Developmental stage-dependent differential gene expression of superoxide dismutase isoenzymes and their localization and physical interaction network in rice (Oryza sativa L.)

OsCSD2 and OsCSD3 Enhance Seed Storability by Modulating Antioxidant Enzymes and Abscisic Acid in Rice

Seed deterioration during storage poses a significant challenge to rice production, leading to a drastic decline in both edible quality and viability, thereby impacting overall crop yield. This study aimed to address this issue by further investigating candidate genes associated with two previously identified QTLs for seed storability through genome association analysis. Among the screened genes, two superoxide dismutase (SOD) genes, OsCSD2 (Copper/zinc Superoxide Dismutase 2) and OsCSD3, were selected for further study. The generation of overexpression and CRISPR/Cas9 mutant transgenic lines revealed that OsCSD2 and OsCSD3 play a positive regulatory role in enhancing rice seed storability. Subsequent exploration of the physiological mechanisms demonstrated that overexpression lines exhibited lower relative electrical conductivity, indicative of reduced cell membrane damage, while knockout lines displayed the opposite trend. Furthermore, the overexpression lines of OsCSD2 and OsCSD3 showed significant increases not only in SOD but also in CAT and POD activities, highlighting an augmented antioxidant system in the transgenic seeds. Additionally, hormone profiling indicated that ABA contributed to the improved seed storability observed in these lines. In summary, these findings provide valuable insights into the regulatory mechanisms of OsCSDs in rice storability, with potential applications for mitigating grain loss and enhancing global food security.

Ethanol suppresses rice seed germination through inhibiting ROS signaling

Ethanol is frequently used not only as priming but also as a solvent to dissolve hardly water-soluble phytohormones gibberellic acid (GA3) and abscisic acid (ABA) in seed germination. However, the molecular and physiological mechanisms of ethanol's impact on seed germination remain elusive. In this report, we investigated how ethanol affected reactive oxygen species (ROS) during rice seed germination. Ethanol at a concentration of 3.5% (v/v) inhibited 90% seed germination, which was almost reversed by H2O2. H2O2 contents in embryos were reduced by ethanol after 18 h imbibition. Antioxidant enzymes assays revealed that only superoxide dismutase (SOD) activities in seed embryos were lowered by ethanol, in line with the suppressed mRNA expression of SOD genes during imbibition. Additionally, compared to the mock condition, ethanol increased ABA contents but decreased GA (GA1 and GA3) in seed embryos, resulting in disharmonizing GA/ABA balance. Conceivably ethanol induced transcription of OsNCEDs, the key genes for ABA biosynthesis, and OsABA8ox3, a key gene for ABA catabolism. Furthermore, ethanol promoted ABA signaling by upregulating ABA receptor genes and ABA-responsive element (ABRE)-binding protein/ABRE-binding factors during imbibition. Overall, our results demonstrate that lowering of H2O2 levels due to suppressed SOD activities in rice germinating seed embryos is the decisive factor for ethanol-induced inhibition of seed germination, and GA/ABA balance and ABA signaling also play important roles in ethanol's inhibitory impact on seed germination.

Superoxide dismutase (SOD) family in durum wheat: promising candidates for improving crop resilience

The SOD family has been extensively analyzed at genome wide level in several crops. However, little is known about this family in durum wheat. In this study, a total of 14 TdSOD genes were identified in whole durum wheat genome including 8 TdCu-ZnSODs, 2 TdMnSODs, and 4 TdFeSODs. In silico analysis evinced that TdSOD family members displayed a closer evolutionary relationship, similar gene structure and protein features with their homologs from other plant species. Furthermore, the analysis of their promoter regions revealed the presence of a great number of cis-regulatory elements related to plant development, abiotic and biotic stresses, phytohormones, and several potential binding sites for transcription factors. Interestingly, 3D structure analysis revealed that TdCu-ZnSOD2A-2 and TdCu-ZnSOD2B-2, belonging to the Cu-Zn group, were modeled as copper chaperone for SOD like their homologs from rice and Arabidopsis. The expression profile of eight TdSOD candidate genes was investigated under salt, drought, cold, and ABA treatments. Notably, TdCu-ZnSOD2A-1, TdFeSOD4A-1, and TdFeSOD7A-1 were significantly up-regulated under all stress treatments. On the other hand, TdCu-ZnSOD7B and TdMnSOD2B were strongly expressed in roots and leaves under cold stress and TdCu-ZnSOD2B-2 was particularly up-regulated in leaves under ABA treatment. Ultimately, these findings provide valuable information for the identification of attractive candidate genes to improve wheat resilience.

