Mitogen-activated protein kinase is involved in abscisic acid-induced antioxidant defense and acts downstream of reactive oxygen species production in leaves of maize plants

Integrative analysis of the transcriptome and metabolome reveals Bacillus atrophaeus WZYH01-mediated salt stress mechanism in maize (Zea mays L.)

Maize is an important food crop that is affected by salt stress during growth, which can hinder plant growth and result in a significant decrease in yield. The application of plant growth-promoting rhizobacteria can improve this situation to a certain extent. However, the gene network of rhizosphere-promoting bacteria regulating the response of maize to salt stress remains elusive. Here, we used metabolomics and transcriptomics techniques to elucidate potential gene networks and salt-response pathways in maize. Phenotypic analysis showed that the Bacillus atrophaeus treatment improved the plant height, leaf area, biomass, ion, nutrient and stomatal indicators of maize. Metabolomic analysis identified that differentially expressed metabolites (DEMs) were primarily concentrated in the arginine, proline and phytohormone signaling metabolic pathways. 4-Hydroxyphenylacetylglutamic acid, L-histidinol, oxoglutaric acid, L-glutamic acid, L-arginine, and L-tyrosine were significantly increased in the Bacillus atrophaeus treatment. Weighted gene coexpression network analysis (WGCNA) identified several hub genes associated with salt response: Zm00001eb155540 and Zm00001eb088790 (ABC transporter family), Zm00001eb419060 (extra-large GTP-binding protein family), Zm00001eb317200 (calcium-transporting ATPase), Zm00001eb384800 (aquaporin NIP1-4) and Zm00001eb339170 (cytochrome P450). Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that genes related to plant hormone signal transduction and the MAPK signaling pathway were involved in the response to the effect of Bacillus atrophaeus under salt stress. In the plant hormone signal transduction pathway, 3 differentially expressed genes (DEGs) encoding EIN3/EILs protein, 3 DEGs encoding GH3, 1 DEG encoding PYR/PYL and 6 DEGs encoding PP2C were all upregulated in Bacillus atrophaeus treatment. In the MAPK signaling pathway, 2 DEGs encoding CAT1 and 2 DEGs encoding WRKY22/WRKY29 were significantly upregulated, and the expression of DEGs encoding RbohD was downregulated by the application of Bacillus atrophaeus. In conclusion, the application of Bacillus atrophaeus under salt stress regulated key physiological and molecular processes in plants, which could stimulate the expression of genes related to ion transport and nutrients in maize, alleviate salt stress and promote maize growth to some extent, deepening our understanding of the application of Bacillus atrophaeus under salt stress to improve the salt-response gene network of maize growth.

The 14-3-3 Protein BdGF14a Increases the Transcriptional Regulation Activity of BdbZIP62 to Confer Drought and Salt Resistance in Tobacco

BdGF14a, a 14-3-3 gene from Brachypodium distachyon, induced by salt, H2O2, and abscisic acid (ABA), improved tolerance to drought and salt in tobacco, with a higher survival rate and longer roots under these stresses. Additionally, physiological index analyses showed that the heterologous expression of BdGF14a induced higher expression levels of antioxidant enzymes and their activities, leading to lighter DAB and NBT staining, denoting decreased H2O2 content. Additionally, the lower MDA content and ion leakage indicated enhanced cell membrane stability. Moreover, exogenous ABA resulted in shorter roots and a lower stomatal aperture in BdGF14a transgenic plants. BdGF14a interacted with NtABF2 and regulated the expression of stress-related genes. However, adding an ABA biosynthesis inhibitor suppressed most of these changes. Furthermore, similar salt and drought resistance phenotypes and physiological indicators were characterized in tobacco plants expressing BdbZIP62, an ABRE/ABF that interacts with BdGF14a. And Y1H and LUC assays showed that BdGF14a could enhance the transcription regulation activity of NtABF2 and BdbZIP62, targeting NtNECD1 by binding to the ABRE cis-element. Thus, BdGF14a confers resistance to drought and salinity through interaction with BdbZIP62 and enhances its transcriptional regulation activity via an ABA-mediated signaling pathway. Therefore, this work offers novel target genes for breeding salt- and drought-tolerant plants.

ROS interplay between plant growth and stress biology: Challenges and future perspectives

In plants, reactive oxygen species (ROS) have emerged as a multifunctional signaling molecules that modulate diverse stress and growth responses. Earlier studies on ROS in plants primarily focused on its toxicity and ROS-scavenging processes, but recent findings are offering new insights on its role in signal perception and transduction. Further, the interaction of cell wall receptors, calcium channels, HATPase, protein kinases, and hormones with NADPH oxidases (respiratory burst oxidase homologues (RBOHs), provides concrete evidence that ROS regulates major signaling cascades in different cellular compartments related to stress and growth responses. However, at the molecular level there are many knowledge gaps regarding how these players influence ROS signaling and how ROS regulate them during growth and stress events. Furthermore, little is known about how plant sensors or receptors detect ROS under various environmental stresses and induce subsequent signaling cascades. In light of this, we provided an update on the role of ROS signaling in plant growth and stress biology. First, we focused on ROS signaling, its production and regulation by cell wall receptor like kinases. Next, we discussed the interplay between ROS, calcium and hormones, which forms a major signaling trio regulatory network of signal perception and transduction. We also provided an overview on ROS and nitric oxide (NO) crosstalk. Furthermore, we emphasized the function of ROS signaling in biotic, abiotic and mechanical stresses, as well as in plant growth and development. Finally, we conclude by highlighting challenges and future perspectives of ROS signaling in plants that warrants future investigation.

Drought and salinity stresses induced physio-biochemical changes in sugarcane: an overview of tolerance mechanism and mitigating approaches

Sugarcane productivity is being hampered globally under changing environmental scenarios like drought and salinity. The highly complex nature of the plant responses against these stresses is determined by a variety of factors such as genotype, developmental phase of the plant, progression rate and stress, intensity, and duration. These factors influence plant responses and can determine whether mitigation approaches associated with acclimation are implemented. In this review, we attempt to summarize the effects of drought and salinity on sugarcane growth, specifically on the plant's responses at various levels, viz., physiological, biochemical, and metabolic responses, to these stresses. Furthermore, mitigation strategies for dealing with these stresses have been discussed. Despite sugarcane's complex genomes, conventional breeding approaches can be utilized in conjunction with molecular breeding and omics technologies to develop drought- and salinity-tolerant cultivars. The significant role of plant growth-promoting bacteria in sustaining sugarcane productivity under drought and salinity cannot be overlooked.

Revisiting the role of MAPK signalling pathway in plants and its manipulation for crop improvement

The mitogen-activated protein kinase (MAPK) pathway is an important signalling event associated with every aspect of plant growth, development, yield, abiotic and biotic stress adaptation. Being a central metabolic pathway, it is a vital target for manipulation for crop improvement. In this review, we have summarised recent advancements in understanding involvement of MAPK signalling in modulating abiotic and biotic stress tolerance, architecture and yield of plants. MAPK signalling cross talks with reactive oxygen species (ROS) and abscisic acid (ABA) signalling events in bringing about abiotic stress adaptation in plants. The intricate involvement of MAPK pathway with plant's pathogen defence ability has also been identified. Further, recent research findings point towards participation of MAPK signalling in shaping plant architecture and yield. These make MAPK pathway an important target for crop improvement and we discuss here various strategies to tweak MAPK signalling components for designing future crops with improved physiology and phenotypes.

Harnessing the role of mitogen-activated protein kinases against abiotic stresses in plants

Crop plants are vulnerable to various biotic and abiotic stresses, whereas plants tend to retain their physiological mechanisms by evolving cellular regulation. To mitigate the adverse effects of abiotic stresses, many defense mechanisms are induced in plants. One of these mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signaling pathway used in the transduction of extracellular stimuli into intercellular responses. This stress signaling pathway is activated by a series of responses involving MAPKKKs→MAPKKs→MAPKs, consisting of interacting proteins, and their functions depend on the collaboration and activation of one another by phosphorylation. These proteins are key regulators of MAPK in various crop plants under abiotic stress conditions and also related to hormonal responses. It is revealed that in response to stress signaling, MAPKs are characterized as multigenic families and elaborate the specific stimuli transformation as well as the antioxidant regulation system. This pathway is directed by the framework of proteins and stopping domains confer the related associates with unique structure and functions. Early studies of plant MAPKs focused on their functions in model plants. Based on the results of whole-genome sequencing, many MAPKs have been identified in plants, such as Arbodiposis, tomato, potato, alfalfa, poplar, rice, wheat, maize, and apple. In this review, we summarized the recent work on MAPK response to abiotic stress and the classification of MAPK cascade in crop plants. Moreover, we highlighted the modern research methodologies such as transcriptomics, proteomics, CRISPR/Cas technology, and epigenetic studies, which proposed, identified, and characterized the novel genes associated with MAPKs and their role in plants under abiotic stress conditions. In-silico-based identification of novel MAPK genes also facilitates future research on MAPK cascade identification and function in crop plants under various stress conditions.

