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For the optimal design of the embedded methods and size parameters of buckypaper in the buckypaper/SMP composites, FLUENT is used to analyze the effect of shape and thickness of buckypaper on the temperature distribution of the buckypaper/SMP composites in the heating process. The analysis show that, compared with composites reinforced by flat buckypaper, the maximum and average temperature of the composites reinforced by pulse bending buckypaper are lower, the heating rate is slowly and the time to reach the steady state is shorter in the heating process under the same working conditions, but the temperature distribution is more even. It is concluded that the shape and thickness of buckypaper can change the unit volume heat of buckypaper, thereby affecting the temperature field distribution of buckypaper/SMP composites. When the unit volume heat of buckypaper is bigger, the heat production is bigger, the maximum and average temperature are higher, and the temperature distribution is more uneven. Because the heat dissipation rate is lower than the increase rate of heat production, it takes longer time for buckypaper/SMP to reach the steady state. [ABSTRACT FROM AUTHOR]

A heat transfer model of polymer composite reinforced by buckypaper was established in this study to analyze how the shapes, heating power and thermal conductivity of polymer matrix affect the temperature distribution and heating uniformity. Thermal responses of the polymer composites reinforced by flat and pulse bending buckypaper were systematically studied, and the heating mechanisms of multiple-field coupling were investigated. The shapes and dimensions of the buckypaper are crucial in the optimization of such the polymer composites for heat generation. Results showed that the polymer composites reinforced by the flat buckypaper had relatively higher maximum and average temperatures in a steady heated state compared with those by the pulse bending ones, whereas the minimum temperature of the composites reinforced by the flat buckypaper was relatively lower, so the temperature distribution in those flat ones was more non-uniform. The overall heating temperature of the polymer composites reinforced by both the flat and pulse bending buckypaper was increased linearly with the applied power. The larger the thermal conductivity of the polymer is, the lower the maximum and average temperatures are. [ABSTRACT FROM AUTHOR]

Purpose – This paper aims to present a phenomenological model to investigate the underlying mechanism and predict the bio-inspired performance under different thermo-temporal conditions. Design/methodology/approach – Flory-Rehner free-energy functions are applied to quantitatively identify the driving forces in the viscously bio-inspired response of a dynamic polymer network. Furthermore, the permeation transition equation is adopted to couple water gradient and water sorption/desorption into the free-energy function. Findings – The results show that the influence of potential energy on deformation can be related to a stretching ratio that uniquely determines water sorption/desorption, locomotion frequency and contractile stress. Finally, by means of combining the free-energy function and Arrhenius equation, a phenomenological thermo-temporal model is developed and verified by the experimental results. Research limitations/implications – This study focuses on exploring the theoretical mechanism and significantly enhances understanding of relevant experimental features reported previously. Originality/value – The outcome of this study will provide a powerful phenomenological and quantitative tool for study on shape memory effect in bio-inspired polymers. [ABSTRACT FROM AUTHOR]

The influence of the porosity on the static mechanical strength of the carbon fiber fabric reinforced epoxy composites laminates was investigated. The tensile, compressive, bending, and interlaminar strength test on the CFRP laminates with porosity of 0.33% and 1.50% were conducted and simulated by a finite element analysis model. The article proposes the failure criterion of the static mechanical strength of the fabric fiber reinforced composites based on the improved Hashin failure criterion that is suitable for the undirectional composite laminates. The basic composite strength parameters are used to evaluate the mechanical properties of CFRP laminates with different porosities. A finite element analysis model is established by using software ABAQUS™ combined with the sudden stiffness degradation model. The experiment results show that the tensile, compressive, bending, and interlaminar strength decrease with the increasing porosities. The tensile, compressive, bending, and interlaminar strength of the fabric carbon fiber reinforced epoxy composites laminates are simulated accurately by the finite element model. [ABSTRACT FROM AUTHOR]

This study investigates the effects of hygrothermal condition on the static bending strength, the bending fatigue and the residual bending strength of carbon/epoxy composite laminates. Displacement-controlled three-point bending fatigue tests were conducted on carbon/epoxy composite laminates of immersion for 0, 7 and 14 days, respectively. After 40000 cycles the fatigue test was stopped and the residual properties were measured on the tested specimens. The effects of hygrothermal condition and fatigue on the micrographs of the specimens have been studied by the metallurgical microscope and scanning electron microscope. Experimental results reveal that moisture absorption can accelerate damage propagation of the composite; the accumulation of irreversible structural damage under the cyclic loading leads to a change in the macroscopic mechanical properties of the composites; the bending strength and the residual strength retention decreased with increased immersion time; hygrothermal aging lowered the threshold level for the onset of fatigue. [ABSTRACT FROM AUTHOR]

This paper investigated the effect of porosities, environmental factors and impact energies on the impact resistance properties of Carbon Fiber Reinforced Polymer/Plastic (CFRP) laminates. Impact tests on the CFRP laminates with three porosity levels were subjected to five energy levels from 3 J to 15 J at the room temperature. The damage area was assessed with combined effects of different impact energies and porosity levels. The damage area was evaluated by visual inspection and ultrasonic C-scan measurement. The thermal deply technique was used to evaluate the damage evolution behavior. Three-point bending tests were conducted on the non-impacted and impacted specimens that were exposed to the room temperature, the hygrothermal and the drying environments. The curves of the impact resistance of the tested laminates mutate at the impact energy of 9 J. The thermal deply technique reveals the failure mechanism of the impact damage mutation of the tested laminates when the impact energy exceeds the threshold 9 J. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a study on the effect of porosity, the environmental factors and impact energies on the impact resistance and damage tolerance properties of carbon/epoxy laminates. Impact tests on the carbon/epoxy laminates with three porosity levels were conducted at five impact energy levels of 3J, 6J, 9J, 12J and 15J at the room temperature. The damage area and the dent depth were assessed combined effects of different impact energy and porosity levels. The damage area was evaluated by visual inspections and ultrasonic C-scan measurement. The thermal deply technique was used to evaluate the damage evolution behavior. Non-impacted and impacted laminates were exposed to the room temperature, the hygrothermal, and the drying environments, followed by tensile test performed at the room temperature. The curves of the impact resistance and damage tolerance of the tested laminates mutated at the impact energy of 9J. The thermal deply technique reveals the failure mechanism of the impact damage mutation of the tested laminates when the impact energy exceeds the threshold 9J. [Copyright &y& Elsevier]