Molecular and Biochemical Analysis of Duplicated Cytosolic CuZn Superoxide Dismutases of Rice and in silico Analysis in Plants

Superoxide dismutases (SODs, EC 1.15.1.1) are ubiquitous antioxidant metalloenzymes important for oxidative stress tolerance and cellular redox environment. Multiple factors have contributed toward the origin and diversity of SOD isoforms among different organisms. In plants, the genome duplication events, responsible for the generation of multiple gene copies/gene families, have also contributed toward the SOD diversity. However, the importance of such molecular events on the characteristics of SODs has not been studied well. This study investigated the effects of divergence on important characteristics of two block-duplicated rice cytosolic CuZn SODs (OsCSD1, OsCSD4), along with in silico assessment of similar events in other plants. The analysis revealed heterogeneity in gene length, regulatory regions, untranslated regions (UTRs), and coding regions of two OsCSDs. An inconsistency in the database-predicted OsCSD1 gene structure was also identified and validated experimentally. Transcript analysis showed differences in the basal levels and stress responsiveness of OsCSD1 and OsCSD4, and indicated the presence of two transcription start sites in the OsCSD1. At the amino acid level, the two OsCSDs showed differences at 18 sites; however, both exist as a homodimer, displaying typical CuZn SOD characteristics, and enhancing the oxidative stress tolerance of Escherichia coli cells. However, OsCSD4 showed higher specific activity as well as stability. The comparison of the two OsCSDs with reported thermostable CSDs from other plants identified regions likely to be associated with stability, while the homology modeling and superposition highlighted structural differences. The two OsCSDs displayed heteromeric interaction capability and forms an enzymatically active heterodimer (OsCSD1:OsCSD4) on co-expression, which may have significance as both are cytosolic. In silico analysis of 74 plant genomes revealed the prevalence of block duplications for multiple CSD copies (mostly cytosolic). The divergence and clustering analysis of CSDs suggested the possibility of an ancestral duplication event in monocots. Conserved SOD features indicating retention of SOD function among CSD duplicates were evident in few monocots and dicots. In most other species, the CSD copies lacked critical features and may not harbor SOD function; however, other feature-associated functions or novel functions might be present. These aspects of divergent CSD copies encoding co-localized CSDs may have implications in plant SOD functions in the cytosol and other organelles.

Transcriptomic analysis of OsRUS1 overexpression rice lines with rapid and dynamic leaf rolling morphology

Moderate leaf rolling helps to form the ideotype of rice. In this study, six independent OsRUS1-GFP overexpression (OsRUS1-OX) transgenic rice lines with rapid and dynamic leaf rolling phenotype in response to sunlight were constructed. However, the mechanism is unknown. Here, RNA-Seq approach was utilized to identify differentially expressed genes between flag leaves of OsRUS1-OX and wildtype under sunlight. 2920 genes were differentially expressed between OsRUS1-OX and WT, of which 1660 upregulated and 1260 downregulated. Six of the 16 genes in GO: 0009415 (response to water stimulus) were significantly upregulated in OsRUS1-OX. The differentially expressed genes between WT and OsRUS1-OX were assigned to 110 KEGG pathways. 42 of the 222 genes in KEGG pathway dosa04075 (Plant hormone signal transduction) were differentially expressed between WT and OsRUS1-OX. The identified genes in GO:0009415 and KEGG pathway dosa04075 were good candidates to explain the leaf rolling phenotype of OsRUS1-OX. The expression patterns of the 15 genes identified by RNA-Seq were verified by qRT-PCR. Based on transcriptomic and qRT-PCR analysis, a mechanism for the leaf rolling phenotype of OsRUS1-OX was proposed. The differential expression profiles between WT and OsRUS1-OX established by this study provide important insights into the molecular mechanism behind the leaf rolling phenotype of OsRUS1-OX.