Nicosulfuron stress on the glyoxalase system and endogenous hormone content in sweet maize seedlings

To reduce the harmful effects of nicosulfuron on sweet corn, the physiological regulation mechanism of sweet corn detoxification was studied. This study analyzed the effects of nicosulfuron stress on the glyoxalase system, hormone content, and key gene expression of nicosulfuron-tolerant "HK301" and nicosulfuron-sensitive "HK320" sweet corn seedling sister lines. After spraying nicosulfuron, the methylglyoxal (MG) content in HK301 increased first and then decreased. Glyoxalase I (GlyI) and glyoxalase II (GlyII) activities, non-enzymatic glutathione (GSH), and the glutathione redox state glutathione/(glutathione + glutathione disulfide) (GSH/(GSH + GSSG)) showed a similar trend as the MG content. Abscisic acid (ABA), gibberellin (GA), and zeatin nucleoside (ZR) also increased first and then decreased, whereas the auxin (IAA) increased continuously. In HK301, all indices after spraying nicosulfuron were significantly greater than those of the control. In HK320, MG accumulation continued to increase after nicosulfuron spraying and GlyI and GlyII activities, and GSH first increased and then decreased after 1 day of stress. The indicators above were significantly greater than the control. The GSH/(GSH + GSSG) ratio showed a decreasing trend and was significantly smaller than the control. Furthermore, ABA and IAA continued to increase, and the GA and ZR first increased and then decreased. Compared with HK320, HK301 significantly upregulated the transcription levels of GlyI and GlyII genes in roots, stems, and leaves. Comprehensive analysis showed that sweet maize seedlings improved their herbicide resistance by changing the glyoxalase system and regulating endogenous hormones. The results provide a theoretical basis for further understanding the response mechanism of the glyoxalase system and the regulation characteristics of endogenous hormones in maize under nicosulfuron stress.

MKKK20 works as an upstream triple-kinase of MKK3-MPK6-MYC2 module in Arabidopsis seedling development

The mitogen-activated protein kinase (MAPK) cascade is involved in several signal transduction processes in eukaryotes. Here, we report a mechanistic function of MAP kinase kinase kinase 20 (MKKK20) in light signal transduction pathways. We show that MKKK20 acts as a negative regulator of photomorphogenic growth at various wavelengths of light. MKKK20 not only regulates the expression of light signaling pathway regulatory genes but also gets regulated by the same pathway genes. The atmyc2 mkkk20 double mutant analysis shows that MYC2 works downstream to MKKK20 in the regulation of photomorphogenic growth. MYC2 directly binds to the promoter of MKKK20 to modulate its expression. The protein-protein interaction study indicates that MKKK20 physically interacts with MYC2, and this interaction likely suppresses the MYC2-mediated promotion of MKKK20 expression. Further, the protein phosphorylation studies demonstrate that MKKK20 works as the upstream kinase of MKK3-MPK6-MYC2 module in photomorphogenesis.

Exogenous SA Applications Alleviate Salinity Stress via Physiological and Biochemical changes in St John's Wort Plants

The plant St. John's wort contains high levels of melatonin, an important biochemical that has both beneficial and adverse effects on stress. Therefore, a method for increasing melatonin levels in plants without adversely affecting their growth is economically important. In this study, we investigated the regulation of melatonin levels in St. John's wort by exposing samples to salinity stress (150 mM) and salicylic acid (0.25 mM) to augment stress tolerance. The results indicated that salinity stress significantly reduced the plant chlorophyll content and damaged the photosystem, plant growth and development. Additionally, these were reconfirmed with biochemical indicators; the levels of abscisic acid (ABA) and proline were increased and the activities of antioxidants were reduced. However, a significant increase was found in melatonin content under salinity stress through upregulation in the relative expression of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), and N-acetylserotonin methyltransferase (ASMT). The salicylic acid (SA) treatment considerably improved their photosynthetic activity, the maximum photochemical quantum yield (133%), the potential activity of PSⅡ (294%), and the performance index of electron flux to the final PS I electron acceptors (2.4%). On the other hand, SA application reduced ABA levels (32%); enhanced the activity of antioxidant enzymes, such as superoxide dismutase (SOD) (15.4%) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) (120%); and increased polyphenol (6.4%) and flavonoid (75.4%) levels in salinity-stressed St. John's wort plants. Similarly, SA application under NaCl stress significantly modulated the melatonin content in terms of ion balance; the level of melatonin was reduced after SA application on salt-treated seedlings but noticeably higher than on only SA-treated and non-treated seedlings. Moreover, the proline content was reduced considerably and growth parameters, such as plant biomass, shoot length, and chlorophyll content, were enhanced following treatment of salinity-stressed St. John's wort plants with salicylic acid. These findings demonstrate the beneficial impact of salt stress in terms of a cost-effective approach to extract melatonin in larger quantities from St. John's wort. They also suggest the efficiency of salicylic acid in alleviating stress tolerance and promoting growth of St. John's wort plants.

Dimethylthiourea Alleviates Drought Stress by Suppressing Hydrogen Peroxide-Dependent Abscisic Acid-Mediated Oxidative Responses in an Antagonistic Interaction with Salicylic Acid in Brassica napus Leaves

In plants, prolonged drought induces oxidative stress, leading to a loss of reducing potential in redox components. Abscisic acid (ABA) is a representative hormonal signal regulating stress responses. This study aimed to investigate the physiological significance of dimethylthiourea (DMTU, an H₂O₂ scavenger) in the hormonal regulation of the antioxidant system and redox control in rapeseed (Brassica napus L.) leaves under drought stress. Drought treatment for 10 days provoked oxidative stress, as evidenced by the increase in O₂^•- and H₂O₂ concentrations, and lipid peroxidation levels, and a decrease in leaf water potential. Drought-induced oxidative responses were significantly alleviated by DMTU treatment. The accumulation of O₂^•- and H₂O₂ in drought-treated plants coincided with the enhanced expression of the NADPH oxidase and Cu/Zn-SOD genes, leading to an up-regulation in oxidative signal-inducible 1 (OXI1) and mitogen-activated protein kinase 6 (MAPK6), with a concomitant increase in ABA levels and the up-regulation of ABA-related genes. DMTU treatment under drought largely suppressed the drought-responsive up-regulation of these genes by depressing ABA responses through an antagonistic interaction with salicylic acid (SA). DMTU treatment also alleviated the drought-induced loss of reducing potential in GSH- and NADPH-based redox by the enhanced expression of glutathione reductase 1 (GR1) and up-regulation of oxidoreductase genes (TRXh5 and GRXC9). These results indicate that DMTU effectively alleviates drought-induced oxidative responses by suppressing ABA-mediated oxidative burst signaling in an antagonistic regulation of SA.

Cellular messengers involved in the inhibition of the Arabidopsis primary root growth by bacterial quorum-sensing signal N-decanoyl-L-homoserine lactone

BACKGROUND

N-acyl-homoserine lactones (AHLs) are used as quorum-sensing signals by Gram-negative bacteria, but they can also affect plant growth and disease resistance. N-decanoyl-L-homoserine lactone (C10-HSL) is an AHL that has been shown to inhibit primary root growth in Arabidopsis, but the mechanisms underlying its effects on root architecture are unclear. Here, we investigated the signaling components involved in C10-HSL-mediated inhibition of primary root growth in Arabidopsis, and their interplay, using pharmacological, physiological, and genetic approaches.

RESULTS

Treatment with C10-HSL triggered a transient and immediate increase in the concentrations of cytosolic free Ca²⁺ and reactive oxygen species (ROS), increased the activity of mitogen-activated protein kinase 6 (MPK6), and induced nitric oxide (NO) production in Arabidopsis roots. Inhibitors of Ca²⁺ channels significantly alleviated the inhibitory effect of C10-HSL on primary root growth and reduced the amounts of ROS and NO generated in response to C10-HSL. Inhibition or scavenging of ROS and NO neutralized the inhibitory effect of C10-HSL on primary root growth. In terms of primary root growth, the respiratory burst oxidase homolog mutants and a NO synthase mutant were less sensitive to C10-HSL than wild type. Activation of MPKs, especially MPK6, was required for C10-HSL to inhibit primary root growth. The mpk6 mutant showed reduced sensitivity of primary root growth to C10-HSL, suggesting that MPK6 plays a key role in the inhibition of primary root growth by C10-HSL.

