Genome Wide Identification of Respiratory Burst Oxidase Homolog (Rboh) Genes in Citrus sinensis and Functional Analysis of CsRbohD in Cold Tolerance

Expression profile and characterization of respiratory burst oxidase homolog genes in rice under MeJA, SA and Xoo treatments

Respiratory burst oxidase homologs (Rboh) genes is essential for synthesizing reactive oxygen species, which play a crucial role in environmental stress response. The Rboh gene family has been studied in model plants such as Arabidopsis. Nevertheless, Rboh remained largely unexplored in Rice (Oryza sativa L.). Here, we performed characterization of the Rboh genes family in rice (OsRboh) under Xanthomonas oryzae pv. oryzae (Xoo), salicylic acid (SA), and methyl jasmonate (MeJA) treatments. Nine OsRboh genes were retrieved distributed across six chromosomes (1, 5, 8, 9, 11, 12).These genes vary in amino acid sequence length (728-1034), isoelectric point (9.05-9.84), and molecular weight (8.341-115.014 kDa). Analysis of gene structure, motifs and conserved domains showed that OsRboh genes have similar protein sequences and functions. The promoter region of OsRboh genes was found to contain mainly cis-acting elements associated with light, jasmonic acid (JA), abscisic acid (ABA), and SA responsiveness. Predictions of functional protein-protein interaction showed that OsRboh genes were associated with MAPK signaling, plant-pathogen interaction, and other mRNA surveillance pathways. Prediction of miRNA targets and post-translational modification sites indicated that OsRboh genes may be regulated by miRNA and protein phosphorylation. Phylogenetic analysis showed that OsRboh genes were distributed into 7 clusters. Furthermore, 9 OsRboh genes were differentially expressed in different tissues (roots, stems, and leaves). OsRbohA, OsRbohB, and OsRbohD are significant genes in rice defense responses, showing unique and increased expression profiles under (Xoo-PXO99), (MeJA), and (SA) treatments. These genes important function in triggering defense mechanisms is further stressed by the high (> 20-fold) changes in expression they exhibit under these treatments. These findings enhance our understanding of rice OsRboh genes functions and contribute to stress tolerance improvement strategies.

Identification of VcRBOH genes in blueberry and functional characterization of VcRBOHF in plant defense

Reactive oxygen species (ROS) serve as signal molecules in plant defense responses, and the respiratory burst oxidase homolog (RBOH) enzyme plays a crucial role in their production. Although numerous RBOH family members have been identified in various plants, little is known about the RBOH genes in blueberries. In this study, we identified six VcRBOH genes from the blueberry genome. Phylogenetic analysis revealed that these VcRBOH genes can be classified into three subgroups. Conserved domain and motif analysis demonstrated high sequence similarity among VcRBOH proteins. Analysis of cis-acting elements suggested that VcRBOH genes may be involved in stress, light, and phytohormone responsiveness. Based on transcriptome data, we observed low expression levels of VcRBOHB, VcRBOHC, and VcRBOHE during the flower_at_anthesis stage. In contrast, VcRBOHA and VcRBOHD showed relatively high expression levels in various tissues. The reverse-transcription quantitative PCR (RT-qPCR) analysis indicated rapid induction of VcRBOHF by flg22 and chitin treatments. Notably, overexpression of VcRBOHF in Arabidopsis promoted PTI responses, including increased expression of marker genes, ROS production, and callose deposition. Moreover, the overexpression of VcRBOHF resulted in enhanced disease resistance against Pseudomonas syringae pv. tomato (Pst) DC3000 infection. These findings provide valuable insights into the roles of VcRBOHF genes in plant defense responses and lay the groundwork for a more comprehensive understanding of the molecular mechanisms underpinning blueberry disease resistance.