Genome-Wide Evolution and Comparative Analysis of Superoxide Dismutase Gene Family in Cucurbitaceae and Expression Analysis of Lagenaria siceraria Under Multiple Abiotic Stresses

Superoxide dismutase (SOD) is an important enzyme that serves as the first line of defense in the plant antioxidant system and removes reactive oxygen species (ROS) under adverse conditions. The SOD protein family is widely distributed in the plant kingdom and plays a significant role in plant growth and development. However, the comprehensive analysis of the SOD gene family has not been conducted in Cucurbitaceae. Subsequently, 43 SOD genes were identified from Cucurbitaceae species [Citrullus lanatus (watermelon), Cucurbita pepo (zucchini), Cucumis sativus (cucumber), Lagenaria siceraria (bottle gourd), Cucumis melo (melon)]. According to evolutionary analysis, SOD genes were divided into eight subfamilies (I, II, III, IV, V, VI, VII, VIII). The gene structure analysis exhibited that the SOD gene family had comparatively preserved exon/intron assembly and motif as well. Phylogenetic and structural analysis revealed the functional divergence of Cucurbitaceae SOD gene family. Furthermore, microRNAs 6 miRNAs were predicted targeting 3 LsiSOD genes. Gene ontology annotation outcomes confirm the role of LsiSODs under different stress stimuli, cellular oxidant detoxification processes, metal ion binding activities, SOD activity, and different cellular components. Promoter regions of the SOD family revealed that most cis-elements were involved in plant development, stress response, and plant hormones. Evaluation of the gene expression showed that most SOD genes were expressed in different tissues (root, flower, fruit, stem, and leaf). Finally, the expression profiles of eight LsiSOD genes analyzed by qRT-PCR suggested that these genetic reserves responded to drought, saline, heat, and cold stress. These findings laid the foundation for further study of the role of the SOD gene family in Cucurbitaceae. Also, they provided the potential for its use in the genetic improvement of Cucurbitaceae.

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.

The Meloidogyne graminicola effector MgMO289 targets a novel copper metallochaperone to suppress immunity in rice

Recent studies have reported that plant-parasitic nematodes facilitate their infection by suppressing plant immunity via effectors, but the inhibitory mechanisms remain poorly understood. This study found that a novel effector MgMO289 is exclusively expressed in the dorsal esophageal gland of Meloidogyne graminicola and is up-regulated at parasitic third-/fourth-stage juveniles. In planta silencing of MgMO289 substantially increased plant resistance to M. graminicola. Moreover, we found that MgMO289 interacts with a new rice copper metallochaperone heavy metal-associated plant protein 04 (OsHPP04), and that rice cytosolic COPPER/ZINC -SUPEROXIDE DISMUTASE 2 (cCu/Zn-SOD2) is the target of OsHPP04. Rice plants overexpressing OsHPP04 or MgMO289 exhibited an increased susceptibility to M. graminicola and a higher Cu/Zn-SOD activity, but lower O2•- content, when compared with wild-type plants. Meanwhile, immune response assays showed that MgMO289 could suppress host innate immunity. These findings reveal a novel pathway for a plant pathogen effector that utilizes the host O2•--scavenging system to eliminate O2•- and suppress plant immunity.

