Cloning of cDNA for maize superoxide dismutase 2 (SOD2)

Protein l-isoAspartyl Methyltransferase (PIMT) and antioxidants in plants

All life forms, including plants, accumulate reactive oxygen species (ROS) as a byproduct of metabolism; however, environmental stresses, including abiotic stresses and pathogen attacks, cause enhanced accumulation of ROS in plants. The increased accumulation of ROS often causes oxidative damage to cells. Organisms are able to maintain levels of ROS below permissible limits by several mechanisms, including efficient antioxidant systems. In addition to antioxidant systems, recent studies suggest that protein l-isoaspartyl methyltransferase (PIMT), a highly conserved protein repair enzyme across evolutionary diverse organisms, plays a critical role in maintaining ROS homeostasis by repairing isoaspartyl-mediated damage to antioxidants in plants. Under stress conditions, antioxidant proteins undergo spontaneous isoaspartyl (isoAsp) modification which is often detrimental to protein structure and function. This reduces the catalytic action of antioxidants and disturbs the ROS homeostasis of cells. This chapter focuses on PIMT and its interaction with antioxidants in plants, where PIMT constitutes a secondary level of protection by shielding a primary level of antioxidants from dysfunction and permitting them to guard during unfavorable situations.

Genome-wide analysis of the maize superoxide dismutase (SOD) gene family reveals important roles in drought and salt responses

Superoxide dismutase proteins (SODs) are antioxidant enzymes with important roles in abiotic stress responses. The SOD gene family has been systematically analyzed in many plants; however, it is still poorly understood in maize. Here, a bioinformatics analysis of maize SOD gene family was conducted by describing gene structure, conserved motifs, phylogenetic relationships, gene duplications, promoter cis-elements and GO annotations. In total, 13 SOD genes were identified in maize and five members were involved in segmental duplication. Phylogenetic analysis indicated that SODs from maize and other plants comprised two groups, which could be further classified into different subgroups, with most members in the same subgroup having the same subcellular localization. The ZmSOD promoters contained 2-10 stress-responsive cis-elements with different distributions. Heatmap analysis indicated that ZmSODs were expressed in most of the detected tissues and organs. The expression patterns of ZmSODs were investigated under drought and salt treatments by qRT-PCR, and most members were responsive to drought or salt stress, especially some ZmSODs with significant expression changes were identified, such as ZmCSD2 and ZmMSD2, suggesting the important roles of ZmSODs in abiotic stress responses. Our results provide an important basis for further functional study of ZmSODs in future study.

Genome-wide identification and expression analysis of the superoxide dismutase (SOD) gene family in Salvia miltiorrhiza

Adverse environmental conditions, such as salinity, cold, drought, heavy metals, and pathogens affect the yield and quality of Salvia miltiorrhiza, a well-known medicinal plant used for the treatment of cardiovascular and cerebrovascular diseases. Superoxide dismutase (SOD), a key enzyme of antioxidant system in plants, plays a vital role in protecting plants against various biotic and abiotic stresses via scavenging the reactive oxygen species produced by organisms. However, little is known about the SOD gene family in S. miltiorrhiza. In this study, eight SOD genes, including three Cu/Zn-SODs, two Fe-SODs and three Mn-SODs, were identified in the S. miltiorrhiza genome. Their gene structures, promoters, protein features, phylogenetic relationships, and expression profiles were comprehensively investigated. Gene structure analysis implied that most SmSODs have different introns/exons distrbution patterns. Many cis-elements related to different stress responses or plant hormones were found in the promoter of each SmSOD. Expression profile analysis indicated that SmSODs exhibited diverse responses to cold, salt, drought, heavy metal, and plant hormones. Additionally, 31 types of TFs regulating SmSODs were predicted and analyzed. These findings provided valuable information for further researches on the functions and applications of SmSODs in S. miltiorrhiza growth and adaptation to stress.

Genome-wide characterization and expression analyses of superoxide dismutase (SOD) genes in Gossypium hirsutum

BACKGROUND

Superoxide dismutases (SODs) are a key antioxidant enzyme family, which have been implicated in protecting plants against the toxic effects of reactive oxygen species. Despite current studies have shown that the gene family are involved in plant growth and developmental processes and biotic and abiotic stress responses, little is known about its functional role in upland cotton.

RESULTS

In the present study, we comprehensively analyzed the characteristics of the SOD gene family in upland cotton (Gossypium hirsutum). Based on their conserved motifs, 18 GhSOD genes were identified and phylogenetically classified into five subgroups which corroborated their classifications based on gene-structure patterns and subcellular localizations. The GhSOD sequences were distributed at different densities across 12 of the 26 chromosomes. The conserved domains, gene family evolution cis-acting elements of promoter regions and miRNA-mediated posttranscriptional regulation were predicted and analyzed. In addition, the expression pattern of 18 GhSOD genes were tested in different tissues/organs and developmental stages, and different abiotic stresses and abscisic acid, which indicated that the SOD gene family possessed temporal and spatial specificity expression specificity and may play important roles in reactive oxygen species scavenging caused by various stresses in upland cotton.

CONCLUSIONS

This study describes the first genome-wide analysis of the upland cotton SOD gene family, and the results will help establish a foundation for the further cloning and functional verification of the GhSOD gene family during stress responses, leading to crop improvement.

Molecular Cloning and Expression Analysis of Cu/Zn SOD Gene from Gynura bicolor DC

Superoxide dismutase is an important antioxidant enzyme extensively existing in eukaryote, which scavenges reactive oxygen species (ROS) and plays an essential role in stress tolerance of higher plants. A full-length cDNA encoding Cu/Zn SOD was cloned from leaves of Gynura bicolor DC. by rapid amplification of cDNA ends (RACE). The full-length cDNA of Cu/Zn SOD is 924 bp and has a 681 bp open reading frame encoding 227 amino acids. Bioinformatics analysis revealed that belonged to the plant SOD super family. Cu/Zn SODs of the Helianthus annuus, Mikania micrantha, and Solidago canadensis var. scabra all have 86% similarity to the G. bicolor Cu/Zn SOD. Analysis of the expression of Cu/Zn SOD under different treatments revealed that Cu/Zn SOD was a stress-responsive gene, especially to 1-MCP. It indicates that the Cu/Zn SOD gene would be an important gene in the resistance to stresses and will be helpful in providing evidence for future research on underlying molecular mechanism and choosing proper postharvest treatments for G. bicolor.

