L-cysteine Desulfhydrase Research Articles

Cinnamaldehyde promotes root branching by regulating endogenous hydrogen sulfide.

Cinnamaldehyde (CA) has been widely applied in medicine and food preservation. However, whether and how CA regulates plant physiology is largely unknown. To address these gaps, the present study investigated the beneficial effect of CA on root branching and its possible biochemical mechanism. The lateral root (LR) formation of pepper seedlings could be markedly induced by CA at specific concentrations without any inhibitory effect on primary root (PR) growth. CA could induce the generation of endogenous hydrogen sulfide (H2S) by increasing the activity of L-cysteine desulfhydrase in roots. By fluorescently tracking endogenous H2S in situ, it could be clearly observed that H2S accumulated in the outer layer cells of the PR where LRs emerge. Sodium hydrosulfide (H2S donor) treatment induced LR formation, while hypotaurine (H2S scavenger) showed an adverse effect. The addition of hypotaurine mitigated the CA-induced increase in endogenous H2S level, which in turn counteracted the inducible effect of CA on LR formation. CA showed great potential in promoting LR formation, which was mediated by endogenous H2S. These results not only shed new light on the application of CA in agriculture but also extend the knowledge of H2S signaling in the regulation of root branching.

Hydrogen sulfide acts as a downstream signal molecule in salicylic acid-induced heat tolerance in maize (Zea mays L.) seedlings

Salicylic acid (SA), 2-hydroxy benzoic acid, is a small phenolic compound with multifunction that is involved in plant growth, development, and the acquisition of stress tolerance. In recent years, hydrogen sulfide (H2S) has been found to have similar functions, but cross talk between SA and H2S in the acquisition of heat tolerance is not clear. In this study, pretreatment of maize seedlings with SA improved the survival percentage of seedlings under heat stress, indicating that SA pretreatment could improve the heat tolerance of maize seedlings. In addition, treatment with SA enhanced the activity of L-cysteine desulfhydrase (L-DES), a key enzyme in H2S biosynthesis, which in turn induced accumulation of endogenous H2S. Interestingly, SA-induced heat tolerance was enhanced by addition of NaHS, a H2S donor, but weakened by specific inhibitors of H2S biosynthesis DL-propargylglycine (PAG) and its scavenger hydroxylamine (HT). Furthermore, pretreatment with paclobutrazol (PAC) and 2-aminoindan-2-phosphonic acid (AIP), inhibitors of SA biosynthesis, had no significant effect on NaHS-induced heat tolerance of maize seedlings. Similarly, significant change in the activities of phenylalanine ammonia lyase (PAL) and benzoic-acid-2-hydroxylase (BA2H), the key enzymes in SA biosynthesis, and the content of endogenous SA, was not observed in maize seedlings by NaHS treatment. All of the above-mentioned results suggest that SA pretreatment could improve the heat tolerance of maize seedlings, and H2S might be a novel downstream signal molecule in SA-induced heat tolerance.

Assessing the transcriptional regulation of L-cysteine desulfhydrase 1 in Arabidopsis thaliana.

Hydrogen sulfide is an important signaling molecule that functions as a physiological gasotransmitter of comparable importance to NO and CO in mammalian systems. In plants, numerous studies have shown that sulfide increases tolerance/resistance to stress conditions and regulates essential processes. The endogenous production of hydrogen sulfide in the cytosol of Arabidopsis thaliana occurs by the enzymatic desulfuration of L-cysteine, which is catalyzed by the L-cysteine desulfhydrase enzyme DES1. To define the functional role of DES1 and the role that the sulfide molecule may play in the regulation of physiological processes in plants, we studied the localization of the expression of this gene at the tissue level. Transcriptional data reveal that DES1 is expressed at all developmental stages and is more abundant at the seedling stage and in mature plants. At the tissue level, we analyzed the expression of a GFP reporter gene fused to promoter of DES1. The GFP fluorescent signal was detected in the cytosol of both epidermal and mesophyll cells, including the guard cells. GFP fluorescence was highly abundant around the hydathode pores and inside the trichomes. In mature plants, fluorescence was detected in floral tissues; a strong GFP signal was detected in sepals, petals, and pistils. When siliques were examined, the highest GFP fluorescence was observed at the bases of the siliques and the seeds. The location of GFP expression, together with the identification of regulatory elements within the DES1 promoter, suggests that DES1 is hormonally regulated. An increase in DES1 expression in response to ABA was recently demonstrated; in the present work, we observe that in vitro auxin treatment significantly repressed the expression of DES1.