Splice Variants of Superoxide Dismutases in Rice and Their Expression Profiles under Abiotic Stresses

The superoxide dismutases (SODs) play vital roles in controlling cellular reactive oxygen species (ROS) that are generated both under optimal as well as stress conditions in plants. The rice genome harbors seven SOD genes (CSD1, CSD2, CSD3, CSD4, FSD1, FSD2, and MSD) that encode seven constitutive transcripts. Of these, five (CSD2, CSD3, CSD4, FSD1, and MSD) utilizes an alternative splicing (AS) strategy and generate seven additional splice variants (SVs) or mRNA variants, i.e., three for CSD3, and one each for CSD2, CSD4, FSD1, and MSD. The exon-intron organization of these SVs revealed variations in the number and length of exons and/or untranslated regions (UTRs). We determined the expression patterns of SVs along with their constitutive forms of SODs in rice seedlings exposed to salt, osmotic, cold, heavy metal (Cu⁺²) stresses, as well as copper-deprivation. The results revealed that all seven SVs were transcriptionally active in both roots and shoots. When compared to their corresponding constitutive transcripts, the profiles of five SVs were almost similar, while two specific SVs (CSD3-SV4 and MSD-SV2) differed significantly, and the differences were also apparent between shoots and roots suggesting that the specific SVs are likely to play important roles in a tissue-specific and stress-specific manner. Overall, the present study has provided a comprehensive analysis of the SVs of SODs and their responses to stress conditions in shoots and roots of rice seedlings.

Genome-wide identification of superoxide dismutase gene families and their expression patterns under low-temperature, salt and osmotic stresses in watermelon and melon

The growth and development of watermelon and melon are affected by abiotic stresses such as cold, salinity and drought. Plant superoxide dismutase (SOD) proteins exerted great effects on plant growth, development and response to abiotic stresses. However, little is known about the characteristics of watermelon and melon SOD gene families and their expression patterns under abiotic stresses. In this study, the genome-wide identification of SOD genes and their expression patterns under abiotic stresses has been done in watermelon and melon. Seven SODs were identified in watermelon and melon, respectively. Chromosome location indicated that the SODs were dispersedly distributed on 4-6 chromosomes. Almost all the SOD proteins contained 300 amino acids or less and the intron numbers of SODs ranged from 5 to 7. On the basis of phylogenetic analysis, the SODs were classified into six sub-groups which was also verified by similar motif composition, gene structure and sub-cellular location. Gene ontology analysis displayed that many SOD proteins participated in binding, catalytic, antioxidant activity and stimulus-response. Cis-regulatory elements related to stresses and hormones were found in the promoters of the SODs. Based on the quantitative real-time PCR, most of CmSOD and ClSOD genes showed obvious up-regulation under low-temperature, NaCl and PEG₆₀₀₀ treatments. The abiotic stress-responsive SOD genes were identified to improve watermelon and melon tolerance against abiotic stresses. This was a preliminary study to describe the genome-wide analysis of SOD gene family in watermelon and melon, and the results would facilitate further study of gene cloning and functional verification of SOD genes response to abiotic stresses in watermelon and melon.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02726-7.

The copper economy response is partially conserved in rice (Oryza sativa L.)

Copper (Cu) is an essential element for plants, especially in photosynthesis, as it is required for plastocyanin function in electron transfer reactions at thylakoid membranes. In Arabidopsis thaliana, Cu deficiency leads to the Cu economy response, in which plants prioritize Cu usage by plastocyanin in detriment of non-essential cupric proteins. In rice (Oryza sativa), however, this response has not been characterized. Rice OsHMA5 is a Cu xylem-loading transporter involved in Cu translocation from roots to shoots, as suggested by the analysis of oshma5 mutant plants. Aiming to understand how rice plants respond to Cu deficiency and how decreased Cu translocation to shoots can affect this response, we characterized the physiological and molecular responses of WT and oshma5 plants under control and Cu deficiency treatments. We found evidence that shoots of oshma5 plants are more prone to Cu deficiency compared to shoots of WT plants, as demonstrated by decreased chlorophyll and Cu concentrations, and electron transport rate. Gene expression analysis revealed that Cu high-affinity transporters OsCOPT1 and OsCOPT5, along with a set of miRNAs and three Cu/Zn superoxide dismutases are responsive to Cu deficiency in both WT and oshma5 plants, suggesting their involvement in the Cu economy response. However, Fe superoxide dismutase was not up-regulated in rice, indicating a difference compared to the A. thaliana Cu economy model. Therefore, we provide evidence for a partially conserved Cu economy response in rice, in comparison to A. thaliana.