Abstract: This study investigates the effect of voids on the static bending and bending fatigue properties of T300/914 composite laminates that are exposed to room temperature, hygrothermal and drying environment, respectively. Displacement-controlled three-point bending fatigue tests were conducted on specimens, while damage in the composite was continuously recorded with a metallurgical microscope. After 40,000cycles the fatigue test was stopped and residual properties were measured on the tested specimens. Reduction in material strength was found to depend on the level of the specimen’s void content. The changes in weight and size gradually increased with an increase in porosity from 0.33% to 1.50% in the hygrothermal environment. It is found that the maximum rate of dimensional change occurred in the thickness direction. Both bending strength and fatigue performance were reduced with increasing porosity. The damage evaluation of aged specimens was more severe than non-aged and drying specimens. [Copyright &y& Elsevier]

The role of ABA in brassinosteroid (BR)-induced stress tolerance and the relationship between BR, nitric oxide (NO) and ABA under water stress induced by polyethylene glycol (PEG) were investigated in leaves of maize (Zea mays) plants. Water stress led to oxidative damage. Pre-treatment with the BR biosynthetic inhibitor brassinazole (Brz) aggravated the oxidative damage induced by PEG treatment, which was alleviated by the application of BR or ABA. Pre-treatment with the ABA biosynthetic inhibitor fluridone also aggravated the oxidative damage induced by PEG treatment; however, this was barely alleviated by the application of BR. BR treatment increased the content of ABA and up-regulated the expression of the ABA biosynthetic gene vp14 in maize leaves, which was blocked by pre-treatments with the NO scavenger cPTIO (2,4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and the nitric oxide synthase inhibitor l-NAME (NG-nitro-l-arginine methyl ester. Moreover, BR treatment induced increases in the generation of NO in mesophyll cells of maize leaves, and treatment with the NO donor sodium nitroprusside (SNP) up-regulated the content of ABA and the expression of vp14 in maize leaves. Our results suggest that BR-induced NO production and NO-activated ABA biosynthesis are important mechanisms for BR-enhanced water stress tolerance in leaves of maize plants. [ABSTRACT FROM AUTHOR]

Using pharmacological and biochemical approaches, the role of maize polyamine oxidase (MPAO) in abscisic acid (ABA)-induced antioxidant defense in leaves of maize ( Zea mays L.) plants was investigated. Exogenous ABA treatment enhanced the expression of the MPAO gene and the activities of apoplastic MPAO. Pretreatment with two different inhibitors for apoplastic MPAO partly reduced hydrogen peroxide (H2O2) accumulation induced by ABA and blocked the ABA-induced expression of the antioxidant genes superoxide dismutase 4 and cytosolic ascorbate peroxidase and the activities of the cytosolic antioxidant enzymes. Treatment with spermidine, the optimum substrate of MPAO, also induced the expression and the activities of the antioxidant enzymes, and the upregulation of the antioxidant enzymes was prevented by two inhibitors of MPAO and two scavengers of H2O2. These results suggest that MPAO contributes to ABA-induced cytosolic antioxidant defense through H2O2, a Spd catabolic product. [ABSTRACT FROM AUTHOR]

• The role of nitric oxide (NO) and the relationship between NO, hydrogen peroxide (H2O2) and mitogen-activated protein kinase (MAPK) in abscisic acid (ABA)-induced antioxidant defense in leaves of maize ( Zea mays) plants were investigated. • Both ABA and H2O2 induced increases in the generation of NO in mesophyll cells of maize leaves, and H2O2 was required for the ABA-induced generation of NO. Pretreatment with NO scavenger and nitric oxide synthase (NOS) inhibitor substantially reduced the ABA-induced production of NO, and partly blocked the activation of a 46 kDa MAPK and the expression and the activities of several antioxidant enzymes induced by ABA. Treatment with the NO donor sodium nitroprusside (SNP) also induced the activation of the MAPK, and enhanced the antioxidant defense systems. • Conversely, SNP treatment did not induce the production of H2O2, and pretreatments with NO scavenger and NOS inhibitor did not affect ABA-induced H2O2 production. • Our results suggest that ABA-induced H2O2 production mediates NO generation, which, in turn, activates MAPK and results in the upregulation in the expression and the activities of antioxidant enzymes in ABA signaling. [ABSTRACT FROM AUTHOR]

Drought stress is a crucial environmental factor that limits plant growth, development, and productivity. Autophagy of misfolded proteins can help alleviate the damage caused in plants experiencing drought. However, the mechanism of autophagy‐mediated drought tolerance in plants remains largely unknown. Here, we cloned the gene for a maize (Zea mays) selective autophagy receptor, NEXT TO BRCA1 GENE 1 (ZmNBR1), and identified its role in the response to drought stress. We observed that drought stress increased the accumulation of autophagosomes. RNA sequencing and reverse transcription‐quantitative polymerase chain reaction showed that ZmNBR1 is markedly induced by drought stress. ZmNBR1 overexpression enhanced drought tolerance, while its knockdown reduced drought tolerance in maize. Our results established that ZmNBR1 mediates the increase in autophagosomes and autophagic activity under drought stress. ZmNBR1 also affects the expression of genes related to autophagy under drought stress. Moreover, we determined that BRASSINOSTEROID INSENSITIVE 1A (ZmBRI1a), a brassinosteroid receptor of the BRI1‐like family, interacts with ZmNBR1. Phenotype analysis showed that ZmBRI1a negatively regulates drought tolerance in maize, and genetic analysis indicated that ZmNBR1 acts upstream of ZmBRI1a in regulating drought tolerance. Furthermore, ZmNBR1 facilitates the autophagic degradation of ZmBRI1a under drought stress. Taken together, our results reveal that ZmNBR1 regulates the expression of autophagy‐related genes, thereby increasing autophagic activity and promoting the autophagic degradation of ZmBRI1a under drought stress, thus enhancing drought tolerance in maize. These findings provide new insights into the autophagy degradation of brassinosteroid signaling components by the autophagy receptor NBR1 under drought stress. [ABSTRACT FROM AUTHOR]

