrogen (NH4+) vs nitrate nitrogen (NO3-)), is critical to improving understanding of the role of plants in participating in the biogeochemical cycles of nitrogen and sulfur in mining areas. In this study, the stable N and S isotopic compositions of two species of aquatic plants (calamus and reed) in Linhuan mining area were analyzed to determine their absorption strategies for different nitrogen and sulfur sources. The results showed that river water was the largest source of nitrogen and sulfur, contributing 54.6% and 53.9% respectively. NO3- is the main form of nitrogen uptake by reed and calamus, followed by NH4+. In order to adapt to the change of nitrogen form in the environment, reed and calamus tend to absorb and utilize NO3- to maintain their absorption of nitrogen. Mine effluents from mining activities provide at least 12.9% and 16.8% sulfate to reed and calamus respectively, and the effect of mine effluents on reed and calamus sulfur has been underestimated. This study reveals the key factors controlling plant isotope composition, and the use of nitrogen and sulfur isotope composition of aquatic plants can help quantify the level of influence of mining activities, and understand the biogeochemical cycle of nitrogen and sulfur in mining areas.

Advances and challenges in biotechnological production of chondroitin sulfate and its oligosaccharides

Chondroitin sulfate (CS) is a member of glycosaminoglycans (GAGs) and has critical physiological functions. CS is widely applied in medical and clinical fields. Currently, the supply of CS relies on traditional animal tissue extraction methods. From the perspective of medical applications, the biggest drawback of animal-derived CS is its uncontrollable molecular weight and sulfonated patterns, which are key factors affecting CS activities. The advances of cell-free enzyme catalyzed systems and de novo biosynthesis strategies have paved the way to rationally regulate CS sulfonated pattern and molecular weight. In this review, we first present a general overview of biosynthesized CS and its oligosaccharides. Then, the advances in chondroitin biosynthesis, 3'-phosphoadenosine-5'-phosphosulfate (PAPS) synthesis and regeneration, and CS biosynthesis catalyzed by sulfotransferases are discussed. Moreover, the progress of mining and expression of chondroitin depolymerizing enzymes for preparation of CS oligosaccharides is also summarized. Finally, we analyze and discuss the challenges faced in synthesizing CS and its oligosaccharides using microbial and enzymatic methods. In summary, the biotechnological production of CS and its oligosaccharides is a promising method in addressing the drawbacks associated with animal-derived CS and enabling the production of CS oligosaccharides with defined structures.

The History of Animal and Plant Sulfite Oxidase-A Personal View

Sulfite oxidase is one of five molybdenum-containing enzymes known in eukaryotes where it catalyzes the oxidation of sulfite to sulfate. This review covers the history of sulfite oxidase research starting out with the early years of its discovery as a hepatic mitochondrial enzyme in vertebrates, leading to basic biochemical and structural properties that have inspired research for decades. A personal view on sulfite oxidase in plants, that sulfates are assimilated for their de novo synthesis of cysteine, is presented by Ralf Mendel with numerous unexpected findings and unique properties of this single-cofactor sulfite oxidase localized to peroxisomes. Guenter Schwarz connects his research to sulfite oxidase via its deficiency in humans, demonstrating its unique role amongst all molybdenum enzymes in humans. In essence, in both the plant and animal kingdoms, sulfite oxidase represents an important player in redox regulation, signaling and metabolism, thereby connecting sulfur and nitrogen metabolism in multiple ways.

Inhibition of RNA degradation integrates the metabolic signals induced by osmotic stress into the Arabidopsis circadian system

The circadian clock system acts as an endogenous timing reference that coordinates many metabolic and physiological processes in plants. Previous studies have shown that the application of osmotic stress delays circadian rhythms via 3'-phospho-adenosine 5'-phosphate (PAP), a retrograde signalling metabolite that is produced in response to redox stress within organelles. PAP accumulation leads to the inhibition of exoribonucleases (XRNs), which are responsible for RNA degradation. Interestingly, we are now able to demonstrate that post-transcriptional processing is crucial for the circadian response to osmotic stress. Our data show that osmotic stress increases the stability of specific circadian RNAs, suggesting that RNA metabolism plays a vital role in circadian clock coordination during drought. Inactivation of XRN4 is sufficient to extend circadian rhythms as part of this response, with PRR7 and LWD1 identified as transcripts that are post-transcriptionally regulated to delay circadian progression.

