ABA signal transduction

A histone deacetylase, FaSRT1-2, plays multiple roles in regulating fruit ripening, plant growth and stresses resistance of cultivated strawberry

Sirtuins (SRTs) are a group of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase that target both histone and nonhistone proteins. The biological function of SRT in horticultural plants has been rarely studied. In this study, FaSRT1-2 was identified as a key member of the 8 FaSRTs encoded in cultivated strawberry genome. Transient overexpression of FaSRT1-2 in strawberry fruit accelerated ripening, increased the content of anthocyanins and sugars, enhanced ripening-related gene expression. Moreover, stable transformation of FaSRT1-2 in strawberry plants resulted in enhanced vegetative growth, increased sensitivity to heat stress and increased susceptibility to Botrytis cinerea infection. Interestingly, knocking out the homologous gene in woodland strawberry had the opposite effects. Additionally, we found the content of stress-related hormone abscisic acid (ABA) was decreased, while the growth-related gibberellin (GA) concentration was increased in FaSRT1-2 overexpression lines. Gene expression analysis revealed induction of heat shock proteins, transcription factors, stress-related and antioxidant genes in the FaSRT1-2-overexpressed plants while knocked-out of the gene had the opposite impact. In conclusion, our findings demonstrated that FaSRT1-2 could positively promote strawberry plant vegetative growth and fruit ripening by affecting ABA and GA pathways. However, it negatively regulates the resistance to heat stress and B. cinerea infection by influencing the related gene expression.

Cloning of the Arabidopsis SMAP2 promoter and analysis of its expression activity

The SMALL ACIDIC PROTEIN (SMAP) gene is evolutionarily indispensable for organisms. There are two copies of the SMAP gene in the Arabidopsis thaliana genome, namely, SMAP1 and SMAP2. The function of SMAP2 is similar to that of SMAP1, and both can mediate 2,4-D responses in the root of Arabidopsis. This study cloned the AtSMAP2 genetic promoter sequence. Two promoter fragments of different lengths were designed according to the distribution of their cis-acting elements, and the corresponding β- glucuronidase (GUS) expression vector was constructed. The expression activity of promoters of two lengths, 1993 bp and 997 bp, was studied by the genetic transformation in Arabidopsis. The prediction results of cis-acting elements in the promoter show that there are many hormone response elements in 997 bp, such as three abscisic acid response elements ABRE, gibberellin response elements P-box and GARE-motif and auxin response element AuxRR-core. Through GUS histochemical staining and qRT‒PCR analysis, it was found that the higher promoter activity of PAtSMAP2-997, compared to PAtSMAP2-1993, drove the expression of GUS genes at higher levels in Arabidopsis, especially in the root system. The results provide an important basis for subsequent studies on the regulation of AtSMAP2 gene expression and biological functions.

Bioinformatic Analysis of the BTB Gene Family in Paulownia fortunei and Functional Characterization in Response to Abiotic and Biotic Stresses

To learn about the gene structure, phylogenetic evolution, and function under biotic and abiotic stresses of BTB (Bric-a-Brac/Tramtrack/Broad Complex) genes in Paulownia fortunei, a whole-genome sequence evaluation was carried out, and a total of 62 PfBTB genes were identified. The phylogenetic analysis showed that PfBTB proteins are divided into eight groups, and these proteins are highly conserved. PfBTB genes were unevenly distributed on 17 chromosomes. The colinearity analysis found that fragment replication and tandem replication are the main modes of gene amplification in the PfBTB family. The analysis of cis-acting elements suggests that PfBTB genes may be involved in a variety of biological processes. The transcriptomic analysis results showed that PfBTB3/12/14/16/19/36/44 responded to Paulownia witches' broom (PaWB), while PfBTB1/4/17/43 responded to drought stress, and the RT-qPCR results further support the reliability of transcriptome data. In addition, the association analysis between miRNA and transcriptome revealed a 91-pair targeting relationship between miRNAs and PfBTBs. In conclusion, the BTB genes in Paulownia are systematically identified in this research. This work provides useful knowledge to more fully appreciate the potential functions of these genes and their possible roles in the occurrence of PaWB and in response to stress.

Genome-wide identification and expression analysis of the cucumber PYL gene family

Abscisic acid (ABA) is a very important hormone in plants. It regulates growth and development of plants and plays an important role in biotic and abiotic stresses. The Pyrabactin resistance 1-like (PYR/PYL) proteins play a central role in ABA signal transduction pathways. The working system of PYL genes in cucumber, an important economical vegetable (Cucumis sativus L.), has not been fully studied yet. Through bioinformatics, a total of 14 individual PYL genes were identified in Chinese long '9930' cucumber. Fourteen PYL genes were distributed on six chromosomes of cucumber, and their encoded proteins predicted to be distributed in cytoplasm and nucleus. Based on the phylogenetic analysis, the PYL genes of cucumber, Arabidopsis, rice, apple, Brachypodium distachyon and soybeancould be classified into three groups. Genetic structures and conserved domains analysis revealed that CsPYL genes in the same group have similar exons and conserved domains. By predicting cis-elements in the promoters, we found that all CsPYL members contained hormone and stress-related elements. Additionally, the expression patterns of CsPYL genes were specific in tissues. Finally, we further examined the expression of 14 CsPYL genes under ABA, PEG, salt stress. The qRT-PCR results showed that most PYL gene expression levels were up-regulated. Furthermore, with different treatments about 3h, the relative expression of PYL8 was up-regulated and more than 20 times higher than 0h. It indicated that this gene may play an important role in abiotic stress.

Integrating Wheat Nucleolus Structure and Function: Variation in the Wheat Ribosomal RNA and Protein Genes

We review the coordinated production and integration of the RNA (ribosomal RNA, rRNA) and protein (ribosomal protein, RP) components of wheat cytoplasmic ribosomes in response to changes in genetic constitution, biotic and abiotic stresses. The components examined are highly conserved and identified with reference to model systems such as human, Arabidopsis, and rice, but have sufficient levels of differences in their DNA and amino acid sequences to form fingerprints or gene haplotypes that provide new markers to associate with phenotype variation. Specifically, it is argued that populations of ribosomes within a cell can comprise distinct complements of rRNA and RPs to form units with unique functionalities. The unique functionalities of ribosome populations within a cell can become central in situations of stress where they may preferentially translate mRNAs coding for proteins better suited to contributing to survival of the cell. In model systems where this concept has been developed, the engagement of initiation factors and elongation factors to account for variation in the translation machinery of the cell in response to stresses provided the precedents. The polyploid nature of wheat adds extra variation at each step of the synthesis and assembly of the rRNAs and RPs which can, as a result, potentially enhance its response to changing environments and disease threats.

A Review of Crop Water Stress Assessment Using Remote Sensing

Currently, the world is facing high competition and market risks in improving yield, crop illness, and crop water stress. This could potentially be addressed by technological advancements in the form of precision systems, improvements in production, and through ensuring the sustainability of development. In this context, remote-sensing systems are fully equipped to address the complex and technical assessment of crop production, security, and crop water stress in an easy and efficient way. They provide simple and timely solutions for a diverse set of ecological zones. This critical review highlights novel methods for evaluating crop water stress and its correlation with certain measurable parameters, investigated using remote-sensing systems. Through an examination of previous literature, technologies, and data, we review the application of remote-sensing systems in the analysis of crop water stress. Initially, the study presents the relationship of relative water content (RWC) with equivalent water thickness (EWT) and soil moisture crop water stress. Evapotranspiration and sun-induced chlorophyll fluorescence are then analyzed in relation to crop water stress using remote sensing. Finally, the study presents various remote-sensing technologies used to detect crop water stress, including optical sensing systems, thermometric sensing systems, land-surface temperature-sensing systems, multispectral (spaceborne and airborne) sensing systems, hyperspectral sensing systems, and the LiDAR sensing system. The study also presents the future prospects of remote-sensing systems in analyzing crop water stress and how they could be further improved.

