Brassinosteroids (BRs) and polyamines (PAs) regulate various responses to abiotic stress, but their involvement in the regulation of copper (Cu) homeostasis in plants exposed to toxic levels of Cu is poorly understood. This study provides an analysis of the effects of exogenously applied BRs and PAs on radish (Raphanus sativus) plants exposed to toxic concentrations of Cu. The interaction of 24-epibrassinolide (EBR, an active BR) and spermidine (Spd, an active PA) on gene expression and the physiology of radish plants resulted in enhanced tolerance to Cu stress. Results indicated that the combined application of EBR and Spd modulated the expression of genes encoding PA enzymes and genes that impact the metabolism of indole-3-acetic acid (IAA) and abscisic acid (ABA) resulting in enhanced Cu stress tolerance. Altered expression of genes implicated in Cu homeostasis appeared to be the main effect of EBR and Spd leading to Cu stress alleviation in radish. Ion leakage, in vivo imaging of H2O2, comet assay, and improved tolerance of Cu-sensitive yeast strains provided further evidence for the ability of EBR and Spd to improve Cu tolerance significantly. The study indicates that co-application of EBR and Spd is an effective approach for Cu detoxification and the maintenance of Cu homeostasis in plants. Therefore, the use of these compounds in agricultural production systems should be explored.
Abscisic acid; brassinosteroids; comet assay; copper transporters; Cu homeostasis; Cu-sensitive yeast; indole-3-acetic acid; oxidative stress; polyamines
The present study deals with the effects of 24-epibrassinolide on growth, lipid peroxidation, antioxidative enzyme activities, non-enzymatic antioxidants and protein content in 30 days old leaves of Brassica juncea (var. PBR 91) under zinc metal stress in field conditions. Surface sterilized seeds of B. juncea were given pre-soaking treatments of 24-EBL (10−10, 10−8 and 10−6 M) for 8 h. Different concentrations of zinc metal in the form of ZnSO4.7H2O (0, 0.5, 1.0, 1.5 and 2.0 mM) were added in the soil kept in experimental pots. Seeds soaked in 24-EBL for 8 h were sown in the earthern pots containing different concentrations of Zn metal. After 30 days of sowing, the plants were analyzed for growth parameters in terms of shoot length and number of leaves. Thereafter, leaves were excised and content of proteins, non-enzymatic antioxidants, malondialdehyde (MDA) and the activities of antioxidative enzymes (superoxide dismutase (SOD) (EC 126.96.36.199) catalase (CAT) (EC 188.8.131.52), ascorbate peroxidase (APOX) (EC 184.108.40.206), guaiacol peroxidase (POD) (EC 220.127.116.11) glutathione reductase (GR) (EC 18.104.22.168), monodehydroascorbate reductase (MDHAR) (EC 22.214.171.124) and dehydroascorbate reductase (DHAR) (EC 126.96.36.199)) were analyzed. It was observed that the growth of plants was inhibited under Zn metal stress. However, 24-EBL seed-presoaking treatment improved the plant growth in terms of increase in shoot length. 24-EBL also mitigated the toxicity of Zn metal by increasing the number of leaves. The activities of antioxidative enzymes (SOD, CAT, POD, GR, APOX, MDHAR and DHAR) and contents of proteins and glutathione were also enhanced in leaves of plants treated with 24-EBL alone, 10−8 M concentration being the most effective. The activities of antioxidative enzymes also increased in leaves of B. juncea plants by the application 24-EBL supplemented Zn metal solutions. Similarly, the content of proteins and glutathione increased considerably in leaves of B. juncea plants treated with 24-EBL, whereas the level of MDA content decreased in 24-EBL treated plants as compared to untreated control plants thereby revealing stress-protective properties of the brassinolide.
Antioxidative enzymes; Brassica juncea; 24-epibrassinolide; Zn toxicity
Polyamines are small, ubiquitous, nitrogenous compounds that scavenge reactive oxygen species and stabilize the structure and function of the photosynthetic apparatus in response to abiotic stresses. Molecular details underlying polyamine-mediated photoprotective mechanisms are not completely resolved. This study investigated the role of spermidine (Spd) in the structure and function of the photosynthetic apparatus. Tomato seedlings were subjected to salinity-alkalinity stress with and without foliar application of Spd, and photosynthetic and morphological parameters were analyzed. Leaf dry weight and net photosynthetic rate were reduced by salinity-alkalinity stress. Salinity-alkalinity stress reduced photochemical quenching parameters, including maximum photochemistry efficiency of photosystem II, quantum yield of linear electron flux, and coefficient of photochemical quenching (qP). Salinity-alkalinity stress elevated nonphotochemical quenching parameters, including the de-epoxidation state of the xanthophyll cycle and nonphotochemical quenching (NPQ). Microscopic analysis revealed that salinity-alkalinity stress disrupted the internal lamellar system of granal and stromal thylakoids. Exogenous Spd alleviated the stress-induced reduction of leaf dry weight, net photosynthetic rate, and qP parameters. The NPQ parameters increased by salinity-alkalinity stress were also alleviated by Spd. Seedlings treated with exogenous Spd had higher zeaxanthin (Z) contents than those without Spd under salinity-alkalinity stress. The chloroplast ultrastructure had a more ordered arrangement in seedlings treated with exogenous Spd than in those without Spd under salinity-alkalinity stress. These results indicate that exogenous Spd can alleviate the growth inhibition and thylakoid membrane photodamage caused by salinity-alkalinity stress. The Spd-induced accumulation of Z also may have an important role in stabilizing the photosynthetic apparatus.