MYB transcription factors play a vital role in response to stress in plant. MYB-CC transcription factors belong to MYB transcription factors, which contain a conserved MYB DNA-binding domain and a coiled-coil (CC) domain. MYB-CC transcription factors participate in the process of plant drought tolerance. However, the underlying molecular mechanisms of ZmMYB-CC in regulating drought tolerance are still largely unknown. Here, we found that ZmMYB-CC10 enhanced drought tolerance by reducing oxidative damage in maize. Further, ZmMYB-CC10 improves the activity of APX and decreases the content of H 2 O 2. Overexpression of ZmMYB-CC10 increases the expression of ZmAPX4 under drought stress. Luciferase assays and Yeast one-hybrid assays (Y1H) showed that ZmMYB-CC10 activates the expression of ZmAPX4 by directly binding to its promoter. Taken together, our results demonstrate that ZmMYB-CC10 enhances tolerance to drought stress by directly activating ZmAPX4 expression, thereby reducing H 2 O 2 content. • ZmMYB-CC10 enhances drought tolerance by reducing oxidative damage in maize. • ZmMYB-CC10 decreases the content of H 2 O 2 by increasing the activity of APX under drought stress. • ZmMYB-CC10 directly binds to ZmAPX4 promotor and activates its expression. [ABSTRACT FROM AUTHOR]

Salinity has become a crucial environmental factor that restricts plant growth, development, and productivity. Nevertheless, the mechanisms by which plants react to salt stress remain inadequately comprehended. In this study, we identified maize brassinosteroid-signaling kinase gene ZmBSK7 which is homologous to AtBSK1. Our results showed that ZmBSK7 is induced by salt stress and ZmBSK7 localizes in the plasma membrane. ZmBSK7 overexpression increases salt tolerance, while its knockdown decreases salt tolerance in maize. ZmBSK7 reduces the malondialdehyde (MDA) content and the percentage of electrolyte leakage, and also elevates the activities of antioxidant enzymes. Furthermore, ZmBSK7 promotes K+ content accumulation and reduces Na+/K+ ratio. Further found that ZmBSK7 physically interacts with K+ efflux antiporter 2 (ZmKEA2) in vivo and in vitro. Salt stress also increased the expression of ZmKEA2. Thus, ZmBSK7 improves salt tolerance in maize by affecting ZmKEA2 expression to promote K+ content accumulation and reduce Na+/K+ ratio. This study enhances the comprehension of BSK proteins and establishes a theoretical foundation for investigating salt stress tolerance in plants. • ZmBSK7 positively enhance the tolerance of salt stress in maize. • Overexpression of ZmBSK7 improves the activities of antioxidant enzymes and maintaining a balance of Na+ and K+. • ZmBSK7 physically interacts with ZmKEA2 in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Summary: 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. [ABSTRACT FROM AUTHOR]

Ca2+ and calmodulin (CaM) have been shown to play an important role in abscisic acid (ABA)-induced antioxidant defense. However, it is unknown whether Ca2+/CaM-dependent protein kinase (CCaMK) is involved in the process. In the present study, the role of rice CCaMK, OsDMI3, in ABA-induced antioxidant defense was investigated in leaves of rice (Oryza sativa) plants. Treatments with ABA, H2O2, and polyethylene glycol (PEG) induced the expression of OsDMI3 and the activity of OsDMI3, and H2O2 is required for the ABA-induced increases in the expression and the activity of OsDMI3 under water stress. Subcellular localization analysis showed that OsDMI3 is located in the nucleus, the cytoplasm, and the plasma membrane. The analysis of the transient expression of OsDMI3 in rice protoplasts and the RNA interference (RNAi) silencing of OsDMI3 in rice protoplasts showed that OsDMI3 is required for ABA-induced increases in the expression and the activities of superoxide dismutase (SOD) and catalase (CAT). Further, the oxidative damage induced by higher concentrations of PEG and H2O2 was aggravated in the mutant of OsDMI3. Moreover, the analysis of the RNAi silencing of OsDMI3 in protoplasts and the mutant of OsDMI3 showed that higher levels of H2O2 accumulation require OsDMI3 activation in ABA signaling, but the initial H2O2 production induced by ABA is not dependent on the activation of OsDMI3 in leaves of rice plants. Our data reveal that OsDMI3 is an important component in ABA-induced antioxidant defense in rice. [ABSTRACT FROM AUTHOR]

In search for components of mitogen-activated protein kinase (MAPK) cascades in maize ( Zea mays) involved in response to abscisic acid (ABA) stimulus, a novel MAPK gene, ZmMPK3, from ABA-treated maize leaves cDNA was isolated and characterized. The full length of the ZmMPK3 gene is 1 520 bp and encodes a 376 amino acid protein with a predicted molecular mass of 43.5 kD and a pI of 5.83. ZmMPK3 contains all 11 MAPK conserved subdomains and the phosphorylation motif TEY. Amino acid sequence alignment revealed that ZmMPK3 shared high identity with group-A MAPK in plants. A time course (30–360 min) experiment using a variety of signal molecules and stresses revealed that the transcripts level of ZmMPK3 accumulated markedly and rapidly when maize seedlings were subjected to exogenous signaling molecules: ABA, H2O2, jasmonic acid and salicylic acid, various abiotic stimuli such as cold, drought, ultraviolet light, salinity, heavy metal and mechanical wounding. Its transcription was also found to be tissue-specific regulated. Here, we show that ABA and H2O2 induced a significant increase in the ZmMPK3 activity using immunoprecipitation and in-gel kinase assay. Furthermore, the results showed that the ZmMPK3 protein is localized mainly to the nucleus. These results suggest that the ZmMPK3 may play an important role in response to environmental stresses. [ABSTRACT FROM AUTHOR]

NAC (NAM, ATAF1/2, and CUC2) transcription factors play vital roles in response to multiple abiotic stresses. Our previous study has demonstrated that ZmNAC84, a maize NAC transcription factor, enhanced the drought tolerance by increasing abscisic acid (ABA)-induced antioxidant enzyme activities of APX and SOD, and Ser-113, a key phosphorylation site, of ZmNAC84 played an important role in this process. However, the target gene of ZmNAC84 in this process is still unknown. Here, we found that ZmNAC84 only regulated the luciferase activity driven by ZmSOD2 promoter in tobacco. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) assay showed that ZmNAC84 directly bound to the CACGTG motif of ZmSOD2 promoter. Furthermore, phosphorylation of ZmNAC84 at Ser-113 up-regulated the ZmSOD2 expression by enhancing the DNA binding ability of ZmNAC84 to ZmSOD2 promoter and improved the drought tolerance. Taken together, our results demonstrate that ZmNAC84 directly regulates ZmSOD2 expression to enhance drought tolerance and Ser-113 of ZmNAC84 is crucial in this process. • ZmNAC84 directly binds to ZmSOD2 promoter in vivo and in vitro. • Phosphorylation of ZmNAC84 at Ser-113 up-regulates the ZmSOD2 expression. • Phosphorylation of ZmNAC84 at Ser-113 enhances the DNA binding ability of ZmNAC84. [ABSTRACT FROM AUTHOR]