Crosstalk between abscisic acid and nitric oxide under heat stress: exploring new vantage points

Heat stress adversely affects plants growth potential. Global warming is reported to increase in the intensity, frequency, and duration of heatwaves, eventually affecting ecology, agriculture and economy. With an expected increase in average temperature by 2-3 °C over the next 30-50 years, crop production is facing a severe threat to sub-optimum growth conditions. Abscisic acid (ABA) and nitric oxide (NO) are growth regulators that are involved in the adaptation to heat stress by affecting each other and changing the adaptation process. The interaction between these molecules has been discussed in various studies in general or under stress conditions; however, regarding high temperature, their interaction has little been worked out. In the present review, the focus is shifted on the role of these molecules under heat stress emphasizing the different possible interactions between ABA and NO as both regulate stomatal closure and other molecules including hydrogen peroxide (H₂O₂), hydrogen sulfide (H₂S), antioxidants, proline, glycine betaine, calcium (Ca²⁺) and heat shock protein (HSP). Exploring the crosstalk between ABA and NO with other molecules under heat stress will provide us with a comprehensive knowledge of plants mechanism of heat tolerance which could be useful to develop heat stress-resistant varieties.

Identification of a 193 bp promoter region of TaNRX1-D gene from common wheat that contributes to osmotic or ABA stress inducibility in transgenic Arabidopsis

BACKGROUND

Cloning and characterizing the drought-inducible promoters is essential for their use in crop resistance's genetic improvement. Previous studies have shown that the TaNRX1-D gene participates in regulating the response of wheat to drought stress. However, its promoter has not yet been identified.

OBJECTIVE

In this study, we aimed to characterize the promoter of the TaNRX1-D gene.

METHODS

The promoter of TaNRX1-D (named P0, 2081 bp) was isolated from common wheat with several cis-acting elements that regulate in response to abiotic stresses and some core cis-acting elements. Functional verification of the promoter, eight 5'-deletion fragments of TaNRX1-D promoter, was fused to the β-glucuronidase (GUS) gene P0::GUS ~ P7::GUS and transformed into Arabidopsis, respectively. Agrobacterium-mediated GUS transient assay the P6a and P6b promoter regions in tobacco leaves under normal, osmotic or ABA stress.

RESULTS

Activity analysis of the full-length promoter (P0) showed that the intensity of stronger β-glucuronidase (GUS) staining in the roots and leaves was obtained during the growth of transgenic Arabidopsis. P0::GUS displayed the GUS activity was much higher in the roots and leaves than in other parts of the transgenic plant under normal conditions, which was similarly within wheat. Analysis of the 5'-deletion fragments revealed that P0::GUS ~ P6::GUS responded well upon exposure to osmotic (polyethylene glycol-6000, PEG6000) and abscisic acid (ABA) stress treatments and expressed significantly higher GUS activity than the CaMV35S promoter (35S::GUS), while P7::GUS did not. GUS transient assay in tobacco leaves showed that the GUS activities of P6a and P6b were lower than P6 in the PEG6000 and ABA stresses.

CONCLUSION

The 193 bp (P6) segment was considered the core region of TaNRX1-D responding to PEG6000 or ABA treatment. GUS activity assay in transgenic Arabidopsis showed that this segment was sufficient for the PEG6000 or ABA stress response. The identified 193 bp promoter of TaNRX1-D in this study will help breed osmotic or ABA tolerant crops. The 36 bp segment between P6 and P6b (-193 to -157 bp) was considered the critical sequence for the TaNRX1-D gene responding to PEG6000 or ABA treatment.

Genome-wide identification and functional analysis of U-box E3 ubiquitin ligases gene family related to drought stress response in Chinese white pear (Pyrus bretschneideri)

BACKGROUND

The plant U-box (PUB) proteins are a family of ubiquitin ligases (E3) enzymes that involved in diverse biological processes, as well as in responses to plant stress response. However, the characteristics and functional divergence of the PUB gene family have not yet been previously studied in the Chinese white pear (Pyrus bretschneideri).

RESULTS

In the present study, we identified 62 PbrPUBs in Chinese white pear genome. Based on the phylogenetic relationship, 62 PUB genes were clustered into five groups. The results of conserved motif and gene structure analysis supported the classification phylogenetic tree. The PbrPUB genes were unevenly distribution on 17 pear chromosomes, chromosome 15 housed most member of PUB family, with eight PUB genes. Cis-acting element analysis indicated that PUB genes might participate in diverse biological processes, especially in the response to abiotic stresses. Based on RNA-data from 'Dangshansuli' at seven tissues, we found that PUB genes exhibited diverse of expression level in seven tissues, and qRT-PCR experiment further supported the reliable of RNA-Seq data. To identify candidate genes associated with resistance, we conducted qRT-PCR experiment the expression level of pear seed plant under four abiotic stresses, including: ABA, dehydration, salt and cold treatment. One candidate PUB gene associated with dehydration stress was selected to conduct further functional experiment. Subcellular localization revealed PbrPUB18 protein was located on cell nucleus. Furthermore, heterologous over-expression of PbrPUB18 in Arabidopsis indicated that the over-expression of PbrPUB18 could enhance resistance in drought treatment. In conclusions, we systematically identified the PUB genes in pear, and provided useful knowledge for functional identification of PUB genes in pear.

Characterization of abscisic acid (ABA) receptors and analysis of genes that regulate rutin biosynthesis in response to ABA in Fagopyrum tataricum

Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) is a nutritional crop, which has high rutin, and is good for health. Until now, plant genetic engineering is insufficient for Tartary buckwheat. Abscisic acid (ABA), as one of phytohormones, is involved in the regulation of plant growth and development, and responses to diverse environmental challenges. Although ABA receptors have been well characterized in Arabidopsis, it is little understood in Tartary buckwheat. In this study, we identified 12 ABA receptors, designated as FtRCAR1 through FtRCAR12 in Tartary buckwheat. FtRCARs are divided into three subfamily. Based on the similarity, we could predict that FtRCARs comprise of the monomeric (FtRCAR1, 3, 4, 5, 9, 10, 11 and 12) and the dimeric (FtRCAR2, 7 and 8) state in solution. The analysis of the transcript pattern indicated that most of FtRCARs were significantly variable among the root, stem, leaf, flower and seed, while FtRCAR4 transcript was undetectable under in all tissues. The transcript levels of FtRCARs under ABA treatment indicated that most FtRCARs transcripts were depressed, indicating a possible feedback regulation of ABA signaling. The analysis of rutin biosynthesis related-genes indicated that ABA up-graduated CHS, CHI, F3'H, F3H and FLS transcript levels, while transcripts of 4CL and PAL were down-regulated. In addition, the transcription factors that mediated the rutin biosynthesis related-genes were also regulated by exogenous ABA. Thus, the identification and the characterization of FtRCARs would enable us to further understand the role of ABA signal in Tartary buckwheat.