Cadmium-induced hydrogen sulfide synthesis is involved in cadmium tolerance in Medicago sativa by reestablishment of reduced (homo)glutathione and reactive oxygen species homeostases.

Until now, physiological mechanisms and downstream targets responsible for the cadmium (Cd) tolerance mediated by endogenous hydrogen sulfide (H2S) have been elusive. To address this gap, a combination of pharmacological, histochemical, biochemical and molecular approaches was applied. The perturbation of reduced (homo)glutathione homeostasis and increased H2S production as well as the activation of two H2S-synthetic enzymes activities, including L-cysteine desulfhydrase (LCD) and D-cysteine desulfhydrase (DCD), in alfalfa seedling roots were early responses to the exposure of Cd. The application of H2S donor sodium hydrosulfide (NaHS), not only mimicked intracellular H2S production triggered by Cd, but also alleviated Cd toxicity in a H2S-dependent fashion. By contrast, the inhibition of H2S production caused by the application of its synthetic inhibitor blocked NaHS-induced Cd tolerance, and destroyed reduced (homo)glutathione and reactive oxygen species (ROS) homeostases. Above mentioned inhibitory responses were further rescued by exogenously applied glutathione (GSH). Meanwhile, NaHS responses were sensitive to a (homo)glutathione synthetic inhibitor, but reversed by the cotreatment with GSH. The possible involvement of cyclic AMP (cAMP) signaling in NaHS responses was also suggested. In summary, LCD/DCD-mediated H2S might be an important signaling molecule in the enhancement of Cd toxicity in alfalfa seedlings mainly by governing reduced (homo)glutathione and ROS homeostases.

Hydrogen sulfide generated by L-cysteine desulfhydrase acts upstream of nitric oxide to modulate abscisic acid-dependent stomatal closure.

Abscisic acid (ABA) is a well-studied regulator of stomatal movement. Hydrogen sulfide (H2S), a small signaling gas molecule involved in key physiological processes in mammals, has been recently reported as a new component of the ABA signaling network in stomatal guard cells. In Arabidopsis (Arabidopsis thaliana), H2S is enzymatically produced in the cytosol through the activity of l-cysteine desulfhydrase (DES1). In this work, we used DES1 knockout Arabidopsis mutant plants (des1) to study the participation of DES1 in the cross talk between H2S and nitric oxide (NO) in the ABA-dependent signaling network in guard cells. The results show that ABA did not close the stomata in isolated epidermal strips of des1 mutants, an effect that was restored by the application of exogenous H2S. Quantitative reverse transcription polymerase chain reaction analysis demonstrated that ABA induces DES1 expression in guard cell-enriched RNA extracts from wild-type Arabidopsis plants. Furthermore, stomata from isolated epidermal strips of Arabidopsis ABA receptor mutant pyrabactin-resistant1 (pyr1)/pyrabactin-like1 (pyl1)/pyl2/pyl4 close in response to exogenous H2S, suggesting that this gasotransmitter is acting downstream, although acting independently of the ABA receptor cannot be ruled out with this data. However, the Arabidopsis clade-A PROTEIN PHOSPHATASE2C mutant abscisic acid-insensitive1 (abi1-1) does not close the stomata when epidermal strips were treated with H2S, suggesting that H2S required a functional ABI1. Further studies to unravel the cross talk between H2S and NO indicate that (1) H2S promotes NO production, (2) DES1 is required for ABA-dependent NO production, and (3) NO is downstream of H2S in ABA-induced stomatal closure. Altogether, data indicate that DES1 is a unique component of ABA signaling in guard cells.

