Defense-Related Enzyme Activities and Metabolomic Analysis Reveal Differentially Accumulated Metabolites and Response Pathways for Sheath Blight Resistance in Rice

Rice sheath blight (RSB), caused by the pathogenic fungus Rhizoctonia solani, poses a significant threat to global food security. The defense mechanisms employed by rice against RSB are not well understood. In our study, we analyzed the interactions between rice and R. solani by comparing the phenotypic changes, ROS content, and metabolite variations in both tolerant and susceptible rice varieties during the early stages of fungal infection. Notably, there were distinct phenotypic differences in the response to R. solani between the tolerant cultivar Zhengdao22 (ZD) and the susceptible cultivar Xinzhi No.1 (XZ). We observed that the activities of five defense-related enzymes in both tolerant and susceptible cultivars changed dynamically from 0 to 72 h post-infection with R. solani. In particular, the activities of superoxide dismutase and peroxidase were closely associated with resistance to RSB. Metabolomic analysis revealed 825 differentially accumulated metabolites (DAMs) between the tolerant and susceptible varieties, with 493 DAMs responding to R. solani infection. Among these, lipids and lipid-like molecules, organic oxygen compounds, phenylpropanoids and polyketides, organoheterocyclic compounds, and organic acids and their derivatives were the most significantly enriched. One DAM, P-coumaraldehyde, which responded to R. solani infection, was found to effectively inhibit the growth of R. solani, Magnaporthe grisea, and Ustilaginoidea virens. Additionally, multiple metabolic pathways, including amino acid metabolism, carbohydrate metabolism, metabolism of cofactors and vitamins, and metabolism of terpenoids and polyketides, are likely involved in RSB resistance. Our research provides valuable insights into the molecular mechanisms underlying the interaction between rice and R. solani.

In vivo antioxidant activity of rabbiteye blueberry (Vaccinium ashei cv. 'Brightwell') anthocyanin extracts

Blueberries are rich in phenolic compounds including anthocyanins which are closely related to biological health functions. The purpose of this study was to investigate the antioxidant activity of blueberry anthocyanins extracted from 'Brightwell' rabbiteye blueberries in mice. After one week of adaptation, C57BL/6J healthy male mice were divided into different groups that were administered with 100, 400, or 800 mg/kg blueberry anthocyanin extract (BAE), and sacrificed at different time points (0.1, 0.5, 1, 2, 4, 8, or 12 h). The plasma, eyeball, intestine, liver, and adipose tissues were collected to compare their antioxidant activity, including total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity and glutathione-peroxidase (GSH-PX/GPX) content, and the oxidative stress marker malondialdehyde (MDA) level. The results showed that blueberry anthocyanins had positive concentration-dependent antioxidant activity in vivo. The greater the concentration of BAE, the higher the T-AOC value, but the lower the MDA level. The enzyme activity of SOD, the content of GSH-PX, and messenger RNA (mRNA) levels of Cu,Zn-SOD, Mn-SOD, and GPX all confirmed that BAE played an antioxidant role after digestion in mice by improving their antioxidant defense. The in vivo antioxidant activity of BAE indicated that blueberry anthocyanins could be developed into functional foods or nutraceuticals with the aim of preventing or treating oxidative stress-related diseases.

Combination of hyperspectral imaging and entropy weight method for the comprehensive assessment of antioxidant enzyme activity in Tan mutton

The antioxidant enzymes play the crucial role in inhibiting mutton spoilage. In this study, visible near-infrared (Vis-NIR) hyperspectral imaging (HSI) combined with entropy weight method (EWM) was developed for the first time to evaluate the antioxidant properties of Tan mutton. The comprehensive index of antioxidant enzymes (AECI) consisting of peroxidase (49.34%), catalase (37.97%) and superoxidase (12.69%) was constructed by the EWM. Partial least squares regression, least squares support vector machine and artificial neural networks (ANN) were developed based on characteristic wavelengths extracted by successful projections algorithm, uninformative variable selection, iteratively retains informative variables (IRIV), regression coefficient and competitive adaptive reweighted sampling (CARS). The textural features (TF) were extracted by the gray level co-occurrence matrix and fused with the spectral data to establish models. Visualization of the changes in antioxidant enzyme activity was constructed from the optimal model. In addition, two-dimensional correlation spectra (2D-COS) with AECI as a perturbation variable was used to identify spectral features, revealing chemical bond changes order under the characteristic peaks at 612-799-473-708-559 nm. The results showed that the IRIV-CARS-TF-ANN model performed the best, with prediction set coefficient of determination (R_P²) of 0.8813, which improved 2.12%, 1.11% and 2.77% over the R_P² of full band, IRIV and IRIV-CARS, respectively. It was suggested that fusion data of HSI may effectively predict the activity of antioxidant enzymes in Tan mutton.