Genome-Wide Characterization of the Sulfate Transporter Gene Family in Oilseed Crops: Camelina sativa and Brassica napus

Sulfate transporters (SULTRs) are responsible for the uptake of sulfate (SO₄^2-) ions in the rhizosphere by roots and their distribution to plant organs. In this study, SULTR family members in the genomes of two oilseed crops (Camelina sativa and Brassica napus) were identified and characterized based on their sequence structures, duplication events, phylogenetic relationships, phosphorylation sites, and expression levels. In total, 36 and 45 putative SULTR genes were recognized in the genomes of C. sativa and B. napus, respectively. SULTR proteins were predicted to be basophilic proteins with low hydrophilicity in both studied species. According to the observed phylogenetic relationships, we divided the SULTRs into five groups, out of which the SULTR 3 group showed the highest variation. Additionally, several duplication events were observed between the SULTRs. The first duplication event occurred approximately five million years ago between three SULTR 3.1 genes in C. sativa. Furthermore, two subunits were identified in the 3D structures of the SULTRs, which demonstrated that the active binding sites differed between C. sativa and B. napus. According to the available RNA-seq data, the SULTRs showed diverse expression levels in tissues and diverse responses to stimuli. SULTR 3 was expressed in all tissues. SULTR 3.1 was more upregulated in response to abiotic stresses in C. sativa, while SULTR 3.3 and SULTR 2.1 were upregulated in B. napus. Furthermore, SULTR 3 and SULTR 4.1 were upregulated in response to biotic stresses in B. napus. Additionally, the qPCR data showed that the SULTRs in C. sativa were involved in the plant's response to salinity. Based on the distribution of cis-regulatory elements in the promoter region, we speculated that SULTRs might be controlled by phytohormones, such as ABA and MeJA. Therefore, it seems likely that SULTR genes in C. sativa have been more heavily influenced by evolutionary processes and have acquired further diversity. The results reveal new insights of the structures and functions of SULTRs in oilseed crops. However, further analyses, related to functional studies, are needed to uncover the role of SULTRs in the plants' development and growth processes, as well as in their response to stimuli.

Sulfur signaling and starvation response in Arabidopsis

As sessile organisms, plants have developed sophisticated mechanism to sense and utilize nutrients from the environment, and modulate their growth and development according to the nutrient availability. Research in the past two decades revealed that nutrient assimilation is not occurring spontaneously, but nutrient signaling networks are complexly regulated and integrate sensing and signaling, gene expression, and metabolism to ensure homeostasis and coordination with plant energy conversion and other processes. Here, we review the importance of the macronutrient sulfur (S) and compare the knowledge of S signaling with other important macronutrients, such as nitrogen (N) and phosphorus (P). We focus on key advances in understanding sulfur sensing and signaling, uptake and assimilation, and we provide new analysis of published literature, to identify core genes regulated by the key transcriptional factor in S starvation response, SLIM1/EIL3, and compare the impact on other nutrient deficiency and stresses on S-related genes.

Response to sulfur in Schizosaccharomyces pombe

Sulfur is an essential component of various biologically important molecules, including methionine, cysteine and glutathione, and it is also involved in coping with oxidative and heavy metal stress. Studies using model organisms, including budding yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe), have contributed not only to understanding various cellular processes but also to understanding the utilization and response mechanisms of each nutrient, including sulfur. Although fission yeast can use sulfate as a sulfur source, its sulfur metabolism pathway is slightly different from that of budding yeast because it does not have a trans-sulfuration pathway. In recent years, it has been found that sulfur starvation causes various cellular responses in S. pombe, including sporulation, cell cycle arrest at G₂, chronological lifespan extension, autophagy induction and reduced translation. This MiniReview identifies two sulfate transporters in S. pombe, Sul1 (encoded by SPBC3H7.02) and Sul2 (encoded by SPAC869.05c), and summarizes the metabolic pathways of sulfur assimilation and cellular response to sulfur starvation. Understanding these responses, including metabolism and adaptation, will contribute to a better understanding of the various stress and nutrient starvation responses and chronological lifespan regulation caused by sulfur starvation.