The role of exogenous spermidine (Spd) in alleviating low temperature (LT) stress in mung bean (Vigna radiata L. cv. BARI Mung-3) seedlings has been investigated. Low temperature stress modulated the non-enzymatic and enzymatic components of ascorbate-glutathione (AsA-GSH) cycle, increased H2O2 content and lipid peroxidation, which indicate oxidative damage of seedlings. Low temperature reduced the leaf relative water content (RWC) and destroyed leaf chlorophyll, which inhibited seedlings growth. Exogenous pretreatment of Spd in LT-affected seedlings significantly increased the contents of non-enzymatic antioxidants of AsA-GSH cycle, which include AsA and GSH. Exogenous Spd decreased dehydroascorbate (DHA), increased AsA/DHA ratio, decreased glutathione disulfide (GSSG) and increased GSH/GSSG ratio under LT stress. Activities of AsA-GSH cycle enzymes such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) increased after Spd pretreatment in LT affected seedlings. Thus, the oxidative stress was reduced. Protective effects of Spd are also reflected from reduction of methylglyoxal (MG) toxicity by improving glyoxalase cycle components, and by maintaining osmoregulation, water status and improved seedlings growth. The present study reveals the vital roles of AsA-GSH and glyoxalase cycle in alleviating LT injury.
abiotic stress; AsA-GSH cycle; glyoxalase system; oxidative stress; polyamine
The present paper deals with the effects of two active forms of brassinosteroids (BRs) as epibrassinosteroid (24-EBL) and homobrassinosteroid (28-HBL) on percentage germination, growth in the form of shoot length, activities of auxinase (IAAO), polyphenol oxidase (PPO), superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APOX) in 10 day old seedlings of Brassica juncea L. (RCM 619) under field conditions. Exogenous application of 240-EBL and 28-HBL significantly ameliorate the total protein content as compared to untreated control seedlings. 10−8 M 28-HBL helps in enhancing the PPO activity very significantly, as compared to all other concentrations of EBL and HBL and also to that of untreated control. Similar trend was observed in IAAO activity. It was observed that all the concentrations of EBL were unable to enhance the APOX activity as compared to untreated control seedlings but 10−8 M HBL significantly ameliorates APOX activity. CAT and SOD activities ameliorate significantly with exogenous application of EBL and HBL. Out of two active forms of BRs, 28-HBL was more effective at germination stage in scavenging the free radicals, which are produced in greater amount during germination from basic metabolic processes, whereas 28-EBL was effective in the initial growth of seedlings in the form of increase in shoot length.
Brassinosteroids; Brassica juncea; Antioxidant enzymes; Polyphenol oxidase; Auxinase; Total Proteins
A composite cytomegalovirus-immediate early gene enhancer/chicken β-actin promoter (CAG) was utilized to generate transgenic mice that overexpress human spermidine synthase (SpdS) in order to determine the impact of elevated spermidine synthase activity on murine development and physiology. CAG-SpdS mice were viable and fertile and tissue SpdS activity was increased up to 9-fold. This increased SpdS activity did not result in a dramatic elevation of spermidine or spermine levels but did lead to a 1.5 to 2-fold reduction in tissue spermine:spermidine ratio in heart, muscle and liver tissues with the highest levels of SpdS activity. This new mouse model enabled simultaneous overexpression of SpdS and other polyamine biosynthetic enzymes by combining transgenic animals. The combined overexpression of both SpdS and spermine synthase (SpmS) in CAG-SpdS/CAG-SpmS bitransgenic mice did not impair viability or lead to overt developmental abnormalities but instead normalized the elevated tissue spermine:spermidine ratios of CAG-SpmS mice. The CAG-SpdS mice were bred to MHC-AdoMetDC mice with a >100-fold increase in cardiac S-adenosylmethionine decarboxylase (AdoMetDC) activity to determine if elevated dcAdoMet would facilitate greater spermidine accumulation in mice with SpdS overexpression. CAG-SpdS/MHC-AdoMetDC bitransgenic animals were produced at the expected frequency and exhibited cardiac polyamine levels comparable to MHC-AdoMetDC littermates. Taken together these results indicate that SpdS levels are not rate limiting in vivo for polyamine biosynthesis and are unlikely to exert significant regulatory effects on cellular polyamine content and function.