Genome-wide identification and transcriptional expression analysis of superoxide dismutase (SOD) family in wheat (Triticum aestivum)

Superoxide dismutases (SODs) are a family of key antioxidant enzymes that play a crucial role in plant growth and development. Previously, this gene family has been investigated in Arabidopsis and rice. In the present study, a genome-wide analysis of the SOD gene family in wheat were performed. Twenty-six SOD genes were identified from the whole genome of wheat, including 17 Cu/Zn-SODs, six Fe-SODs, and three Mn-SODs. The chromosomal location mapping analysis indicated that these three types of SOD genes were only distributed on 2, 4, and 7 chromosomes, respectively. Phylogenetic analyses of wheat SODs and several other species revealed that these SOD proteins can be assigned to two major categories. SOD1 mainly comprises of Cu/Zn-SODs, and SOD2 mainly comprises of Fe-SODs and Mn-SODs. Gene structure and motif analyses indicated that most of the SOD genes showed a relatively conserved exon/intron arrangement and motif composition. Analyses of transcriptional data indicated that most of the wheat SOD genes were expressed in almost all of the examined tissues and had important functions in abiotic stress resistance. Finally, quantitative real-time polymerase chain reaction (qRT-PCR) analysis was used to reveal the regulating roles of wheat SOD gene family in response to NaCl, mannitol, and polyethylene glycol stresses. qRT-PCR showed that eight randomly selected genes with relatively high expression levels responded to all three stresses based on released transcriptome data. However, their degree of response and response patterns were different. Interestingly, among these genes, TaSOD1.7, TaSOD1.9, TaSOD2.1, and TaSOD2.3 feature research value owing to their remarkable expression-fold change in leaves or roots under different stresses. Overall, our results provide a basis of further functional research on the SOD gene family in wheat and facilitate their potential use for applications in the genetic improvement on wheat in drought and salt stress environments.

Highlight on the expression and the function of a novel MnSOD from diploid wheat (T. monococcum) in response to abiotic stress and heavy metal toxicity

Superoxide dismutases (SODs) play a pivotal role in improving abiotic stress tolerance in plant cells. A novel manganese superoxide dismutase gene, denoted as TmMnSOD, was identified from Triticum monococcum. The encoded protein displayed high sequence identity with MnSOD family members and was highly homologous to TdMnSOD from durum wheat. Furthermore, the 3D structure analysis revealed that TmMnSOD displayed homotetramer subunit organization, incorporating four Mn²⁺ ions. Notably, TmMnSOD structure contains predominantly alpha helices with three beta sheets. On the other hand, under stress conditions, TmMnSOD transcript level was significantly up-regulated by salt, oxidative and heavy metal stresses. At the functional level, TmMnSOD imparts tolerance of yeast and E. coli cells under diverse stresses. Promoter analysis of TmMnSOD gene showed the presence of a great number of salt and pathogen-responsive cis-regulatory elements, highlighting the interest of this gene in breeding programs towards improved tolerance to salt stress in wheat.

Genome-Wide Analysis of ROS Antioxidant Genes in Resurrection Species Suggest an Involvement of Distinct ROS Detoxification Systems during Desiccation

Abiotic stress is one of the major threats to plant crop yield and productivity. When plants are exposed to stress, production of reactive oxygen species (ROS) increases, which could lead to extensive cellular damage and hence crop loss. During evolution, plants have acquired antioxidant defense systems which can not only detoxify ROS but also adjust ROS levels required for proper cell signaling. Ascorbate peroxidase (APX), glutathione peroxidase (GPX), catalase (CAT) and superoxide dismutase (SOD) are crucial enzymes involved in ROS detoxification. In this study, 40 putative APX, 28 GPX, 16 CAT, and 41 SOD genes were identified from genomes of the resurrection species Boea hygrometrica, Selaginella lepidophylla, Xerophyta viscosa, and Oropetium thomaeum, and the mesophile Selaginellamoellendorffii. Phylogenetic analyses classified the APX, GPX, and SOD proteins into five clades each, and CAT proteins into three clades. Using co-expression network analysis, various regulatory modules were discovered, mainly involving glutathione, that likely work together to maintain ROS homeostasis upon desiccation stress in resurrection species. These regulatory modules also support the existence of species-specific ROS detoxification systems. The results suggest molecular pathways that regulate ROS in resurrection species and the role of APX, GPX, CAT and SOD genes in resurrection species during stress.