Selenium transport and metabolism in plants: Phytoremediation and biofortification implications

The aim of this review is to synthesize current knowledge of selenium (Se) transport and metabolism in plants, with a focus on implications for biofortification and phytoremediation. Selenium is a necessary human micronutrient, and around a billion people worldwide may be Se deficient. This can be ameliorated by Se biofortification of staple crops. Selenium is also a potential toxin at higher concentrations, and multiple environmental disasters over the past 50 years have been caused by Se pollution from agricultural and industrial sources. Phytoremediation by plants able to take up large amounts of Se is an important tool to combat pollution issues. Both biofortification and phytoremediation applications require a thorough understanding of how Se is taken up and metabolized by plants. Selenium uptake and translocation in plants are largely accomplished via sulfur (S) transport proteins. Current understanding of these transporters is reviewed here, and transporters that may be manipulated to improve Se uptake are discussed. Plant Se metabolism also largely follows the S metabolic pathway. This pathway is reviewed here, with special focus on genes that have been, or may be manipulated to reduce the accumulation of toxic metabolites or enhance the accumulation of nontoxic metabolites. Finally, unique aspects of Se transport and metabolism in Se hyperaccumulators are reviewed. Hyperaccumulators, which can accumulate Se at up to 1000 times higher concentrations than normal plants, present interesting specialized systems of Se transport and metabolism. Selenium hyperaccumulation mechanisms and potential applications of these mechanisms to biofortification and phytoremediation are presented.

Regulation of glucosinolate biosynthesis

Glucosinolates are secondary defense metabolites produced by plants of the order Brassicales, which includes the model species Arabidopsis and many crop species. In the past 13 years, the regulation of glucosinolate synthesis in plants has been intensively studied, with recent research revealing complex molecular mechanisms that connect glucosinolate production with responses to other central pathways. In this review, we discuss how the regulation of glucosinolate biosynthesis is ecologically relevant for plants, how it is controlled by transcription factors, and how this transcriptional machinery interacts with hormonal, environmental, and epigenetic mechanisms. We present the central players in glucosinolate regulation, MYB and basic helix-loop-helix transcription factors, as well as the plant hormone jasmonate, which together with other hormones and environmental signals allow the coordinated and rapid regulation of glucosinolate genes. Furthermore, we highlight the regulatory connections between glucosinolates, auxin, and sulfur metabolism and discuss emerging insights and open questions on the regulation of glucosinolate biosynthesis.

The oxygen isotopic signature of soil- and plant-derived sulphate is controlled by fertilizer type and water source

The oxygen isotope signature of sulphate (δ¹⁸ O_sulphate ) is increasingly used to study nutritional fluxes and sulphur transformation processes in a variety of natural environments. However, mechanisms controlling the δ¹⁸ O_sulphate signature in soil-plant systems are largely unknown. The objective of this study was to determine key factors, which affect δ¹⁸ O_sulphate values in soil and plants. The impact of an ¹⁸ O-water isotopic gradient and different types of fertilizers was investigated in a soil incubation study and a radish (Raphanus sativus L.) greenhouse growth experiment. Water provided 31-64% of oxygen atoms in soil sulphate formed via mineralization of organic residues (green and chicken manures) while 49% of oxygen atoms were derived from water during oxidation of elemental sulphur. In contrast, δ¹⁸ O_sulphate values of synthetic fertilizer were not affected by soil water. Correlations between soil and plant δ¹⁸ O_sulphate values were controlled by water δ¹⁸ O values and fertilizer treatments. Additionally, plant δ³⁴ S data showed that the sulphate isotopic composition of plants is a function of S assimilation. This study documents the potential of using compound-specific isotope ratio analysis for investigating and tracing fertilization strategies in agricultural and environmental studies.