polyamine; aminopropyltransferase; transgenic mice; S-adenosylmethionine decarboxylase; spermidine; spermine
MicroRNAs (miRNAs) are endogenous non-coding small RNAs that play vital regulatory roles in plant growth, development, and environmental stress responses. Cadmium (Cd) is a non-essential heavy metal that is highly toxic to living organisms. To date, a number of conserved and non-conserved miRNAs have been identified to be involved in response to Cd stress in some plant species. However, the miRNA-mediated gene regulatory networks responsive to Cd stress in radish (Raphanus sativus L.) remain largely unexplored. To dissect Cd-responsive miRNAs and their targets systematically at the global level, two small RNA libraries were constructed from Cd-treated and Cd-free roots of radish seedlings. Using Solexa sequencing technology, 93 conserved and 16 non-conserved miRNAs (representing 26 miRNA families) and 28 novel miRNAs (representing 22 miRNA families) were identified. In all, 15 known and eight novel miRNA families were significantly differently regulated under Cd stress. The expression patterns of a set of Cd-responsive miRNAs were validated by quantitative real-time PCR. Based on the radish mRNA transcriptome, 18 and 71 targets for novel and known miRNA families, respectively, were identified by the degradome sequencing approach. Furthermore, a few target transcripts including phytochelatin synthase 1 (PCS1), iron transporter protein, and ABC transporter protein were involved in plant response to Cd stress. This study represents the first transcriptome-based analysis of miRNAs and their targets responsive to Cd stress in radish roots. These findings could provide valuable information for functional characterization of miRNAs and their targets in regulatory networks responsive to Cd stress in radish.
Cadmium stress; degradome; high-throughput sequencing; microRNAs; Raphanus sativus; transcriptome.
The grain weight of wheat is strongly influenced by filling. Polyamines (PA) are involved in regulating plant growth. However, the effects of PA on wheat grain filling and its mechanism of action are unclear. The objective of the present study was to investigate the relationship between PAs and hormones in the regulation of wheat grain filling. Three PAs, spermidine (Spd), spermine (Spm), and putrescine (Put), were exogenously applied, and the grain filling characteristics and changes in endogenous PA and hormones, i.e., indole-3-acetic acid (IAA), zeatin (Z) + zeatin riboside (ZR), abscisic acid (ABA), ethylene (ETH) and gibberellin 1+4 (GAs), were quantified during wheat grain filling. Exogenous applications of Spd and Spm significantly increased the grain filling rate and weight, but exogenous Put had no significant effects on these measures. Exogenous Spd and Spm significantly increased the endogenous Spd, Spm, Z+ZR, ABA, and IAA contents and significantly decreased ETH evolution in grains. The endogenous Spd, Spm and Z+ZR contents were positively and significantly correlated with the grain filling rate and weight of wheat, and the endogenous ETH evolution was negatively and significantly correlated with the wheat grain filling rate and weight. Based upon these results, we concluded that PAs were involved in the balance of hormones that regulated the grain filling of wheat.
Soil salinity affects a large proportion of rural area and limits agricultural productivity. To investigate differential adaptation to soil salinity, we studied salt tolerance of 18 varieties of Oryza sativa using a hydroponic culture system. Based on visual inspection and photosynthetic parameters, cultivars were classified according to their tolerance level. Additionally, biomass parameters were correlated with salt tolerance. Polyamines have frequently been demonstrated to be involved in plant stress responses and therefore soluble leaf polyamines were measured. Under salinity, putrescine (Put) content was unchanged or increased in tolerant, while dropped in sensitive cultivars. Spermidine (Spd) content was unchanged at lower NaCl concentrations in all, while reduced at 100 mM NaCl in sensitive cultivars. Spermine (Spm) content was increased in all cultivars. A comparison with data from 21 cultivars under long-term, moderate drought stress revealed an increase of Spm under both stress conditions. While Spm became the most prominent polyamine under drought, levels of all three polyamines were relatively similar under salt stress. Put levels were reduced under both, drought and salt stress, while changes in Spd were different under drought (decrease) or salt (unchanged) conditions. Regulation of polyamine metabolism at the transcript level during exposure to salinity was studied for genes encoding enzymes involved in the biosynthesis of polyamines and compared to expression under drought stress. Based on expression profiles, investigated genes were divided into generally stress-induced genes (ADC2, SPD/SPM2, SPD/SPM3), one generally stress-repressed gene (ADC1), constitutively expressed genes (CPA1, CPA2, CPA4, SAMDC1, SPD/SPM1), specifically drought-induced genes (SAMDC2, AIH), one specifically drought-repressed gene (CPA3) and one specifically salt-stress repressed gene (SAMDC4), revealing both overlapping and specific stress responses under these conditions.
polyamines; salt stress; drought stress; gene expression; rice; natural variety
Brassinosteroids play a significant role in the amelioration of various biotic and abiotic stresses. To investigate the effects of exogenously applied brassinosteroids on the thermotolerance of plants, reactive oxygen species (ROS), antioxidant defense and methylglyoxal (MG) detoxification systems were examined in Ficus concinna seedlings with or without 24-epibrassinolide (EBR) application. Our results showed that EBR treatment reduced high temperature-induced increases in the levels of ROS, MG and lipid peroxidation. We also demonstrate that EBR attenuates high temperature-induced oxidative stress by simultaneously increasing non-enzymatic and enzymatic antioxidant responses, as well as MG detoxification systems.