Synthesis, Functionalization, and Bioapplications of Two-Dimensional Boron Nitride Nanomaterials

Two-dimensional boron nitride nanostructures (2D-BNNs) have been increasingly investigated for their applications in several scientific and technological areas. This considerable interest is due to their unique physicochemical properties, which include high hydrophobicity, heat and electrical insulation, resistance to oxidation, antioxidation capacity, thermal conductivity, high chemical stability, mechanical strength, and hydrogen storage capacity. They are also used as fillers, antibacterial agents, protective coating agents, lubricants, boron neutron capture therapy agents, nanocarriers for drug delivery, and for the receptor phase in chemosensors. The investigations for their use in medicine and biomedicine are very promising, including cancer therapy and wound healing. In this review, 2D-BNNs synthesis and their surface modification strategies, biocompatibility, and bioapplication studies are discussed. Finally, a perspective for the future use of these novel nanomaterials in the biomedical field is provided.

Responses of PYR/PYL/RCAR ABA Receptors to Contrasting stresses, Heat and Cold in Arabidopsis

Plants growing in natural habitats have evolved a wide range of mechanisms to copy with environmental challenging, including biotic and abiotic stresses. Abiotic stresses-induced increases in Abscisic acid (ABA) levels in plants suffering from stresses, including drought, cold or heat stress. To explore the function of the core components in ABA signaling, we used the overexpression of RCARs transgenic plants to expose in heat or cold stress. In this study, overexpression of RCAR12 or RCAR13 (R12-OE or R13-OE) transgenic plants had higher germination and survival rate than the wild-type (WT) Arabidopsis, indicating that they are both positively responsive to the high temperature. And the heat shock genes HSP18.2 and HSP70 were significantly induced by RCAR12 or RCAR13. Further, the results inferred that the over-expression of RCAR12 or RCAR13 could tolerance the cold stress, through induction CBFs expressions, the cold-responsive genes when plants were challenged the cold tress. And when complementation of RCAR12 to the 1124 mutant (R12:1124), the results indicated that RCAR12 could recover the insensitivity of 1124 to heat and cold stresses. Hence, we propose that RCAR12 and RCAR13, the ABA receptors, may play the positive roles in regulating the extreme temperature, including cold and high temperature in Arabidopsis.

The Role of the S40 Gene Family in Leaf Senescence

Senescence affect different traits of plants, such as the ripening of fruit, number, quality and timing of seed maturation. While senescence is induced by age, growth hormones and different environmental stresses, a highly organized genetic mechanism related to substantial changes in gene expression regulates the process. Only a few genes associated to senescence have been identified in crop plants despite the vital significance of senescence for crop yield. The S40 gene family has been shown to play a role in leaf senescence. The barley HvS40 gene is one of the senescence marker genes which shows expression during age-dependent as well as dark-induced senescence. Like barley HvS40, the Arabidopsis AtS40-3 gene is also induced during natural senescence as well as in response to treatment with abscisic acid, salicylic acid, darkness and pathogen attack. It is speculated that rice OsS40 has a similar function in the leaf senescence of rice.

'Bending' models of halotropism: incorporating protein phosphatase 2A, ABCB transporters, and auxin metabolism

Salt stress causes worldwide reductions in agricultural yields, a problem that is exacerbated by the depletion of global freshwater reserves and the use of contaminated or recycled water (i.e. effluent water). Additionally, salt stress can occur as cultivated areas are subjected to frequent rounds of irrigation followed by periods of moderate to severe evapotranspiration, which can result in the heterogeneous aggregation of salts in agricultural soils. Our understanding of the later stages of salt stress and the mechanisms by which salt is transported out of cells and roots has greatly improved over the last decade. The precise mechanisms by which plant roots perceive salt stress and translate this perception into adaptive, directional growth away from increased salt concentrations (i.e. halotropism), however, are not well understood. Here, we provide a review of the current knowledge surrounding the early responses to salt stress and the initiation of halotropism, including lipid signaling, protein phosphorylation cascades, and changes in auxin metabolism and/or transport. Current models of halotropism have focused on the role of PIN2- and PIN1-mediated auxin efflux in initiating and controlling halotropism. Recent studies, however, suggest that additional factors such as ABCB transporters, protein phosphatase 2A activity, and auxin metabolism should be included in the model of halotropic growth.

Design and Functional Characterization of a Novel Abscisic Acid Analog

The phytohormone abscisic acid (ABA) plays a crucial role in mediating plant growth and development by recruiting genetically redundant ABA receptors. To overcome its oxidation inactivation, we developed a novel ABA analog named 2',3'-benzo-iso-ABA (iso-PhABA) and studied its function and structural characterization with A. thaliana ABA receptors. The (+)-iso-PhABA form showed much higher ABA-like activities than (+)-ABA including inhibitory effects on the seed germination of lettuce and A. thaliana, wheat embryo germination and rice seedling elongation. The PP2C (protein phosphatases 2C) activity assay showed that (+)-iso-PhABA acted as a potent and selective ABA receptor agonist, which is preferred to PYL10. In some cases, (-)-iso-PhABA showed moderate to high activity for the PYL protein inhibiting PP2C activity, suggesting different mechanisms of action of iso-PhABA and ABA. The complex crystal structure of iso-PhABA with PYL10 was determined and elucidated successfully, revealing that (+)-iso-PhABA was better coordinated in the same binding pocket compared to (+)-ABA. Moreover, the detailed interaction network of iso-PhABA/PYL10 was disclosed and involves hydrogen bonds and multiple hydrophobic interactions that provide a robust framework for the design of novel ABA receptor agonists/antagonists.

Role of abscisic acid (ABA) in activating antioxidant tolerance responses to desiccation stress in intertidal seaweed species

The hormone ABA regulates the oxidative stress state under desiccation in seaweed species; an environmental condition generated during daily tidal changes. Desiccation is one of the most important factors that determine the distribution pattern of intertidal seaweeds. Among most tolerant seaweed is Pyropia orbicularis, which colonizes upper intertidal zones along the Chilean coast. P. orbicularis employs diverse mechanisms of desiccation tolerance (DT) (among others, e.g., antioxidant activation, photoinhibition, and osmo-compatible solute overproduction) such as those used by resurrection plants and bryophytes. In these organisms, the hormone abscisic acid (ABA) plays an important role in regulating responses to water deficit, including gene expression and the activity of antioxidant enzymes. The present study determined the effect of ABA on the activation of antioxidant responses during desiccation in P. orbicularis and in the sensitive species Mazzaella laminarioides and Lessonia spicata. Changes in endogenous free and conjugated ABA, water content during the hydration-desiccation cycle, enzymatic antioxidant activities [ascorbate peroxidase (AP), catalase (CAT) and peroxiredoxine (PRX)], and levels of lipid peroxidation and cell viability were evaluated. The results showed that P. orbicularis had free ABA levels 4-7 times higher than sensitive species, which was overproduced during water deficit. Using two ABA inhibitors (sodium tungstate and ancymidol), ABA was found to regulate the activation of the antioxidant enzymes activities during desiccation. In individuals exposed to exogenous ABA the enzyme activity increased, concomitant with low lipid peroxidation and high cell viability. These results demonstrate the participation of ABA in the regulation of DT in seaweeds, and suggest that regulatory mechanisms with ABA signaling could be of great importance for the adaptation of these organisms to dehydration.