Expression of enzymes for 3'-phosphoadenosine-5'-phosphosulfate (PAPS) biosynthesis and their preparation for PAPS synthesis and regeneration

The synthesis of sulfated polysaccharides involves the sulfation of simpler polysaccharide substrates, through the action sulfotransferases using the cofactor, 3'-phosphoadenosine-5'-phosphosulfate (PAPS). Three enzymes are essential for the in vitro synthesis of PAPS, namely, pyrophosphatase (PPA), adenosine 5'-phosphosulfate kinase (APSK), and ATP sulfurylase (ATPS). The optimized enzyme expression ratio and effect on PAPS synthesis were evaluated using ePathBrick, a novel synthetic biology tool that assemble multiple genes in a single vector. The introduction of multiple promoters and stop codons at different location enable the bacterial system to fine tune expression level of the genes inserted. Recombinant vectors expressing PPA (U39393.1), ATPS (CP021243.1), and PPA (CP047127.1) were used for fermentations and resulted in volumetric yields of 400-1380 mg/L with accumulation of 34-66% in the soluble fraction. The enzymes from soluble fraction, without any further purification, were used for PAPS synthesis. The PAPS was used for the chemoenzymatic synthesis of a heparan sulfate polysaccharide and coupled with a PAPS-ASTIV regeneration system. ASTIV catalyzes the regeneration of PAPS. A recombinant vector expressing the enzyme ASTIV (from Rattus norvegicus) was used for fermentations and resulted in volumetric yield of 1153 mg/L enzyme with accumulation of 48% in the soluble fraction. In conclusion, we have successfully utilized a metabolic engineering approach to optimize the overall PAPS synthesis productivity. In addition, we have demonstrated that the ePathBrick system could be applied towards study and improvement of enzymatic synthesis conditions. In parallel, we have successfully demonstrated an autoinduction microbial fermentation towards the production of mammalian enzyme (ASTIV). KEY POINTS : • ePathBrick used to optimize expression levels of enzymes. • Protocols have been used for the production of recombinant enzymes. • High cell density fed-batch fermentations with high yields of soluble enzymes. • Robust fermentation protocol successfully transferred to contract manufacturing and research facilities.

A light-dependent molecular link between competition cues and defence responses in plants

Growth responses to competition¹ and defence responses to the attack of consumer organisms² are two classic examples of adaptive phenotypic plasticity in plants. However, the mechanistic and functional links between these responses are not well understood. Jasmonates, a family of lipid-derived signals, are potent growth inhibitors and central regulators of plant immunity to herbivores and pathogens^3,4, with both roles being evolutionarily conserved from bryophytes⁵ to angiosperms⁶. When shade-intolerant plants perceive the proximity of competitors using the photoreceptor phytochrome B, they activate the shade-avoidance syndrome and downregulate jasmonate responses⁷. Despite the central implications of this light-mediated change in the growth/defence balance for plant adaptation and crop yield^8,9, the mechanisms by which photoreceptors relay light cues to the jasmonate signalling pathway remain poorly understood¹⁰. Here, we identify a sulfotransferase (ST2a) that is strongly upregulated by plant proximity perceived by phytochrome B via the phytochrome B-phytochrome interacting factor signalling module. By catalysing the formation of a sulfated jasmonate derivative, ST2a acts to reduce the pool of precursors of active forms of jasmonates and represents a direct molecular link between photoreceptors and hormone signalling in plants. The metabolic step defined by this enzyme provides a molecular mechanism for prioritizing shade avoidance over defence under intense plant competition.

A sulfur-containing volatile emitted by potato-associated bacteria confers protection against late blight through direct anti-oomycete activity

Plant diseases are a major cause for yield losses and new strategies to control them without harming the environment are urgently needed. Plant-associated bacteria contribute to their host’s health in diverse ways, among which the emission of disease-inhibiting volatile organic compounds (VOCs). We have previously reported that VOCs emitted by potato-associated bacteria caused strong in vitro growth inhibition of the late blight causing agent Phytophthora infestans. This work focuses on sulfur-containing VOCs (sVOCs) and demonstrates the high in planta protective potential of S-methyl methane thiosulfonate (MMTS), which fully prevented late blight disease in potato leaves and plantlets without phytotoxic effects, in contrast to other sVOCs. Short exposure times were sufficient to protect plants against infection. We further showed that MMTS’s protective activity was not mediated by the plant immune system but lied in its anti-oomycete activity. Using quantitative proteomics, we determined that different sVOCs caused specific proteome changes in P. infestans, indicating perturbations in sulfur metabolism, protein translation and redox balance. This work brings new perspectives for plant protection against the devastating Irish Famine pathogen, while opening new research avenues on the role of sVOCs in the interaction between plants and their microbiome.