CONCLUSION

Our results indicate that MPK6 acts downstream of ROS and upstream of NO in the response to C10-HSL. Our data also suggest that Ca²⁺, ROS, MPK6, and NO are all involved in the response to C10-HSL, and may participate in the cascade leading to C10-HSL-inhibited primary root growth in Arabidopsis.

Abscisic Acid Signaling in the Regulation of Postharvest Physiological Deterioration of Sliced Cassava Tuberous Roots

Phytohormone abscisic acid (ABA) influences the shelf life of fruit, vegetables, and tubers after harvest. However, little is known about the core signaling module involved in ABA's control of the postharvest physiological process. Exogenous ABA alleviated postharvest physiological deterioration (PPD) symptoms of sliced cassava tuberous roots, increased endogenous ABA levels, and reduced endogenous H₂O₂ content. The specific ABA signaling module during the PPD process was identified as MePYL6-MePP2C16-MeSnRK2.1-MebZIP5/34. MebZIP5/MebZIP34 directly binds to and activates the promoters of MeGRX6/MeMDAR1 through ABRE elements. Exogenous ABA significantly induced the expression of genes involved in this module, glutaredoxin content, and monodehydroascorbate reductase activity. We presented a hypothesis suggesting that MePYL6-MePP2C16-MeSnRK2.1-MebZIP5/34-MeGRX6/MeMDAR1 is involved in ABA-induced antioxidative capacity, thus alleviating PPD symptoms in cassava tuberous roots. The identification of the specific signaling module involved in ABA's control of PPD provides a basis and potential targets for extending the shelf life of cassava tuberous roots.

Cold-Induced Nuclear Import of CBF4 Regulates Freezing Tolerance

C-repeat binding factors (CBFs) are crucial transcriptional activators in plant responses to low temperature. CBF4 differs in its slower, but more persistent regulation and its role in cold acclimation. Cold acclimation has accentuated relevance for tolerance to late spring frosts as they have become progressively more common, as a consequence of blurred seasonality in the context of global climate change. In the current study, we explore the functions of CBF4 from grapevine, VvCBF4. Overexpression of VvCBF4 fused to GFP in tobacco BY-2 cells confers cold tolerance. Furthermore, this protein shuttles from the cytoplasm to the nucleus in response to cold stress, associated with an accumulation of transcripts for other CBFs and the cold responsive gene, ERD10d. This response differs for chilling as compared to freezing and is regulated differently by upstream signalling involving oxidative burst, proteasome activity and jasmonate synthesis. The difference between chilling and freezing is also seen in the regulation of the CBF4 transcript in leaves from different grapevines differing in their cold tolerance. Therefore, we propose the quality of cold stress is transduced by different upstream signals regulating nuclear import and, thus, the transcriptional activation of grapevine CBF4.

De novo transcriptome analysis of high-salinity stress-induced antioxidant activity and plant phytohormone alterations in Sesuvium portulacastrum

Sesuvium portulacastrum has a strong salt tolerance and can grow in saline and alkaline coastal and inland habitats. This study investigated the physiological and molecular responses of S. portulacastrum to high salinity by analyzing the changes in plant phytohormones and antioxidant activity, including their differentially expressed genes (DEGs) under similar high-salinity conditions. High salinity significantly affected proline (Pro) and hydrogen peroxide (H2O2) in S. portulacastrum seedlings, increasing Pro and H2O2 contents by 290.56 and 83.36%, respectively, compared to the control. Antioxidant activities, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), significantly increased by 83.05, 205.14, and 751.87%, respectively, under high salinity. Meanwhile, abscisic acid (ABA) and gibberellic acid (GA3) contents showed the reverse trend of high salt treatment. De novo transcriptome analysis showed that 36,676 unigenes were matched, and 3,622 salt stress-induced DEGs were identified as being associated with the metabolic and biological regulation processes of antioxidant activity and plant phytohormones. POD and SOD were upregulated under high-salinity conditions. In addition, the transcription levels of genes involved in auxin (SAURs and GH3), ethylene (ERF1, ERF3, ERF114, and ABR1), ABA (PP2C), and GA3 (PIF3) transport or signaling were altered. This study identified key metabolic and biological processes and putative genes involved in the high salt tolerance of S. portulacastrum and it is of great significance for identifying new salt-tolerant genes to promote ecological restoration of the coastal strand.

SlHSP17.7 Ameliorates Chilling Stress-Induced Damage by Regulating Phosphatidylglycerol Metabolism and Calcium Signal in Tomato Plants

Tomatoes (Solanum lycopersicum L.) are sensitive to chilling temperatures between 0 °C and 12 °C owing to their tropical origin. SlHSP17.7, a cytoplasmic heat shock protein, interacts with cation/calcium exchanger 1-like (SlCCX1-like) protein and promotes chilling tolerance in tomato fruits (Zhang, et al., Plant Sci., 2020, 298, 1-12). The overexpression of SlHSP17.7 can also promote cold tolerance in tomato plants, but its specific mechanism remains unclear. In this study, we show that the overexpression of SlHSP17.7 in tomato plants enhances chilling tolerance with better activity of photosystem II (PSII). Metabolic analyses revealed that SlHSP17.7 improved membrane fluidity by raising the levels of polyunsaturated fatty acids. Transcriptome analyses showed that SlHSP17.7 activated Ca2+ signaling and induced the expression of C-repeat binding factor (CBF) genes, which in turn inhibited the production of reactive oxygen species (ROS). The gene coexpression network analysis showed that SlHSP17.7 is coexpressed with SlMED26b. SlMED26b silencing significantly lowered OE-HSP17.7 plants' chilling tolerance. Thus, SlHSP17.7 modulates tolerance to chilling via both membrane fluidity and Ca2+-mediated CBF pathway in tomato plants.

Mitogen-Activated Protein Kinase Is Involved in Salt Stress Response in Tomato (Solanum lycopersicum) Seedlings

Salt stress impairs plant growth and development, thereby causing low yield and inferior quality of crops. In this study, tomato (Solanum lycopersicum L. ‘Micro-Tom’) seedlings treated with different concentrations of sodium chloride (NaCl) were investigated in terms of decreased plant height, stem diameter, dry weight, fresh weight, leaves relative water content and root activity. To reveal the response mechanism of tomato seedlings to salt stress, the transcriptome of tomato leaves was conducted. A total of 6589 differentially expressed genes (DEGs) were identified and classified into different metabolic pathways, especially photosynthesis, carbon metabolism, biosynthesis of amino acids and mitogen-activated protein kinase (MAPK) signaling pathway. Of these, approximately 42 DEGs were enriched in the MAPK signaling pathway, most of which mainly included plant hormone, hydrogen peroxide (H₂O₂), wounding and pathogen infection signaling pathways. To further explore the roles of MAPK under salt stress, MAPK phosphorylation inhibitor SB203580 (SB) was applied. We found that SB further decreased endogenous jasmonic acid, abscisic acid and ethylene levels under salt stress condition. Additionally, in comparison with NaCl treatment alone, SB + NaCl treatment reduced the content of O²⁻ and H₂O₂ and the activities of antioxidant enzyme and downregulated the expression levels of genes related to pathogen infection. Together, the results revealed that MAPK might be involved in the salinity response of tomato seedlings by regulating hormone balance, ROS metabolism, antioxidant capacity and plant immunity.

OsDMI3-mediated OsUXS3 phosphorylation improves oxidative stress tolerance by modulating OsCATB protein abundance in rice

Calcium (Ca²⁺ )/calmodulin (CaM)-dependent protein kinase (CCaMK) is an important positive regulator of antioxidant defenses and tolerance against oxidative stress. However, the underlying molecular mechanisms are largely unknown. Here, we report that the rice (Oryza sativa) CCaMK (OsDMI3) physically interacts with and phosphorylates OsUXS3, a cytosol-localized UDP-xylose synthase. Genetic and biochemical evidence demonstrated that OsUXS3 acts downstream of OsDMI3 to enhance the oxidative stress tolerance conferred by higher catalase (CAT) activity. Indeed, OsUXS3 interacted with CAT isozyme B (OsCATB), and this interaction was required to increase OsCATB protein abundance under oxidative stress conditions. Furthermore, we showed that OsDMI3 phosphorylates OsUXS3 on residue Ser-245, thereby further promoting the interaction between OsUXS3 and OsCATB. Our results indicate that OsDMI3 promotes the association of OsUXS3 with OsCATB to enhance CAT activity under oxidative stress. These findings reveal OsUXS3 as a direct target of OsDMI3 and demonstrate its involvement in antioxidant defense.