Although brassinosteroids (BRs) play crucial roles in plant development and stress tolerance, the mechanisms by which they have these effects are poorly understood. Here, we investigated the possible mechanism of exogenously applied BRs on reactive oxygen species (ROS), antioxidant defence and methylglyoxal (MG) detoxification systems in Ficus concinna seedlings grown under high-temperature (HT) stress for 48 h. Our results showed that the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione peroxidase (GPX) and glyoxalase II (Gly II) were increased under two levels of HT stress. Compared with control the activities of catalase (CAT) and dehydroascorbate reductase (DHAR) were not changed due to HT stress. The activities of glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and glyoxalase I (Gly I) were increased only at moderate HT stress. Despite these protective mechanisms, HT stress induced oxidative stress in F. concinna seedlings, as indicated by the increased levels of ROS, malondialdehyde (MDA) and MG, and the reductions in chlorophyll levels and relative water content. The contents of reduced glutathione (GSH) and ascorbate (AsA) were not changed under moderate HT stress. Spraying with 24-epibrassinolide (EBR) alone had little influence on the non-enzymatic antioxidants and the activities of antioxidant enzymes. However, EBR pretreatment under HT stress resulted in an increase in GSH and AsA content, maintenance of high redox state of GSH and AsA, and enhanced ROS and MG detoxification by further elevating the activities of SOD, GST, GPX, APX, MDHAR, GR, DHAR, Gly I and Gly II, as evident by lower level of ROS, MDA and MG. It may be concluded that EBR could alleviate the HT-induced oxidative stress by increasing the enzymatic and non-enzymatic antioxidant defence, and glyoxalase systems in F. concinna seedlings.
Antioxidants; brassinosteroids; glyoxalase system; high-temperature stress; methylglyoxal
To figure out whether spermidine (Spd) can alleviate oxidative damage on rice (Oryza sativa L.) caused by submergence stress, Ningjing 3 was used in this study. The results showed that, spraying Spd on rice leaves at a concentration of 0.5 mM promoted the growth recovery of rice after drainage, such as green leaves, tillers, and aboveground dry mass. According to physiological analysis, Spd accelerate restored chlorophylls damage by submergence, and decreased the rate of O2·− generation and H2O2 content, inhibited submergence-induced lipid peroxidation. Spd also helped to maintain antioxidant enzyme activities after drainage, such as superoxide dismutase, peroxidase, and GR, which ultimately improved the recovery ability of submerged rice. With the effect of Spd, the rice yields increased by 12.1, 17.9, 13.5, and 18.0%, of which submerged for 1, 3, 5, 7 days, respectively. It is supposed that exogenous Spd really has an alleviate effect on submergence damage and reduce yield loss of rice.
rice; submergence stress; exogenous spermidine; tillering stage; physiological characteristics
The polyamines, putrescine, spermidine and spermine, are ubiquitous multifunctional cations essential for cellular proliferation. One specific function of spermidine in cell growth is its role as a butylamine donor for hypusine synthesis in the eukaryotic initiation factor 5A (eIF5A). Here, we report a novel series of mono-methylated spermidine analogs (α-MeSpd, β-MeSpd, γ-MeSpd, and ω-MeSpd) and their role in the hypusination of eIF5A and in supporting the growth of DFMO-treated DU145 cells. We also tested them as substrates and inhibitors for deoxyhypusine synthase (DHS) in vitro. Of these compounds, α-MeSpd, β-MeSpd, and γ-MeSpd (but not ω-MeSpd) were substrates for DHS in vitro, while they all inhibited the enzyme reaction. As racemic mixtures, only α-MeSpd and β-MeSpd supported long-term growth (9–18 days) of spermidine-depleted DU145 cells, whereas γ-MeSpd and ω-MeSpd did not. The S-enantiomer of α-MeSpd, which supported long-term growth, was a good substrate for DHS in vitro, whereas the R isomer was not. The long-term growth of DFMO-treated cells correlated with the hypusine-modification of eIF5A by intracellular methylated spermidine analogs. These results underscore the critical requirement for hypusine modification in mammalian cell proliferation and provide new insights into the specificity of the deoxyhypusine synthase reaction.