Plant Sulfate Transporters in the Low Phytic Acid Network: Some Educated Guesses

A few new papers report that mutations in some genes belonging to the group 3 of plant sulfate transporter family result in low phytic acid phenotypes, drawing novel strategies and approaches for engineering the low-phytate trait in cereal grains. Here, we shortly review the current knowledge on phosphorus/sulfur interplay and sulfate transport regulation in plants, to critically discuss some hypotheses that could help in unveiling the physiological links between sulfate transport and phosphorus accumulation in seeds.

Structural biology of plant sulfur metabolism: from sulfate to glutathione

Sulfur is an essential element for all organisms. Plants must assimilate this nutrient from the environment and convert it into metabolically useful forms for the biosynthesis of a wide range of compounds, including cysteine and glutathione. This review summarizes structural biology studies on the enzymes involved in plant sulfur assimilation [ATP sulfurylase, adenosine-5'-phosphate (APS) reductase, and sulfite reductase], cysteine biosynthesis (serine acetyltransferase and O-acetylserine sulfhydrylase), and glutathione biosynthesis (glutamate-cysteine ligase and glutathione synthetase) pathways. Overall, X-ray crystal structures of enzymes in these core pathways provide molecular-level information on the chemical events that allow plants to incorporate sulfur into essential metabolites and revealed new biochemical regulatory mechanisms, such as structural rearrangements, protein-protein interactions, and thiol-based redox switches, for controlling different steps in these pathways.

Integration of sulfate assimilation with carbon and nitrogen metabolism in transition from C3 to C4 photosynthesis

The first product of sulfate assimilation in plants, cysteine, is a proteinogenic amino acid and a source of reduced sulfur for plant metabolism. Cysteine synthesis is the convergence point of the three major pathways of primary metabolism: carbon, nitrate, and sulfate assimilation. Despite the importance of metabolic and genetic coordination of these three pathways for nutrient balance in plants, the molecular mechanisms underlying this coordination, and the sensors and signals, are far from being understood. This is even more apparent in C4 plants, where coordination of these pathways for cysteine synthesis includes the additional challenge of differential spatial localization. Here we review the coordination of sulfate, nitrate, and carbon assimilation, and show how they are altered in C4 plants. We then summarize current knowledge of the mechanisms of coordination of these pathways. Finally, we identify urgent questions to be addressed in order to understand the integration of sulfate assimilation with carbon and nitrogen metabolism particularly in C4 plants. We consider answering these questions to be a prerequisite for successful engineering of C4 photosynthesis into C3 crops to increase their efficiency.

Sulfation pathways from red to green

Sulfur is present in the amino acids cysteine and methionine and in a large range of essential coenzymes and cofactors and is therefore essential for all organisms. It is also a constituent of sulfate esters in proteins, carbohydrates, and numerous cellular metabolites. The sulfation and desulfation reactions modifying a variety of different substrates are commonly known as sulfation pathways. Although relatively little is known about the function of most sulfated metabolites, the synthesis of activated sulfate used in sulfation pathways is essential in both animal and plant kingdoms. In humans, mutations in the genes encoding the sulfation pathway enzymes underlie a number of developmental aberrations, and in flies and worms, their loss-of-function is fatal. In plants, a lower capacity for synthesizing activated sulfate for sulfation reactions results in dwarfism, and a complete loss of activated sulfate synthesis is also lethal. Here, we review the similarities and differences in sulfation pathways and associated processes in animals and plants, and we point out how they diverge from bacteria and yeast. We highlight the open questions concerning localization, regulation, and importance of sulfation pathways in both kingdoms and the ways in which findings from these "red" and "green" experimental systems may help reciprocally address questions specific to each of the systems.