Signaling in the plant cytosol: cysteine or sulfide?

Cysteine (Cys) is the first organic compound containing reduced sulfur that is synthesized in the last stage of plant photosynthetic assimilation of sulfate. It is a very important metabolite not only because it is crucial for the structure, function and regulation of proteins but also because it is the precursor molecule of an enormous number of sulfur-containing metabolites essential for plant health and development. The biosynthesis of Cys is accomplished by the sequential reaction of serine acetyltransferase (SAT) and O-acetylserine(thiol)synthase (OASTL). In Arabidopsis thaliana, the analysis of specific mutants of members of the SAT and OASTL families has demonstrated that the cytosol is the compartment where the bulk of Cys synthesis takes place and that the cytosolic OASTL enzyme OAS-A1 is the responsible enzyme. Another member of the OASTL family is DES1, a novel L-cysteine desulfhydrase that catalyzes the desulfuration of Cys to produce sulfide, thus acting in a manner opposite to that of OAS-A1. Detailed studies of the oas-a1 and des1 null mutants have revealed the involvement of the DES1 and OAS-A1 proteins in coordinate regulation of Cys homeostasis and the generation of sulfide in the cytosol for signaling purposes. Thus, the levels of Cys in the cytosol strongly affect plant responses to both abiotic and biotic stress conditions, while sulfide specifically generated from the degradation of Cys negatively regulates autophagy induced in different situations. In conclusion, modulation of the levels of Cys and sulfide is likely critical for plant performance.

Endogenous hydrogen sulfide enhances salt tolerance by coupling the reestablishment of redox homeostasis and preventing salt-induced K+ loss in seedlings of Medicago sativa

Despite the external application of hydrogen sulfide (H2S) conferring plant tolerance against various environmental cues, the physiological significance of l-cysteine desulfhydrase (L-DES)-associated endogenous H2S production involved in salt-stress signaling was poorly understood. To address this gap, the participation of in planta changes of H2S homeostasis involved in alfalfa salt tolerance was investigated. The increasing concentration of NaCl (from 50 to 300mM) progressively caused the induction of total l-DES activity and the increase of endogenous H2S production. NaCl-triggered toxicity symptoms (175mM), including seedling growth inhibition and lipid peroxidation, were alleviated by sodium hydrosulfide (NaHS; 100μM), a H2S donor, whereas aggravated by an inhibitor of l-DES or a H2S scavenger. A weaker or negative response was observed in lower or higher dose of NaHS. Further results showed that endogenous l-DES-related H2S modulated several genes/activities of antioxidant defence enzymes, and also regulated the contents of antioxidant compounds, thus counterbalancing the NaCl-induced lipid peroxidation. Moreover, H2S maintained K+/Na+ homeostasis by preventing the NaCl-triggered K+ efflux, which might be result form the impairment of SKOR expression. Together, our findings indicated that endogenous H2S homeostasis enhance salt tolerance by coupling the reestablishment of redox balance and restraining K+ efflux in alfalfa seedlings.

Hydrogen sulfide is a novel gasotransmitter with pivotal role in regulating lateral root formation in plants

Hydrogen sulfide (H2S), the third gasotransmitter after nitric oxide (NO) and carbon monoxide (CO), is a critical neuromodulator in the pathogenesis of various diseases from neurodegenerative diseases to diabetes or heart failure. The crosstalk between NO and H2S has been well established in mammalian physiology. In planta, NO is demonstrated to regulate lateral root formation by acting downstream of auxin. The recent reports revealed that H2S is a novel inducer of lateral root (LR) formation by stimulating the expression of cell cycle regulatory genes (CCRGs), acting similarly with NO, CO, and IAA. Interestingly, during the initiation of lateral root primordia, IAA is a potent inducer of endogenous H2S and CO, which is produced by L-cysteine desulfhydrase (LCD) and heme oxygenase-1 (HO-1), respectively. The increasing evidences suggest that H2S-promoted LR growth is dependent on the endogenous production of CO. In addition, our results indicate that the H2S signaling in the regulation of LR formation can be associated to NO and Ca2+. In this addendum, we advanced a proposed schematic model for H2S-mediated signaling pathway of plant LR development.