Molecular cloning and characterization of two manganese superoxide dismutases from Miscanthus × giganteus

Six MnSOD genes were isolated from five Miscanthus species. MgMnSOD1 functions in mitochondria and MgMnSOD1 seems to be the main MnSOD gene involved in stress response of M. × giganteus. Miscanthus × giganteus is a promising biomass energy crop with advantages of vigorous growth, high yield, low fertilizer and pesticide inputs. However, poor overwinter ability limits its widespread cultivation. Moreover, narrow genetic base may increase the risk of susceptibility to diseases and pests. Manganese superoxide dismutase (MnSOD), an important antioxidant enzyme involved in stress tolerance is able to protect plant cells from accumulated reactive oxygen species by converting superoxide to peroxide and oxygen. In many plants, overexpression of MnSOD has shown the ability to enhance the resistance to various stresses. This article describes the studies performed in an attempt to elucidate the molecular and enzymatic properties of MnSODs in M. × giganteus. MnSOD genes from M. × giganteus (MgMnSOD1, MgMnSOD2), M. lutarioriparia (MlMnSOD), M. sacchariflora (MsaMnSOD), M. sinensis (MsiMnSOD), and M. floridulus (MfMnSOD) were cloned and sequenced. The sequence analysis and expression patterns of MgMnSOD1 and MgMnSOD2 suggest that they were orthologous genes which were inherited from the two parents, M. sacchariflora and M. sinensis, respectively. In addition, MgMnSOD1 is predicted to be the main MnSOD gene involved in stress response of M. × giganteus. The activity of purified recombinant MgMnSOD1 was 1854.79 ± 39.98 U mg(-1) (mean ± SD). Further enzymatic assays revealed that the protein exhibited an outstanding thermal stability. MgMnSOD1 is predicted to be targeted to mitochondria and involved in removing the superoxide radical generated by respiration. The presence and sequences of other SOD isozymes transcripts were also investigated in this study.

Molecular cloning and expression analysis of a Cu/Zn SOD gene (BcCSD1) from Brassica campestris ssp. chinensis

Superoxide dismutases (SODs) are a family of metalloproteins extensively exists in eukaryote, which plays an essential role in stress-tolerance of higher plants. A full-length cDNA encoding Cu/Zn SOD (BcCSD1) was isolated from young seedlings of non-heading Chinese cabbage (Brassica campestris ssp. chinensis) by rapid amplification of cDNA ends (RACE). Bioinformatics analysis revealed that BcCSD1 belonged to the plant SOD super family and had the closest relationship with SOD from Brassica napus. Tissue expression pattern analysis revealed that the BcCSD1 was constitutively expressed in all the tested tissues, and strongest in leaf, moderate in stem, lowest in root. The expression profiles under different stress treatments such as drought, NaCl, high temperature and ABA were also investigated, and the results revealed that BcCSD1 was a stress-responsive gene, especially to ABA. These results provide useful information for further understanding the role of BcCSD1 resistant to abiotic stress in Brassica campestris in the future.

Intestinal cell targeting of a stable recombinant Cu-Zn SOD from Cucumis melo fused to a gliadin peptide

The mRNA encoding full length chloroplastic Cu-Zn SOD (superoxide dismutase) of Cucumis melo (Cantaloupe melon) was cloned. This sequence was then used to generate a mature recombinant SOD by deleting the first 64 codons expected to encode a chloroplastic peptide signal. A second hybrid SOD was created by inserting ten codons to encode a gliadin peptide at the N-terminal end of the mature SOD. Taking account of codon bias, both recombinant proteins were successfully expressed and produced in Escherichia coli. Both recombinant SODs display an enzymatic activity of ~5000U mg(-1) and were shown to be stable for at least 4h at 37°C in biological fluids mimicking the conditions of intestinal transit. These recombinant proteins were capable in vitro, albeit at different levels, of reducing ROS-induced-apoptosis of human epithelial cells. They also stimulated production and release in a time-dependent manner of an autologous SOD activity from cells located into jejunum biopsies. Nevertheless, the fused gliadin peptide enable the recombinant Cu-Zn SOD to maintain a sufficiently sustained interaction with the intestinal cells membrane in vivo rather than being eliminated with the flow. According to these observations, the new hybrid Cu-Zn SOD should show promise in applications for managing inflammatory bowel diseases.

Differential expression of copper-zinc superoxide dismutase gene of Polygonum sibiricum leaves, stems and underground stems, subjected to high-salt stress

In aerobic organisms, protection against oxidative damage involves the combined action of highly specialized antioxidant enzymes, such as copper-zinc superoxide dismutase. In this work, a cDNA clone which encodes a copper-zinc superoxide dismutase gene, named PS-CuZnSOD, has been identified from P. sibiricum Laxm. by the rapid amplification of cDNA ends method (RACE). Analysis of the nucleotide sequence reveals that the PS-CuZnSOD gene cDNA clone consists of 669 bp, containing 87 bp in the 5′ untranslated region; 459 bp in the open reading frame (ORF) encoding 152 amino acids; and 123 bp in 3′ untranslated region. The gene accession nucleotide sequence number in GenBank is GQ472846. Sequence analysis indicates that the protein, like most plant superoxide dismutases (SOD), includes two conserved ecCuZnSOD signatures that are from the amino acids 43 to 51, and from the amino acids 137 to 148, and it has a signal peptide extension in the front of the N-terminus (1–16 aa). Expression analysis by real-time quantitative PCR reveals that the PS-CuZnSOD gene is expressed in leaves, stems and underground stems. PS-CuZnSOD gene expression can be induced by 3% NaHCO₃. The different mRNA levels’ expression of PS-CuZnSOD show the gene’s different expression modes in leaves, stems and underground stems under the salinity-alkalinity stress.