H2O2 inhibits ABA-signaling protein phosphatase HAB1

Due to its ability to be rapidly generated and propagated over long distances, H₂O₂ is an important second messenger for biotic and abiotic stress signaling in plants. In response to low water potential and high salt concentrations sensed in the roots of plants, the stress hormone abscisic acid (ABA) activates NADPH oxidase to generate H₂O₂, which is propagated in guard cells in leaves to induce stomatal closure and prevent water loss from transpiration. Using a reconstituted system, we demonstrate that H₂O₂ reversibly prevents the protein phosphatase HAB1, a key component of the core ABA-signaling pathway, from inhibiting its main target in guard cells, SnRK2.6/OST1 kinase. We have identified HAB1 C186 and C274 as H₂O₂-sensitive thiols and demonstrate that their oxidation inhibits both HAB1 catalytic activity and its ability to physically associate with SnRK2.6 by formation of intermolecular dimers.

MADS-box transcription factor AGL21 regulates lateral root development and responds to multiple external and physiological signals

Plant root system morphology is dramatically influenced by various environmental cues. The adaptation of root system architecture to environmental constraints, which mostly depends on the formation and growth of lateral roots, is an important agronomic trait. Lateral root development is regulated by the external signals coordinating closely with intrinsic signaling pathways. MADS-box transcription factors are known key regulators of the transition to flowering and flower development. However, their functions in root development are still poorly understood. Here we report that AGL21, an AGL17-clade MADS-box gene, plays a crucial role in lateral root development. AGL21 was highly expressed in root, particularly in the root central cylinder and lateral root primordia. AGL21 overexpression plants produced more and longer lateral roots while agl21 mutants showed impaired lateral root development, especially under nitrogen-deficient conditions. AGL21 was induced by many plant hormones and environmental stresses, suggesting a function of this gene in root system plasticity in response to various signals. Furthermore, AGL21 was found positively regulating auxin accumulation in lateral root primordia and lateral roots by enhancing local auxin biosynthesis, thus stimulating lateral root initiation and growth. We propose that AGL21 may be involved in various environmental and physiological signals-mediated lateral root development and growth.

Antagonistic regulation of Arabidopsis growth by brassinosteroids and abiotic stresses

To withstand ever-changing environmental stresses, plants are equipped with phytohormone-mediated stress resistance mechanisms. Salt stress triggers abscisic acid (ABA) signaling, which enhances stress tolerance at the expense of growth. ABA is thought to inhibit the action of growth-promoting hormones, including brassinosteroids (BRs). However, the regulatory mechanisms that coordinate ABA and BR activity remain to be discovered. We noticed that ABA-treated seedlings exhibited small, round leaves and short roots, a phenotype that is characteristic of the BR signaling mutant, brassinosteroid insensitive1-9 (bri1-9). To identify genes that are antagonistically regulated by ABA and BRs, we examined published Arabidopsis microarray data sets. Of the list of genes identified, those upregulated by ABA but downregulated by BRs were enriched with a BRRE motif in their promoter sequences. After validating the microarray data using quantitative RT-PCR, we focused on RD26, which is induced by salt stress. Histochemical analysis of transgenic Arabidopsis plants expressing RD26pro:GUS revealed that the induction of GUS expression after NaCl treatment was suppressed by co-treatment with BRs, but enhanced by co-treatment with propiconazole, a BR biosynthetic inhibitor. Similarly, treatment with bikinin, an inhibitor of BIN2 kinase, not only inhibited RD26 expression, but also reduced the survival rate of the plant following exposure to salt stress. Our results suggest that ABA and BRs act antagonistically on their target genes at or after the BIN2 step in BR signaling pathways, and suggest a mechanism by which plants fine-tune their growth, particularly when stress responses and growth compete for resources.

Silencing of TaBTF3 gene impairs tolerance to freezing and drought stresses in wheat

Basic transcription factor 3 (BTF3), the β-subunit of the nascent polypeptide-associated complex, is responsible for the transcriptional initiation of RNA polymerase II and is also involved in cell apoptosis, translation initiation regulation, growth, development, and other functions. Here, we report the impact of BTF3 on abiotic tolerance in higher plants. The transcription levels of the TaBTF3 gene, first isolated from wheat seedlings in our lab, were differentially regulated by diverse abiotic stresses and hormone treatments, including PEG-induced stress (20 % polyethylene glycol 6000), cold (4 °C), salt (100 mM NaCl), abscisic acid (100 μM), methyl jasmonate (50 μM), and salicylic acid (50 μM). Southern blot analysis indicated that, in the wheat genome, TaBTF3 is a multi-copy gene. Compared to BSMV-GFP-infected wheat plants (control), under freezing (-8 °C for 48 h) or drought stress (withholding water for 15 days) conditions, TaBTF3-silenced wheat plants showed lower survival rates, free proline content, and relative water content and higher relative electrical conductivity and water loss rate. These results suggest that silencing of the TaBTF3 gene may impair tolerance to freezing and drought stresses in wheat and that it may be involved in the response to abiotic stresses in higher plants.

Transcriptomic responses to aluminum stress in soybean roots

Aluminum (Al) toxicity is the primary limitation to crop production and plant growth in acid soils. Soybean has multiple mechanisms of Al resistance including the complexing and exclusion of Al in root apices by Al-induced citrate secretion. Microarray analysis is available for the identification of genes in soybean. In the present study, Affymetrix soybean genome array was used to identify the Al-induced differentially expressed genes in Al-resistant genotype Jiyu 70. With a cutoff of > 2.0-fold (p < 0.05) between non Al-treated and Al-treated root apices, 561 genes were upregulated and 78 genes were downregulated when roots were exposed to 30 μmol/L AlCl(3) for 4 h. Quantitative real-time PCR was used to test the microarray data. The analysis showed that nearly half of the Al-responsive genes were of unknown biological function. A higher proportion of genes related to transcription regulation and cell wall processes were observed in Al-induced up- and downregulated genes, respectively. Some genes homologous to the citrate transporter MATE family gene or C(2)H(2) family transcription factor gene, STOP1, were detected in our analysis. Some genes related to lignin deposition were upregulated, which might be related to Al-induced root elongation inhibition.

Developing a model of plant hormone interactions

Plant growth and development is influenced by mutual interactions among plant hormones. The five classical plant hormones are auxins, cytokinins, gibberellins, abscisic acid and ethylene. They are small diffusible molecules that easily penetrate between cells. In addition, newer classes of plant hormones have been identified such as brassinosteroids, jasmonic acid, salicylic acid and various small proteins or peptides. These hormones also play important roles in the regulation of plant growth and development. This review begins with a brief summary of the current findings on plant hormones. Based on this knowledge, a conceptual model about interactions among plant hormones is built so as to link and develop an understanding of the diverse functions of different plant hormones as a whole in plants.

Abscisic acid activates the murine microglial cell line N9 through the second messenger cyclic ADP-ribose

Abscisic acid (ABA) is a phytohormone regulating important functions in higher plants, notably responses to abiotic stress. Recently, chemical or physical stimulation of human granulocytes was shown to induce production and release of endogenous ABA, which activates specific cell functions. Here we provide evidence that ABA stimulates several functional activities of the murine microglial cell line N9 (NO and tumor necrosis factor-alpha production, cell migration) through the second messenger cyclic ADP-ribose and an increase of intracellular calcium. ABA production and release occur in N9 cells stimulated with bacterial lipopolysaccharide, phorbol myristate acetate, the chemoattractant peptide f-MLP, or beta-amyloid, the primary plaque component in Alzheimer disease. Finally, ABA priming stimulates N9 cell migration toward beta-amyloid. These results indicate that ABA is a pro-inflammatory hormone inducing autocrine microglial activation, potentially representing a new target for anti-inflammatory therapies aimed at limiting microglia-induced tissue damage in the central nervous system.