polyamine; methylated spermidine; cell growth; deoxyhypusine synthase; hypusine; eIF5A
Knowledge of the in vivo physiology and metabolism of Streptococcus pneumoniae is limited, even though pneumococci rely on efficient acquisition and metabolism of the host nutrients for growth and survival. Because the nutrient-limited, hypoxic host tissues favor mixed-acid fermentation, we studied the role of the pneumococcal pyruvate formate lyase (PFL), a key enzyme in mixed-acid fermentation, which is activated posttranslationally by PFL-activating enzyme (PFL-AE). Mutations were introduced to two putative pfl genes, SPD0235 and SPD0420, and two putative pflA genes, SPD0229 and SPD1774. End-product analysis showed that there was no formate, the main end product of the reaction catalyzed by PFL, produced by mutants defective in SPD0420 and SPD1774, indicating that SPD0420 codes for PFL and SPD1774 for putative PFL-AE. Expression of SPD0420 was elevated in galactose-containing medium in anaerobiosis compared to growth in glucose, and the mutation of SPD0420 resulted in the upregulation of fba and pyk, encoding, respectively, fructose 1,6-bisphosphate aldolase and pyruvate kinase, under the same conditions. In addition, an altered fatty acid composition was detected in SPD0420 and SPD1774 mutants. Mice infected intranasally with the SPD0420 and SPD1774 mutants survived significantly longer than the wild type-infected cohort, and bacteremia developed later in the mutant cohort than in the wild type-infected group. Furthermore, the numbers of CFU of the SPD0420 mutant were lower in the nasopharynx and the lungs after intranasal infection, and fewer numbers of mutant CFU than of wild-type CFU were recovered from blood specimens after intravenous infection. The results demonstrate that there is a direct link between pneumococcal fermentative metabolism and virulence.
Although, intracellular polyamine levels are highly regulated, it is unclear whether intracellular putrescine (PUT), spermidine (SPD), or spermine (SPM) levels act as a sensor to regulate their synthesis or uptake. Polyamines have been shown to induce AZ1 expression through a unique +1 frameshifting mechanism. However, under physiological conditions which particular polyamine induces AZ1, and thereby ODC activity, is unknown due to their inter-conversion. In this study we demonstrate that SPD regulates AZ1 expression under physiological conditions in IEC-6 cells. PUT and SPD showed potent induction of AZ1 within 4h in serum starved confluent cells grown in DMEM (control) medium. Unlike control cells, PUT failed to induce AZ1 in cells grown in DFMO containing medium, however, SPD caused a robust AZ1 induction in these cells. SPM showed very little effect on AZ1 expression in both the control and polyamine depleted cells. Only SPD induced AZ1 when S-adenosylmethionine decarboxylase (SAMDC) and/or ODC were inhibited. Surprisingly, addition of DENSpm along with DFMO restored AZ1 induction by putrescine in polyamine-depleted cells suggesting that the increased SSAT activity in response to DENSpm converted SPM to SPD leading to the expression of AZ1. This study shows that intracellular SPD levels controls AZ1 synthesis.
Putrescine; Spermine; S-adenosylmethionine decarboxylase (SAMDC); Cadavarine; N-spermidine/spermine acetyltransferase (N-SSAT); ornithine decarboxylase (ODC); Intestinal epithelial cells (IEC-6)
In this work, we have studied the transcriptional profiles of polyamine biosynthetic genes and analyzed polyamine metabolic fluxes during a gradual drought acclimation response in Arabidopsis thaliana and the resurrection plant Craterostigma plantagineum. The analysis of free putrescine, spermidine and spermine titers in Arabidopsis arginine decarboxylase (adc1–3, adc2–3), spermidine synthase (spds1–2, spds2–3) and spermine synthase (spms-2) mutants during drought stress, combined with the quantitative expression of the entire polyamine biosynthetic pathway in the wild-type, has revealed a strong metabolic canalization of putrescine to spermine induced by drought. Such canalization requires spermidine synthase 1 (SPDS1) and spermine synthase (SPMS) activities and, intriguingly, does not lead to spermine accumulation but to a progressive reduction in spermidine and spermine pools in the wild-type. Our results suggest the participation of the polyamine back-conversion pathway during the drought stress response rather than the terminal catabolism of spermine. The putrescine to spermine canalization coupled to the spermine to putrescine back-conversion confers an effective polyamine recycling-loop during drought acclimation. Putrescine to spermine canalization has also been revealed in the desiccation tolerant plant C. plantagineum, which conversely to Arabidopsis, accumulates high spermine levels which associate with drought tolerance. Our results provide a new insight to the polyamine homeostasis mechanisms during drought stress acclimation in Arabidopsis and resurrection plants.
Arabidopsis; Craterostigma plantagineum; drought; polyamines; polyamine oxidase; abiotic stress
Objective: High temperature adversely affects quality and yield of tomato fruit. Polyamine can alleviate heat injury in plants. This study is aimed to investigate the effects of polyamine and high temperature on transcriptional profiles in ripening tomato fruit. Methods: An Affymetrix tomato microarray was used to evaluate changes in gene expression in response to exogenous spermidine (Spd, 1 mmol/L) and high temperature (33/27 °C) treatments in tomato fruits at mature green stage. Results: Of the 10 101 tomato probe sets represented on the array, 127 loci were differentially expressed in high temperature-treated fruits, compared with those under normal conditions, functionally characterized by their involvement in signal transduction, defense responses, oxidation reduction, and hormone responses. However, only 34 genes were up-regulated in Spd-treated fruits as compared with non-treated fruits, which were involved in primary metabolism, signal transduction, hormone responses, transcription factors, and stress responses. Meanwhile, 55 genes involved in energy metabolism, cell wall metabolism, and photosynthesis were down-regulated in Spd-treated fruits. Conclusions: Our results demonstrated that Spd might play an important role in regulation of tomato fruit response to high temperature during ripening stage.