Jasmonates: News on Occurrence, Biosynthesis, Metabolism and Action of an Ancient Group of Signaling Compounds

: Jasmonic acid (JA) and its related derivatives are ubiquitously occurring compounds of land plants acting in numerous stress responses and development. Recent studies on evolution of JA and other oxylipins indicated conserved biosynthesis. JA formation is initiated by oxygenation of α-linolenic acid (α-LeA, 18:3) or 16:3 fatty acid of chloroplast membranes leading to 12-oxo-phytodienoic acid (OPDA) as intermediate compound, but in Marchantiapolymorpha and Physcomitrellapatens, OPDA and some of its derivatives are final products active in a conserved signaling pathway. JA formation and its metabolic conversion take place in chloroplasts, peroxisomes and cytosol, respectively. Metabolites of JA are formed in 12 different pathways leading to active, inactive and partially active compounds. The isoleucine conjugate of JA (JA-Ile) is the ligand of the receptor component COI1 in vascular plants, whereas in the bryophyte M. polymorpha COI1 perceives an OPDA derivative indicating its functionally conserved activity. JA-induced gene expressions in the numerous biotic and abiotic stress responses and development are initiated in a well-studied complex regulation by homeostasis of transcription factors functioning as repressors and activators.

More to NAD+ than meets the eye: A regulator of metabolic pools and gene expression in Arabidopsis

Since its discovery more than a century ago, nicotinamide adenine dinucleotide (NAD⁺) is recognised as a fascinating cornerstone of cellular metabolism. This ubiquitous energy cofactor plays vital roles in metabolic pathways and regulatory processes, a fact emphasised by the essentiality of a balanced NAD⁺ metabolism for normal plant growth and development. Research on the role of NAD in plants has been predominantly carried out in the model plant Arabidopsis thaliana (Arabidopsis) with emphasis on the redox properties and cellular signalling functions of the metabolite. This review examines the current state of knowledge concerning how NAD can regulate both metabolic pools and gene expression in Arabidopsis. Particular focus is placed on recent studies highlighting the complexity of metabolic regulations involving NAD, more particularly in the mitochondrial compartment, and of signalling roles with respect to interactions with environmental fluctuations most specifically those involving plant immunity.

Sterol Sulfates and Sulfotransferases in Marine Diatoms

Sterol sulfates are widely occurring molecules in marine organisms. Their importance has been so far underestimated although many of these compounds are crucial mediators of physiological and ecological functions in other organisms. Biosynthesis of sterol sulfates is controlled by cytosolic sulfotransferases (SULTs), a varied family of enzymes that catalyze the transfer of a sulfo residue (-SO₃H) from the universal donor 3'-phosphoadenosine-5'-phosphosulfate to the hydroxyl function at C-3 of the steroid skeleton. The absence of molecular tools has been the main impediment to the development of a biosynthetic study of this class of compounds in marine organisms. In fact, there is very limited information about these enzymes in marine environments. SULT activity has, however, been reported in several marine species, and, recently, the production of sterol sulfates has been linked to the control of growth in marine diatoms. In this chapter, we describe methods for the study of sterol sulfates in this lineage of marine microalgae. The main aim is to provide the tools useful to deal with the biosynthesis and regulation of these compounds and to circumvent the bottleneck of the lack of molecular information. The protocols have been designed for marine diatoms, but most of the procedures can be used for other marine organisms.

The Oxylipin Pathways: Biochemistry and Function

Plant oxylipins form a constantly growing group of signaling molecules that comprise oxygenated fatty acids and metabolites derived therefrom. In the last decade, the understanding of biosynthesis, metabolism, and action of oxylipins, especially jasmonates, has dramatically improved. Additional mechanistic insights into the action of enzymes and insights into signaling pathways have been deepened for jasmonates. For other oxylipins, such as the hydroxy fatty acids, individual signaling properties and cross talk between different oxylipins or even with additional phytohormones have recently been described. This review summarizes recent understanding of the biosynthesis, regulation, and function of oxylipins.