Tissue-specific expression of the PNZIP promoter is mediated by combinatorial interaction of different cis-elements and a novel transcriptional factor

Recent studies demonstrated that PNZIP and its homologs encode a special cyclase and play an important role in chlorophyll biosynthesis in higher plants. To investigate the molecular mechanism governing the PNZIP gene, the PNZIP promoter was isolated and analyzed. Deletion analysis indicated that G-box is an important element in the regulation of the reporter gene expression. Further mutation assay demonstrated that G-box and GATACT elements are necessary and sufficient for the high and tissue-specific expression of the GUS gene. Using yeast one-hybrid screening, we have isolated a novel tobacco bZIP protein, NtbZIP, which can specifically recognize the G-box of the PNZIP promoter. The NtbZIP protein shares a limited amino acid homology to Arabidopsis ABI5 and AtAREB1 and very low homology to other bZIP proteins. Northern blot analysis showed that the NtbZIP gene is not induced by exogenous ABA and is expressed in different tobacco organs. Cotransformation assays showed that the NtbZIP protein could activate the transcription of the GUS gene driven by the PNZIP promoter. Transgenic tobaccos analysis demonstrated that constitutively expressing antisense NtbZIP gene resulted in a lower NTZIP synthesis and reduced chlorophyll levels. We suggest that NTZIP is a target gene of NtbZIP, which is involved in the regulation of chlorophyll biosynthesis.

Abscisic acid is an endogenous stimulator of insulin release from human pancreatic islets with cyclic ADP ribose as second messenger

Abscisic acid (ABA) is a plant stress hormone recently identified as an endogenous pro-inflammatory cytokine in human granulocytes. Because paracrine signaling between pancreatic beta cells and inflammatory cells is increasingly recognized as a pathogenetic mechanism in the metabolic syndrome and type II diabetes, we investigated the effect of ABA on insulin secretion. Nanomolar ABA increases glucose-stimulated insulin secretion from RIN-m and INS-1 cells and from murine and human pancreatic islets. The signaling cascade triggered by ABA in insulin-releasing cells sequentially involves a pertussis toxin-sensitive G protein, cAMP overproduction, protein kinase A-mediated activation of the ADP-ribosyl cyclase CD38, and cyclic ADP-ribose overproduction. ABA is rapidly produced and released from human islets, RIN-m, and INS-1 cells stimulated with high glucose concentrations. In conclusion, ABA is an endogenous stimulator of insulin secretion in human and murine pancreatic beta cells. Autocrine release of ABA by glucose-stimulated pancreatic beta cells, and the paracrine production of the hormone by activated granulocytes and monocytes suggest that ABA may be involved in the physiology of insulin release as well as in its dysregulation under conditions of inflammation.

Novel rice OsSIPK is a multiple stress responsive MAPK family member showing rhythmic expression at mRNA level

We report isolation and transcriptional profiling of rice (Oryza sativa L.) mitogen-activated protein kinase (MAPK), OsSIPK (salicylic acid-induced protein kinase). OsSIPK gene is located on chromosome 6 most probably existing as a single copy in the rice genome, and encodes 398 amino acid polypeptide having the MAPK family signature and phosphorylation activation motif TEY. Steady state mRNA analyses of OsSIPK showed weak constitutive expression in leaves of 2-week-old rice seedlings. A time course (30-120 min) experiment using a variety of elicitors and stresses revealed that the OsSIPK mRNA is strongly induced by jasmonic acid (JA), salicylic acid (SA), ethephon, abscisic acid, cycloheximide (CHX), JA/SA + CHX, cantharidin, okadaic acid, hydrogen peroxide, chitosan, sodium chloride, and cold stress (12 degrees C), but not with wounding by cut, gaseous pollutants ozone, and sulfur dioxide, high temperature, ultraviolet C irradiation, sucrose, and drought. Its transcription was also found to be tissue-specifically regulated, and followed a rhythmic dark induction in leaves. Finally, we showed that the OsSIPK protein is localized to the nucleus. From these results, OsSIPK can be implicated in diverse stimuli-responsive signaling cascades and transcription of certain genes.

Combinatorial interactions of multiple cis-elements regulating the induction of the Arabidopsis XERO2 dehydrin gene by abscisic acid and cold

Multiple combinations of mutations in the promoter of the XERO2 dehydrin gene were used to identify elements involved in ABA and cold induction. Mutating one of the three ACGT elements (ACGT1) increases expression in the absence of cold or ABA. An AT-rich element is a novel partner (coupling element) of ACGT-containing ABA-responsive cis-elements. A 12-bp palindrome also acts as a coupling element for ABA induction and includes one of the three dehydration-responsive element/C-repeat (DRE/CRT) elements and two overlapping motifs (TGTCG and TCGGC) previously shown to be statistically enriched in ABA-dependent and 'VP1 or ABA'-dependent activated genes (Plant Physiol. 2005; 139:437). At least two of the DRE/CRT elements are required for significant cold induction. During cold induction the AT-rich element also functions as a coupling element and ACGT1 is involved in repressing this induction. Two of the ACGT and DRE/CRT elements overlap, and mutating a single base in the ACGT of either of the two GCCGACGT sequences while retaining a DRE element reduced both ABA and cold induction. Changing the spatial relationships between the elements by deletion, inversion or insertion of DNA sequences reduced both cold and ABA induction. Overexpression of CBF1, -2 or -3 induced XERO2 expression in untreated plants. The ABI5 transcription factor may have a role in ABA-induced XERO2 expression, whereas ABI3 and ABI4 do not. The GCA2 gene was essential for both cold and ABA induction. A combination of the same overlapping and shared elements is used in the regulation of transcription by ABA and cold.

Identification of new ABA- and MEJA-activated sugarcane bZIP genes by data mining in the SUCEST database

Sugarcane is generally propagated by cuttings of the stalk containing one or more lateral buds, which will develop into a new plant. The transition from the dormant into the active stage constitutes a complex phenomenon characterized by changes in accumulation of phytohormones and several other physiological aspects. Abscisic acid (ABA) and methyl-jasmonate (MeJA) are major signaling molecules, which influence plant development and stress responses. These plant regulators modulate gene expression with the participation of many transcriptional factors. Basic leucine zipper proteins (bZIPs) form a large family of transcriptional factors involved in a variety of plant physiological processes, such as development and responses to stress. Query sequences consisting of full-length protein sequence of each of the Arabidopsis bZIP families were utilized to screen the sugarcane EST database (SUCEST) and 86 sugarcane assembled sequences (SAS) coding for bZIPs were identified. cDNA arrays and RNA-gel blots were used to study the expression of these sugarcane bZIP genes during early plantlet development and in response to ABA and MeJA. Six bZIP genes were found to be differentially expressed during development. ABA and MeJA modulated the expression of eight sugarcane bZIP genes. Our findings provide novel insights into the expression of this large protein family of transcriptional factors in sugarcane.