Identification and expression analysis of the RBOH gene family of Isatis indigotica Fort. and the potential regulation mechanism of RBOH gene on H2O2 under salt stress

KEY MESSAGE

RBOH gene may regulate the resistance of Isatis indigotica Fort. to salt stress by mediating the production of H2O2. RBOH gene plays an important role in plant growth and development, abiotic and biotic stress response, and hormone signalling. However, studies on RBOH gene expression and molecular mechanism of Isatis indigotica Fort. under salt stress have not been reported. This study identified 10 genes of the I. indigotica RBOH gene family (IiRBOH) and divided them into five subfamilies (I-V). Genes within the same class show conserved structural features and similar amino acid sequences. Analysis of CRE suggested that IiRBOH genes might play roles in growth and development, metabolism, hormone regulation, and stress response. Two physiological indicators of I. indigotica treated with salt for different days were detected. It was found that the content of H2O2 in the I. indigotica tissue first increased, then decreased and increased again. The catalase activity also showed a trend of first increasing and then decreasing. The qRT-PCR results showed that these IiRBOH genes showed different expression patterns in response to salt stress, and some of these genes may be involved in the resistance of I. indigotica to salt stress. Through RT-PCR analysis and screening on the PlantCARE website, it was found that IiRBOHA and IiRBOHC not only possess W-box CRE but also exhibit high expression under salt stress. Y1H experiments were conducted with the WRKY genes predicted by phylogenetic analysis to regulate salt stress potentially, and it was discovered that IiWRKY6 and IiWRKY54 can directly activate the transcription of the IiRBOHA gene promoter. This study preliminarily explored the mechanism by which the RBOH gene in I. indigotica mediates H2O2 to resist salt stress, thus laying a foundation for further research on the biological functions of the RBOH gene in I. indigotica.

The transcription factor FcMYB3 responds to 60Co γ-ray irradiation of axillary buds in Ficus carica L. by activating the expression of the NADPH oxidase, FcRbohD

Plant irradiation has been used to induce genetic variation in crop germplasm. However, the underlying mechanisms of plant responses to ionizing radiation stress are still unclear. In plants, reactive oxygen species (ROS) are produced with abiotic stress. Respiratory burst oxidative homologs (Rboh) genes are important regulators of plant ROS stress responses, but little is known of their involvement in the response to ionizing radiation stress. In this study, young branches of Ficus carica L. were irradiated with 60Co γ-rays and axillary buds were collected after 3- 48 h after irradiation. The differentially expressed genes (DEGs; p< 0.05) detected included an early (6 h) and sustained increase in member of the MAPK signaling pathway. The activities of superoxide dismutase SOD, POD and CAT in fig axillary buds showed a trend of first decrease and then increase with time, while the contents of MDA and H2O2 maintained an overall upward trend. The analysis of differentially expressed genes (DEGs; p < 0.05) indicated an early (6 h) and sustained increase in member of the MAPK signaling pathway. DEGs for glutathione-s-transferase and genes involved in phenylpropanoid and flavonoid biosynthesis pathways were detected at all time points, indicating that γ-irradiation induced an increased capacity for in ROS-scavenging. Substantial changes in the expression of MYB, NAC and bHLH transcription factor family members were also seen to occur within 6 h after irradiation. Taking Rboh-derived ROS signaling pathway as the entry point, the MYB transcription factor, FcMYB3, was identified as an potential upstream regulator of FcRbohD in a yeast one hybrid assay and this interaction verified by LUC and EMSA experiments. The knock-down and overexpression of FcMYB3 indicated that FcMYB3 is a positive regulator of ROS accumulation in response to γ-ray radiation stress responses in fig. Our results will provide a better understanding of the mechanisms of radiation tolerance in plant materials.

The Characteristics and Expression Analysis of the Tomato SlRBOH Gene Family under Exogenous Phytohormone Treatments and Abiotic Stresses

Respiratory burst oxidase homologs (RBOHs), also known as NADPH oxidases, contribute significantly to the production of ROS in plants, alongside other major sources such as photosynthesis and electron transport in chloroplasts. It has been shown that plant RBOHs play an active role in plant adversity response and electron transport. However, the phylogenetic analysis and characterization of the SlRBOH gene family in tomatoes have not been systematically studied. This study identified 11 SlRBOH genes in the tomato genome using a genome-wide search approach. The physicochemical properties, chromosomal localization, subcellular localization, secondary structure, conserved motifs, gene structure, phylogenetics, collinear relationships, cis-acting elements, evolutionary selection pressures, tissue expressions, and expression patterns under exogenous phytohormones (ABA and MeJA) and different abiotic stresses were also analyzed. We found that the SlRBOHs are distributed across seven chromosomes, collinearity reflecting their evolutionary relationships with corresponding genes in Arabidopsis thaliana and rice. Additionally, all the SlRBOH members have five conserved domains and 10 conserved motifs and have similar gene structures. In addition, the results of an evolutionary selection pressure analysis showed that SlRBOH family members evolved mainly by purifying selection, making them more structurally stable. Cis-acting element analyses showed that SlRBOHs were responsive to light, hormone, and abiotic stresses. Tissue expression analysis showed that SlRBOH family members were expressed in all tissues of tomato to varying degrees, and most of the SlRBOHs with the strongest expression were found in the roots. In addition, the expressions of tomato SlRBOH genes were changed by ABA, MeJA, dark period extension, NaCl, PEG, UV, cold, heat, and H2O2 treatments. Specifically, SlRBOH4 was highly expressed under NaCl, PEG, heat, and UV treatments, while SlRBOH2 was highly expressed under cold stress. These results provide a basis for further studies on the function of SlRBOHs in tomato.