Molecular characterization of a cDNA encoding Cu/Zn superoxide dismutase from Deschampsia antarctica and its expression regulated by cold and UV stresses

BACKGROUND

The Copper/Zinc superoxide dismutase (Cu/ZnSOD) gene, SOD gene, was isolated from a Deschampsia antarctica Desv. by cDNA library screening. The expression of SOD gene in the leaves of D. antarctica was determined by RT-PCR and its differential expression of gene transcripts in conditions of cold and UV radiation stresses was revealed by northern blot.

FINDINGS

The molecular characterization shows that SOD cDNA is 709 bp in length, which translates an ORF of 152 amino acids that correspond to a protein of predicted molecular mass of 15 kDa. The assay shows that the expression of SOD gene increases when D. antarctica is acclimatised to 4 degrees C and exposed to UV radiation. These results indicate that the SOD gene of D. antarctica is involved in the antioxidative process triggered by oxidative stress induced by the conditions of environmental change in which they live.

CONCLUSION

The present results allow us to know the characteristics of Cu/ZnSOD gene from D. antarctica and understand that its expression is regulated by cold and UV radiation.

The expression of manganese superoxide dismutase gene from Nelumbo nucifera responds strongly to chilling and oxidative stresses

A manganese superoxide dismutase (Mn-SOD) gene, NnMSD1, was identified from embryonic axes of the sacred lotus (Nelumbo nucifera Gaertn.). The NnMSD1 protein contains all conserved residues of the Mn-SOD protein family, including four consensus metal binding domains and a signal peptide for mitochondrial targeting. Southern blot analysis suggests the existence of two Mn-SOD genes in sacred lotus. NnMSD1 was highly expressed in developing embryonic axes during seed development, but appeared in cotyledons only at the early stage of development and became undetectable in the cotyledons during late embryogenesis. The expression of the NnMSD1 gene in germinating embryonic axes, in response to various stresses such as heat shock, chilling, and exposure to stress-related chemicals, was also studied. Heat shock strongly inhibited the expression of the NnMSD1 gene, whereas the NnMSD1 transcript level increased strongly in chilling stress treatment. An increase in expression was also highly induced by H2O2 in germinating embryonic axes. The results suggest that the expression pattern of the NnMSD1 gene differed between developing axes and cotyledons, and that the NnMSD1 gene expression responds strongly to chilling and oxidative stress.

Comparison of maize (Zea mays L.) F1-hybrid and parental inbred line primary root transcriptomes suggests organ-specific patterns of nonadditive gene expression and conserved expression trends

The phenomenon of heterosis describes the increased agronomic performance of heterozygous F(1) plants compared to their homozygous parental inbred plants. Heterosis is manifested during the early stages of root development in maize. The goal of this study was to identify nonadditive gene expression in primary roots of maize hybrids compared to the average expression levels of their parental inbred lines. To achieve this goal a two-step strategy was used. First, a microarray preselection of nonadditively expressed candidate genes was performed. Subsequently, gene expression levels in a subset of genes were determined via high-throughput quantitative real-time (qRT)-PCR experiments. Initial microarray experiments identified 1941 distinct microarray features that displayed nonadditive gene expression in at least 1 of the 12 analyzed hybrids compared to the midparent value of their parental inbred lines. Most nonadditively expressed genes were expressed between the parental values (>89%). Comparison of these 1941 genes with nonadditively expressed genes identified in maize shoot apical meristems via the same experimental procedure in the same genotypes revealed significantly less overlap than expected by pure chance. This finding suggests organ-specific patterns of nonadditively expressed genes. qRT-PCR analyses of 64 of the 1941 genes in four different hybrids revealed conserved patterns of nonadditively expressed genes in different hybrids. Subsequently, 22 of the 64 genes that displayed nonadditive expression in all four hybrids were analyzed in 12 hybrids that were generated from four inbred lines. Among those genes a superoxide dismutase 2 was expressed significantly above the midparent value in all 12 hybrids and might thus play a protective role in heterosis-related antioxidative defense in the primary root of maize hybrids. The findings of this study are consistent with the hypothesis that both global expression trends and the consistent differential expression of specific genes contribute to the organ-specific manifestation of heterosis.

Enhanced tolerance to sulfur dioxide and salt stress of transgenic Chinese cabbage plants expressing both superoxide dismutase and catalase in chloroplasts

To explore the possibility of overcoming the highly phytotoxic effect of SO(2) and salt stress, we introduced the maize Cu/ZnSOD and/or CAT genes into chloroplasts of Chinese cabbage (Brassica campestris L. ssp. pekinensis cv. Tropical Pride) (referred to as SOD, CAT and SOD+CAT plants). SOD+CAT plants showed enhanced tolerance to 400 ppb SO(2), and visible damage was one-sixth that of wild-type (CK) plants. In addition, when SOD+CAT plants were exposed to a high salt treatment of 200 mM NaCl for 4 weeks, the photosynthetic activity of the plants decreased by only 6%, whereas that of CK plants decreased by 72%. SOD plants had higher total APX and GR activities than CK plants. As expected, SOD plants showed levels of protection from SO(2) and salt stress that were moderately improved compared to CK plants. However, CAT plants showed inhibition of APX activity and provided only limited improvements in plant stress tolerance. Moreover, SOD+CAT plants accumulated more K(+), Ca(2+) and Mg(2+) and less Na(+) in their leaves compared with those of CK plants. These results suggest that the expression of SOD and CAT simultaneously is suitable for the introduction of increased multiple stress protection.

Superoxide dismutase transgenes in sugarbeets confer resistance to oxidative agents and the fungus C. beticola

Sugarbeets carrying superoxide dismutase transgenes were developed in order to investigate the possibility of enhancing their resistance to oxidative stress. Binary T-DNA vectors carrying the chloroplastic and cytosolic superoxide dismutase genes from tomato, were used for Agrobacterium-mediated transformation of sugarbeet petioles. The transgenic plants were subjected to treatments known to cause oxidative stress, such as the herbicide methyl viologen and a natural photosensitizer toxin produced by the fungus Cercospora beticola, namely cercosporin. The transgenic plants exhibited increased tolerance to methyl viologen, to pure cercosporin, as well as to leaf infection with the fungus C. beticola.