Stress inducible expression of the DREB1A transcription factor from xeric, Hordeum spontaneum L. in turf and forage grass (Paspalum notatum Flugge) enhances abiotic stress tolerance

The dehydration-responsive element binding proteins (DREB1)/C-repeat (CRT) binding factors (CBF) function as transcription activators and bind to the DRE/CRT cis-acting element commonly present in the promoters of abiotic stress-regulated genes. A DREB1A transcription factor ortholog was isolated from a xeric, wild barley (Hordeum spontaneum L.) accession, originating from the Negev desert. Sequence comparison revealed a very high degree of sequence conservation of HsDREB1A to the published barley (Hordeum vulgare L.) DREB1A. Constitutive expression of the HsDREB1A gene was able to trans-activate a reporter gene under transcriptional control of the stress-inducible HVA1s and Dhn8 promoters. HsDREB1A was subcloned under transcriptional control of the stress-inducible barley HVA1s promoter and introduced into the apomictic bahiagrass (Paspalum notatum Flugge) cultivar 'Argentine'. HsDREB1A integration and stress inducible expression was detected in primary transgenic bahiagrass plants and apomictic seed progeny by Southern blot, RT-PCR and northern blot analysis respectively. Transgenic bahiagrass plants with stress-inducible expression of HsDREB1A survived severe salt stress and repeated cycles of severe dehydration stress under controlled environment conditions, in contrast to non-transgenic plants. The observed abiotic stress tolerance is very desirable in turf and forage grasses like bahiagrass, where seasonal droughts and irrigation restrictions affect establishment, persistence or productivity of this perennial crop.

A rice dehydration-inducible SNF1-related protein kinase 2 phosphorylates an abscisic acid responsive element-binding factor and associates with ABA signaling

By a differential cDNA screening technique, we have isolated a dehydration-inducible gene (designated OSRK1) that encodes a 41.8 kD protein kinase of SnRK2 family from Oryza sativa. The OSRK1 transcript level was undetectable in vegetative tissues, but significantly increased by hyperosmotic stress and Abscisic acid (ABA). To determine its biochemical properties, we expressed and isolated OSRK1 and its mutants as glutathione S-transferase fusion proteins in Escherichia coli. In vitro kinase assay showed that OSRK1 can phosphorylate itself and generic substrates as well. Interestingly, OSRK1 showed strong substrate preference for rice bZIP transcription factors and uncommon cofactor requirement for Mn(2+) over Mg(2+). By deletion of C-terminus 73 amino acids or mutations of Ser-158 and Thr-159 to aspartic acids (Asp) in the activation loop, the activity of OSRK1 was dramatically decreased. OSRK1 can transphosphorylate the inactive deletion protein. A rice family of abscisic acid-responsive element (ABRE) binding factor, OREB1 was phosphorylated in vitro by OSRK1 at multiple sites of different functional domains. MALDI-TOF analysis identified a phosphorylation site at Ser44 of OREB1 and mutation of the residue greatly decreased the substrate specificity for OSRK1. The recognition motif for OSRK1, RQSS is highly similar to the consensus substrate sequence of AMPK/SNF1 kinase family. We further showed that OSRK1 interacts with OREB1 in a yeast two-hybrid system and co-localized to nuclei by transient expression analysis of GFP-fused protein in onion epidermis. Finally, ectopic expression of OSRK1 in transgenic tobacco resulted in a reduced sensitivity to ABA in seed germination and root elongation. These findings suggest that OSRK1 is associated with ABA signaling, possibly through the phosphorylation of ABF family in vivo. The interaction between SnRK2 family kinases and ABF transcription factors may constitute an important part of cross-talk mechanism in the stress signaling networks in plants.

Intracellular pH signals in the induction of secondary pathways--the case of Eschscholzia californica

Transient peaks of the cytoplasmic pH are essential elements in a number of signal cascades that activate environmental responses or developmental processes in plant cells but little is known about the mechanisms of their generation. In many plant cells, elicitation of the hypersensitive response is preceded by a perturbation of the ionic balance at the plasma membrane including the inhibition of the proton pump and the influx of H+ from the apoplast. A basically different mechanism of cytoplasmic acidification that is fed by vacuolar protons has been discovered in cell suspensions of the California Poppy (Eschscholzia californica). These cells react to a yeast glycoprotein elicitor with the overproduction of benzophenanthridine alkaloids. Low elicitor concentrations trigger the biosynthesis of these phytoalexins without invoking elements of the hypersensitive response. Accumulated data support the existence of a signal path that includes the following steps: Links between the above events that connect them within a distinct signal path are substantiated by the phenotypes of transformed cell lines that either display lowered Galpha levels due to antisense transformation or express Galpha-binding antibodies in the cytoplasm. All of these cell lines lack the elicitor-activation of PLA2 and of vacuolar proton fluxes and show an impaired phytoalexin response to low elicitor concentrations. High elicitor concentrations trigger alkaloid biosynthesis via an increase of jasmonate at a pH-independent signal path.

Preferential localization of abscisic acid in primordial and nursing cells of reproductive organs of Arabidopsis and cucumber

Abscisic acid (ABA) is known to function in plant stress responses and seed dormancy, and much is known about its detailed mechanisms of signal transduction. Recent studies suggest that this hormone may also play important roles in sugar signaling and assimilate distribution during fruit development. However, little is known about the role of ABA in actively growing or differentiating fruits and other plant organs or tissues. To explore whether ABA functions during the early development of reproductive organs, we carried out ABA immunolocalization using monoclonal antibodies. The specific ABA accumulation pattern was verified by gas chromatography-mass spectrometry (GC-MS). ABA was not only detected in primordial cells of flower organs, but was also detected in nursing cells (e.g. tapetum and integuments), which function in supplying nutrition for germ cell development. These findings suggest that, in addition to its well-known function as a 'negative hormone', ABA may play some 'positive' roles during plant development, including possible involvement in the regulation of assimilate distribution.

Monitoring the expression profiles of genes induced by hyperosmotic, high salinity, and oxidative stress and abscisic acid treatment in Arabidopsis cell culture using a full-length cDNA microarray

Transcriptional regulation in response to hyperosmotic, high-salinity and oxidative stress, and abscisic acid (ABA) treatment in Arabidopsis suspension-cultured cell line T87 was investigated with a cDNA microarray containing 7000 independent full-length Arabidopsis cDNAs. The transcripts of 102, 11, 84 and 73 genes were increased more than 5-fold within 5h after treatment with 0.5M mannitol, 0.1M NaCl, 50 microM ABA and 10mM H2O2, respectively. On the other hand, the transcripts of 44, 57, 25 and 34 genes were down-regulated to less than one-third within 5h after treatment with 0.5M mannitol, 0.1M NaCl, 50 microM ABA and 10mM H2O2, respectively. Venn diagram analysis revealed 11 genes were induced significantly by mannitol, NaCl, and ABA, indicating crosstalk among these signaling pathways. Comparison of the genes induced by each stress revealed that 32%, 17% and 33% of mannitol-, NaCl- and ABA-inducible genes were also induced by H2O2, indicating the crosstalk between the signaling pathways for osmotic stress and oxidative stress. Although the expression profiles revealed that the T87 cells had most of the regulatory systems seen in Arabidopsis seedlings, the T87 cells did not have one of ABA-dependent signaling pathways.