The Effect of Single and Multiple SERAT Mutants on Serine and Sulfur Metabolism

The gene family of serine acetyltransferases (SERATs) constitutes an interface between the plant pathways of serine and sulfur metabolism. SERATs provide the activated precursor, O-acetylserine for the fixation of reduced sulfur into cysteine by exchanging the serine hydroxyl moiety by a sulfhydryl moiety, and subsequently all organic compounds containing reduced sulfur moieties. We investigate here, how manipulation of the SERAT interface results in metabolic alterations upstream or downstream of this boundary and the extent to which the five SERAT isoforms exert an effect on the coupled system, respectively. Serine is synthesized through three distinct pathways while cysteine biosynthesis is distributed over the three compartments cytosol, mitochondria, and plastids. As the respective mutants are viable, all necessary metabolites can obviously cross various membrane systems to compensate what would otherwise constitute a lethal failure in cysteine biosynthesis. Furthermore, given that cysteine serves as precursor for multiple pathways, cysteine biosynthesis is highly regulated at both, the enzyme and the expression level. In this study, metabolite profiles of a mutant series of the SERAT gene family displayed that levels of the downstream metabolites in sulfur metabolism were affected in correlation with the reduction levels of SERAT activities and the growth phenotypes, while levels of the upstream metabolites in serine metabolism were unchanged in the serat mutants compared to wild-type plants. These results suggest that despite of the fact that the two metabolic pathways are directly connected, there seems to be no causal link in metabolic alterations. This might be caused by the difference of their pool sizes or the tight regulation by homeostatic mechanisms that control the metabolite concentration in plant cells. Additionally, growth conditions exerted an influence on metabolic compositions.

Integrative Transcriptomic Analysis Uncovers Novel Gene Modules That Underlie the Sulfate Response in Arabidopsis thaliana

Sulfur is an essential nutrient for plant growth and development. Sulfur is a constituent of proteins, the plasma membrane and cell walls, among other important cellular components. To obtain new insights into the gene regulatory networks underlying the sulfate response, we performed an integrative meta-analysis of transcriptomic data from five different sulfate experiments available in public databases. This bioinformatic approach allowed us to identify a robust set of genes whose expression depends only on sulfate availability, indicating that those genes play an important role in the sulfate response. In relation to sulfate metabolism, the biological function of approximately 45% of these genes is currently unknown. Moreover, we found several consistent Gene Ontology terms related to biological processes that have not been extensively studied in the context of the sulfate response; these processes include cell wall organization, carbohydrate metabolism, nitrogen compound transport, and the regulation of proteolysis. Gene co-expression network analyses revealed relationships between the sulfate-responsive genes that were distributed among seven function-specific co-expression modules. The most connected genes in the sulfate co-expression network belong to a module related to the carbon response, suggesting that this biological function plays an important role in the control of the sulfate response. Temporal analyses of the network suggest that sulfate starvation generates a biphasic response, which involves that major changes in gene expression occur during both the early and late responses. Network analyses predicted that the sulfate response is regulated by a limited number of transcription factors, including MYBs, bZIPs, and NF-YAs. In conclusion, our analysis identified new candidate genes and provided new hypotheses to advance our understanding of the transcriptional regulation of sulfate metabolism in plants.

Engineering sulfur storage in maize seed proteins without apparent yield loss

Sulfur assimilation may limit the pool of methionine and cysteine available for incorporation into zeins, the major seed storage proteins in maize. This hypothesis was tested by producing transgenic maize with deregulated sulfate reduction capacity achieved through leaf-specific expression of the Escherichia coli enzyme 3'-phosphoadenosine-5'-phosphosulfate reductase (EcPAPR) that resulted in higher methionine accumulation in seeds. The transgenic kernels have higher expression of the methionine-rich 10-kDa δ-zein and total protein sulfur without reduction of other zeins. This overall increase in the expression of the S-rich zeins describes a facet of regulation of these proteins under enhanced sulfur assimilation. Transgenic line PE5 accumulates 57.6% more kernel methionine than the high-methionine inbred line B101. In feeding trials with chicks, PE5 maize promotes significant weight gain compared with nontransgenic kernels. Therefore, increased source strength can improve the nutritional value of maize without apparent yield loss and may significantly reduce the cost of feed supplementation.