Molecular characterization of a cDNA encoding copper/zinc superoxide dismutase from cultured cells of Manihot esculenta

Superoxide dismutase (SOD) cDNA, mSOD2, encoding cytosolic copper/zinc SOD (CuZnSOD) cDNA was isolated from suspension-cultured cells of cassava (Manihot esculenta Crantz) by cDNA library screening, and its expression was investigated in relation to environmental stress. mSOD2 is 774 bp in length with an open reading frame (ORF) of 152 amino acids, corresponding to a protein of predicted molecular mass 15 kDa and a pI of 5.22. One copy of the mSOD2 gene was found to be present in the cassava genome by Southern analysis using an mSOD2 cDNA-specific probe. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed diverse expression patterns for the mSOD2 gene in various tissues of intact cassava plants, at various stages of the growth in suspension cultures, and in the leaf tissues exposed to different stresses. The mSOD2 gene was highly expressed in suspension-cultured cells and in the stems of intact plants. However, it was expressed at low levels in leaves and roots. During suspension cell growth, the mSOD2 transcript progressively increased during culture. Moreover, the mSOD2 gene in excised cassava leaves responded to various stresses in different ways. In particular, it was highly induced in leaf tissue by several abiotic stresses, including high temperature (37 degrees C), chilling (4 degrees C), methyl viologen (MV) exposure, and wounding treatment. These results indicate that the mSOD2 gene is involved in the antioxidative process triggered by oxidative stress induced by environmental change.

Mining the enzymes involved in the detoxification of reactive oxygen species (ROS) in sugarcane

Summary Adopting the sequencing of expressed sequence tags (ESTs) of a sugarcane database derived from libraries induced and not induced by pathogens, we identified EST clusters homologous to genes corresponding to enzymes involved in the detoxification of reactive oxygen species. The predicted amino acids of these enzymes are superoxide dismutases (SODs), glutathione-S-transferase (GST), glutathione peroxidase (GPX), and catalases. Three MnSOD mitochondrial precursors and 10 CuZnSOD were identified in sugarcane: the MnSOD mitochondrial precursor is 96% similar to the maize MnSOD mitochondrial precursor and, of the 10 CuZnSOD identified, seven were 98% identical to maize cytosolic CuZnSOD4 and one was 67% identical to putative peroxisomal CuZnSOD from Arabidopsis. Three homologues to class Phi GST were 87-88% identical to GST III from maize. Five GPX homologues were identified: three were homologous to cytosolic GPX from barley, one was 88% identical to phospholipid hydroperoxide glutathione peroxidase (PHGPX) from rice, and the last was 71% identical to GPX from A. thaliana. Three enzymes similar to maize catalase were identified in sugarcane: two were similar to catalase isozyme 3 and catalase chain 3 from maize, which are mitochondrial, and one was similar to catalase isozyme 1 from maize, whose location is peroxisomal subcellular. All enzymes were induced in all sugarcane libraries (flower, seed, root, callus, leaves) and also in the pathogen-induced libraries, except for CuZnSOD whose cDNA was detected in none of the libraries induced by pathogens (Acetobacter diazotroficans and Herbaspirillum rubrisubalbicans). The expression of the enzymes SOD, GST, GPX, and catalases involved in the detoxification was examined using reverse transcriptase-polymerase chain reaction in cDNA from leaves of sugarcane under biotic stress conditions, inoculated with Puccinia melanocephala, the causal agent of sugarcane rust disease.

Molecular evolution and structure--function relationships of the superoxide dismutase gene families in angiosperms and their relationship to other eukaryotic and prokaryotic superoxide dismutases

This study assesses whether the phylogenetic relationships between SODs from different organisms could assist in elucidating the functional relationships among these enzymes from evolutionarily distinct species. Phylogenetic trees and intron positions were compared to determine the relationships among these enzymes. Alignment of Cu/ZnSOD amino acid sequences indicates high homology among plant sequences, with some features that distinguish chloroplastic from cytosolic Cu/ZnSODs. Among eukaryotes, the plant SODs group together. Alignment of the Mn and FeSOD amino acid sequences indicates a higher degree of homology within the group of MnSODs (>70%) than within FeSODs (approximately 60%). Tree topologies are similar and reflect the taxonomic classification of the corresponding species. Intron number and position in the Cu/Zn Sod genes are highly conserved in plants. Genes encoding cytosolic SODs have seven introns and genes encoding chloroplastic SODs have eight introns, except the chloroplastic maize Sod1, which has seven. In Mn Sod genes the number and position of introns are highly conserved among plant species, but not among nonplant species. The link between the phylogenetic relationships and SOD functions remains unclear. Our findings suggest that the 5' region of these genes played a pivotal role in the evolution of function of these enzymes. Nevertheless, the system of SODs is highly structured and it is critical to understand the physiological differences between the SODs in response to different stresses in order to compare their functions and evolutionary history.

A novel superoxide dismutase with a high isoelectric point in higher plants. expression, regulation, and protein localization

Several isoforms of superoxide dismutase (SOD) with a high isoelectric point (pI) have been identified by isoelectric focusing chromatography in protein extracts from Scots pine (Pinus sylvestris) needles. One of these isoforms, a CuZn-SOD with a pI of about 10 and thus denoted hipI-SOD, has been isolated and purified to apparent homogeneity. A cDNA encoding the hipI-SOD protein was cloned and sequenced. Northern hybridization of mRNA isolated from different organs and tissues showed that hipI-SOD has a markedly different pattern of expression compared with chloroplastic and cytosolic SOD. Furthermore, the transcript levels of hipI-SOD and cytosolic SOD were found to respond differently to mechanical wounding, treatment with oxidized glutathione, paraquat, and ozone. Immunogold electron microscopy localized the hipI-SOD in the plasma membrane of sieve cells and the Golgi apparatus of albuminous cells. Moreover, high protein density was also detected in extracellular spaces such as secondary cell wall thickenings of the xylem and sclerenchyma and in intercellular spaces of parenchyma cells.