Metabolic Pathway of Natural Antioxidants, Antioxidant Enzymes and ROS Providence

Based on the origin, we can classify different types of stress. Environmental factors, such as high light intensity, adverse temperature, drought, or soil salinity, are summarized as abiotic stresses and discriminated from biotic stresses that are exerted by pathogens and herbivores, for instance. It was an unexpected observation that overproduction of reactive oxygen species (ROS) is a common response to all kinds of stress investigated so far. With respect to applied aspects in agriculture and crop breeding, this observation allows using ROS production as a measure to rank the stress perception of individual plants. ROS are important messengers in cell signaling, but exceeding a concentration threshold causes damage. This requires fine-tuning of ROS production and degradation rates. In general, there are two options to control cellular ROS levels, (I) ROS scavenging at the expense of antioxidant consumption and (II) enzyme-controlled degradation of ROS. As antioxidants are limited in quantity, the first strategy only allows temporarily buffering of a certain cellular ROS level. This way, it prevents spells of eventually damaging ROS concentrations. In this review, we focus on the second strategy. We discuss how enzyme-controlled degradation of ROS integrates into plant metabolism. Enzyme activities can be continuously operative. Cellular homeostasis can be achieved by regulation of respective gene expression and subsequent regulation of the enzyme activities. A better understanding of this interplay allows for identifying traits for stress tolerance breeding of crops. As a side effect, the result also may be used to identify cultivation methods modifying crop metabolism, thus resulting in special crop quality.

RNA-seq profiling of primary calli induced by different media and photoperiods for japonica rice 'Yunyin'

The induction of embryogenic calli plays a vital role in the genetic transformation and regeneration of rice (Oryza sativa L.). Despite progress in rice tissue culture, the molecular mechanisms of embryogenic callus induction remain unknown. In this study, gene expression profiles associated with calli were comprehensively analyzed during callus induction of japonica rice 'Yunyin'. We first confirmed that NMB medium with 24 h of light and 0 h of dark (NMB-L) was the optimal condition for 'Yunyin' callus induction, while J3 medium with 0 h of light and 24 h of dark (J3-D) was the worst condition. After transcriptome analysis, 33,597 unigenes were assembled, among which we identified 6,063 DEGs (Differentially Expressed Genes) related to media and seven DEGs related to photoperiod. Phenylpropanoid biosynthesis, plant hormone signal, and starch and sucrose metabolism were the top three pathways affected by media, while the circadian rhythm-plant pathway was associated with photoperiod. Furthermore, we identified two candidate genes, Os01g0965900 and Os12g0555200, affected by both medium and photoperiod. Statistical analysis of RNA-seq libraries showed that the expression levels of these two genes in J3-D calli were over 2.5 times higher than those in NMB-L calli, which was further proved by RT-qPCR analysis. Based on FPKM (Fragments Per Kilobase of transcript Per Million mapped reads), unigenes belonging to the NMB-L group were mainly assigned to ribosome, carbon metabolism, biosynthesis of amino acids, protein processing in endoplasmic reticulum, and plant hormone signal transduction pathways. We transformed Os12g0555200Nip and Os12g05552009311 into 'Nipponbare' calli and observed their effects on the growth and development process of rice calli using TEM (Transmission Electron Microscopy) and SEM (Scanning Electron Microscopy). Observations showed that Os12g05552009311 was more disadvantageous to rice callus growth than Os12g0555200Nip. Our results reveal that the Os12g0555200, identified from transcriptomic profiles, has a negative influence during 'Yunyin' callus induction.

Supplementary information

The online version contains supplementary material available at 10.1007/s11032-022-01283-y.

MAPK5 and MAPK10 overexpression influences strawberry fruit ripening, antioxidant capacity and resistance to Botrytis cinerea

FaMAPK5 and FaMAPK10 genes were involved in ABA-mediated strawberry fruit ripening and could enhance the antioxidant capacity by increasing non-enzymatic components and enzymatic antioxidants. Mitogen-activated protein kinases (MAPKs) are the key proteins involved in plant stress response by activating an antioxidant defense system, which cooperates with plant hormones. However, the involvement of MAPKs in the regulation of strawberry fruit ripening and resistance is unclear. In this study, two genes, FaMAPK5 and FaMAPK10, were isolated, and their expression pattern and function analysis were conducted. The results showed FaMAPK5 and FaMAPK10 were expressed in all tested tissue/organ types and reached the highest expression level at the white stage during strawberry fruit development and ripening. Transient overexpression of FaMAPK5 and FaMAPK10 increased the fruit anthocyanin, abscisic acid (ABA), total sugar, and glucose contents. ABA and especially hydrogen peroxide (H₂O₂) treatment induced the production of large amounts of H₂O₂ and noticeably increased the expression levels of FaMAPK5 and FaMAPK10 in strawberry fruit, while the reduced glutathione (GSH) had the opposite effect. The level of total phenol and activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) significantly increased in FaMAPK5 overexpression fruit, and increased activities of SOD and CAT were observed in FaMAPK10 overexpression fruit. In addition, Botrytis cinerea treatment showed that overexpression of FaMAPK5 conferred retarded disease symptom development and enhanced fruit disease resistance. Our research revealed that FaMAPK5 and FaMAPK10 might participate in ABA-mediated H₂O₂ signaling in regulating strawberry fruit ripening and resistance.

Detoxification of phenanthrene in Arabidopsis thaliana involves a Dioxygenase For Auxin Oxidation 1 (AtDAO1)

Polycyclic aromatic hydrocarbon (PAH) contamination has a negative impact on ecosystems. PAHs are a large group of toxins with two or more benzene rings that are persistent in the environment. Some PAHs can be cytotoxic, teratogenic, and/or carcinogenic. In the bacterium Pseudomonas, PAHs can be modified by dioxygenases, which increase the reactivity of PAHs. We hypothesize that some plant dioxygenases are capable of PAH biodegradation. Herein, we investigate the involvement of Arabidopsis thaliana At1g14130 in the degradation of phenanthrene, our model PAH. The At1g14130 gene encodes Dioxygenase For Auxin Oxidation 1 (AtDAO1), an enzyme involved in the oxidative inactivation of the hormone auxin. Expression analysis using a β-glucuronidase (GUS) reporter revealed that At1g14130 is prominently expressed in new leaves of plants exposed to media with phenanthrene. Analysis of the oxidative state of gain-of-function mutants showed elevated levels of H₂O₂ after phenanthrene treatments, probably due to an increase in the oxidation of phenanthrene by AtDAO1. Biochemical assays with purified AtDAO1 and phenanthrene suggest an enzymatic activity towards the PAH. Thus, data presented in this study support the hypothesis that an auxin dioxygenase, AtDAO1, from Arabidopsis thaliana contributes to the degradation of phenanthrene and that there is possible toxic metabolite accumulation after PAH exposure.

Overexpression of Cu/Zn Superoxide Dismutase (Cu/Zn SOD) in Synechococcus elongatus PCC 7942 for Enhanced Azo Dye Removal through Hydrogen Peroxide Accumulation

Discharge of recalcitrant azo dyes to the environment poses a serious threat to environmental health. However certain microorganisms in nature have developed their survival strategies by degrading these toxic dyes. Cyanobacteria are one such prokaryotic, photosynthetic group of microorganisms that degrade various xenobiotic compounds, due to their capability to produce various reactive oxygen species (ROS), and particularly the hydrogen peroxide (H2O2) when released in their milieu. The accumulation of H2O2 is the result of the dismutation of superoxide radicals by the enzyme superoxide dismutase (SOD). In this study, we have genetically modified the cyanobacterium Synechococcus elongatus PCC 7942 by integrating Cu/Zn SOD gene (sodC) from Synechococcus sp. PCC 9311 to its neutral site through homologous recombination. The overexpression of sodC in the derivative strain was driven using a strong constitutive promoter of the psbA gene. The derivative strain resulted in constitutive production of sodC, which was induced further during dye-treated growth. The genetically engineered Synechococcus elongatus PCC 7942 (MS-sodC+) over-accumulated H2O2 during azo dye treatment with a higher dye removal rate than the wild-type strain (WS-sodC-). Therefore, enhanced H2O2 accumulation through SODs overexpression in cyanobacteria may serve as a valuable bioremediation tool.