Genome-wide analysis of bromodomain gene family in Arabidopsis and rice

The bromodomain-containing proteins (BRD-proteins) belongs to family of 'epigenetic mark readers', integral to epigenetic regulation. The BRD-members contain a conserved 'bromodomain' (BRD/BRD-fold: interacts with acetylated-lysine in histones), and several additional domains, making them structurally/functionally diverse. Like animals, plants also contain multiple Brd-homologs, however the extent of their diversity and impact of molecular events (genomic duplications, alternative splicing, AS) therein, is relatively less explored. The present genome-wide analysis of Brd-gene families of Arabidopsis thaliana and Oryza sativa showed extensive diversity in structure of genes/proteins, regulatory elements, expression pattern, domains/motifs, and the bromodomain (w.r.t. length, sequence, location) among the Brd-members. Orthology analysis identified thirteen ortholog groups (OGs), three paralog groups (PGs) and four singleton members (STs). While more than 40% Brd-genes were affected by genomic duplication events in both plants, AS-events affected 60% A. thaliana and 41% O. sativa genes. These molecular events affected various regions (promoters, untranslated regions, exons) of different Brd-members with potential impact on expression and/or structure-function characteristics. RNA-Seq data analysis indicated differences in tissue-specificity and stress response of Brd-members. Analysis by RT-qPCR revealed differential abundance and salt stress response of duplicate A. thaliana and O. sativa Brd-genes. Further analysis of AtBrd gene, AtBrdPG1b showed salinity-induced modulation of splicing pattern. Bromodomain (BRD)-region based phylogenetic analysis placed the A. thaliana and O. sativa homologs into clusters/sub-clusters, mostly consistent with ortholog/paralog groups. The bromodomain-region displayed several conserved signatures in key BRD-fold elements (α-helices, loops), along with variations (1-20 sites) and indels among the BRD-duplicates. Homology modeling and superposition identified structural variations in BRD-folds of divergent and duplicate BRD-members, which might affect their interaction with the chromatin histones, and associated functions. The study also showed contribution of various duplication events in Brd-gene family expansion among diverse plants, including several monocot and dicot plant species.

Peroxisome-Mediated Reactive Oxygen Species Signals Modulate Programmed Cell Death in Plants

Peroxisomes are a class of simple organelles that play an important role in plant reactive oxygen species (ROS) metabolism. Experimental evidence reveals the involvement of ROS in programmed cell death (PCD) in plants. Plant PCD is crucial for the regulation of plant growth, development and environmental stress resistance. However, it is unclear whether the ROS originated from peroxisomes participated in cellular PCD. Enzymes involved in the peroxisomal ROS metabolic pathways are key mediators to figure out the relationship between peroxisome-derived ROS and PCD. Here, we summarize the peroxisomal ROS generation and scavenging pathways and explain how peroxisome-derived ROS participate in PCD based on recent progress in the functional study of enzymes related to peroxisomal ROS generation or scavenging. We aimed to elucidate the role of the peroxisomal ROS regulatory system in cellular PCD to show its potential in terms of accurate PCD regulation, which contribute to environmental stress resistance.

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.

Comprehensive characterization and molecular insights into the salt tolerance of a Cu, Zn-superoxide dismutase from an Indian Mangrove, Avicennia marina

Superoxide dismutases are important group of antioxidant metallozyme and play important role in ROS homeostasis in salinity stress. The present study reports the biochemical properties of a salt-tolerant Cu, Zn-superoxide from Avicennia marina (Am_SOD). Am_SOD was purified from the leaf and identified by mass-spectrometry. Recombinant Am_SOD cDNA was bacterially expressed as a homodimeric protein. Enzyme kinetics revealed a high substrate affinity and specific activity of Am_SOD as compared to many earlier reported SODs. An electronic transition in 360-400 nm spectra of Am_SOD is indicative of Cu2+-binding. Am_SOD activity was potentially inhibited by diethyldithiocarbamate and H2O2, a characteristic of Cu, Zn-SOD. Am_SOD exhibited conformational and functional stability at high NaCl concentration as well in alkaline pH. Introgression of Am_SOD in E. coli conferred tolerance to oxidative stress under highly saline condition. Am_SOD was moderately thermostable and retained functional activity at ~ 60 °C. In-silico analyses revealed 5 solvent-accessible N-terminal residues of Am_SOD that were less hydrophobic than those at similar positions of non-halophilic SODs. Substituting these 5 residues with non-halophilic counterparts resulted in > 50% reduction in salt-tolerance of Am_SOD. This indicates a cumulative role of these residues in maintaining low surface hydrophobicity of Am_SOD and consequently high salt tolerance. The molecular information on antioxidant activity and salt-tolerance of Am_SOD may have potential application in biotechnology research. To our knowledge, this is the first report on salt-tolerant SOD from mangrove.

A highly efficient, thermo stable and broad pH adaptable copper-zinc super oxide dismutase (AmSOD1) mediates hydrogen peroxide tolerance in Avicennia marina

Avicennia marina is a widely distributed mangrove species with high tolerance to salt, oxidative stress and heavy metals. In the preset work, we found that superoxide dismutase (SOD) activity increases in Avicennia marina leaves in response to salt and hydrogen peroxide. Monitoring the SOD using Western blot analysis revealed that the accumulation of SOD increased in response to hydrogen peroxide but not in response to salinity stress. Here we also isolated and cloned a gene encoding AmSOD1 which was classified into the group of plant CuZnSODs based on amino acid sequence analysis. AmSOD1 was heterologously expressed in the soluble fraction of E. coli strain Rosetta (DE3). The cells expressing His-AmSOD1 were more tolerant in response to hydrogen peroxide treatment but not salt stress, suggesting the involvement of AmSOD1 in hydrogen peroxide tolerance. The enzyme His-AmSOD1 exhibited a molecular mass of 38 kDa, but it could be monomer in reducing conditions indicating a double-strand protein with intra-molecular disulfide bridge. There are two copper and two zinc moles per mole of dimer form of His-AmSOD1 suggesting the binding of one copper and one zinc ions to each monomer. The Pure His-AmSOD1 was highly active in vitro and its activity was considerably enhanced when the growth medium of the cells producing AmSOD1 was supplemented with Cu²⁺. The high stability of the recombinant AmSOD1 after incubation in a broad range pH and high temperature is a distinctive feature for AmSOD1, which may open new insights for application of AmSOD1 as a protein drug in different medical purposes.

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.