Auxin-induced hydrogen sulfide generation is involved in lateral root formation in tomato

Similar to auxin, hydrogen sulfide (H2S), mainly produced by l-cysteine desulfhydrase (DES; EC 4.4.1.1) in plants, could induce lateral root formation. The objective of this study was to test whether H2S is also involved in auxin-induced lateral root development in tomato (Solanum lycopersicum L.) seedlings. We observed that auxin depletion-induced down-regulation of transcripts of SlDES1, decreased DES activity and endogenous H2S contents, and the inhibition of lateral root formation were rescued by sodium hydrosulfide (NaHS, an H2S donor). However, No additive effects were observed when naphthalene acetic acid (NAA) was co-treated with NaHS (lower than 10 mM) in the induction of lateral root formation. Subsequent work revealed that a treatment with NAA or NaHS could simultaneously induce transcripts of SlDES1, DES activity and endogenous H2S contents, and thereafter the stimulation of lateral root formation. It was further confirmed that H2S or HS−, not the other sulfur-containing components derived from NaHS, was attributed to the stimulative action. The inhibition of lateral root formation and decreased of H2S metabolism caused by an H2S scavenger hypotaurine (HT) were reversed by NaHS, but not NAA. Molecular evidence revealed that both NaHS- or NAA-induced modulation of some cell cycle regulatory genes, including the up-regulation of SlCDKA;1, SlCYCA2;1, together with simultaneous down-regulation of SlKRP2, were differentially reversed by HT pretreatment. To summarize, above results clearly suggested that H2S might, at least partially, act as a downstream component of auxin signaling to trigger lateral root formation.

Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression

Hydrogen sulfide (H2S) is considered as a cellular signaling intermediate in higher plants, but corresponding molecular mechanisms and signal transduction pathways in plant biology are still limited. In the present study, a combination of pharmacological and biochemical approaches was used to study the effect of H2S on the alleviation of GA-induced programmed cell death (PCD) in wheat aleurone cells. The results showed that in contrast with the responses of ABA, GA brought about a gradual decrease of l-cysteine desulfhydrase (LCD) activity and H2S production, and thereafter PCD occurred. Exogenous H2S donor sodium hydrosulfide (NaHS) not only effectively blocked the decrease of endogenous H2S release, but also alleviated GA-triggered PCD in wheat aleurone cells. These responses were sensitive to hypotaurine (HT), a H2S scavenger, suggesting that this effect of NaHS was in an H2S-dependent fashion. Further experiment confirmed that H2S, rather than other sodium- or sulphur-containing compounds derived from the decomposing of NaHS, was attributed to the rescuing response. Importantly, the reversing effect was associated with glutathione (GSH) because the NaHS triggered increases of endogenous GSH content and the ratio of GSH/oxidized GSH (GSSG) in GA-treated layers, and the NaHS-mediated alleviation of PCD was markedly eliminated by l-buthionine-sulfoximine (BSO, a selective inhibitor of GSH biosynthesis). The inducible effect of NaHS was also ascribed to the modulation of heme oxygenase-1 (HO-1), because the specific inhibitor of HO-1 zinc protoporphyrin IX (ZnPP) significantly suppressed the NaHS-related responses. By contrast, the above inhibitory effects were reversed partially when carbon monoxide (CO) aqueous solution or bilirubin (BR), two of the by-products of HO-1, was added, respectively. NaHS-triggered HO-1 gene expression in GA-treated layers was also confirmed. Together, the above results clearly suggested that the H2S-delayed PCD in GA-treated wheat aleurone cells was associated with the modulation of GSH homeostasis and HO-1 gene expression.