Arbuscular mycorrhizal fungal contribution towards plant resilience to drought conditions

Climate changes cause altering rainfall patterns resulting in an increase in drought occurrences globally. These events are disrupting plants and agricultural productivity. To evade droughts, plants try to adapt and modify in the best capacities possible. The plants have adapted by structurally modifying roots, stems, and leaves, as well as modifying functions. Lately, the association of microbial communities with plants has also been proven to be an important factor in aiding resilience. The fungal representatives of the microbial community also help safeguard the plants against drought. We discuss how these fungi associate with plants and contribute to evading drought stress. We specifically focus on Arbuscular mycorrhizal fungi (AMF) mediated mechanisms involving antioxidant defenses, phytohormone mediations, osmotic adjustments, proline expressions, fungal water absorption and transport, morphological modifications, and photosynthesis. We believe understanding the mechanisms would help us to optimize the use of fungi in agricultural practices. That way we could better prepare the plants for the anticipated future drought events.

Genome-wide analysis of respiratory burst oxidase homolog (Rboh) genes in Aquilaria species and insight into ROS-mediated metabolites biosynthesis and resin deposition

Respiratory burst oxidase homolog (Rboh) generates reactive oxygen species (ROS) as a defense response during biotic and abiotic stress. In Aquilaria plants, wounding and fungal infection result in biosynthesis and deposition of secondary metabolites as defense responses, which later form constituents of fragrant resinous agarwood. During injury and fungal invasion, Aquilaria tree generates ROS species via the Rboh enzymes. Despite the implication of Rboh genes in agarwood formation, no comprehensive genomic-level study of the Rboh gene family in Aquilaria is present. A systematic illustration of their role during stress and involvement in initiating signal cascades for agarwood metabolite biosynthesis is missing. In this study, 14 Rboh genes were retrieved from genomes of two Aquilaria species, A. agallocha and A. sinensis, and were classified into five groups. The promoter regions of the genes had abundant of stress-responsive elements. Protein-protein network and in silico expression analysis suggested their functional association with MAPK proteins and transcription factors such as WRKY and MYC2. The study further explored the expression profiles of Rboh genes and found them to be differentially regulated in stress-induced callus and stem tissue, suggesting their involvement in ROS generation during stress in Aquilaria. Overall, the study provides in-depth insight into two Rboh genes, AaRbohC and AaRbohA, highlighting their role in defense against fungal and abiotic stress, and likely during initiation of agarwood formation through modulation of genes involved in secondary metabolites biosynthesis. The findings presented here offer valuable information about Rboh family members, which can be leveraged for further investigations into ROS-mediated regulation of agarwood formation in Aquilaria species.

Genome-Wide Identification and Expression Analysis of Respiratory Burst Oxidase Homolog (RBOH) Gene Family in Eggplant (Solanum melongena L.) under Abiotic and Biotic Stress