Summary: 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. [ABSTRACT FROM AUTHOR]

Calcium (Ca2+)/calmodulin (CaM)-dependent protein kinase (CCaMK) is an important positive regulator of abscisic acid (ABA) and abiotic stress signaling in plants and is believed to act upstream of mitogen-activated protein kinase (MAPK) in ABA signaling. However, it is unclear how CCaMK activates MAPK in ABA signaling. Here, we show that OsDMI3, a rice (Oryza sativa) CCaMK, directly interacts with and phosphorylates OsMKK1, a MAPK kinase (MKK) in rice, in vitro and in vivo. OsDMI3 was found to directly phosphorylate Thr-25 in the N-terminus of OsMKK1, and this Thr-25 phosphorylation is OsDMI3-specific in ABA signaling. The activation of OsMKK1 and its downstream kinase OsMPK1 is dependent on Thr-25 phosphorylation of OsMKK1 in ABA signaling. Moreover, ABA treatment induces phosphorylation in the activation loop of OsMKK1, and the two phosphorylations, in the N-terminus and in the activation loop, are independent. Further analyses revealed that OsDMI3-mediated phosphorylation of OsMKK1 positively regulates ABA responses in seed germination, root growth, and tolerance to both water stress and oxidative stress. Our results indicate that OsMKK1 is a direct target of OsDMI3, and OsDMI3-mediated phosphorylation of OsMKK1 plays an important role in activating the MAPK cascade and ABA signaling. [ABSTRACT FROM AUTHOR]

Salinity severely reduces plant growth and limits agricultural productivity. Dynamic changes and rearrangement of the plant cell wall is an important response to salt stress, but relatively little is known about the biological importance of specific cell wall components in the response. Here, we demonstrate a specific function of β-1,4-galactan in salt hypersensitivity. We found that salt stress induces the accumulation of β-1,4-galactan in root cell walls by up regulating the expression of GALACTAN SYNTHASE 1 (GALS1), which encodes a β-1,4-galactan synthase. The accumulation of β-1,4-galactan negatively affects salt tolerance. Exogenous application of D-galactose (D-Gal) causes an increase in β-1,4-galactan levels in the wild type and GALS1 mutants, especially in GALS1 overexpressors, which correlated with the aggravated salt hypersensitivity. Furthermore, we discovered that the BARLEY B RECOMBINANT/BASIC PENTACYSTEINE transcription factors BPC1/BPC2 positively regulate plant salt tolerance by repressing GALS1 expression and β-1,4-galactan accumulation. Genetic analysis suggested that GALS1 is genetically epistatic to BPC1/BPC2 with respect to the control of salt sensitivity as well as accumulation of β-1,4-galactan. Taken together, our results reveal a new regulatory mechanism by which β-1,4-galactan regulated by the BPC1/BPC2-GALS1 module aggravates salt sensitivity in Arabidopsis thaliana. Dynamic changes and rearrangement of the plant cell wall is an important response to salt stress, but relatively little is known about the underlying mechanisms. This study discovers a new regulatory mechanism by which cell wall β-1,4-galactan regulated by the BPC1/BPC2-GALS1 module aggravates salt sensitivity. [ABSTRACT FROM AUTHOR]

Drought stress severely limits the growth, development, and productivity of crops, and therefore understanding the mechanisms by which plants respond to drought is crucial. In this study, we cloned a maize NAC transcription factor, ZmNAC49 , and identified its function in response to drought stress. We found that ZmNAC49 is localized in the nucleus and has transcriptional activation activity. ZmNAC49 expression is rapidly and strongly induced by drought stress, and overexpression enhances stress tolerance in maize. Overexpression also significant decreases the transpiration rate, stomatal conductance, and stomatal density in maize. Detailed study showed that ZmNAC49 overexpression affects the expression of genes related to stomatal development, namely ZmTMM , ZmSDD1 , ZmMUTE , and ZmFAMA. In addition, we found that ZmNAC49 can directly bind to the promoter of ZmMUTE and suppress its expression. Taken together, our results show that the transcription factor ZmNAC49 represses ZmMUTE expression, reduces stomatal density, and thereby enhances drought tolerance in maize. [ABSTRACT FROM AUTHOR]

Backgrounds: Paphiopedilum is an important genus of the orchid family Orchidaceae and has high horticultural value. The wild populations are under threat of extinction because of overcollection and habitat destruction. Mature seeds of most Paphiopedilum species are difficult to germinate, which severely restricts their germplasm conservation and commercial production. The factors inhibiting germination are largely unknown. Results: In this study, large amounts of non-methylated lignin accumulated during seed maturation of Paphiopedilum armeniacum (P. armeniacum), which negatively correlates with the germination rate. The transcriptome profiles of P. armeniacum seed at different development stages were compared to explore the molecular clues for non-methylated lignin synthesis. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that a large number of genes associated with phenylpropanoid biosynthesis and phenylalanine metabolism during seed maturation were differentially expressed. Several key genes in the lignin biosynthetic pathway displayed different expression patterns during the lignification process. PAL, 4CL, HCT, and CSE upregulation was associated with C and H lignin accumulation. The expression of CCoAOMT, F5H, and COMT were maintained at a low level or down-regulated to inhibit the conversion to the typical G and S lignin. Quantitative real-time RT-PCR analysis confirmed the altered expression levels of these genes in seeds and vegetative tissues. Conclusions: This work demonstrated the plasticity of natural lignin polymer assembly in seed and provided a better understanding of the molecular mechanism of seed-specific lignification process. [ABSTRACT FROM AUTHOR]