Modulation of antioxidant responses by arsenic in maize

The effects of arsenic on the expression of the antioxidant genes encoding superoxide dismutase, catalase, and glutathione S-transferase, as well as the activity of SOD and CAT enzymes, were examined at different developmental stages and in different tissues. Both CAT and SOD activities increased in response to low concentrations (0.01-0.1 mM) of arsenic in developing maize embryos. In germinating embryos both CAT and SOD activities increased in response to a wide range of arsenic concentrations (0.01-10 mM). Cat1 transcript increased in response to arsenic in developing and germinating embryos and in young leaves. Conversely, Cat2 increased at low concentrations of arsenic only in germinating embryos. Cat3 transcript levels increased in response to low concentrations of arsenic only in developing embryos. Sod3 transcript increased at low concentrations of arsenic in developing, germinating embryos and in leaves. The cytosolic Sod4 and Sod4A increased in response to arsenic in germinating embryos, while only Sod4 transcript increased in response to arsenic in leaves. Expression of Gst1 was similar to that of Cat1 in all tissues examined. These results indicate that arsenic triggers tissue and developmental stage specific defense responses of antioxidant and detoxification related genes in maize.

Molecular cloning and expression patterns of Cu/Zn-superoxide dismutases in developing soybean seeds

Assuming that the amount of superoxide radicals generated in vivo correlates with the production of ergastic substances such as storage proteins, the coordinated response of detoxication enzymes such as superoxide dismutases is largely exploited to understand the self-defense systems of plant. Here we examined expression of the genes for superoxide dismutases during seed development of soybean. The cDNAs encoding a cytosolic copper/zinc form and an iron form of the above enzyme have been cloned and then employed as probes, separately. Northern blotting results suggested that both superoxide dismutase mRNAs are expressed at the maximum level, preceding a developmental stage when mRNA encoding glycinin, soybean 11S-storage protein, at the maximum.

A comparison of the structure and function of the highly homologous maize antioxidant Cu/Zn superoxide dismutase genes, Sod4 and Sod4A

Two highly similar cytosolic Cu/Zn Sod (Sod4 and Sod4A) genes have been isolated from maize. Sod4A contains eight exons and seven introns. The Sod4 partial sequence contains five introns. The introns in both genes are located in the same position and have highly homologous sequences in several regions. The largest intron (> 1200 bp) interrupts the 5' leader sequence. The presence of different regulatory motifs in the promoter region of each gene may indicate distinct responses to various conditions. Zymogram and RNA blot analyses show that Sod4 and Sod4A are expressed in all tissues of the maize plant. The developmental profiles of Sod4 and Sod4A mRNA accumulation differ in scutella during sporophytic development. RNA blot analysis of the respective Sod mRNAs indicates a differential, tissue-specific response of each gene to certain stressors. RNA isolated from stem tissue of ethephon-treated seedlings shows an increase in the Sod4 but not the Sod4A transcript while there is no change in transcripts of either gene in leaves or roots. There is differential mRNA accumulation between the two genes in leaf and stem tissue of paraquat-treated seedlings. Other agents that can cause oxidative stress were also tested for differential expression of the genes.

Cloning and characterization of a cDNA encoding the cytosolic copper/zinc-superoxide dismutase from sweet potato tuberous root

A full-length cDNA clone encoding a putative copper/zinc-superoxide dismutase (SOD) of sweet potato, Ipomoea batatas (L.) Lam. cv Tainong 57, was isolated from a cDNA library constructed in lambda gt10 from tuber root mRNA. Nucleotide sequence analysis of this cDNA clone revealed that it comprises a complete open reading frame coding for 152 amino acid residues. The deduced amino acid sequence showed higher homology (78-86%) with the sequence of the cytosolic SOD than that of the chloroplast SOD from other plant species. The residues required for coordinating copper and zinc are conserved as they are among all reported Cu/Zn-SOD sequences. In addition, it lacks recognizable plastic or mitochondrial targeting sequences. These data suggest that the isolated sweet potato clone encodes a cytosolic Cu/Zn-SOD.

Aging and resistance to oxidative damage in Caenorhabditis elegans

The dauer larva state and the age-1 mutation, both of which extend life-span in Caenorhabditis elegans, were tested for hyperresistance to cellular damage that may be relevant to aging. The age-1 strain TJ401 displayed hyperresistance to oxidative stress relative to its parental strain. The activities of two enzymes that protect cells from oxidative damage, superoxide dismutase (SOD) and catalase, showed an age-dependent increase in mutant animals, which was not seen in the parental strain. These increases in activities paralleled the time course of the hyperresistance. The results are consistent with the age-1 gene product functioning as a negative regulator of SOD and catalase activities. In wild-type and age-1 dauer larvae, elevated levels of SOD activity, but not of catalase activity, were present when compared with young adults. The common increase in SOD activity prompted cloning the C. elegans Cu/Zn SOD gene. Its position on the physical map of the genome was in the region to which the age-1 gene has been genetically mapped, but it is unlikely that a mutation at the SOD locus confers the Age phenotype. Results support the free radical theory of aging by suggesting that the increased resistance to oxidative stress may be among the causes of increased longevity in both strain TJ401 and in the dauer larva.

Enhanced oxidative-stress defense in transgenic potato expressing tomato Cu,Zn superoxide dismutases

The two cDNAs coding for the cytosolic (cyt) and the chloroplast-located (chl) Cu,Zn superoxide dismutases (SODs) of tomato (Perl-Treves et al. 1988) were cloned into respective binary vectors and mobilized into Agrobacterium strains. Potato tuber discs were infected with either of the two agrobacterial strains and cultured on selective medium containing kanaymcin. The integration of either of the cyt or the chl SOD transgenes was verified by Southern-blot hybridization. The enzymatic activity of the additional tomato chl Cu,Zn SOD could be distinguished from endogenous SOD activity since the latter isozyme migrated faster on SOD-activity gels. Several transgenic potato lines harboring either the cyt or the chl SOD genes of tomato showed elevated tolerance to the superoxide-generating herbicide paraquat (methyl viologen). After exposure of shoots to paraquat, tolerance was recorded either by scoring symptoms visually or by measurements of photosynthesis using the photoacoustic method. Root cultures from transgenic lines that harbored the additional cyt Cu,Zn SOD gene of tomato were tolerant to methyl viologen up to 10(-5) M; a lower tolerance was recorded in roots of transgenic lines that expressed the additional chl Cu,Zn SOD of tomato.