L-Cysteine Desulfhydrase 1 modulates the generation of the signaling molecule sulfide in plant cytosol

Consistent with data in animal systems, experimental evidence highlights sulfide as a signaling molecule of equal importance to NO and H2O2 in plant systems. In mammals, two cytosolic enzymes, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), have been shown to be responsible for the endogenous production of sulfide. L-cysteine desulfhydrase 1 (DES1) has been recently established as the only enzyme that is involved in the generation of hydrogen sulfide in plant cytosol. Although plants have an available source of sulfide within chloroplasts, the basic stromal pH prevents sulfide release into the cytosol. Therefore, DES1 is essential for the production of sulfide for signaling purposes.

Hydrogen Sulfide Regulates Ethylene‐induced Stomatal Closure in Arabidopsis thaliana

Hydrogen sulfide (H2 S) is a newly-discovered signaling molecule in plants and has caused increasing attention in recent years, but its function in stomatal movement is unclear. In plants, H2 S is synthesized via cysteine degradation catalyzed by D-/L-cysteine desulfhydrase (D-/L-CDes). AtD-/L-CDes::GUS transgenic Arabidopsis thaliana (L.) Heynh. plants were generated and used to investigate gene expression patterns, and results showed that AtD-/L-CDes can be expressed in guard cells. We also determined the subcellular localization of AtD-/L-CDes using transgenic plants of AtD-/L-CDes::GFP, and the results showed that AtD-CDes and AtL-CDes are located in the chloroplast and in the cytoplasm, respectively. The transcript levels of AtD-CDes and AtL-CDes were affected by the chemicals that cause stomatal closure. Among these factors, ACC, a precursor of ethylene, has the most significant effect, which indicates that the H2 S generated from D-/L-CDes may play an important role in ethylene-induced stomatal closure. Meanwhile, H2 S synthetic inhibitors significantly inhibited ethylene-induced stomatal closure in Arabidopsis. Ethylene treatment caused an increase of H2 S production and of AtD-/L-CDes activity in Arabidopsis leaves. AtD-/L-CDes over-expressing plants exhibited enhanced induction of stomatal closure compared to the wild-type after ethylene treatment; however, the effect was not observed in the Atd-cdes and Atl-cdes mutants. In conclusion, our results suggest that the D-/L-CDes-generated H2 S is involved in the regulation of ethylene-induced stomatal closure in Arabidopsis thaliana.

Molecular Cloning, Characterization, and Expression Analysis of a Novel Gene Encoding l-Cysteine Desulfhydrase from Brassica napus

L-Cysteine desulfhydrase (DES; EC 4.4.1.1) is the most important enzyme that catalyzes the decomposition of L-cysteine to pyruvate, ammonia, and hydrogen sulfide (H2S), the latter of which has recently been recognized as the third gasotransmitter for multiple signaling events in plants. Previous results showed the existence of DES activity in Brassica napus; however, the gene encoding the true DES protein has not been characterized yet. Here, a rapeseed DES gene was isolated and sequenced. It shared high homology with Arabidopsis DES1, and encodes a polypeptide with 323 amino acids of 34.5 kDa. Subsequently, prokaryotic expression and biochemical analysis demonstrated that this protein predominantly catalyzes the breakdown of L-cysteine with the side reaction of L-cysteine synthesis [O-acetyl-L-serine(thiol)lyase activity], and was designated as BnDES1. Corresponding analysis of structural features was also in agreement with the above proposition. Molecular evidence showed that BnDES1 mRNA was widely expressed, but with the higher expression level in flowers. Further results showed that the BnDES1 transcripts were differentially up-regulated by several plant growth regulators and chemicals. Overall, the above findings provide evidence showing that BnDES1 is a potentially important enzyme responsible for the H2S production, and may play an important role in plant growth regulators and chemical stimuli responses.