Calcium/calmodulin-dependent protein kinase (CCaMK) has been shown to play important roles in brassinosteroid (BR)-induced antioxidant defense and enhancing the tolerance of plants to drought stress. The autophosphorylation of CCaMK is a key step for the activation of CCaMK, thus promoting substrate phosphorylation. However, how CCaMK autophosphorylation function in BR-induced antioxidant defense is not known yet. Here, seven potential autophosphorylation sites of ZmCCaMK were identified using mass spectroscopy (liquid chromatography-tandem mass spectrometry [LC-MS/MS]) analysis. The transient gene expression analysis in maize protoplasts showed that Thr420 and Ser454 of ZmCCaMK were important for BR-induced antioxidant defense. Furthermore, Thr420 and Ser454 of ZmCCaMK were crucial for improving drought tolerance and alleviating drought induced oxidative damage of plants via overexpressing various mutant versions of ZmCCaMK in tobacco (Nicotiana tabacum). Mutations of Thr420 and Ser454 in ZmCCaMK substantially blocked the autophosphorylation and substrate phosphorylation of ZmCCaMK in vitro. Taken together, our results demonstrate that Thr420 and Ser454 of ZmCCaMK are crucial for BR-induced antioxidant defense and drought tolerance through modulating the autophosphorylation and substrate phosphorylation activities of ZmCCaMK. • Thr420 and Ser454 of ZmCCaMK are crucial for BR-induced antioxidant defense in maize. • Phosphorylation of Thr420 and Ser454 of ZmCCaMK enhance drought tolerance in plants. • T420A and S454A of ZmCCaMK affect the kinase activity of ZmCCaMK in vitro. [ABSTRACT FROM AUTHOR]

Summary: l‐Arabinose (l‐Ara) is a major monosaccharide in plant polysaccharides and glycoproteins, and functions in plant growth and development. However, the potential role of l‐Ara during abscisic acid (ABA)‐mediated seed germination has been largely ignored. Here, our results showed a function of l‐Ara during ABA‐mediated seed germination.ABA slowed down the reduction of l‐Ara in seed cell wall, and exogenous l‐Ara aggravated the inhibition of ABA on germination. We further found that MUR4, encoding URIDINE 5′‐DIPHOSPHATE‐d‐XYLOSE 4‐EPIMERASE 1, played a vital role in ABA‐mediated germination. MUR4 was highly expressed in embryo and induced by ABA in both seeds and seedlings. Overexpression of MUR4 conferred hypersensitive seed germination and early postgermination growth to ABA.Further analysis revealed that ABSCISIC ACID INSENSITIVE4 (ABI4) positively modulated the MUR4 expression by directly binding the Coupling Element1 motif of MUR4 promoter. Consistently, abi4‐1 mutant had a lower l‐Ara content in seed cell wall, while a higher l‐Ara content in seed cell wall was observed in ABI4 overexpressors. Genetic analysis suggested that overexpression of MUR4 in abi4‐1 partly restored the ABA sensitivity of abi4‐1.We established the link between ABA and l‐Ara during ABA‐mediated seed germination and cotyledon greening in Arabidopsis and revealed the potential molecular mechanism. [ABSTRACT FROM AUTHOR]

Plants have evolved various strategies to sense and respond to saline environments, which severely reduce plant growth and limit agricultural productivity. Alteration to the cell wall is one strategy that helps plants adapt to salt stress. However, the physiological mechanism of how the cell wall components respond to salt stress is not fully understood. Here, we show that expression of XTH30 , encoding xyloglucan endotransglucosylase-hydrolase30, is strongly up-regulated in response to salt stress in Arabidopsis. Loss-of-function of XTH30 leads to increased salt tolerance and overexpression of XTH30 results in salt hypersensitivity. XTH30 is located in the plasma membrane and is highly expressed in the root, flower, stem, and etiolated hypocotyl. The NaCl-induced increase in xyloglucan (XyG)-derived oligosaccharide (XLFG) of the wild type is partly blocked in xth30 mutants. Loss-of-function of XTH30 slows down the decrease of crystalline cellulose content and the depolymerization of microtubules caused by salt stress. Moreover, lower Na+ accumulation in shoot and lower H2O2 content are found in xth30 mutants in response to salt stress. Taken together, these results indicate that XTH30 modulates XyG side chains, altered abundance of XLFG, cellulose synthesis, and cortical microtubule stability, and negatively affecting salt tolerance. [ABSTRACT FROM AUTHOR]

In plants, Ca2+/calmodulin-dependent protein kinase (CCaMK) is a positive regulator of abscisic acid (ABA) responses, including root growth, antioxidant defense, and tolerance of both water stress and oxidative stress. However, the underlying molecular mechanisms are poorly understood. Here, we show a direct interaction between DMI3 (Doesn't Make Infections 3), a rice (Oryza sativa) CCaMK and PP45, a type 2C protein phosphatase in rice (PP2C). This interaction involves the CaM binding domain of DMI3 and the PP2C domain of PP45. In the absence of ABA, PP45 directly inactivates DMI3 by dephosphorylating Thr-263 in DMI3. However, in the presence of ABA, ABA-induced H2O2 production by the NADPH oxidases RbohB/E inhibits the activity of PP45 not only by inhibiting the expression of PP45 but also by oxidizing Cys-350 and Cys-428 residues to form PP45 intermolecular dimers. ABA-induced oxidation of Cys-350 and Cys-428 in PP45 blocked the interaction between PP45 and DMI3 and substantially prevented PP45-mediated inhibition in DMI3 activity. Genetic analysis indicated that PP45 is an important negative regulator of ABA signaling. These results reveal important pathways for the inhibition of DMI3 under the basal state and for its ABA-induced activation in rice. [ABSTRACT FROM AUTHOR]

Abstract The alteration of cell wall component and structure is an important adaption to saline environment. Pectins, a major cell wall component, are often present in a highly methylesterified form. The level of methyl esterification determined by pectin methylesterases (PMEs) influences many important wall properties that are believed to relate to the adaption to saline stress. However, little is known about the function of PMEs in response to salt stress. Here, we established a link between pectin methylesterase31 (PME31) and salt stress tolerance. Salt stress significantly increases PME31 expression. PME31 is located in the plasma membrane and the expression level of PME31 was high in dry seeds. Knock-down mutants in PME31 conferred hypersensitive phenotypes to salt stress in seed germination and post-germination growth. Real-time PCR analysis revealed that the transcript levels of several stress genes (DREB2A , RD29A and RD29B) are lower in pme31-2 mutant than that in the wild type in response to salt stress. These results suggested that PME31 could positively modulate salt stress tolerance. Highlights • Salt stress could significantly increase PME31 expression. • pme31 mutants are hypersensitive to salt stress. • PME31 positively modulate the expression levels of salt stress-induced genes. [ABSTRACT FROM AUTHOR]