Osa-miR398b boosts H2 O2 production and rice blast disease-resistance via multiple superoxide dismutases

miRNAs contribute to plant resistance against pathogens. Previously, we found that the function of miR398b in immunity in rice differs from that in Arabidopsis. However, the underlying mechanisms are unclear. In this study, we characterized the mutants of miR398b target genes and demonstrated that multiple superoxide dismutase genes contribute to miR398b-regulated rice immunity against the blast fungus Magnaporthe oryzae. Out of the four target genes of miR398b, mutations in Cu/Zn-Superoxidase Dismutase1 (CSD1), CSD2 and Os11g09780 (Superoxide DismutaseX, SODX) led to enhanced resistance to M. oryzae and increased hydrogen peroxide (H₂ O₂ ) accumulation. By contrast, mutations in Copper Chaperone for Superoxide Dismutase (CCSD) resulted in enhanced susceptibility. Biochemical studies revealed that csd1, csd2 and sodx displayed altered expression of CSDs and other superoxide dismutase (SOD) family members, leading to increased total SOD enzyme activity that positively contributed to higher H₂ O₂ production. By contrast, the ccsd mutant showed CSD protein deletion, resulting in decreased CSD and total SOD enzyme activity. Our results demonstrate the roles of different SODs in miR398b-regulated resistance to rice blast disease, and uncover an integrative regulatory network in which miR398b boosts total SOD activity to upregulate H₂ O₂ concentration and thereby improve disease resistance.

Genome-wide identification, characterization, and expression analysis of superoxide dismutase (SOD) genes in foxtail millet (Setaria italica L.)

Superoxide dismutases (SODs) play important roles in plant growth, development, and response to abiotic stresses. Despite SOD gene families have been identified in various plant species, little is known in foxtail millet (Setaria italica L.). In this study, a systematic analysis of SOD gene family was performed in foxtail millet and the expression pattern of SOD genes in response to abiotic stressors was analyzed at the whole-genomic level. Eight SOD genes were identified in foxtail millet, including 4 Cu/ZnSODs, 3 FeSODs, and 1 MnSOD. These SiSODs are unevenly distributed across 5 of the 9 chromosomes. Phylogenetic analysis showed that SOD proteins could be divided into two major categories (Cu/ZnSODs and Fe-MnSODs), containing seven subgroups, from foxtail millet and other plant species. SOD genes have conserved motif and exon/intron composition in the same subgroup among Setaria italica, Setaria viridis, and Oryza sativa. Additionally, many cis-elements that respond to different stressors were distributed at different densities in the promoters of 8 SiSODs. The expression patterns of SiSODs in different tissues and different abiotic stressors indicated that the SiSODs may play important roles in reactive oxygen species scavenging, caused by various stressors in foxtail millet. This study provides a foundation for the further cloning and functional verification of the SOD gene family response to environmental stimuli in foxtail millet.

In silico identification and expression analysis of superoxide dismutase (SOD) gene family in Medicago truncatula