Hydrogen sulfide interacting with abscisic acid in stomatal regulation responses to drought stress in Arabidopsis

Hydrogen sulfide (H(2)S) plays a crucial role in the regulation of stomatal closure in plant response to drought stress, and l-cysteine desulfhydrase (LCD) has been identified as being mainly responsible for the degradation of cysteine to generate H(2)S. In view of the similar roles to abscisic acid (ABA), in this study, the lcd, aba3 and abi1 mutants were studied to investigate the close inter-relationship between H(2)S and ABA. The lcd mutant showed enlarged stomatal aperture and more sensitivity to drought stress than wild-type plants. Expression of Ca(2+) channel and outward-rectifying K(+) channel coding genes decreased in the lcd mutant, and conversely, expression of inward-rectifying K(+) increased. The stomatal aperture of aba3 and abi1 mutants decreased after treatment with NaHS (a H(2)S donor), but stomatal closure in responses to ABA was impaired in the lcd mutant. The expression of LCD and H(2)S production rate decreased in both the aba3 and abi1 mutants. Transcriptional expression of ABA receptor candidates was upregulated in the lcd mutant and decreased with NaHS treatment. The above results suggested that H(2)S may be an important link in stomatal regulation by ABA via ion channels; H(2)S affected the expression of ABA receptor candidates; and ABA also influenced H(2)S production. Thus, H(2)S interacted with ABA in the stomatal regulation responsible for drought stress in Arabidopsis.

Cysteine-Generated Sulfide in the Cytosol Negatively Regulates Autophagy and Modulates the Transcriptional Profile in Arabidopsis

In Arabidopsis thaliana, DES1 is the only identified L-Cysteine desulfhydrase located in the cytosol, and it is involved in the degradation of cysteine and the concomitant production of H(2)S in this cell compartment. Detailed characterization of the T-DNA insertion mutants des1-1 and des1-2 has provided insight into the role of sulfide metabolically generated in the cytosol as a signaling molecule. Mutations of L-CYS DESULFHYDRASE 1 (DES1) impede H(2)S generation in the Arabidopsis cytosol and strongly affect plant metabolism. Senescence-associated vacuoles are detected in mesophyll protoplasts of des1 mutants. Additionally, DES1 deficiency promotes the accumulation and lipidation of the ATG8 protein, which is associated with the process of autophagy. The transcriptional profile of the des1-1 mutant corresponds to its premature senescence and autophagy-induction phenotypes, and restoring H(2)S generation has been shown to eliminate the phenotypic defects of des1 mutants. Moreover, sulfide is able to reverse ATG8 accumulation and lipidation, even in wild-type plants when autophagy is induced by carbon starvation, suggesting a general effect of sulfide on autophagy regulation that is unrelated to sulfur or nitrogen limitation stress. Our results suggest that cysteine-generated sulfide in the cytosol negatively regulates autophagy and modulates the transcriptional profile of Arabidopsis.

L-cysteine desulfhydrase-an enzyme which can be assayed in soil but is unlikely to function in the environment

An assay was developed to measure the activity of the enzyme L-cysteine desulfhydrase (CDA) in an agricultural loam soil. The optimum temperature for CDA in this soil was 60°C and the optimum pH for CDA in the soil was 8.5. CDA in the soil required the addition of pyridoxal phosphate to exhibit its maximum activity. However since no pyridoxal phosphate was found in this soil it is likely that activity of this enzyme in the soil will be limited by the lack of this cofactor. Our studies illustrate the important point that not all enzymes which can be assayed in soils under laboratory conditions will function in the environment, since some, as in the case of CDA, will be limited by a lack of an essential co-factor. Key words: Enzyme activity, enzyme L-cysteine desulfhydrase, agricultural loam soil, pyridoxal phosphate, microbial activity.

Hydrogen sulfide is a mediator in H2O2-induced seed germination in Jatropha Curcas

Hydrogen peroxide (H2O2), a second messenger, plays a vital role in seed germination and plant growth, development as well as the acquisition of stress tolerance, while hydrogen sulfide (H2S) is considered as a new emerging cell signal molecule in higher plants. In the present study, soaking of H2O2 greatly improved germination percentage of Jatropha curcas seeds, stimulated the increase of l-cysteine desulfhydrase activity, which in turn induced accumulation of H2S. On the contrary, pretreatment of aminooxyacetic acid (AOA), inhibitor of H2S biosynthesis, eliminated H2O2 stimulated the increase of activity of l-cysteine desulfhydrase and accumulation of H2S as well as improvement of germination percentage. In addition, exogenously applied H2S also could improve germination percentage of seeds of J. curcas. These results suggested that pretreatment of H2O2 could improve germination percentage of J. curcas seeds and this improvement was mediated by H2S.