How do rice seedlings of landrace Pokkali survive in saline fields after transplantation? Physiology, biochemistry, and photosynthesis

Rice, one of the most important staple food crops in the world, is highly sensitive to soil salinity at the seedling stage. The ultimate yield of this crop is a function of the number of seedlings surviving after transplantation in saline water. Oryza sativa cv. IR64 is a high-yielding salinity-sensitive variety, while Pokkali is a landrace traditionally cultivated by the local farmers in the coastal regions in India. However, the machinery responsible for the seedling-stage tolerance in Pokkali is not understood. To bridge this gap, we subjected young seedlings of these contrasting genotypes to salinity and performed detailed investigations about their growth parameters, ion homeostasis, biochemical composition, and photosynthetic parameters after every 24 h of salinity for three days. Taken together, all the physiological and biochemical indicators, such as proline accumulation, K⁺/Na⁺ ratio, lipid peroxidation, and electrolyte leakage, clearly revealed significant differences between IR64 and Pokkali under salinity, establishing their contrasting nature at this stage. In response to salinity, the F_v/F_m ratio (maximum quantum efficiency of Photosystem II as inferred from Chl a fluorescence) and the energy conserved for the electron transport after the reduction of Q_A (the primary electron acceptor of PSII), to Q_A^-, and reduction of the end electron acceptor molecules towards the PSI (Photosystem I) electron acceptor side was higher in Pokkali than IR64 plants. These observations reflect a direct contribution of photosynthesis towards seedling-stage salinity tolerance in rice. These findings will help to breed high-yielding crops for salinity prone agricultural lands.

ZmMPK5 phosphorylates ZmNAC49 to enhance oxidative stress tolerance in maize

Mitogen-activated protein kinase (MPK) is a critical regulator of the antioxidant defence system in response to various stimuli. However, how MPK directly and exactly regulates antioxidant enzyme activities is still unclear. Here, we demonstrated that a NAC transcription factor ZmNAC49 mediated the regulation of antioxidant enzyme activities by ZmMPK5. ZmNAC49 expression is induced by oxidative stress. ZmNAC49 enhances oxidative stress tolerance in maize, and it also reduces superoxide anion generation and increases superoxide dismutase (SOD) activity. A detailed study showed that ZmMPK5 directly interacts with and phosphorylates ZmNAC49 in vitro and in vivo. ZmMPK5 directly phosphorylates Thr-26 in NAC subdomain A of ZmNAC49. Mutation at Thr-26 of ZmNAC49 does not affect the interaction with ZmMPK5 and its subcellular localisation. Further analysis found that ZmNAC49 activates the ZmSOD3 expression by directly binding to its promoter. ZmMPK5-mediated ZmNAC49 phosphorylation improves its ability to bind to the ZmSOD3 promoter. Thr-26 of ZmNAC49 is essential for its transcriptional activity. In addition, ZmSOD3 enhances oxidative stress tolerance in maize. Our results show that phosphorylation of Thr-26 in ZmNAC49 by ZmMPK5 increased its DNA-binding activity to the ZmSOD3 promoter, enhanced SOD activity and thereby improved oxidative stress tolerance in maize.

In-silico genome wide analysis of Mitogen activated protein kinase kinase kinase gene family in C. sinensis

Mitogen activated protein kinase kinase kinase (MAPKKK) form the upstream component of MAPK cascade. It is well characterized in several plants such as Arabidopsis and rice however the knowledge about MAPKKKs in tea plant is largely unknown. In the present study, MAPKKK genes of tea were obtained through a genome wide search using Arabidopsis thaliana as the reference genome. Among 59 candidate MAPKKK genes in tea, 17 genes were MEKK-like, 31 genes were Raf-like and 11 genes were ZIK- like. Additionally, phylogenetic relationships were established along with structural analysis, which includes gene structure, its location as well as conserved motifs, cis-acting regulatory elements and functional domain signatures that were systematically examined. Also, on the basis of one orthologous gene found between tea and Arabidopsis, functional interaction was carried out in C. sinensis based on an Arabidopsis association model. The expressional profiles indicated major involvement of MAPKKK genes from tea in response to various abiotic stress factors. Taken together, this study provides the targets for additional inclusive identification, functional study, and provides comprehensive knowledge for a better understanding of the MAPKKK cascade regulatory network in C. sinensis.

Physiological and transcriptomic analysis of Cabernet Sauvginon (Vitis vinifera L.) reveals the alleviating effect of exogenous strigolactones on the response of grapevine to drought stress

Drought stress can significantly affect the growth and yield of grapevine. The application of exogenous strigolactone can relieve the drought symptoms of grapevine; however, little is known about the transcription levels in grapevine under drought stress following exogenous strigolactone application. The mitigative effect of exogenous strigolactone on grapevine leaves under drought stress was studied by transcriptome analysis based on RNA sequencing. On the 10th day of drought stress, the strigolactone treatment group had a higher relative water content and lower electrical conductivity, which significantly alleviated the drought damage. Compared to the drought (D) group, a total of 5955 differentially expressed genes (DEGs) (2966 up-regulated genes and 2989 down-regulated genes) were detected in the exogenous strigolactone (DG) groups. Based on Gene Ontology analysis, the DEGs in the D and DG treatments were enriched in the processes of photosynthesis and organic acid catabolism. Pathway analysis showed that the DEGs in the D and DG treatments were enriched in carbon metabolism, ribosome, starch and sucrose metabolism, flavonoid biosynthesis, and circadian rhythm. Additionally, in the DG group, the antioxidant enzyme genes of CAT1, GSHPX1, GSHPX2, POD42, APX6, and SODCP were up-regulated, two NAC, three WRKY, and four MYB transcription factor genes were down-regulated, and the key gene of strigolactone synthesis D14 was up-regulated, compared with that in the D group. The results provide a new perspective for studying the adaptation of plants to drought stress.

A Method for Assaying of Protein Kinase Activity In Vivo and Its Use in Studies of Signal Transduction in Strawberry Fruit Ripening

Strawberry (Fragaria × ananassa) fruit ripening is regulated by a complex of cellular signal transduction networks, in which protein kinases are key components. Here, we report a relatively simple method for assaying protein kinase activity in vivo and specifically its application to study the kinase, FaMPK6, signaling in strawberry fruit. Green fluorescent protein (GFP)-tagged FaMPK6 was transiently expressed in strawberry fruit and after stimuli were applied to the fruit it was precipitated using an anti-GFP antibody. The precipitated kinase activity was measured in vitro using ³²P-ATP and myelin basic protein (MBP) as substrates. We also report that FaMPK6 is not involved in the abscisic acid (ABA) signaling cascade, which is closely associated with FaMPK6 signaling in other plant species. However, methyl jasmonate (MeJA), low temperature, and high salt treatments were all found to activate FaMPK6. Transient manipulation of FaMPK6 expression was observed to cause significant changes in the expression patterns of 2749 genes, of which 264 were associated with MeJA signaling. The data also suggest a role for FaMPK6 in modulating cell wall metabolism during fruit ripening. Taken together, the presented method is powerful and its use will contribute to a profound exploration to the signaling mechanism of strawberry fruit ripening.

ZmWRKY104 Transcription Factor Phosphorylated by ZmMPK6 Functioning in ABA-Induced Antioxidant Defense and Enhance Drought Tolerance in Maize

Simple Summary

Current knowledge about the downstream substrate proteins of MAPKs is still limited. Our study screened a new WRKY IIa transcription factor as the substrate protein of ZmMPK6, and its phosphorylation at Thr-59 is critical to the role of ZmWRKY104 in ABA-induced antioxidant defense. Moreover, overexpression ZmWRKY104 in maize enhances the drought tolerance of transgenic plants. These findings define a mechanism for the function of ZmWRKY104 phosphorylated by ZmMPK6 in ABA-induced antioxidant defense and drought tolerance.

Abstract

Mitogen-activated protein kinase (MAPK) cascades are primary signaling pathways involved in various signaling pathways triggered by abiotic and biotic stresses in plants. The downstream substrate proteins of MAPKs in maize, however, are still limited. Here, we screened a WRKY IIa transcription factor (TF) in maize (Zeamays L.), ZmWRKY104, and found that it is a substrate of ZmMPK6. ZmWRKY104 physically interacts with ZmMPK6 in vitro and in vivo. Liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis results showed that threonine-59 (Thr-59, T59) was the major phosphorylation site of ZmWRKY104 by ZmMPK6. Subcellular localization analysis suggested that ZmWRKY104 acts in the nucleus and that ZmMPK6 acts in the nucleus and cytoplasmic membrane in the cytosol. Functional analysis revealed that the role of ZmWRKY104 in ABA-induced antioxidant defense depends on ZmMPK6. Moreover, overexpression of ZmWRKY104 in maize can enhance drought tolerance and relieve drought-induced oxidative damage in transgenic lines. The above results help define the mechanism of the function of ZmWRKY104 phosphorylated by ZmMPK6 in ABA-induced antioxidant defense and drought tolerance in maize.