Purification of Two Superoxide Dismutase Isozymes and Their Subcellular Localization in Needles and Roots of Norway Spruce (Picea abies L.) Trees

Two isozymes of superoxide dismutase (SOD; EC 1.15.1.1) were purified from Norway spruce (Picea abies L.) needles to apparent electrophoretic homogeneity. Purification factors were 354 for SOD I and 265 for SOD II. The native molecular mass of both purified enzymes was approximately 33 kD, as determined by gel filtration. The subunit molecular weights, as estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis, were 20,000 for SOD I and 16,000 for SOD II in the presence of 2-mercaptoethanol, and 15,800 and 15,000, respectively, in its absence. These results indicate that the native enzymes were homodimers whose subunits contained intrachain disulfide bonds. Isoelectric points determined by nondenaturing isoelectric focusing were 4.5 and 5.5 for SOD I and II, respectively. NH(2)-terminal sequence analysis of the first 22 to 23 amino acids revealed 70 to 75% sequence identity with chloroplastic CuZn SODs from other plant species for SOD I, and 75% sequence identity with the cytosolic CuZn SOD from Scots pine for SOD II. SOD I was the major activity in needles and it was associated with chloroplasts. SOD II activity was dominant in roots.

Differential regulation of superoxide dismutases in plants exposed to environmental stress

Superoxide dismutases (SODs) are metalloproteins that catalyze the dismutation of superoxide radicals to hydrogen peroxide and oxygen. The enzyme is ubiquitous in aerobic organisms where it plays a major role in defense against oxygen radical-mediated toxicity. In plants, environmental adversity often leads to the increased generation of reduced oxygen species and, consequently, SOD has been proposed to be important in plant stress tolerance. Here we describe the isolation of a cDNA clone encoding a cytosolic copper/zinc SOD from Nicotiana plumbaginifolia. Using this, together with previously isolated cDNAs encoding the mitochondrial manganese SOD and the chloroplastic iron SOD as probes in RNA gel blot analyses, we have studied SOD transcript abundance during different stress conditions: in response to light, during photoinhibitory conditions (light combined with high or low temperatures), and in response to a xenobiotic stress imposed by the herbicide paraquat. Evidence is presented that iron SOD mRNA abundance increases whenever there is a chloroplast-localized oxidative stress, similar to the previous finding that manganese SOD responds to mitochondria-localized events. The diverse effects of the different stress conditions on SOD mRNA abundance thus might provide an insight into the way that each treatment affects the different subcellular compartments.

Nutritional effect and expression of SODs: induction and gene expression; diagnostics; prospective protection against oxygen toxicity

The effect of micronutrient stress (either deficiency or toxicity) on the expression of different superoxide dismutase isoenzymes in plants is reviewed. The induction of Fe-SOD and Mn-SOD by different metals and the potential use of the metalloenzyme system SOD for the appraisal of the micronutrient status of plants, is examined. At subcellular level, evidence for the participation of peroxisomal SOD in the molecular mechanism of plant tolerance to Cu is presented, and the activated oxygen-dependent toxicity of a xenobiotic (clofibrate) in plant peroxisomes is examined.

Isolation, Purification, and Subcellular Localization of Isozymes of Superoxide Dismutase from Scots Pine (Pinus sylvestris L.) Needles

Two of four isozymes of superoxide dismutase (SOD) (EC 1.15.1.1) were purified from Scots pine (Pinus sylvestris L.) needles. One form was cytosolic (SOD-1) and the other was associated with chloroplasts (SOD-3). The holoenzyme molecular masses was estimated at approximately 35 kilodaltons by gel filtration. The subunit molecular weight of the dimeric enzymes was estimated to 16.5 kilodaltons (SOD-1) and 20.4 kilodaltons (SOD-3) on sodium dodecyl sulfatepolyacrylamide gels. The NH(2)-terminal sequence of the pine enzymes showed similarities to other purified superoxide dismutases located in the corresponding compartment. The cytosolic form revealed two additional amino acids at position 1 and 2 at the NH(2)-terminal. Both forms were cyanide- and hydrogenperoxide-sensitive and SOD-3 was found to contain approximately one copper atom per subunit, indicating that they belong to the cupro-zinc SODs. The isoelectric point was 4.9 and 4.5 for SOD-1 and SOD-3, respectively.

Evolutionary aspects of superoxide dismutase: the copper/zinc enzyme

Copper/zinc superoxide dismutase is typically an enzyme of eukaryotes. The presence of the enzyme in the ponyfish symbiont Photobacterium leiognathi and some free living bacteria does not have an immediate explanation. Amino acid sequence alignment of 19 Cu/Zn superoxide dismutases shows 21 invariant residues in key positions related to maintenance of the beta-barrel fold, the active site structure including the electrostatic channel loop, and dimer contacts. Nineteen other residues are invariant in 18 of the 19 sequences. Thirteen of these nearly invariant residues show substitutions in Photobacterium Cu/Zn superoxide dismutase. Copper/zinc superoxide dismutase from the trematode Schistosoma mansoni shows an N-terminal sub-domain with a hydrophobic leader peptide, as in human extracellular superoxide dismutase which is a Cu/Zn enzyme. The latter also has a C-terminal sub-domain with preponderance of hydrophilic and positively charged residues. The amino acid sequence of this superoxide dismutase between the N-terminal and C-terminal regions shares many features of cytosolic Cu/Zn superoxide dismutase, including 20 of the 21 invariant residues found in 19 Cu/Zn enzymes, suggesting a similar type of beta-barrel fold and active site structure for the extracellular enzyme.