Hydrogen sulfide improves drought resistance in Arabidopsis thaliana

Hydrogen sulfide (H2S) plays a crucial role in human and animal physiology. Its ubiquity and versatile properties have recently caught the attention of plant physiologists and biochemists. Two cysteine desulfhydrases (CDes), l-cysteine desulfhydrase and d-cysteine desulfhydrase, were identified as being mainly responsible for the degradation of cysteine in order to generate H2S. This study investigated the expression regulation of these genes and their relationship to drought tolerance in Arabidopsis. First, the expression pattern of CDes in Arabidopsis was investigated. The expression levels of CDes gradually increased in an age-dependent manner. The expression of CDes was significantly higher in stems and cauline leaves than in roots, rosette leaves and flowers. Second, the protective effect of H2S against drought was evaluated. The expression pattern of CDes was similar to the drought associated genes induced by dehydration, and H2S fumigation was found to stimulate further the expression of drought associated genes. Drought also significantly induced increased H2S production, a process that was reversed by re-watering. In addition, seedlings after treatment with NaHS (a H2S donor) showed a higher survival rate and displayed a significant reduction in the size of the stomatal aperture compared to the control. These findings provide evidence that H2S, as a gasotransmitter, improves drought resistance in Arabidopsis.

Streptococcus anginosusl‐cysteine desulfhydrase gene expression is associated with abscess formation in BALB/c mice

Streptococcus anginosus, an anginosus group bacterium, is frequently isolated from odontogenic abscesses, and is the oral bacterium that is primarily responsible for producing hydrogen sulfide from l-cysteine through the action of its l-cysteine desulfhydrase (βC-S lyase) enzyme. However, the relationship between its production of hydrogen sulfide and abscess formation has not been investigated. To elucidate the etiological role of hydrogen sulfide in abscess formation, we initially measured, using specific primers, expression of the lcd gene, which encodes βC-S lyase, in the pus of abscesses that formed in BALB/c mice following subcutaneous injection of S.anginosus into the dorsa. Expression of lcd was >15-fold higher when l-cysteine was present than when it was absent. A mouse virulence assay revealed that the mean diameter of abscesses caused by S.anginosus FW73 plus l-cysteine was greater than that of abscesses caused by S.anginosus FW73 in the absence of l-cysteine. These findings demonstrate that the lcd gene of S.anginosus is upregulated in mouse abscesses and that hydrogen sulfide, the product of a reaction catalyzed by βC-S lyase, plays an etiological role in odontogenic abscess formation.

Isolation and genetic improvement of Pseudomonas sp. strain HUT-78, capable of enzymatic production of L-cysteine from DL-2-amino-Δ2-thiazoline-4-carboxylic acid

Microorganisms able to bioconvert DL-2-amino-Δ(2)-thiazoline-4-carboxylic acid (DL-ATC) into L-cysteine were originally isolated from 10 soil samples with DL-ATC as the sole nitrogen source. Ninety-seven L-cysteine-producing bacterial strains were screened out and obtained in pure culture. Among them, a strain, designated as HUT-78, was selected as the best producer, with a molar bioconversion rate of 60%. Based on the 16S rRNA gene sequence analysis, this isolate was placed within the genus Pseudomonas. A novel mutant of this strain with a significantly reduced activity of L-cysteine desulfhydrase, a L-cysteine-decomposing enzyme, was derived by UV-mutagenesis. This mutant, designated as mHUT-78, exhibited a 42% increase in L-cysteine producing activity. Moreover, the bioconversion reactions in both the parent and the mutant strain were significantly accelerated by co-overexpression of the two key enzymes, AtcB and AtcC, involved in the bioconversion reaction.