Cross-Talk between Hydrogen Peroxide and Nitric Oxide during Plant Development and Responses to Stress

Nitric oxide (NO) and hydrogen peroxide (H₂O₂) are gradually becoming established as critical regulators in plants under physiological and stressful conditions. Strong spatiotemporal correlations in their production and distribution have been identified in various plant biological processes. In this context, NO and H₂O₂ act synergistically or antagonistically as signals or stress promoters depending on their respective concentrations, engaging in processes such as the hypersensitive response, stomatal movement, and abiotic stress responses. Moreover, proteins identified as potential targets of NO-based modifications include a number of enzymes related to H₂O₂ metabolism, reinforcing their cross-talk. In this review, several processes of well-characterized functional interplay between H₂O₂ and NO are discussed with respect to the most recent reported evidence on hypersensitive response-induced programmed cell death, stomatal movement, and plant responses to adverse conditions and, where known, the molecular mechanisms and factors underpinning their cross-talk.

BRASSINOSTEROID-SIGNALING KINASE 1 phosphorylating CALCIUM/CALMODULIN-DEPENDENT PROTEIN KINASE functions in drought tolerance in maize

Drought stress seriously limits crop productivity. Although studies have been carried out, it is still largely unknown how plants respond to drought stress. Here we find that drought treatment can enhance the phosphorylation activity of brassinosteroid-signaling kinase 1 (ZmBSK1) in maize (Zea mays). Our genetic studies reveal that ZmBSK1 positively affects drought tolerance in maize plants. ZmBSK1 localizes in plasma membrane, interacts with calcium/calmodulin (Ca²⁺ /CaM)-dependent protein kinase (ZmCCaMK), and phosphorylates ZmCCaMK. Ser-67 is a crucial phosphorylation site of ZmCCaMK by ZmBSK1. Drought stress enhances not only the interaction between ZmBSK1 and ZmCCaMK but also the phosphorylation of Ser-67 in ZmCCaMK by ZmBSK1. Furthermore, Ser-67 phosphorylation in ZmCCaMK regulates its Ca²⁺ /CaM binding, autophosphorylation and transphosphorylation activity, and positively affects its function in drought tolerance in maize. Our results reveal an important role for ZmBSK1 in drought tolerance and suggest a direct regulatory mode of ZmBSK1 phosphorylating ZmCCaMK.

Degradation of mitochondrial structure and deficiency of complex I were associated with the transgenic CMS of rice

BACKGROUND

Mitochondria play a significant role in plant cytoplasmic male sterility (CMS). In our previous study, mitochondrial complex I genes, nad4, nad5, and nad7 showed polymorphisms between the transgenic CMS line M2BS and its wild type M2B. The sterility mechanism of the M2BS at cytological, physiological, biochemical, and molecular level is not clear.

RESULTS

Cytological observation showed that the anthers were light yellow, fissured, invalid in KI-I2, and full of irregularly typical abortion pollen grains in M2BS. Transmission electron microscopic (TEM) observation revealed no nucleus and degraded mitochondria with obscure cristae in anther cells of M2BS. The results of staining for H2O2 presented a large number of electron dense precipitates (edp) in intercellular space of anther cells of M2BS at anthesis. Moreover, the anther respiration rate and complex I activity of M2BS were significantly lower than those of wild type M2B during pollen development. Furthermore, RNA editing results showed only nad7 presented partially edited at 534th nucleotides. The expression of nad5 and nad7 revealed significant differences between M2B and M2BS.

CONCLUSIONS

Our data demonstrated that mitochondrial structural degradation and complex I deficiency might be associated with transgenic CMS of rice.

Comparative proteomics analysis reveals the molecular mechanism of enhanced cold tolerance through ROS scavenging in winter rapeseed (Brassica napus L.)

Two winter rapeseed cultivars, "NS" (cold tolerant) and "NF" (cold sensitive), were used to reveal the morphological, physiological, and proteomic characteristics in leaves of plants after treatment at -4°C for 12 h(T1) and 24 h(T2), and at room temperature(T0), to understand the molecular mechanisms of cold tolerance. Antioxidant activity and osmotic adjustment ability were higher, and plasma membrane injury was less obvious, in NS than in NF under cold stress. We detected different abundant proteins (DAPs) related to cold tolerance in winter rapeseed through data-independent acquisition (DIA). Compared with NF, A total of 1,235 and 1,543 DAPs were identified in the NSs under T1 and T2, respectively. Compared with NF, 911 proteins were more abundant in NS only after cold treatment. Some of these proteins were related to ROS scavenging through four metabolic pathways: lysine degradation; phenylalanine, tyrosine, and tryptophan; flavonoid biosynthesis; and ubiquinone and other terpenoid-quinone biosynthesis. Analysis of these proteins in the four candidate pathways revealed that they were rapidly accumulated to quickly enhance ROS scavenging and improve the cold tolerance of NS. These proteins were noticeably more abundant during the early stage of cold stress, which was critical for avoiding ROS damage.

Overexpression of BrAFP1 gene from winter rapeseed (Brassica rapa) confers cold tolerance in Arabidopsis

Antifreeze proteins (AFPs) can bind to ice crystals and restrain the formation of larger crystals, a strategy vital to the survival of plants in freezing environments. The BrAFP1 from winter rapeseed cultivars 'Longyou 7' with high cold tolerance was cloned and overexpressed in Arabidopsis. BrAFP1 was localized in the cytoplasm and nucleus. Under cold stress, SOD activity and free proline content were higher, MDA content and relative conductivity were lower in transgenic lines than those in wide-type Arabidopsis. Frostbite of transgenic plants was minimized, whereas frostbite of the Arabidopsis afp1 mutant was severe. Transition of the amino acid at position 17 of BrAFP1 was related to the increased winter survival of the rapeseed cultivar. Cultivars with higher survival rates had a predilection for tyrosine, not tryptophan, at the 17th site in the amino sequence of BrAFP1. Transcription of BrAFP1 was induced more rapidly, and the expression of the gene was also higher, in Longyou 7 than that in Tianyou 4 under cold stress. Overall, the high expression of BrAPF1 confers more cold-tolerance in Longyou 7.

Current breeding and genomic approaches to enhance the cane and sugar productivity under abiotic stress conditions

Sugarcane (Saccharum spp.) crop is vulnerable to many abiotic stresses such as drought, salinity, waterlogging, cold and high temperature due to climate change. Over the past few decades new breeding and genomic approaches have been used to enhance the genotypic performance under abiotic stress conditions. In sugarcane, introgression of genes from wild species and allied genera for abiotic stress tolerance traits plays a significant role in the development of several stress-tolerant varieties. Moreover, the genomics and transcriptomics approaches have helped to elucidate the key genes/TFs and pathways involved in abiotic stress tolerance in sugarcane. Several novel miRNAs families /proteins or regulatory elements that are responsible for drought, salinity, and cold tolerance have been identified through high-throughput sequencing. The existing sugarcane monoploid genome sequence information opens new gateways and opportunities for researchers to improve the desired traits through efficient genome editing tools, such as the clustered regularly interspaced short palindromic repeat-Cas (CRISPR/Cas) system. TALEN mediated mutations in a highly conserved region of the caffeic acid O-methyltransferase (COMT) of sugarcane significantly reduces the lignin content in the cell wall which is amenable for biofuel production from lignocellulosic biomass. In this review, we focus on current breeding with genomic approaches and their substantial role in enhancing cane production under the abiotic stress conditions, which is expected to provide new insights to plant breeders and biotechnologists to modify their strategy in developing stress-tolerant sugarcane varieties, which can highlight the future demand of cane, bio-energy, and viability of sugar industries.

Effects on photosynthesis and polyphenolic compounds in crop plant mung bean (Vigna radiata) following simulated accidental exposure to hydrogen peroxide

Hydrogen peroxide (H₂O₂) is a strong oxidizer and bleaching agent included in the list of substances requiring accident preparedness by the National Chemical Information System, Korea. Although chemical accidents related to H₂O₂ frequently occur globally, few studies have evaluated its toxicity and risk to soil ecosystems. Herein, accidental exposure to H₂O₂ was simulated in a microcosm including crop plant mung bean (Vigna radiata), and its long-term effects on photosynthetic activities and polyphenolic compounds were measured. Plants were evaluated based on the concentration and amount of H₂O₂ exposure, distance from H₂O₂ source, and duration post exposure. Plants exposed to high concentrations and large amounts of H₂O₂ at a close distance were most damaged; their photosynthetic activities and polyphenolic compound levels significantly decreased compared to the controls. H₂O₂ consistently damaged plants and affected their activities, but plants with minor damage recovered their photosynthetic activities and polyphenolic compound levels. Additionally, moderate oxidative stress from H₂O₂ exposure induced the synthesis of polyphenolic antioxidants including flavonol and anthocyanin. Thus, we suggest that flavonol and anthocyanin levels are the most sensitive indicators of adverse effects of H₂O₂ exposure in V. radiata. Our results highlight the risk of H₂O₂ and serve as a reference for chemical accidents.