Chloroplast and cytosol isozymes of CuZn-superoxide dismutase: their characteristic amino acid sequences

Isozymes of CuZn-superoxide dismutase (SOD) were purified from angiosperms (spinach and rice), fern (horsetail) and green alga (Spirogyra). Occurrence of CuZn-SOD was confirmed by its purification in the group of green algae which shows the phragmoplast type of cell division. Purified CuZn-SODs are divided to chloroplast and cytosol types by their cellular localization and immunological properties. Their amino acid compositions, absorption spectra, CD spectra, and sensitivity to hydrogen peroxide also are distinguished from each other. All organisms including Spirogyra contain both types of isozyme. Thus, the divergence of the two types of CuZn-SOD isozyme occurred immediately after its acquisition by the most evolved green algae. Amino acid sequences of amino-terminal regions of CuZn-SOD isozymes from spinach, rice and horsetail were determined and compared with those of CuZn-SODs from other plants. The chloroplast and cytosol isozymes of CuZn-SOD show each characteristic sequences. Sequence differences among the cytosol CuZn-SODs are greater than those among the chloroplast CuZn-SODs. These observations indicate that each type of isozyme had independently evolved after the acquisition of CuZn-SOD.

Probing the structural basis for enzyme-substrate recognition in Cu,Zn superoxide dismutase

A full understanding of enzyme-substrate interactions requires a detailed knowledge of their structural basis at atomic resolution. Crystallographic and biochemical data have been analyzed with coupled computational and computer graphic approaches to characterize the molecular basis for recognition of the superoxide anion substrate by Cu,Zn superoxide dismutase (SOD). Detailed analysis of the bovine SOD structure aligned with SOD sequences from 15 species provides new results concerning the significance and molecular basis for sequence conservation. Specific roles have been assigned for all 23 invariant residues and additional residues exhibiting functional equivalence. Sequence invariance is dominated by 15 residues that form the active site stereochemistry, supporting a primary biological function of superoxide dismutation. Using data from crystallographic structures and site-directed mutants, we are testing the role of individual residues in the active site channel, including (in human SOD) Glu 132, Glu 133, Lys 136, Thr 137, and Arg 143. Electrostatic calculations incorporating molecular flexibility suggest that the region of positive electrostatic potential in and over the active site channel above the Cu ion sweeps through space during molecular motion to enhance the facilitated diffusion responsible for the enzyme's rapid catalytic rate.

Expression of the catalase and superoxide dismutase genes in mature pollen in maize

The expression of the Cat and Sod genes encoding the multiple catalases and superoxide dismutases in maize has been studied in maize pollen at anther dehiscence. Pollen from three catalase activity variant inbred lines was examined. Zymorgram analysis, immunoassays, and RNA blots show that, in the lines used, only the CAT-1 catalase isozyme is expressed in mature pollen; the CAT-2 and CAT-3 isozymes are not. The data presented further demonstrate that the Cat1 gene is transcribed and translated after tetrad formation. The relative protein levels of the various superoxide dismutase (SOD) isozymes appear to be similar in pollen and scutella, and correspond to the relatively low levels observed for the different Sod transcripts in these tissues. The presence of "double" transcripts for Sod3 and Sod4A is discussed.

Genetic mapping of tomato cDNA clones encoding the chloroplastic and the cytosolic isozymes of superoxide dismutase

The isozyme pattern of superoxide dismutase (SOD) in tomato consists of two Cu,Zn isozymes located, respectively, in the chloroplast and in the cytosol, as well as additional isozymes of the Mn or Fe SOD type. We have shown that SOD-1 is the chloroplastic Cu,Zn SOD and is related to cDNA clone T10. Restriction fragment length polymorphism (RFLP) analysis was performed with two cDNA clones representing tomato Cu,Zn-superoxide dismutases. T10, coding for the chloroplast isozyme, was thus mapped to chromosome 11, between marker TG46 and TG108, while clone P31, coding for the cytosolic Cu,Zn SOD isozyme, was mapped to chromosome 1 between TG24 and TG81. SOD is associated with the response of plants to various environmental stresses; the mapping information presented here would permit the demonstration of this association by genetic analysis.

Transformed plants with elevated levels of chloroplastic SOD are not more resistant to superoxide toxicity

The petunia nuclear gene which encodes the chloroplast isozyme of superoxide dismutase, SOD-1, has been fused with an efficient rbcS promoter fragment and 3' flanking region and introduced into tobacco and tomato cells. Transformed plants carrying this chimeric gene have up to 50-fold the levels of SOD-1 which occur in wild-type plants. However, tobacco plants with 30- to 50-fold the normal SOD-1 activity do not exhibit resistance to the light-activated herbicide paraquat. Similarly, tomato plants with 2- to 4-fold increases in SOD-1 do not exhibit tolerance to photoinhibitory conditions known to increase superoxide levels (high light, low temperatures and low CO2 concentrations). Our data indicate that increasing the chloroplastic SOD level in a plant cell is not sufficient to reduce the toxicity of superoxide.

Codon usage in higher plants, green algae, and cyanobacteria

Codon usage is the selective and nonrandom use of synonymous codons by an organism to encode the amino acids in the genes for its proteins. During the last few years, a large number of plant genes have been cloned and sequenced, which now permits a meaningful comparison of codon usage in higher plants, algae, and cyanobacteria. For the nuclear and organellar genes of these organisms, a small set of preferred codons are used for encoding proteins. Codon usage is different for each genome type with the variation mainly occurring in choices between codons ending in cytidine (C) or guanosine (G) versus those ending in adenosine (A) or uridine (U). For organellar genomes, chloroplastic and mitochrondrial proteins are encoded mainly with codons ending in A or U. In most cyanobacteria and the nuclei of green algae, proteins are encoded preferentially with codons ending in C or G. Although only a few nuclear genes of higher plants have been sequenced, a clear distinction between Magnoliopsida (dicot) and Liliopsida (monocot) codon usage is evident. Dicot genes use a set of 44 preferred codons with a slight preference for codons ending in A or U. Monocot codon usage is more restricted with an average of 38 codons preferred, which are predominantly those ending in C or G. But two classes of genes can be recognized in monocots. One set of monocot genes uses codons similar to those in dicots, while the other genes are highly biased toward codons ending in C or G with a pattern similar to nuclear genes of green algae. Codon usage is discussed in relation to evolution of plants and prospects for intergenic transfer of particular genes.