Solanum lycopersicum L.; Spermidine; High temperature; Microarray; Gene expression
Radish (Raphanus sativus L.) is an important worldwide root vegetable crop with high nutrient values and is adversely affected by non-essential heavy metals including chromium (Cr). Little is known about the molecular mechanism underlying Cr stress response in radish. In this study, RNA-Seq technique was employed to identify differentially expressed genes (DEGs) under Cr stress. Based on de novo transcriptome assembly, there were 30,676 unigenes representing 60,881 transcripts isolated from radish root under Cr stress. Differential gene analysis revealed that 2985 uingenes were significantly differentially expressed between Cr-free (CK) and Cr-treated (Cr600) libraries, among which 1424 were up-regulated and 1561 down-regulated. Gene ontology (GO) analysis revealed that these DEGs were mainly involved in primary metabolic process, response to abiotic stimulus, cellular metabolic process and small molecule metabolic process. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis showed that the DEGs were mainly involved in protein processing in endoplasmic reticulum, starch and sucrose metabolism, amino acid metabolism, glutathione metabolism, drug and xenobiotics by cytochrome P450 metabolism. RT-qPCR analysis showed that the expression patterns of 12 randomly selected DEGs were highly accordant with the results from RNA-seq. Furthermore, many candidate genes including signaling protein kinases, transcription factors and metal transporters, chelate compound biosynthesis and antioxidant system, were involved in defense and detoxification mechanisms of Cr stress response regulatory networks. These results would provide novel insight into molecular mechanism underlying plant responsiveness to Cr stress and facilitate further genetic manipulation on Cr uptake and accumulation in radish.
radish; transcriptome; Solexa sequencing; Cr stress; DEGs; RT-qRCR
Salt stress is one of the most representative abiotic stresses that severely affect plant growth and development. MicroRNAs (miRNAs) are well known for their significant involvement in plant responses to abiotic stresses. Although miRNAs implicated in salt stress response have been widely reported in numerous plant species, their regulatory roles in the adaptive response to salt stress in radish (Raphanus sativus L.), an important root vegetable crop worldwide, remain largely unknown.
Solexa sequencing of two sRNA libraries from NaCl-free (CK) and NaCl-treated (Na200) radish roots were performed for systematical identification of salt-responsive miRNAs and their expression profiling in radish. Totally, 136 known miRNAs (representing 43 miRNA families) and 68 potential novel miRNAs (belonging to 51 miRNA families) were identified. Of these miRNAs, 49 known and 22 novel miRNAs were differentially expressed under salt stress. Target prediction and annotation indicated that these miRNAs exerted a role by regulating specific stress-responsive genes, such as squamosa promoter binding-like proteins (SPLs), auxin response factors (ARFs), nuclear transcription factor Y (NF-Y) and superoxide dismutase [Cu-Zn] (CSD1). Further functional analysis suggested that these target genes were mainly implicated in signal perception and transduction, regulation of ion homeostasis, basic metabolic processes, secondary stress responses, as well as modulation of attenuated plant growth and development under salt stress. Additionally, the expression patterns of ten miRNAs and five corresponding target genes were validated by reverse-transcription quantitative PCR (RT-qPCR).
With the sRNA sequencing, salt-responsive miRNAs and their target genes in radish were comprehensively identified. The results provide novel insight into complex miRNA-mediated regulatory network of salt stress response in radish, and facilitate further dissection of molecular mechanism underlying plant adaptive response to salt stress in root vegetable crops.
Electronic supplementary material
The online version of this article (doi:10.1186/s12864-015-1416-5) contains supplementary material, which is available to authorized users.
Radish (Raphanus sativus L.); Salt stress; MicroRNA; Target gene; RT-qPCR; High-throughput sequencing
Spermidine (SPD) is a ubiquitous polycation that is commonly distributed in living organisms. Intracellular levels of SPD are tightly regulated, and SPD controls cell proliferation and death. However, SPD undergoes oxidation in the presence of serum, producing aldehydes, hydrogen peroxide, and ammonia, which exert cytotoxic effect on cells. Hemeoxygenase-1 (HO-1) is thought to have a protective effect against oxidative stress. Upregulation of HO-1 in endothelial cells is considered to be beneficial in the cardiovascular disease. In the present study, we demonstrate that the ubiquitous polyamine, SPD, induces HO-1 in human umbilical vein endothelial cells (HUVECs). SPD-induced HO-1 expression was examined by Western blot and reverse transcription-polymerase chain reaction (RT-PCR). Involvement of reactive oxygen species, serum amine oxidase, PI3K/Akt signaling pathway, and transcription factor Nrf2 in the induction of HO-1 by SPD was also investigated. Furthermore, small interfering RNA knockdown of Nrf2 or HO-1 and treatment with the specific HO-1 inhibitor ZnPP exhibited a noteworthy increase of death of SPD-stimulated HUVECs. In conclusion, these results suggest that SPD induces PI3K/Akt-Nrf2-mediated HO-1 expression in human endothelial cells, which may have a role in cytoprotection of the cells against oxidative stress-induced death.