An Overview of Hazardous Impacts of Soil Salinity in Crops, Tolerance Mechanisms, and Amelioration through Selenium Supplementation

Soil salinization is one of the major environmental stressors hampering the growth and yield of crops all over the world. A wide spectrum of physiological and biochemical alterations of plants are induced by salinity, which causes lowered water potential in the soil solution, ionic disequilibrium, specific ion effects, and a higher accumulation of reactive oxygen species (ROS). For many years, numerous investigations have been made into salinity stresses and attempts to minimize the losses of plant productivity, including the effects of phytohormones, osmoprotectants, antioxidants, polyamines, and trace elements. One of the protectants, selenium (Se), has been found to be effective in improving growth and inducing tolerance against excessive soil salinity. However, the in-depth mechanisms of Se-induced salinity tolerance are still unclear. This review refines the knowledge involved in Se-mediated improvements of plant growth when subjected to salinity and suggests future perspectives as well as several research limitations in this field.

Molecular evolution and lineage-specific expansion of the PP2C family in Zea mays

97 ZmPP2Cs were clustered into 10 subfamilies with biased subfamily evolution and lineage-specific expansion. Segmental duplication after the divergence of maize and sorghum might have led to primary expansion of ZmPP2Cs. The protein phosphatase 2C (PP2C) enzymes control many stress responses and developmental processes in plants. In Zea mays, a comprehensive understanding of the evolution and expansion of the PP2C family is still lacking. In the current study, 97 ZmPP2Cs were identified and clustered into 10 subfamilies. Through the analysis of the PP2C family in monocots, the ZmPP2C subfamilies displayed biased subfamily molecular evolution and lineage-specific expansion, as evidenced by their differing numbers of member genes, expansion and evolutionary rates, conserved subdomains, chromosomal distributions, expression levels, responsive-regulatory elements and regulatory networks. Moreover, while segmental duplication events have caused the primary expansion of the ZmPP2Cs, the majority of their diversification occurred following the additional whole-genome duplication that took place after the divergence of maize and sorghum (Sorghum bicolor). After this event, the PP2C subfamilies showed asymmetric evolutionary rates, with the D, F₂ and H subfamily likely the most closely to resemble its ancestral subfamily's genes. These findings could provide novel insights into the molecular evolution and expansion of the PP2C family in maize, and lay the foundation for the functional analysis of these enzymes in maize and related monocots.

Phosphorylation of bip130 by OsMPK1 regulates abscisic acid-induced antioxidant defense in rice

In rice (Oryza sativa), the mitogen-activated protein kinase 1, OsMPK1, has been shown to play an important role in abscisic acid (ABA)-induced antioxidant defense and to enhance the tolerance of plants to drought, salinity and oxidative stress. However, its downstream molecular mechanisms are poorly understood. Here, we identified a BRI1-KD interacting protein 130, bip130, which interacts with OsMPK1 in vitro and in vivo. A transient expression analysis in combination with mutant analysis in rice protoplasts revealed that bip130 is required for ABA-induced antioxidant defense in an OsMPK1-dependent manner. Furthermore, bip130 can be phosphorylated by OsMPK1 at Thr-153 in vitro, and Thr-153 is essential for the ABA-induced antioxidant defense by OsMPK1. These results reveal that OsMPK1 phosphorylates bip130 at Thr-153 to regulate ABA-induced antioxidant defense.

Abnormal tapetum development and energy metabolism associated with sterility in SaNa-1A CMS of Brassica napus L

Abnormal tapetum degradation and anther development in cytoplasmic male sterility SaNa-1A are the main reasons for the anther abortion. SaNa-1A is a novel cytoplasmic male sterility (CMS) line of Brassica napus derived from somatic hybrids of B. napus-Sinapis alba, and SaNa-1B is the corresponding maintainer line. Ultrastructural comparison between developing anthers of sterile and maintainer lines revealed abnormal subcellular structure of pollen mother cells (PMCs) in the CMS line. The PMC volume and size of nucleus and nucleolus in the CMS line were smaller than those in the maintainer line. The abnormal tapetum cell development and delayed tapetum degradation inhibited microspore development. Finally, anther abortion in the CMS line occurred. Physiological and biochemical analyses of developing anthers and mitochondria revealed that over-accumulation of reactive oxygen species (ROS) in the SaNa-1A and deficiency in antioxidant enzyme system aggravated the oxidization of membrane lipids, resulting in malondialdehyde (MDA) accumulation in anthers. High MDA content in the CMS line was toxic to the cells. ROS accumulation in SaNa-1A also affected anther development. Abnormal structure and function of terminal oxidase, which participates in the electron transport chain of mitochondrial membrane, were observed and affected the activity of cytochrome c oxidase and F₁F₀-ATPase, which inhibited ATP biosynthesis. Proline deficiency in SaNa-1A also affected anther development. Few hybridization signals of programmed cell death (PCD) in tetrads of SaNa-1A were identified using TdT-mediated dUTP Nick-End Labeling assay. PCD was not obvious in tapetum cells of SaNa-1A until the unicellular stage. These results validated the cytological differences mentioned above, and proved that abnormal tapetum degradation and anther development in SaNa-1A were the main reasons for the anther abortion.

Transcriptomic analysis of grain filling in rice inferior grains under moderate soil drying

Moderate soil drying imposed at the post-anthesis stage significantly increases starch accumulation in inferior grains of rice, but how this process is regulated at the level of gene expression remains unclear. In this study, we applied moderate drying (MD) treatments to the soil at the post-anthesis stage and followed the dynamics of the conversion process of soluble sugars to starch in inferior grains using RNA-seq analysis. An elevated level of ABA induced by MD was consistently associated with down-regulation of ABA8ox2, suggesting that lower expression of this gene may be responsible for the higher ABA content, potentially resulting in better filling in inferior grains. In addition, MD treatments up-regulated genes encoding five key enzymes involved sucrose-to-starch conversion and increased the activities of enzymes responsible for soluble-sugar reduction and starch accumulation in inferior grains. Differentially expressed transcription factors, including NAC, GATA, WRKY, and M-type MADS, were predicted to interact with other proteins in mediating filling of inferior grains as a response to MD. Transient expression analysis showed that NAC activated WAXY expression by binding to its promoter, indicating that NAC played a key role in starch synthesis of inferior grains under MD treatment. Our results provide new insights into the molecular mechanisms that regulate grain filling in inferior grains of rice under moderate soil drying.

Preparing plants for improved cold tolerance by priming

Cold is a major stressor, which limits plant growth and development in many parts of the world, especially in the temperate climate zones. A large number of experimental studies has demonstrated that not only acclimation and entrainment but also the experience of single short stress events of various abiotic or biotic kinds (priming stress) can improve the tolerance of plants to chilling temperatures. This process, called priming, depends on a stress "memory". It does not change cold sensitivity per se but beneficially modifies the response to cold and can last for days, months, or even longer. Elicitor factors and antagonists accumulate due to increased biosynthesis or decreased degradation either during or after the priming stimulus. Comparison of priming studies investigating improved tolerance to chilling temperatures highlighted key regulatory functions of ROS/RNS and antioxidant enzymes, plant hormones, especially jasmonates, salicylates, and abscisic acid, and signalling metabolites, such as β- and γ-aminobutyric acid (BABA and GABA) and melatonin. We conclude that these elicitors and antagonists modify local and systemic cold tolerance by integration into cold-induced signalling cascades.