Respiratory burst oxidase homologs (RBOHs) are important proteins that catalyze the production of reactive oxygen species (ROS), which play important roles in growth and stress response. For a comprehensive analysis of SmRBOH genes, we conducted genome-wide identification of the SmRBOH gene family in eggplant (Solanum melongena L.) and analyzed the expression of SmRBOHs under abiotic (salt, high-temperature, and low-temperature) and biotic stress (Verticillium dahliae inoculation) by quantitative real-time PCR (qRT-PCR). The result showed that a total of eight SmRBOH members were identified from the genome database of eggplant, and they were relatively evenly distributed across seven chromosomes. The analysis of Motif and the conserved domain showed that SmRBOHs have high similarity in protein sequences and functions. Based on phylogenetics, SmRBOHs were classified into three distinct clades. Furthermore, the promoter regions of SmRBOHs were found to contain different cis-elements. Additionally, the results of the qRT-PCR demonstrated differential expression patterns of SmRBOHs in different tissues (the roots, stems, and leaves) and stress conditions. SmRBOHB, SmRBOHD, SmRBOHH1, and SmRBOHH2 showed significant upregulation (>20-fold) under at least one stress condition. Subcellular localization analysis of the above four members further confirmed that they localized on the plasma membrane. This study provides a theoretical foundation for understanding the functions of SmRBOHs in eggplant.

Sensing, signalling, and regulatory mechanism of cold-stress tolerance in plants

Cold stress is a crucial environmental factor influencing growth and distribution and possessing yield penalties. To survive in the cold, plants have evolved to use a range of molecular mechanisms. The major regulatory pathway under low-temperature stress involves the conversion of external stimulus into an internal signal that triggers a defence mechanism through a transcriptional cascade to counter stress. Cold-receptive mechanism and cell signalling involve cold-related signalling molecules, sensors, calcium signals, MAPK cascade, and ICE-COR-CBF pathway that modulate signal transduction in plants. Of these, the ICE-CBF-COR signalling is considered to be an important regulator for cold-stress acclimation. ICE stimulates acclimation to cold and plays a pivotal role in regulating CBF-mediated cold-tolerance mechanism. Thus, CBFs regulate COR gene expression by binding to its promoter. Similarly, the C-repeat binding factor-dependent signalling cascade also stimulates osmotic stress-regulatory gene expression. This review elucidates the regulatory mechanism underlying cold stress, i.e., signal molecules, cold receptors, signal-transduction pathways, metabolic regulation under cold stress, and crosstalk of regulatory pathways with other abiotic stresses in plants. The results may pave the way for crop improvement in low-temperature environments.

Evolutionary Analysis of Respiratory Burst Oxidase Homolog (RBOH) Genes in Plants and Characterization of ZmRBOHs

The respiratory burst oxidase homolog (RBOH), as the key producer of reactive oxygen species (ROS), plays an essential role in plant development. In this study, a bioinformatic analysis was performed on 22 plant species, and 181 RBOH homologues were identified. A typical RBOH family was identified only in terrestrial plants, and the number of RBOHs increased from non-angiosperms to angiosperms. Whole genome duplication (WGD)/segmental duplication played a key role in RBOH gene family expansion. Amino acid numbers of 181 RBOHs ranged from 98 to 1461, and the encoded proteins had molecular weights from 11.1 to 163.6 kDa, respectively. All plant RBOHs contained a conserved NADPH_Ox domain, while some of them lacked the FAD_binding_8 domain. Plant RBOHs were classified into five main subgroups by phylogenetic analysis. Most RBOH members in the same subgroup showed conservation in both motif distribution and gene structure composition. Fifteen ZmRBOHs were identified in maize genome and were positioned in eight maize chromosomes. A total of three pairs of orthologous genes were found in maize, including ZmRBOH6/ZmRBOH8, ZmRBOH4/ZmRBOH10 and ZmRBOH15/ZmRBOH2. A Ka/Ks calculation confirmed that purifying selection was the main driving force in their evolution. ZmRBOHs had typical conserved domains and similar protein structures. cis-element analyses together with the expression profiles of the ZmRBOH genes in various tissues and stages of development suggested that ZmRBOH was involved in distinct biological processes and stress responses. Based on the RNA-Seq data and qRT-PCR analysis, the transcriptional response of ZmRBOH genes was examined under various abiotic stresses, and most of ZmRBOH genes were up-regulated by cold stress. These findings provide valuable information for further revealing the biological roles of ZmRBOH genes in plant development and abiotic stress responses.