Superoxide dismutase (SOD) proteins are crucial antioxidant enzymes that play critical roles in plant growth, development, and response to various abiotic stresses. The SOD gene family has been characterized in various plant species, but not in Medicago truncatula yet. Here, a total of 7 MtSOD genes were first identified from the whole genome of M. truncatula, including 1 MnSOD, 2 FeSODs, and 4 Cu/ZnSODs, which are unevenly distributed in five out of the eight chromosomes. Phylogenetic analysis showed that SOD proteins from M. truncatula and other plant species could be classified into two main categories (Cu/ZnSODs and Fe-MnSODs), which could be further divided into eight subgroups, and members within the same subgroup tended to share the same subcellular localization. In addition, MtSOD genes together with AtSODs and OsSODs within the same subgroup also displayed similar motif compositions and exon-intron structures. Most MtSOD genes were ubiquitously expressed in various tissues, particularly in leaves, seeds and root nodules at different developmental stages. Moreover, microarray analysis and high-throughput sequencing showed that most MtSOD genes were differentially expressed under salt, drought, and cold treatments, indicating their pivotal roles in stress response of M. truncatula. These findings provide useful information for the functional characterization of SOD family genes for growth, development, and stress response of M. truncatula.

Relationship of ROS accumulation and superoxide dismutase isozymes in developing anther with floret fertility of rice under heat stress

High temperature (HT) at meiosis stage is one of most important environment constraint affecting spikelet fertility and rice yield. In this paper, the effects of HT exposure at meiosis stage on the ROS (reactive oxygen species) accumulation, various superoxide dismutase (SOD, EC1.15.1.11) isozymes in developing anther, and its relationship with HT-induced decline in pollen viability and floret fertility were investigated by using four rice cultivars differing in heat tolerance under well-controlled climatic condition. Results showed that HT exposure significantly increased ROS level and malondialdehyde (MDA) content in rice anther, and this occurrence was strongly responsible for the HT-induced decline in pollen viability and harmful effect of HT adversity on floret fertility. However, the increased extent of ROS concentration in rice anther under HT exposure was greatly variable, depending on both the intensity and duration of HT exposure and different rice cultivars used. The SOD and CAT activities of HT-sensitive cultivars decreased more profoundly than those of HT-tolerant cultivars under the same HT regimes. Among various types of SOD enzymes, Cu/Zn-SODa expressed highly in rice anther and responded sensitively to HT exposure, while Cu/Zn-SODb expressed weakly in rice anther and preferentially in rice leaves. HT exposure suppressed the expression of Cu/Zn-SODa in developing anther, which was closely associated with the down-regulated transcripts of cCu/Zn-SOD1 gene. Hence, Cu/Zn-SODa may play a central role in the regulation of total SOD activity and ROS detoxification in rice anther as affected by HT exposure at meiosis stage.

Tolerance analysis of chloroplast OsCu/Zn-SOD overexpressing rice under NaCl and NaHCO3 stress

The 636-bp-long cDNA sequence of OsCu/Zn-SOD (AK059841) was cloned from Oryza sativa var. Longjing11 via reverse transcription polymerase chain reaction (RT-PCR). The encoded protein comprised of 211 amino acids is highly homologous to Cu/Zn-SOD proteins from tuscacera rice and millet. Quantitative RT-PCR revealed that in rice, the level of OsCu/Zn-SOD gene expression was lowest in roots and was highest in petals and during the S5 leaf stage. Moreover, the expression level of OsCu/Zn-SOD gene expression decreased during the L5 leaf stage to maturity. The level of OsCu/Zn-SOD gene expression, however, was increased under saline–sodic stress and NaHCO₃ stress. Germination tests under 125, 150, and 175 mM NaCl revealed that OsCu/Zn-SOD-overexpressing lines performed better than the non-transgenic (NT) Longjing11 lines in terms of germination rate and height. Subjecting seedlings to NaHCO₃ and water stress revealed that OsCu/Zn-SOD-overexpressing lines performed better than NT in terms of SOD activity, fresh weight, root length, and height. Under simulated NaHCO₃ stress, OsCu/Zn-SOD-overexpressing lines performed better than NT in terms of survival rate (25.19% > 6.67%) and yield traits (average grain weight 20.6 > 18.15 g). This study showed that OsCu/Zn-SOD gene overexpression increases the detoxification capacity of reactive oxygen species in O. sativa and reduces salt-induced oxidative damage. We also revealed the regulatory mechanism of OsCu/Zn-SOD enzyme in saline–sodic stress resistance in O. sativa. Moreover, we provided an experimental foundation for studying the mechanism of OsCu/Zn-SOD enzymes in the chloroplast.