As the major resource of reactive oxygen species (ROS), the NADPH oxidases (Rbohs) have been shown to play important roles in plant cells under normal growth and stress conditions. Although many family members of Rbohs were studied, little is known about the function of RbohI in Arabidopsis thaliana . Here, we report that exogenous ABA application decreases RbohI expression and mannitol significantly increases RbohI expression at transcript level. The RbohI transcripts were strongly detected in dry seeds and roots. The loss-of-function mutant rbohI exhibited sensitivity to ABA and mannitol stress during germination. Furthermore, the lateral root growth of rbohI was severely inhibited after treatment with mannitol stress. Overexpression of RbohI in Arabidopsis significantly improves the drought tolerance. Moreover, more H 2 O 2 accumulated in RbohI overexpressors than in wild type plants in response to mannitol stress. Our conclusion is that AtRbohI functions in drought-stress response in Arabidopsis thaliana. [ABSTRACT FROM AUTHOR]

In maize ( Zea mays), the mitogen-activated protein kinase Zm MPK5 has been shown to be involved in abscisic acid ( ABA)-induced antioxidant defence and to enhance the tolerance of plants to drought, salt stress and oxidative stress. However, the underlying molecular mechanisms are poorly understood. Here, using Zm MPK5 as bait in yeast two-hybrid screening, a protein interacting with Zm MPK5 named Zm ABA2, which belongs to a member of the short-chain dehydrogenase/reductase family, was identified. Pull-down assay and bimolecular fluorescence complementation analysis and co-immunoprecipitation test confirmed that Zm MPK5 interacts with Zm ABA2 in vitro and in vivo. Phosphorylation of Ser173 in Zm ABA2 by Zm MPK5 was shown to increase the activity of Zm ABA2 and the protein stability. Various abiotic stimuli induced the expression of Zm ABA2 in leaves of maize plants. Pharmacological, biochemical and molecular biology and genetic analyses showed that both Zm MPK5 and Zm ABA2 coordinately regulate the content of ABA. Overexpression of Zm ABA2 in tobacco plants was found to elevate the content of ABA, regulate seed germination and root growth under drought and salt stress and enhance the tolerance of tobacco plants to drought and salt stress. These results suggest that Zm ABA2 is a direct target of Zm MPK5 and is involved in ABA biosynthesis and functions. [ABSTRACT FROM AUTHOR]

In this study, the role of the rice (Oryza sativa L.) histidine kinase OsHK3 in abscisic acid (ABA)-induced antioxidant defense was investigated. Treatments with ABA, H2O2, and polyethylene glycol (PEG) induced the expression of OsHK3 in rice leaves, and H2O2 is required for ABA-induced increase in the expression of OsHK3 under water stress. Subcellular localization analysis showed that OsHK3 is located in the cytoplasm and the plasma membrane. The transient expression analysis and the transient RNA interference test in rice protoplasts showed that OsHK3 is required for ABA-induced upregulation in the expression of antioxidant enzymes genes and the activities of antioxidant enzymes. Further analysis showed that OsHK3 functions upstream of the calcium/ calmodulin-dependent protein kinase OsDMI3 and the mitogen- activated protein kinase OsMPK1 to regulate the activities of antioxidant enzymes in ABA signaling. Moreover, OsHK3 was also shown to regulate the expression of nicotinamide adenine dinucleotide phosphate oxidase genes, OsrbohB and OsrbohE, and the production of H2O2 in ABA signaling. Our data indicate that OsHK3 play an important role in the regulation of ABA-induced antioxidant defense and in the feedback regulation of H2O2 production in ABA signaling. [ABSTRACT FROM AUTHOR]

In this study it was found that ZFP36 is required for ABA-induced antioxidant defence and for the regulation of the cross-talk between NADPH oxidase, H2O2, and MAPK in ABA signalling.C2H2-type zinc finger proteins (ZFPs) have been shown to play important roles in the responses of plants to oxidative and abiotic stresses, and different members of this family might have different roles during stresses. Here a novel abscisic acid (ABA)- and hydrogen peroxide (H2O2)-responsive C2H2-type ZFP gene, ZFP36, is identified in rice. The analyses of ZFP36-overexpressing and silenced transgenic rice plants showed that ZFP36 is involved in ABA-induced up-regulation of the expression and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX). Overexpression of ZFP36 in rice plants was found to elevate the activities of antioxidant enzymes and to enhance the tolerance of rice plants to water stress and oxidative stress. In contrast, an RNA interference (RNAi) mutant of ZFP36 had lower activities of antioxidant enzymes and was more sensitive to water stress and oxidative stress. ABA-induced H2O2 production and ABA-activated mitogen-activated protein kinases (MAPKs) were shown to regulate the expression of ZFP36 in ABA signalling. On the other hand, ZFP36 also regulated the expression of NADPH oxidase genes, the production of H2O2, and the expression of OsMPK genes in ABA signalling. These results indicate that ZFP36 is required for ABA-induced antioxidant defence, for the tolerance of rice plants to water stress and oxidative stress, and for the regulation of the cross-talk between NADPH oxidase, H2O2, and MAPK in ABA signalling. [ABSTRACT FROM AUTHOR]

In rice, the Ca2+/calmodulin ( CaM)-dependent protein kinase ( CCaMK) OsDMI3 has been shown to be required for abscisic acid ( ABA)-induced antioxidant defence. However, it is not clear how OsDMI3 participates in this process in rice. In this study, the cross-talk between OsDMI3 and the major ABA-activated MAPK OsMPK1 in ABA-induced antioxidant defence was investigated. ABA treatment induced the expression of OsDMI3 and OsMPK1 and the activities of OsDMI3 and OsMPK1 in rice leaves. In the mutant of OsDMI3, the ABA-induced increases in the expression and the activity of OsMPK1 were substantially reduced. But in the mutant of OsMPK1, the ABA-induced increases in the expression and the activity of OsDMI3 were not affected. Pretreatments with MAPKK inhibitors also did not affect the ABA-induced activation of OsDMI3. Further, a transient expression analysis in combination with mutant analysis in rice protoplasts showed that OsMPK1 is required for OsDMI3-induced increases in the activities of antioxidant enzymes and the production of H2O2. Our data indicate that there exists a cross-talk between OsDMI3 and OsMPK1 in ABA signalling, in which OsDMI3 functions upstream of OsMPK1 to regulate the activities of antioxidant enzymes and the production of H2O2 in rice. [ABSTRACT FROM AUTHOR]