Two cDNAs encode two nearly identical Cu/Zn superoxide dismutase proteins in maize

SOD-4, a cytosolic form of superoxide dismutase in maize, originally was defined as a single band of activity by zymogram analysis. The protein was purified to "homogeneity" as shown by a single band on native or denaturing polyacrylamide gels and a single spot on two dimensional gels. The N-terminal amino acid sequence for the first 20 residues was determined for the purified SOD-4 protein. All residues were clearly determined except for residue twelve, where both glutamic and aspartic acids were found. A maize lambda gt11 cDNA library was constructed from scutellar poly(A)+ RNA. Two cDNAs were isolated, restriction mapped, and their DNA sequences determined. The amino acid sequence deduced from both cDNAs matched perfectly the N-terminal sequence of the purified protein except for the residue at position 12. Significantly, at the twelfth codon, one cDNA was found to code for glutamic acid and the other cDNA had a codon for aspartic acid. Both cDNAs contained similar but not identical 5' and 3' untranslated sequences. Both cDNAs contained polyadenylation signals and tails. cDNA isolations, RNA, and genomic DNA blots confirm the existence and expression of two genes that produce indistinguishable SOD-4 proteins.

The induction of manganese superoxide dismutase in response to stress in Nicotiana plumbaginifolia

Superoxide dismutases (SODs) are metalloproteins that catalyse the dismutation of superoxide radicals to oxygen and hydrogen peroxide. The enzyme has been found in all aerobic organisms examined, where it plays a major role in the defence against toxic reduced oxygen species which are generated in many biological oxidations. Here we report the complete primary structure of a plant manganese superoxide dismutase (MnSOD), deduced from a cDNA clone of Nicotiana plumbaginifolia. The plant protein is highly homologous to MnSODs from other organisms and also contains an N-terminal leader sequence resembling a transit peptide for mitochondrial targeting. The location of the mature protein within the mitochondria has been demonstrated by subcellular fractionation experiments. We have analysed the expression profile of this MnSOD and found that it is dramatically induced during stress conditions, most notably in tissue culture as a result of sugar metabolism and also as part of the pathogenesis response of the plant, being induced by ethylene, salicylic acid, and Pseudomonas syringae infection. This induction is always accompanied by an increase in cytochrome oxidase activity, which suggests a specific protective role for MnSOD during conditions of increased mitochondrial respiration.

Evolution of CuZn superoxide dismutase and the Greek key beta-barrel structural motif

Detailed analysis of the CuZn superoxide dismutase (SOD) structure provides new results concerning the significance and molecular basis for sequence conservation, intron-exon boundary locations, gene duplication, and Greek key beta-barrel evolution. Using 15 aligned sequences, including a new mouse sequence, specific roles have been assigned to all 23 invariant residues and additional residues exhibiting functional equivalence. Sequence invariance is dominated by 15 residues that form the active site stereochemistry, supporting a primary biological function of superoxide dismutation. The beta-strands have no sequence insertions and deletions, whereas insertions occur within the loops connecting the beta-strands and at both termini. Thus, the beta-barrel with only four invariant residues is apparently over-determined, but dependent on multiple cooperative side chain interactions. The regions encoded by exon I, a proposed nucleation site for protein folding, and exon III, the Zn loop involved in stability and catalysis, are the major structural subdomains not included in the internal twofold axis of symmetry passing near the catalytic Cu ion. This provides strong confirmatory evidence for gene evolution by duplication and fusion followed by the addition of these two exons. The proposed evolutionary pathway explains the structural versatility of the Greek key beta-barrel through functional specialization and subdomain insertions in new loop connections, and provides a rationale for the size of the present day enzyme.

Cloning and characterization of a cDNA encoding the chloroplastic copper/zinc-superoxide dismutase from pea

A cDNA encoding the chloroplastic copper/zinc-superoxide dismutase of pea (Pisum sativum L.) was isolated from a cDNA library constructed in lambda gt11 from leaf mRNA. Nucleotide sequence analysis of the 875-base-pair clone revealed that it contained the complete coding sequence of the mature superoxide dismutase isozyme subunit, along with sequence information for a 48-amino acid N-terminal transit peptide. The deduced amino acid sequence of the mature subunit proved to be 64-87% homologous with amino acid sequences of copper/zinc-superoxide dismutases from other plant species. In vitro transcription, followed by cell-free translation, of the cDNA resulted in the formation of a 23.5-kDa precursor polypeptide, which, upon incubation with isolated pea chloroplasts, was imported and processed to its mature subunit molecular mass of 17.4 kDa.

Isolation of two cDNA clones from tomato containing two different superoxide dismutase sequences

A cDNA library was derived from the poly(A)(+) RNA of young tomato leaves. The library was cloned in a λgt11 system and screened by synthetic oligonucleotide probes having sequences that match the codes of conserved regions of amino acid sequences of Cu,Zn superoxide dismutase (SOD) proteins from a wide range of eukaryotic organisms. Two cDNAs were isolated, cloned and sequenced. One of the cDNAs, P31, had a full-size open reading frame of 456 bp with a deduced amino acid sequence having an 80% homology with the deduced amino acid sequence of the cytosolic SOD-2 cDNA of maize. The other cDNA, T10 (extended by T1), had a 651 bp open reading frame that revealed, upon computer translation, 90% homology to the amino acid sequence of mature spinach chloroplast SOD. The 5' end of the reading frame seems to code for a putative transit peptide. This work thus suggests for the first time an amino acid sequence for the transit peptide of chloroplast SOD. Northern hybridizations indicated that each of the P31 and T10 clones hybridized to a blotted poly(A)(+) RNA species. These two species are differentially expressed in the plant organs: e.g., the species having the T10 sequence was detected in the leaves but not in roots, while the one with the P31 sequence was expressed in both leaves and roots. The cDNA clones P31 and T10 were also hybridized to Southern blots of endonuclease fragmented tomato DNA. The clones hybridized to specific fragments and no cross hybridization between the two clones was revealed under stringent hybridization conditions; the hybridization pattern indicated that, most probably, only one locus is coding for each of the two mRNA species.