Genome-Wide Identification and Transcriptional Expression Analysis of Cucumber Superoxide Dismutase (SOD) Family in Response to Various Abiotic Stresses

Superoxide dismutase (SOD) proteins are widely present in the plant kingdom and play important roles in different biological processes. However, little is known about the SOD genes in cucumber. In this study, night SOD genes were identified from cucumber (Cucumis sativus) using bioinformatics-based methods, including 5 Cu/ZnSODs, 3 FeSODs, and 1 MnSOD. Gene structure and motif analysis indicated that most of the SOD genes have relatively conserved exon/intron arrangement and motif composition. Phylogenetic analyses with SODs from cucumber and several other species revealed that these SOD proteins can be traced back to two ancestral SODs before the divergence of monocot and dicot plants. Many cis-elements related to stress responses and plant hormones were found in the promoter sequence of each CsSOD gene. Gene expression analysis revealed that most of the CsSOD genes are expressed in almost all the tested tissues. qRT-PCR analysis of 8 selected CsSOD genes showed that these genes could respond to heat, cold, osmotic, and salt stresses. Our results provide a basis for further functional research on SOD gene family in cucumber and facilitate their potential applications in the genetic improvement of cucumber.

Genome-Wide Characterization and Expression Profiles of the Superoxide Dismutase Gene Family in Gossypium

Superoxide dismutase (SOD) as a group of significant and ubiquitous enzymes plays a critical function in plant growth and development. Previously this gene family has been investigated in Arabidopsis and rice; it has not yet been characterized in cotton. In our study, it was the first time for us to perform a genome-wide analysis of SOD gene family in cotton. Our results showed that 10 genes of SOD gene family were identified in Gossypium arboreum and Gossypium raimondii, including 6 Cu-Zn-SODs, 2 Fe-SODs, and 2 Mn-SODs. The chromosomal distribution analysis revealed that SOD genes are distributed across 7 chromosomes in Gossypium arboreum and 8 chromosomes in Gossypium raimondii. Segmental duplication is predominant duplication event and major contributor for expansion of SOD gene family. Gene structure and protein structure analysis showed that SOD genes have conserved exon/intron arrangement and motif composition. Microarray-based expression analysis revealed that SOD genes have important function in abiotic stress. Moreover, the tissue-specific expression profile reveals the functional divergence of SOD genes in different organs development of cotton. Taken together, this study has imparted new insights into the putative functions of SOD gene family in cotton. Findings of the present investigation could help in understanding the role of SOD gene family in various aspects of the life cycle of cotton.

ROS Regulation During Abiotic Stress Responses in Crop Plants

Abiotic stresses such as drought, cold, salt and heat cause reduction of plant growth and loss of crop yield worldwide. Reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide anions (O2 (•-)), hydroxyl radical (OH•) and singlet oxygen ((1)O2) are by-products of physiological metabolisms, and are precisely controlled by enzymatic and non-enzymatic antioxidant defense systems. ROS are significantly accumulated under abiotic stress conditions, which cause oxidative damage and eventually resulting in cell death. Recently, ROS have been also recognized as key players in the complex signaling network of plants stress responses. The involvement of ROS in signal transduction implies that there must be coordinated function of regulation networks to maintain ROS at non-toxic levels in a delicate balancing act between ROS production, involving ROS generating enzymes and the unavoidable production of ROS during basic cellular metabolism, and ROS-scavenging pathways. Increasing evidence showed that ROS play crucial roles in abiotic stress responses of crop plants for the activation of stress-response and defense pathways. More importantly, manipulating ROS levels provides an opportunity to enhance stress tolerances of crop plants under a variety of unfavorable environmental conditions. This review presents an overview of current knowledge about homeostasis regulation of ROS in crop plants. In particular, we summarize the essential proteins that are involved in abiotic stress tolerance of crop plants through ROS regulation. Finally, the challenges toward the improvement of abiotic stress tolerance through ROS regulation in crops are discussed.