Amine oxidases (AOs) oxidize polyamines (PAs) to aldehydes, simultaneously producing the removed amine moiety and hydrogen peroxide (H2O2). AOs, which include copper-containing amine oxidases (CuAOs) and flavin-containing amine oxidases (PAOs), are stress-inducible enzymes involved in both PA homeostasis and H2O2 production. Here, we suggest that H2O2 derived from PAO-mediated PA catabolism has a role in inducing root xylem differentiation during plant stress responses, whereas its involvement in this event during plant development under physiological conditions is not suitably supported by the currently available data. Moreover, we show that spermidine (Spd) supply leads to a higher induction of cell death in wild-type (WT) tobacco (Nicotiana tabacum) plants as compared to tobacco plants over-expressing maize (Zea mays) PAO (S-ZmPAO) in the cell wall, in apparent contradiction with the already reported results obtained by the analysis of the corresponding WT and S-ZmPAO Spd-untreated plants. Considering this last observation, we propose that PAs diversely affect plant development and stress responses depending on the expression levels of AOs, which in turn may lead to different plant responses by altering the PAs/H2O2 balance.
copper amine oxidase; hydrogen peroxide; PCD; polyamine; polyamine oxidase; xylem
Plasmodium falciparum, the causative agent of severe human malaria, has evolved to become resistant to previously successful antimalarial chemotherapies, most notably chloroquine and the antifolates. The prevalence of resistant strains has necessitated the discovery and development of new chemical entities with novel modes-of-action. Although much effort has been invested in the creation of analogues based on existing drugs and the screening of chemical and natural compound libraries, a crucial shortcoming in current Plasmodial drug discovery efforts remains the lack of an extensive set of novel, validated drug targets. A requirement of these targets (or the pathways in which they function) is that they prove essential for parasite survival. The polyamine biosynthetic pathway, responsible for the metabolism of highly abundant amines crucial for parasite growth, proliferation and differentiation, is currently under investigation as an antimalarial target. Chemotherapeutic strategies targeting this pathway have been successfully utilized for the treatment of Trypanosomes causing West African sleeping sickness. In order to further evaluate polyamine depletion as possible antimalarial intervention, the consequences of inhibiting P. falciparum spermidine synthase (PfSpdSyn) were examined on a morphological, transcriptomic, proteomic and metabolic level.
Morphological analysis of P. falciparum 3D7 following application of the PfSpdSyn inhibitor cyclohexylamine confirmed that parasite development was completely arrested at the early trophozoite stage. This is in contrast to untreated parasites which progressed to late trophozoites at comparable time points. Global gene expression analyses confirmed a transcriptional arrest in the parasite. Several of the differentially expressed genes mapped to the polyamine biosynthetic and associated metabolic pathways. Differential expression of corresponding parasite proteins involved in polyamine biosynthesis was also observed. Most notably, uridine phosphorylase, adenosine deaminase, lysine decarboxylase (LDC) and S-adenosylmethionine synthetase were differentially expressed at the transcript and/or protein level. Several genes in associated metabolic pathways (purine metabolism and various methyltransferases) were also affected. The specific nature of the perturbation was additionally reflected by changes in polyamine metabolite levels.
This study details the malaria parasite's response to PfSpdSyn inhibition on the transcriptomic, proteomic and metabolic levels. The results corroborate and significantly expand previous functional genomics studies relating to polyamine depletion in this parasite. Moreover, they confirm the role of transcriptional regulation in P. falciparum, particularly in this pathway. The findings promote this essential pathway as a target for antimalarial chemotherapeutic intervention strategies.
Lead (Pb), one of the most toxic heavy metals, can be absorbed and accumulated by plant roots and then enter the food chain resulting in potential health risks for human beings. The radish (Raphanus sativus L.) is an important root vegetable crop with fleshy taproots as the edible parts. Little is known about the mechanism by which radishes respond to Pb stress at the molecular level. In this study, Next Generation Sequencing (NGS)–based RNA-seq technology was employed to characterize the de novo transcriptome of radish roots and identify differentially expressed genes (DEGs) during Pb stress. A total of 68,940 assembled unique transcripts including 33,337 unigenes were obtained from radish root cDNA samples. Based on the assembled de novo transcriptome, 4,614 DEGs were detected between the two libraries of untreated (CK) and Pb-treated (Pb1000) roots. Gene Ontology (GO) and pathway enrichment analysis revealed that upregulated DEGs under Pb stress are predominately involved in defense responses in cell walls and glutathione metabolism-related processes, while downregulated DEGs were mainly involved in carbohydrate metabolism-related pathways. The expression patterns of 22 selected genes were validated by quantitative real-time PCR, and the results were highly accordant with the Solexa analysis. Furthermore, many candidate genes, which were involved in defense and detoxification mechanisms including signaling protein kinases, transcription factors, metal transporters and chelate compound biosynthesis related enzymes, were successfully identified in response to heavy metal Pb. Identification of potential DEGs involved in responses to Pb stress significantly reflected alterations in major biological processes and metabolic pathways. The molecular basis of the response to Pb stress in radishes was comprehensively characterized. Useful information and new insights were provided for investigating the molecular regulation mechanism of heavy metal Pb accumulation and tolerance in root vegetable crops.