Brassinosteroid (BR)-induced antioxidant defence has been shown to enhance stress tolerance. In this study, the role of the maize 65kDa microtubule-associated protein (MAP65), ZmMAP65-1a, in BR-induced antioxidant defence was investigated. Treatment with BR increased the expression of ZmMAP65-1a in maize (Zea mays) leaves and mesophyll protoplasts. Transient expression and RNA interference silencing of ZmMAP65-1a in mesophyll protoplasts further revealed that ZmMAP65-1a is required for the BR-induced increase in expression and activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX). Both exogenous and BR-induced endogenous H2O2 increased the expression of ZmMAP65-1a. Conversely, transient expression of ZmMAP65-1a in maize mesophyll protoplasts enhanced BR-induced H2O2 accumulation, while transient silencing of ZmMAP65-1a blocked the BR-induced expression of NADPH oxidase genes and inhibited BR-induced H2O2 accumulation. Inhibiting the activity and gene expression of ZmMPK5 significantly prevented the BR-induced expression of ZmMAP65-1a. Likewise, transient expression of ZmMPK5 enhanced BR-induced activities of the antioxidant defence enzymes SOD and APX in a ZmMAP65- 1a-dependent manner. ZmMPK5 directly interacted with ZmMAP65-1a in vivo and phosphorylated ZmMAP65-1a in vitro. These results suggest that BR-induced antioxidant defence in maize operates through the interaction of ZmMPK5 with ZmMAP65-1a. Furthermore, ZmMAP65-1a functions in H2O2 self-propagation via regulation of the expression of NADPH oxidase genes in BR signalling. [ABSTRACT FROM AUTHOR]

Calcium-dependent protein kinases (CDPKs) have been shown to be involved in abscisic acid (ABA)-mediated physiological processes, including seed germination, post-germination growth, stomatal movement, and plant stress tolerance. However, it is not clear whether CDPKs are involved in ABA-induced antioxidant defence. In the present study, the role of the maize CDPK ZmCPK11 in ABA-induced antioxidant defence and the relationship between ZmCPK11 and ZmMPK5, a maize ABA-activated mitogen-activated protein kinase (MAPK), in ABA signalling were investigated. Treatments with ABA and H2O2 induced the expression of ZmCPK11 and increased the activity of ZmCPK11, while H2O2 was required for the ABA-induced increases in the expression and the activity of ZmCPK11. The transient gene expression analysis and the transient RNA interference (RNAi) test in protoplasts showed that ZmCPK11 is involved in ABA-induced up-regulation of the expression and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), and in the production of H2O2. Further, ZmCPK11 was shown to be required for the up-regulation of the expression and the activity of ZmMPK5 in ABA signalling, but ZmMPK5 had very little effect on the ABA-induced up-regulation of the expression and the activity of ZmCPK11. Moreover, the transient gene expression analysis in combination with the transient RNAi test in protoplasts showed that ZmCPK11 acts upstream of ZmMPK5 to regulate the activities of antioxidant enzymes. These results indicate that ZmCPK11 is involved in ABA-induced antioxidant defence and functions upstream of ZmMPK5 in ABA signalling in maize. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO), hydrogen peroxide (H2O2), and calcium (Ca2+)/calmodulin (CaM) are all required for abscisic acid (ABA)-induced antioxidant defence. Ca2+/CaM-dependent protein kinase (CCaMK) is a strong candidate for the decoder of Ca2+ signals. However, whether CCaMK is involved in ABA-induced antioxidant defence is unknown. The results of the present study show that exogenous and endogenous ABA induced increases in the activity of ZmCCaMK and the expression of ZmCCaMK in leaves of maize. Subcellular localization analysis showed that ZmCCaMK is located in the nucleus, the cytoplasm, and the plasma membrane. The transient expression of ZmCCaMK and the RNA interference (RNAi) silencing of ZmCCaMK analysis in maize protoplasts revealed that ZmCCaMK is required for ABA-induced antioxidant defence. Moreover, treatment with the NO donor sodium nitroprusside (SNP) induced the activation of ZmCCaMK and the expression of ZmCCaMK. Pre-treatments with an NO scavenger and inhibitor blocked the ABA-induced increases in the activity and the transcript level of ZmCCaMK. Conversely, RNAi silencing of ZmCCaMK in maize protoplasts did not affect the ABA-induced NO production, which was further confirmed using a mutant of OsCCaMK, the homologous gene of ZmCCaMK in rice. Moreover, H2O2 was also required for the ABA activation of ZmCCaMK, and pre-treatments with an NO scavenger and inhibitor inhibited the H2O2-induced increase in the activity of ZmCCaMK. Taken together, the data clearly suggest that ZmCCaMK is required for ABA-induced antioxidant defence, and H2O2-dependent NO production plays an important role in the ABA-induced activation of ZmCCaMK. [ABSTRACT FROM PUBLISHER]

C2H2-type zinc finger proteins (ZFPs) are thought to play important roles in modulating the responses of plants to drought, salinity and oxidative stress. However, direct evidence is lacking for the involvement of these ZFPs in abscisic acid (ABA)-induced antioxidant defense in plants. In this study, the role of the rice ( Oryza sativa L. sub. japonica cv. Nipponbare) C2H2-type ZFP ZFP182 in ABA-induced antioxidant defense and the relationship between ZFP182 and two rice MAPKs, OsMPK1 and OsMPK5 in ABA signaling were investigated. ABA treatment induced the increases in the expression of ZFP182, OsMPK1 and OsMPK5, and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in rice leaves. The transient gene expression analysis and the transient RNA interference (RNAi) analysis in protoplasts showed that ZFP182, OsMPK1 and OsMPK5 are involved in ABA-induced up-regulation in the activities of SOD and APX. Besides, OsMPK1 and OsMPK5 were shown to be required for the up-regulation in the expression of ZFP182 in ABA signaling, but ZFP182 did not mediate the ABA-induced up-regulation in the expression of OsMPK1 and OsMPK5. These results indicate that ZFP182 is required for ABA-induced antioxidant defense and the expression of ZFP182 is regulated by rice MAPKs in ABA signaling. [ABSTRACT FROM AUTHOR]