The Citrus Laccase Gene CsLAC18 Contributes to Cold Tolerance

Plant laccases, as multicopper oxidases, play an important role in monolignol polymerization, and participate in the resistance response of plants to multiple biotic/abiotic stresses. However, little is currently known about the role of laccases in the cold stress response of plants. In this study, the laccase activity and lignin content of C. sinensis leaves increased after the low-temperature treatment, and cold treatment induced the differential regulation of 21 CsLACs, with 15 genes being upregulated and 6 genes being downregulated. Exceptionally, the relative expression level of CsLAC18 increased 130.17-fold after a 48-h treatment. The full-length coding sequence of CsLAC18 consists of 1743 nucleotides and encodes a protein of 580 amino acids, and is predominantly expressed in leaves and fruits. CsLAC18 was phylogenetically related to AtLAC17, and was localized in the cell membrane. Overexpression of CsLAC18 conferred enhanced cold tolerance on transgenic tobacco; however, virus-induced gene silencing (VIGS)-mediated suppression of CsLAC18 in Poncirus trifoliata significantly impaired resistance to cold stress. As a whole, our findings revealed that CsLAC18 positively regulates a plant's response to cold stress, providing a potential target for molecular breeding or gene editing.

Arbuscular mycorrhizal fungi contribute to reactive oxygen species homeostasis of Bombax ceiba L. under drought stress

Drought stress is one of the major abiotic factors limiting plant growth and causing ecological degradation. The regulation of reactive oxygen species (ROS) generation and ROS scavenging is essential to plant growth under drought stress. To investigate the role of arbuscular mycorrhizal fungi (AMF) on ROS generation and ROS scavenging ability under drought stress in Bombax ceiba, the ROS content, the expression levels of respiratory burst oxidase homologue (Rbohs), and the antioxidant response were evaluated in AMF and NMF (non-inoculated AMF) plants under drought stress. 14 BcRboh genes were identified in the B. ceiba genome and divided into five subgroups based on phylogenetic analysis. The effect of AMF on the expression profiles of BcRbohs were different under our conditions. AMF mainly downregulated the expression of Rbohs (BcRbohA, BcRbohD, BcRbohDX2, BcRbohE, BcRbohFX1, and BcRbohI) in drought-stressed seedlings. For well-water (WW) treatment, AMF slightly upregulated Rbohs in seedlings. AMF inoculation decreased the malondialdehyde (MDA) content by 19.11 and 20.85%, decreased the O2⋅– production rate by 39.69 and 65.20% and decreased H2O2 content by 20.06 and 43.21% compared with non-mycorrhizal (NMF) plants under drought stress in root and shoot, respectively. In addition, AMF inoculation increased the non-enzymatic antioxidants glutathione (GSH) and ascorbic acid (AsA) content in roots by 153.52 and 28.18% under drought stress, respectively. The activities of antioxidant enzymes (SOD, PX, CAT, APX, GPX, GR, MDAR, and DHAR) all increased ranging from 19.47 - 131.54% due to AMF inoculation under drought stress. In conclusion, these results reveal that AMF inoculation can maintain ROS homeostasis by mitigating drought-induced ROS burst, via decreasing ROS generation and enhancing ROS scavenging ability of B. ceiba seedlings.

Identification of Respiratory Burst Oxidase Homolog (Rboh) Family Genes From Pyropia yezoensis and Their Correlation With Archeospore Release

Reactive oxygen species (ROS) play important regulatory roles in plant growth and development, as well as in cell differentiation and stress responses. Respiratory burst oxidase homolog (RBOH) is the key enzyme in ROS production. So far, the Rboh family genes in Pyropia yezoensis have not been comprehensively characterized, and whether their function was involved in the formation of archeospores is still unknown. In this study, a total of 11 PyRboh genes were identified from the P. yezoensis genome by homology mining. Through phylogenetic analysis, it is suggested that the PyRboh genes were evolutionarily conserved among the lineages of red algae, but a few genes exhibited a species-specific manner. The treatment of P. yezoensis blades with NADPH oxidase inhibitor diphenylene iodonium (DPI) could significantly inhibit the formation of archeospores, suggesting that RBOH may be involved in the formation of archeospores. According to PyRboh gene expression analysis using the P. yezoensis strains with obvious differences in releasing archeospores, it is showed that the expression trends of most genes were consistent, with no significant difference between strains, whereas the expression pattern of the two P. yezoensis-specific genes (PyRbohJ and PyRbohK) was positively correlated with the amount of archeospores. Furthermore, as treatment of blades with allantoin resulted in a significant increase in the release of archeospores, the expression levels of PyRbohJ and PyRbohK were also consistently upregulated, further confirming the relationship between the two genes and archeospore formation. These findings provide insights into the molecular mechanism of P. yezoensis archeospore formation.