Jasmonates: biosynthesis, metabolism, and signaling by proteins activating and repressing transcription

The lipid-derived phytohormone jasmonate (JA) regulates plant growth, development, secondary metabolism, defense against insect attack and pathogen infection, and tolerance to abiotic stresses such as wounding, UV light, salt, and drought. JA was first identified in 1962, and since the 1980s many studies have analyzed the physiological functions, biosynthesis, distribution, metabolism, perception, signaling, and crosstalk of JA, greatly expanding our knowledge of the hormone's action. In response to fluctuating environmental cues and transient endogenous signals, the occurrence of multilayered organization of biosynthesis and inactivation of JA, and activation and repression of the COI1-JAZ-based perception and signaling contributes to the fine-tuning of JA responses. This review describes the JA biosynthetic enzymes in terms of gene families, enzymatic activity, location and regulation, substrate specificity and products, the metabolic pathways in converting JA to activate or inactivate compounds, JA signaling in perception, and the co-existence of signaling activators and repressors.

Fire and Brimstone: Molecular Interactions between Sulfur and Glucosinolate Biosynthesis in Model and Crop Brassicaceae

Glucosinolates (GSLs) represent one of the most widely studied classes of plant secondary metabolite, and have a wide range of biological activities. Their unique properties also affect livestock and human health, and have been harnessed for food and other end-uses. Since GSLs are sulfur (S)-rich there are many lines of evidence suggesting that plant S status plays a key role in determining plant GSL content. However, there is still a need to establish a detailed knowledge of the distribution and remobilization of S and GSLs throughout the development of Brassica crops, and to represent this in terms of primary and secondary sources and sinks. The increased genome complexity, gene duplication and divergence within brassicas, together with their ontogenetic plasticity during crop development, appear to have a marked effect on the regulation of S and GSLs. Here, we review the current understanding of inorganic S (sulfate) assimilation into organic S forms, including GSLs and their precursors, the intracellular and inter-organ transport of inorganic and organic S forms, and the accumulation of GSLs in specific tissues. We present this in the context of overlapping sources and sinks, transport processes, signaling molecules and their associated molecular interactions. Our analysis builds on recent insights into the molecular regulation of sulfate uptake and transport by different transporters, transcription factors and miRNAs, and the role that these may play in GSL biosynthesis. We develop a provisional model describing the key processes that could be targeted in crop breeding programs focused on modifying GSL content.

Restriction of Aerobic Metabolism by Acquired or Innate Arylsulfatase B Deficiency: A New Approach to the Warburg Effect

Aerobic respiration is required for optimal efficiency of metabolism in mammalian cells. Under circumstances when oxygen utilization is impaired, cells survive by anerobic metabolism. The malignant cell has cultivated the use of anerobic metabolism in an aerobic environment, the Warburg effect, but the explanation for this preference is not clear. This paper presents evidence that deficiency of the enzyme arylsulfatase B (ARSB; N-acetylgalactosamine 4-sulfatase), either innate or acquired, helps to explain the Warburg phenomenon. ARSB is the enzyme that removes 4-sulfate groups from the non-reducing end of chondroitin 4-sulfate and dermatan sulfate. Previous reports indicated reduced ARSB activity in malignancy and replication of the effects of hypoxia by decline in ARSB. Hypoxia reduced ARSB activity, since molecular oxygen is needed for post-translational modification of ARSB. In this report, studies were performed in human HepG2 cells and in hepatocytes from ARSB-deficient and normal C57BL/6J control mice. Decline of ARSB, in the presence of oxygen, profoundly reduced the oxygen consumption rate and increased the extracellular acidification rate, indicating preference for aerobic glycolysis. Specific study findings indicate that decline in ARSB activity enhanced aerobic glycolysis and impaired normal redox processes, consistent with a critical role of ARSB and sulfate reduction in mammalian metabolism.