The antagonism between abscisic acid (ABA) and gibberellin (GA) plays a key role in controlling seed germination, but the mechanism of antagonism during this process is not known. The possible links among ABA, reactive oxygen species (ROS), ascorbic acid (ASC), and GA during rice seed germination were investigated. Unlike in non-seed tissues where ROS production is increased by ABA, ABA reduced ROS production in imbibed rice seeds, especially in the embryo region. Such reduced ROS also led to an inhibition of ASC production. GA accumulation was also suppressed by a reduced ROS and ASC level, which was indicated by the inhibited expression of GA biosynthesis genes, amylase genes, and enzyme activity. Application of exogenous ASC can partially rescue seed germination from ABA treatment. Production of ASC, which acts as a substrate in GA biosynthesis, was significantly inhibited by lycorine which thus suppressed the accumulation of GA. Consequently, expression of GA biosynthesis genes was suppressed by the low levels of ROS and ASC in ABA-treated seeds. It can be concluded that ABA regulates seed germination in multiple dimensions. ROS and ASC are involved in its inhibition of GA biosynthesis. [ABSTRACT FROM PUBLISHER]

Abstract: Hexavalent chromium (VI) is a cytotoxic metal ion in plants. However, the mechanisms involved in the cellular response to the metal have not yet been well established. In plants, mitogen-activated protein kinase (MAPK) cascades play an important role in signal transduction related to biotic and abiotic stresses. In the present study, we investigated the Cr(VI)-induced MAPKs activation and the correlative mechanism of activation in maize (Zea mays L.) roots. Cr(VI) elicited a remarkable increase in a 45-kDa myelin basic protein (MBP) kinase activity with MAPK-like characteristics, which was identified as ZmMPK5 by immunokinase and immunoblot assays. Pretreatment with DMTU, a peroxide hydrogen (H2O2) scavenger, and DPI, a NADPH oxidase inhibitor, the Cr(VI)-induced ZmMPK5 activation was almost completely suppressed, suggesting that Cr(VI)-activated ZmMPK5 requires for H2O2. Application of exogenous sodium nitroprusside (SNP), a nitric oxide (NO) donor, could activate ZmMPK5. Pretreatment with cPTIO and l-NAME, a NO scavenger and a nitric oxide synthase (NOS) inhibitor, respectively, Cr(VI)-induced ZmMPK5 activation was attenuated effectively, implying that NO is involved in Cr(VI)-activated ZmMPK5. Furthermore, a calcium-dependent protein kinase (CDPK) antagonist, W7, abolished Cr(VI)-stimulated ZmMPK5 activation, indicating that CDPKs may participate in the ZmMPK5 activation. The results obtained suggest that Cr(VI)-induced activation of ZmMPK5, a candidate for MAPK signaling cascades, can be modulated by other distinct signaling pathways. [Copyright &y& Elsevier]

Using pharmacological and biochemical approaches, the role of protein phosphorylation and the interrelationship between water stress-enhanced kinase activity, antioxidant enzyme activity, hydrogen peroxide (H2O2) accumulation and endogenous abscisic acid in maize ( Zea mays L.) leaves were investigated. Water-stress upregulated the activities of total protein phosphorylation and Ca2+-dependent protein kinase, and the upregulation was blocked in abscisic acid-deficient vp5 mutant. Furthermore, pretreatments with a nicotinamide adenine dinucleotide phosphate oxidase inhibitor and a scavenger of H2O2 significantly reduced the increased activities of total protein kinase and Ca2+-dependent protein kinase in maize leaves exposed to water stress. Pretreatments with different protein kinase inhibitors also reduced the water stress-induced H2O2 production and the water stress-enhanced activities of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase. The data suggest that protein phosphorylation and H2O2 generation are required for water stress-induced antioxidant defense in maize leaves and that crosstalk between protein phosphorylation and H2O2 generation may occur. [ABSTRACT FROM AUTHOR]

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. 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. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is a bioactive molecule involved in many biological events, and has been reported as pro-oxidant as well as anti-oxidant in plants. In the present study, the sources of NO production under water stress, the role of NO in water stress-induced hydrogen peroxide (H2O2) accumulation and subcellular activities of anti-oxidant enzymes in leaves of maize ( Zea mays L.) plants were investigated. Water stress induced defense increases in the generation of NO in maize mesphyll cells and the activity of nitric oxide synthase (NOS) in the cytosolic and microsomal fractions of maize leaves. Water stress-induced defense increases in the production of NO were blocked by pretreatments with inhibitors of NOS and nitrate reductase (NR), suggesting that NO is produced from NOS and NR in leaves of maize plants exposed to water stress. Water stress also induced increases in the activities of the chloroplastic and cytosolic anti-oxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), and the increases in the activities of anti-oxidant enzymes were reduced by pretreatments with inhibitors of NOS and NR. Exogenous NO increases the activities of water stress-induced subcellular anti-oxidant enzymes, which decreases accumulation of H2O2. Our results suggest that NOS and NR are involved in water stress-induced NO production and NOS is the major source of NO. The potential ability of NO to scavenge H2O2 is, at least in part, due to the induction of a subcellular anti-oxidant defense. [ABSTRACT FROM AUTHOR]

Background: We previously developed several strategies to engineer plants to produce cost-efficient biofuels from plant biomass. Engineered Arabidopsis plants with low xylan and lignin content showed normal growth and improved saccharification efficiency under standard growth conditions. However, it remains to be determined whether these engineered plants perform well under drought stress, which is the primary source of abiotic stress in the field. Results: Upon exposing engineered Arabidopsis plants to severe drought, we observed better survival rates in those with a low degree of xylan acetylation, low lignin, and low xylan content compared to those in wild-type plants. Increased pectic galactan content had no effect on drought tolerance. The drought-tolerant plants exhibited low water loss from leaves, and drought-responsive genes ( RD29A , RD29B , DREB2A ) were generally up-regulated under drought stress, which did not occur in the well-watered state. When compared with the wild type, plants with low lignin due to expression of QsuB, a 3-dehydroshikimate dehydratase, showed a stronger response to abscisic acid (ABA) in assays for seed germination and stomatal closure. The low-lignin plants also accumulated more ABA in response to drought than the wild-type plants. On the contrary, the drought tolerance in the engineered plants with low xylan content and low xylan acetylation was not associated with differences in ABA content or response compared to the wild type. Surprisingly, we found a significant increase in galactose levels and sugar released from the low xylan-engineered plants under drought stress. Conclusions: This study shows that plants engineered to accumulate less lignin or xylan are more tolerant to drought and activate drought responses faster than control plants. This is an important finding because it demonstrates that modification of secondary cell walls does not necessarily render the plants less robust in the environment, and it shows that substantial changes in biomass composition can be achieved without compromising plant resilience. [ABSTRACT FROM AUTHOR]