Cytokinin stimulates polyribosome loading of nuclear-encoded mRNAs for the plastid ATP synthase in etioplasts of Lupinus luteus: the complex accumulates in the inner-envelope membrane with the CF(1) moiety located towards the stromal space

Three of the nine subunits of the plastid ATP synthase, including the subunit of the CF(1) moiety (gene AtpC), are encoded in the nucleus. Application of cytokinin to etiolated lupine seedlings induces polyribosome association of their mRNAs. This appears to be specific as no such regulation was observed for messages for three ribosomal proteins. Cytokinin-mediated polyribosome loading was also observed for the spinach AtpC message in etiolated transgenic tobacco seedlings. Analysis of various spinach AtpC mRNA derivatives uncovered that the 5' untranslated region (5' UTR) of this message is sufficient to direct polyribosome loading, and that sequences at the 3' end of the AtpC 5' UTR, including an UC-rich motif, are crucial for this regulation. The increase in polyribosome loading of the AtpC message correlated with an increased synthesis of the polypeptide. The subunit, together with the ATP synthase complex, accumulates in the inner-envelope membrane with the CF(1) moiety located towards the stromal space of the etioplast. These results suggest that cytokinin promotes accumulation of the ATP synthase in the inner-envelope membrane of lupine etioplasts by stimulating the translation efficiency of their nuclear-encoded messages.

Plasma membrane depolarization induced by abscisic acid in Arabidopsis suspension cells involves reduction of proton pumping in addition to anion channel activation, which are both Ca2+ dependent

In Arabidopsis suspension cells a rapid plasma membrane depolarization is triggered by abscisic acid (ABA). Activation of anion channels was shown to be a component leading to this ABA-induced plasma membrane depolarization. Using experiments employing combined voltage clamping, continuous measurement of extracellular pH, we examined whether plasma membrane H(+)-ATPases could also be involved in the depolarization. We found that ABA causes simultaneously cell depolarization and medium alkalinization, the second effect being abolished when ABA is added in the presence of H+ pump inhibitors. Inhibition of the proton pump by ABA is thus a second component leading to the plasma membrane depolarization. The ABA-induced depolarization is therefore the result of two different processes: activation of anion channels and inhibition of H(+)-ATPases. These two processes are independent because impairing one did not suppress the depolarization. Both processes are however dependent on the [Ca2+]cyt increase induced by ABA since increase in [Ca(2+)](cyt) enhanced anion channels and impaired H(+)-ATPases.

Regulation of the ABA-sensitive Arabidopsis potassium channel gene GORK in response to water stress

The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time- and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abi1-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 12-24 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, GORK expression as well as K+(out) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately.

Tumour development in Arabidopsis thaliana involves the Shaker-like K+ channels AKT1 and AKT2/3

After completion of the Arabidopsis genome-sequencing programme, crown galls induced by Agrobacterium tumefaciens may become a model system to study plant tumour development. The molecular mechanisms of nutrient supply to support tumour growth and development are still unknown. In this study, we have identified a unique profile of Shaker-like potassium channels in agrobacteria-induced Arabidopsis tumours. Comparing the gene expression pattern of rapidly growing tumours with that of non-infected tissues, we found the suppression of shoot in favour of root-specific K+ channels. Among these, the upregulation of AKT1 and AtKC1 and the suppression of AKT2/3 and GORK were most pronounced. As a consequence, K+ uptake and accumulation were elevated in the tumour (163 mm) compared to control tissues (92 mm). Patch clamp studies on tumour protoplasts identified a population expressing the electrical properties of the AKT1 K+ channel. Furthermore, plants lacking a functional AKT1 or the AKT2/3 phloem K+ channel gene did not support tumour growth. This indicates that the delivery of potassium by AKT1 and the direction of assimilates, triggered by AKT2/3, are essential for tumour growth.

The abi1-1 mutation blocks ABA signaling downstream of cADPR action

Arabidopsis thaliana abscisic acid insensitive 1-1 (abi1-1) is a dominant mutant that is insensitive to the inhibition of germination and growth by the plant hormone, abscisic acid (ABA). The mutation severely decreases the catalytic activity of the ABI1 type 2C protein phosphatase (PP2C). However, the site of action of the abi1-1/ABI1 in the ABA signal transduction pathway has not yet been determined. Using single cell assays, we showed that microinjecting mutant abi1-1 protein inhibited the activation of RD29A-GUS and KIN2-GUS in response to ABA, cyclic ADP-ribose (cADPR), and Ca2+. The inhibitory effect of the mutant protein, however, was reversed by co-microinjection of an excess amount of the ABI1 protein. In transgenic Arabidopsis plants, overexpression of abi1-1 rendered the plants insensitive to ABA during germination, whereas overexpression of ABI1 did not have any apparent effect. Moreover, transgenic plants overexpressing abi1-1 were blocked in the induction of ABA-responsive genes; however, overexpression of ABI1 did not affect gene expression. Taken together, our results demonstrate that abi1-1 is likely to be a dominant negative mutation and ABI1 likely acts downstream of cADPR in the ABA-signaling pathway. Our results on ABI1 overexpression in Arabidopsis are not compatible with a negative regulatory role of this phosphatase in ABA responses.

Interaction between two cis-acting elements, ABRE and DRE, in ABA-dependent expression of Arabidopsis rd29A gene in response to dehydration and high-salinity stresses

Many abiotic stress-inducible genes contain two cis-acting elements, namely a dehydration-responsive element (DRE; TACCGACAT) and an ABA-responsive element (ABRE; ACGTGG/TC), in their promoter regions. We precisely analyzed the 120 bp promoter region (-174 to -55) of the Arabidopsis rd29A gene whose expression is induced by dehydration, high-salinity, low-temperature, and abscisic acid (ABA) treatments and whose 120 bp promoter region contains the DRE, DRE/CRT-core motif (A/GCCGAC), and ABRE sequences. Deletion and base substitution analyses of this region showed that the DRE-core motif functions as DRE and that the DRE/DRE-core motif could be a coupling element of ABRE. Gel mobility shift assays revealed that DRE-binding proteins (DREB1s/CBFs and DREB2s) bind to both DRE and the DRE-core motif and that ABRE-binding proteins (AREBs/ABFs) bind to ABRE in the 120 bp promoter region. In addition, transactivation experiments using Arabidopsis leaf protoplasts showed that DREBs and AREBs cumulatively transactivate the expression of a GUS reporter gene fused to the 120 bp promoter region of rd29A. These results indicate that DRE and ABRE are interdependent in the ABA-responsive expression of the rd29A gene in response to ABA in Arabidopsis.

Identification of ABA-responsive genes in rice shoots via cDNA macroar-

Phytohormone abscisic acid (ABA) was critical for many plant growth and developmental processes including seed maturation, germination and response to environmental factors. With the purpose to detect the possible ABA related signal transduction pathways, we tried to isolate ABA-regulated genes through cDNA macroarray technology using ABA-treated rice seedling as materials (under treatment for 2, 4, 8 and 12 h). Of 6144 cDNA clones tested, 37 differential clones showing induction or suppression for at least one time, were isolated. Of them 30 and 7 were up- or down-regulated respectively. Sequence analyses revealed that the putative encoded proteins were involved in different possible processes, including transcription, metabolism and resistance, photosynthesis, signal transduction, and seed maturation. 6 cDNA clones were found to encode proteins with unknown functions. Regulation by ABA of 7 selected clones relating to signal transduction or metabolism was confirmed by reverse transcription PCR. In addition, some clones were further shown to be regulated by other plant growth regulators including auxin and brassinosteroid, which, however, indicated the complicated interactions of plant hormones. Possible signal transduction pathways involved in ABA were discussed.