The photo-stability of photosystem I (PSI) is of high importance for the photosynthetic processes. For this reason, we studied the protective action of two biogenic polyamines (PAs) spermine (Spm) and spermidine (Spd) on PSI activity in isolated thylakoid membranes subjected to photoinhibition. Our results show that pre-loading thylakoid membranes with Spm and Spd reduced considerably the inhibition of O2 uptake rates, P700 photooxidation and the accumulation of superoxide anions (O2−) induced by light stress. Spm seems to be more effective than Spd in preserving PSI photo-stability. The correlation of the extent of PSI protection, photosystem II (PSII) inhibition and O2− generation with increasing Spm doses revealed that PSI photo-protection is assumed by two mechanisms depending on the PAs concentration. Given their antioxidant character, PAs scavenge directly the O2− generated in thylakoid membranes at physiological concentration (1 mM). However, for non-physiological concentration, the ability of PAs to protect PSI is due to their inhibitory effect on PSII electron transfer.
Polyamines, including spermine (Spm) and spermidine (Spd), are aliphatic cations that are reportedly synthesized by all living organisms. They exert pleiotropic effects on cells and are required for efficient nucleic acid and protein synthesis. Here, we report that the human pathogen Staphylococcus aureus lacks identifiable polyamine biosynthetic genes, and consequently produces no Spm/Spd or their precursor compounds putrescine and agmatine. Moreover, while supplementing defined medium with polyamines generally enhances bacterial growth, Spm and Spd exert bactericidal effects on S. aureus at physiologic concentrations. Small colony variants specifically lacking menaquinone biosynthesis arose after prolonged Spm exposure and exhibited reduced polyamine-sensitivity. However, other respiratory-defective mutants were no less susceptible to Spm implying menaquinone itself rather than general respiration is required for full Spm-toxicity. Polyamine hypersensitivity distinguishes S. aureus from other bacteria and is exhibited by all tested strains save those belonging to the USA-300 group of Community-Associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA). We identified one gene within the USA-300-specific Arginine Catabolic Mobile Element (ACME) encoding a Spm/Spd N-acetyltransferase that is necessary and sufficient for polyamine resistance. S. aureus encounters significant polyamine levels during infection, however the acquisition of ACME encoded speG allows USA-300 clones to circumvent polyamine-hypersensitivity, a peculiar trait of S. aureus.
Salinity–alkalinity stress is known to adversely affect a variety of processes in plants, thus inhibiting growth and decreasing crop yield. Polyamines protect plants against a variety of environmental stresses. However, whether exogenous spermidine increases the tolerance of tomato seedlings via effects on chloroplast antioxidant enzymes and chlorophyll metabolism is unknown. In this study, we examined the effect of exogenous spermidine on chlorophyll synthesis and degradation pathway intermediates and related enzyme activities, as well as chloroplast ultrastructure, gene expression, and antioxidants in salinity–alkalinity–stressed tomato seedlings.
Salinity–alkalinity stress disrupted chlorophyll metabolism and hindered uroorphyrinogen III conversion to protoporphyrin IX. These effects were more pronounced in seedlings of cultivar Zhongza No. 9 than cultivar Jinpengchaoguan. Under salinity–alkalinity stress, exogenous spermidine alleviated decreases in the contents of total chlorophyll and chlorophyll a and b in seedlings of both cultivars following 4 days of stress. With extended stress, exogenous spermidine reduced the accumulation of δ–aminolevulinic acid, porphobilinogen, and uroorphyrinogen III and increased the levels of protoporphyrin IX, Mg–protoporphyrin IX, and protochlorophyllide, suggesting that spermidine promotes the conversion of uroorphyrinogen III to protoporphyrin IX. The effect occurred earlier in cultivar Jinpengchaoguan than in cultivar Zhongza No. 9. Exogenous spermidine also alleviated the stress–induced increases in malondialdehyde content, superoxide radical generation rate, chlorophyllase activity, and expression of the chlorophyllase gene and the stress–induced decreases in the activities of antioxidant enzymes, antioxidants, and expression of the porphobilinogen deaminase gene. In addition, exogenous spermidine stabilized the chloroplast ultrastructure in stressed tomato seedlings.
The tomato cultivars examined exhibited different capacities for responding to salinity–alkalinity stress. Exogenous spermidine triggers effective protection against damage induced by salinity–alkalinity stress in tomato seedlings, probably by maintaining chloroplast structural integrity and alleviating salinity–alkalinity–induced oxidative damage, most likely through regulation of chlorophyll metabolism and the enzymatic and non–enzymatic antioxidant systems in chloroplast. Exogenous spermidine also exerts positive effects at the transcription level, such as down–regulation of the expression of the chlorophyllase gene and up–regulation of the expression of the porphobilinogen deaminase gene.
Spermidine; Tomato; Salinity–alkalinity stress; Chloroplast; Chlorophyll precursor; Antioxidant system