Airborne signals synchronize the defenses of neighboring plants in response to touch

Plants activate defense-related pathways in response to subtle abiotic or biotic disturbances, changing their volatile profile rapidly. How such perturbations reach and potentially affect neighboring plants is less understood. We evaluated whether brief and light touching had a cascade effect on the profile of volatiles and gene expression of the focal plant and a neighboring untouched plant. Within minutes after contact, Zea mays showed an up-regulation of certain defense genes and increased the emission of specific volatiles that primed neighboring plants, making them less attractive for aphids. Exposure to volatiles from touched plants activated many of the same defense-related genes in non-touched neighboring plants, demonstrating a transcriptional mirroring effect for expression of genes up-regulated by brief contact. Perception of so-far-overlooked touch-induced volatile organic compounds was of ecological significance as these volatiles are directly involved in plant-plant communication as an effective trigger for rapid defense synchronization among nearby plants. Our findings shed new light on mechanisms of plant responses to mechanical contact at the molecular level and on the ecological role of induced volatiles as airborne signals in plant-plant interactions.

Sodium Selenate Treatment Using a Combination of Seed Priming and Foliar Spray Alleviates Salinity Stress in Rice

Soil salinity is one of the important abiotic stress factors that affect rice productivity and quality. Research with several dicotyledonous plants indicated that the detrimental effects associated with salinity stress can (partly) be overcome by the external application of antioxidative substances. For instance, sodium selenate (Na₂SeO₄) significantly improved the growth and productivity of several crops under various abiotic stress conditions. At present there is no report describing the impact of Na₂SeO₄ on salinity stressed cereals such as rice. Rice cultivation is threatened by increasing salinity stress, and in future this problem will further be aggravated by global warming and sea level rise, impacting coastal areas. The current study reports on the effect of Na₂SeO₄ in alleviating salinity stress in rice plants. The optimal concentration of Na₂SeO₄ and the most efficient mode of selenium application were investigated. Selenium, sodium, and potassium contents in leaves were determined. Antioxidant enzyme activities as well as proline, hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) concentrations were analyzed. In addition, the transcript levels for OsNHX1, an important Na⁺/H⁺ antiporter, were quantified. Treatment of 2-week-old rice plants under 150 mM NaCl stress with 6 mg l^-1 Na₂SeO₄ improved the total biomass. A significantly higher biomass was observed for the plants that received Na₂SeO₄ by a combination of seed priming and foliar spray compared to the individual treatments. The Na₂SeO₄ application enhanced the activity of antioxidant enzymes (SOD, APX, CAT, and GSH-Px), increased the proline content, and reduced H₂O₂ and MDA concentrations in plants under NaCl stress. These biochemical changes were accompanied by increased transcript levels for OsNHX1 resulting in a higher K⁺/Na⁺ ratio in the rice plants under NaCl stress. The results suggest that Na₂SeO₄ treatment alleviates the adverse effect of salinity on rice plant growth through enhancing the antioxidant defense system and increase of OsNHX1 transcript levels.

Chloroplasts at the Crossroad of Photosynthesis, Pathogen Infection and Plant Defense

Photosynthesis, pathogen infection, and plant defense are three important biological processes that have been investigated separately for decades. Photosynthesis generates ATP, NADPH, and carbohydrates. These resources are utilized for the synthesis of many important compounds, such as primary metabolites, defense-related hormones abscisic acid, ethylene, jasmonic acid, and salicylic acid, and antimicrobial compounds. In plants and algae, photosynthesis and key steps in the synthesis of defense-related hormones occur in chloroplasts. In addition, chloroplasts are major generators of reactive oxygen species and nitric oxide, and a site for calcium signaling. These signaling molecules are essential to plant defense as well. All plants grown naturally are attacked by pathogens. Bacterial pathogens enter host tissues through natural openings or wounds. Upon invasion, bacterial pathogens utilize a combination of different virulence factors to suppress host defense and promote pathogenicity. On the other hand, plants have developed elaborate defense mechanisms to protect themselves from pathogen infections. This review summarizes recent discoveries on defensive roles of signaling molecules made by plants (primarily in their chloroplasts), counteracting roles of chloroplast-targeted effectors and phytotoxins elicited by bacterial pathogens, and how all these molecules crosstalk and regulate photosynthesis, pathogen infection, and plant defense, using chloroplasts as a major battlefield.

Overexpression of Brassica campestris BcICE1 gene increases abiotic stress tolerance in tobacco

In this study, a cDNA of ICE1 (inducer of CBF expression 1) gene, named BcICE1, was isolated from Brassica campestris 'Longyou 6'. The deduced protein has 499 amino acids containing a typical bHLH domain and is highly identical with AtICE1 (85.9%) from Arabidopsis thaliana. BcICE1 is located in the nucleus. The activities of SOD, CAT, POD, and APX and the transcriptional levels of SOD, CAT, and POD genes were higher in BcICE1-transgenic tobacco than in wild-type (WT) tobacco under cold stress. Compared with WT tobacco, proline, soluble sugar, and chlorophyll were enhanced, whereas malondialdehyde and relative conductivity were decreased in BcICE1-transgenic tobacco. The overexpression of BcICE1 in tobacco increased the expression of CBF1, CBF2, and other stress-related genes. Moreover, under salt and PEG (25%) stress, the activities of APX and GPX and content of soluble sugar and chlorophyll in BcICE1-transgenic tobacco were higher than those in WT tobacco. Our results suggest that BcICE1 plays an important role in the response to abiotic stress.

A C2H2 zinc-finger protein OsZFP213 interacts with OsMAPK3 to enhance salt tolerance in rice

Improvement of salt tolerance is one of the major targets in rice breeding. Here, we report that the zinc-finger protein (ZFP) OsZFP213 functions in enhancing salt tolerance in rice. OsZFP213 is localized in the nucleus and has transactivation activity. Transgenic rice overexpressing OsZFP213 showed enhanced salt tolerance compared with wild type and OsZFP213 RNAi plants. Furthermore, OsZFP213 overexpression plants showed higher transcription levels of antioxidant system genes and higher catalytic activity of scavenging enzymes of reactive oxygen, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR), and a lower level of ROS accumulation than that in wild type and OsZFP213 RNAi plants under salt treatment. Yeast two-hybrid, pull-down, and BiFC analysis showed that OsMAPK3 is a direct partner of OsZFP213, and this interaction enhanced the transactivation activity of OsZFP213. Taken together, these results suggest that OsZFP213 cooperates with OsMAPK3 in the regulation of rice salt stress tolerance by enhancing the ability of scavenging reactive oxygen.

Copper-caused oxidative stress triggers the activation of antioxidant enzymes via ZmMPK3 in maize leaves

Copper (Cu) is a necessary trace element participated in many physiological processes in plants. But excessive Cu2+ is toxic, which can activate intracellular signals that lead to cellular damage. The mitogen-activated protein kinase (MAPK) cascade is at the center of cell signal transduction and has been reported to be involved in stress-related signaling pathways. ZmMPK3, a kind of MAPKs in maize cells, can be activated by diverse abiotic stresses. In the present study, we investigated the effects of Cu2+ on hydrogen peroxide (H2O2) level, ZmMPK3 activity as well as the activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbic acid peroxidase (APX) using maize leaf as an experimental model. The results demonstrated that acute Cu2+ exposure for 24 hours led to rapid increases of H2O2 level and the increase in ZmMPK3 activity as well as the total activities of antioxidant enzymes SOD, CAT and APX. H2O2 scavenger, dimethylthiourea (DMTU), effectively inhibited the Cu2+-increased H2O2 level and the activity of ZmMPK3 as well as the activities of the antioxidant enzymes SOD, CAT and APX. Pre-treatment with the MAPK inhibitor, PD98059, significantly blocked the Cu2+-increased activities of ZmMPK3, CAT, APX and SOD, but didn't affect the accumulation of H2O2. Our results suggest that Cu2+ causes oxidative stress to the maize leaves which then activates defense antioxidant enzymes via MAPK pathway. Thus, the signaling pathway is Cu2+-H2O2-ZmMPK3-antioxidant enzymes.

A cytosolic class II small heat shock protein, PfHSP17.2, confers resistance to heat, cold, and salt stresses in transgenic Arabidopsis

We cloned and characterized the full-length coding sequence of a small heat shock (sHSP) gene, PfHSP17.2, from Primula forrestii leaves following heat stress treatment. Homology and phylogenetic analysis suggested that PfHSP17.2 is a cytosolic class II sHSP, which was further supported by the cytosolic localization of transient expression of PfHSP17.2 fused with green fluorescent protein reporter. Expression analysis showed that PfHSP17.2 was highly inducible by heat stress in almost all the vegetative and generative tissues and was expressed under salt, cold, and oxidative stress conditions as well. Moreover, the expression of PfHSP17.2 in P. forrestii was detected in certain developmental growth stages. Transgenic Arabidopsis thaliana constitutively expressing PfHSP17.2 displayed increased thermotolerance and higher resistance to salt and cold compared with wild type plants. It is suggested that PfHSP17.2 plays a key role in heat and other abiotic stresses.