Molecular cloning and mRNA expression analysis of a novel rice (Oryzasativa L.) MAPK kinase kinase, OsEDR1, an ortholog of Arabidopsis AtEDR1, reveal its role in defense/stress signalling pathways and development

Mitogen-activated protein kinase (MAPK) cascade(s) is important for plant defense/stress responses. Though MAPKs have been identified and characterized in rice (Oryza sativa L.), a monocot cereal crop research model, the first upstream component of the kinase cascade, namely MAPK kinase kinase (MAPKKK) has not yet been identified. Here we report the cloning of a novel rice gene encoding a MAPKKK, OsEDR1, designated based on its homology with the Arabidopsis MAPKKK, AtEDR1. OsEDR1, a single copy gene in the genome of rice, encodes a predicted protein with molecular mass of 113046.13 and a pI of 9.03. Using our established two-week-old rice seedling in vitro model system, we show that OsEDR1 has a constitutive expression in seedling leaves and is further up-regulated within 15 min upon wounding by cut, treatment with the global signals jasmonic acid (JA), salicylic acid (SA), ethylene (ethephon, ET), abscisic acid, and hydrogen peroxide. In addition, protein phosphatase inhibitors, fungal elicitor chitosan, drought, high salt and sugar, and heavy metals also dramatically induce its expression. Moreover, OsEDR1 expression was altered by co-application of JA, SA, and ET, and required de novo synthesized protein factor(s) in its transient regulation. Furthermore, using an in vivo system we also show that OsEDR1 responds to changes in temperature and environmental pollutants-ozone and sulfur dioxide. Finally, OsEDR1 expression varied significantly in vegetative and reproductive tissues. These results suggest a role for OsEDR1 in defense/stress signalling pathways and development.

Novel rice MAP kinases OsMSRMK3 and OsWJUMK1 involved in encountering diverse environmental stresses and developmental regulation

We report isolation of two novel rice (Oryza sativa L.) mitogen-activated protein kinases (MAPKs), OsMSRMK3 (multiple stress responsive) and OsWJUMK1 (wound- and JA-uninducible) that most likely exist as single copy genes in its genome. OsMSRMK3 and OsWJUMK1 encode 369 and 569 amino acid polypeptides having the MAPK family signature and phosphorylation activation motifs TEY and TDY, respectively. Steady state mRNA analyses of these MAPKs with constitutive expression in leaves of two-week-old seedlings revealed that OsMSRMK3 was up-regulated upon wounding (by cut), jasmonic acid (JA), salicylic acid (SA), ethylene, abscisic acid, hydrogen peroxide (H(2)O(2)), protein phosphatase inhibitors, chitosan, high salt/sugar, and heavy metals, whereas OsWJUMK1 not induced by either wounding, JA or SA, showed up-regulation only by H(2)O(2), heavy metals, and cold stress (12 degrees C). Moreover, these MAPKs were developmentally regulated. These results strongly suggest a role for OsMSRMK3 and OsWJUMK1 in both stress-signalling pathways and development in rice.

Two different novel cis-acting elements of erd1, a clpA homologous Arabidopsis gene function in induction by dehydration stress and dark-induced senescence

Many plant genes have been shown to be induced by water stress and function in stress tolerance. The erd1 gene has been shown to be upregulated in response to both water stress and etiolation. Promoter studies using the erd1 promoter region fused to the luciferase (LUC) reporter gene in Arabidopsis thaliana were performed to identify the putative cis elements involved. Results indicated that the cis elements, responsible for gene expression during dehydration and etiolation, are separately located in two discrete portions of the erd1 promoter. Base substitution analysis showed that a 14-bp region from -599 to -586, and a myc recognition motif from -466 to -461 are necessary for the induction of LUC activity in dehydrated plants. On the other hand, base substitution analysis revealed that both an abscisic acid responsive element (ABRE)-like sequence (from -199 to -195) and an ACGT sequence (from -155 to -152) are required for an etiolation-induced increase in LUC activity. LUC activity measurements from etiolated transgenic plants incubated in either water, N6-benzyleadenine (BA), or a 1% sucrose solution found that while BA was able to delay the increase in LUC activity seen in water-treated plants, no increase in LUC activity was seen in plants incubated in sucrose. These results indicate that the erd1 promoter contains two different regulatory systems that are involved in upregulation by dehydration stress and dark-induced senescence.

Cross-talk in abscisic acid signaling

"Cross-talk" in hormone signaling reflects an organism's ability to integrate different inputs and respond appropriately, a crucial function at the heart of signaling network operation. Abscisic acid (ABA) is a plant hormone involved in bud and seed dormancy, growth regulation, leaf senescence and abscission, stomatal opening, and a variety of plant stress responses. This review summarizes what is known about ABA signaling in the control of stomatal opening and seed dormancy and provides an overview of emerging knowledge about connections between ABA, ethylene, sugar, and auxin synthesis and signaling.

From common signalling components to cell specific responses: insights from the cereal aleurone

Studies into the molecules underlying plant signal transduction events continue to reveal the involvement of highly conserved factors such as Ca2+, calmodulin, cyclic GMP and phospholipases in a remarkably diverse array of physiological processes. The hormonal response systems in the aleurone cells of the cereal grain and in the stomatal guard cell are beginning to reveal how diversity of response can be hard wired into these cells despite the use of these common signalling intermediates. In both the aleurone and the guard cell ABA signalling operates through the action of phospholipase D and alterations in a Ca2+-dependent signalling system. The role of phospholipase D is highly analogous in these two divergent cell types, perhaps reflecting the closeness of this enzyme to a conserved ABA receptor. However, specificity in response becomes evident in elements downstream from PLD, such as in the Ca2+ signalling system. For example, ABA has opposite effects on cytoplasmic Ca2+ in the aleurone and guard cell. Combining the Ca2+-dependent signalling activities in networks with parallel regulatory activities such as cyclic GMP appears to underlie the flexible regulatory systems that are the hallmark of plant cell function.

Isolation of novel rice (Oryza sativa L.) multiple stress responsive MAP kinase gene, OsMSRMK2, whose mRNA accumulates rapidly in response to environmental cues

In search for components of MAPK (mitogen-activated protein kinase) cascades in rice (Oryza sativa L. cv. Nipponbare), we identified a single copy gene called OsMSRMK2 from jasmonic acid (JA) treated rice seedling leaf cDNA library. This gene has a conserved protein kinase domain, including a MAPK family signature, and encodes a 369 amino acid polypeptide with a predicted molecular mass of 42995.43 and a pI of 5.48. OsMSRMK2 did not show constitutive expression in leaves and was induced within 15 min in response to wounding by cut. Using in vitro system, we show that the expression of OsMSRMK2 mRNA was potently enhanced within 15 min by signalling molecules, protein phosphatase inhibitors, ultraviolet irradiation, fungal elicitor, heavy metals, high salt and sucrose, and drought. OsMSRMK2 expression was further modulated by co-application of JA, salicylic acid, and ethylene and required de novo synthesized protein factor(s) in its transient regulation. Moreover, high (37 degrees C) and low temperatures (12 degrees C) and environmental pollutants-ozone and sulfur dioxide-differentially regulate the OsMSRMK2 mRNA accumulation in leaves of intact plants. Present results demonstrating dramatic transcriptional and transient regulation of the OsMSRMK2 expression by diverse biotic/abiotic stresses, a first report for any rice (or plant) MAPK to date, suggest a role for OsMSRMK2 in rice defense/stress response pathways.