ABA is a major phytohormone that regulates a broad range of plant traits and is especially important for adaptation to environmental conditions. Our understanding of the molecular basis of ABA ...responses in plants improved dramatically in 2009 and 2010, banner years for ABA research. There are three major components; PYR/PYL/ RCAR (an ABA receptor), type 2C protein phosphatase (PP2C; a negative regulator) and SNF1-related protein kinase 2 (SnRK2; a positive regulator), and they offer a double negative regulatory system, PYR/PYL/RCAR--| PP2C--| SnRK2. In the absence of ABA, PP2C inactivates SnRK2 by direct dephosphorylation. In response to environmental or developmental cues, ABA promotes the interaction of PYR/PYL/RCAR and PP2C, resulting in PP2C inhibition and SnRK2 activation. This signaling complex can work in both the nucleus and cytosol, as it has been shown that SnRK2 phosphorylates basic-domain leucine zipper (bZIP) transcription factors or membrane proteins. Several structural analyses of PYR/PYL/RCAR have provided the mechanistic basis for this 'core signaling' model, by elucidating the mechanism of ABA binding of receptors, or the 'gate-latch-lock' mechanism of interaction with PP2C in inhibiting activity. On the other hand, intercellular ABA transport had remained a major issue, as had intracellular ABA signaling. Recently, two plasma membrane-type ABC transporters were identified and shed light on the influx/efflux system of ABA, resolving how ABA is transported from cell to cell in plants. Our knowledge of ABA responses in plants has been greatly expanded from intracellular signaling to intercellular transport of ABA.
Plants respond to survive under water-deficit conditions via a series of physiological, cellular, and molecular processes culminating in stress tolerance. Many drought-inducible genes with various ...functions have been identified by molecular and genomic analyses in Arabidopsis, rice, and other plants, including a number of transcription factors that regulate stress-inducible gene expression. The products of stress-inducible genes function both in the initial stress response and in establishing plant stress tolerance. In this short review, recent progress resulting from analysis of gene expression during the drought-stress response in plants as well as in elucidating the functions of genes implicated in the stress response and/or stress tolerance are summarized. A description is also provided of how various genes involved in stress tolerance were applied in genetic engineering of dehydration stress tolerance in transgenic Arabidopsis plants.
Plant-specific NAC transcription factors (TFs) play important roles in regulating diverse biological processes, including development, senescence, growth, cell division and responses to environmental ...stress stimuli. Within the soybean genome, we identified 152 full-length GmNAC TFs, including 11 membrane-bound members. In silico analysis of the GmNACs, together with their Arabidopsis and rice counterparts, revealed similar NAC architecture. Next, we explored the soybean Affymetrix array and Illumina transcriptome sequence data to analyse tissue-specific expression profiles of GmNAC genes. Phylogenetic analysis using stress-related NAC TFs from Arabidopsis and rice as seeding sequences identified 58 of the 152 GmNACs as putative stress-responsive genes, including eight previously reported dehydration-responsive GmNACs. We could design gene-specific primers for quantitative real-time PCR verification of 38 out of 50 newly predicted stress-related genes. Twenty-five and six GmNACs were found to be induced and repressed 2-fold or more, respectively, in soybean roots and/or shoots in response to dehydration. GmNAC085, whose amino acid sequence was 39%; identical to that of well-known SNAC1/ONAC2, was the most induced gene upon dehydration, showing 390-fold and 20-fold induction in shoots and roots, respectively. Our systematic analysis has identified excellent tissue-specific and/or dehydration-responsive candidate GmNAC genes for in-depth characterization and future development of improved drought-tolerant transgenic soybeans.
cis-Acting regulatory elements are important molecular switches involved in the transcriptional regulation of a dynamic network of gene activities controlling various biological processes, including ...abiotic stress responses, hormone responses and developmental processes. In particular, understanding regulatory gene networks in stress response cascades depends on successful functional analyses of
cis-acting elements. The ever-improving accuracy of transcriptome expression profiling has led to the identification of various combinations of
cis-acting elements in the promoter regions of stress-inducible genes involved in stress and hormone responses. Here we discuss major
cis-acting elements, such as the ABA-responsive element (ABRE) and the dehydration-responsive element/C-repeat (DRE/CRT), that are a vital part of ABA-dependent and ABA-independent gene expression in osmotic and cold stress responses.
The genomes of three plants, Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa), and soybean (Glycine max), have been sequenced, and their many genes and promoters have been predicted. In ...Arabidopsis, cis-acting promoter elements involved in cold- and dehydration-responsive gene expression have been extensively analysed; however, the characteristics of such cis-acting promoter sequences in cold- and dehydration-inducible genes of rice and soybean remain to be clarified. In this study, we performed microarray analyses using the three species, and compared characteristics of identified cold- and dehydration-inducible genes. Transcription profiles of the cold- and dehydration-responsive genes were similar among these three species, showing representative upregulated (dehydrin/LEA) and downregulated (photosynthesis-related) genes. All (46 = 4096) hexamer sequences in the promoters of the three species were investigated, revealing the frequency of conserved sequences in cold- and dehydration-inducible promoters. A core sequence of the abscisic acid-responsive element (ABRE) was the most conserved in dehydration-inducible promoters of all three species, suggesting that transcriptional regulation for dehydration-inducible genes is similar among these three species, with the ABRE-dependent transcriptional pathway. In contrast, for cold-inducible promoters, the conserved hexamer sequences were diversified among these three species, suggesting the existence of diverse transcriptional regulatory pathways for cold-inducible genes among the species.
The transcription factors dehydration-responsive element-binding protein 1s (DREB1s)/C-repeat-binding factors (CBFs) specifically interact with the DRE/CRT cisacting element and control the ...expression of many stress-inducible genes in Arabidopsis. The genes for DREB1 orthologs, OsDREB1A and OsDREB1B from rice, are induced by cold stress, and overexpression of DREB1 or OsDREB1 induced strong expression of stress-responsive genes in transgenic Arabidopsis plants, resulting in increased tolerance to high-salt and freezing stresses. In this study, we generated transgenic rice plants overexpressing the OsDREB1 or DREB1 genes. These transgenic rice plants showed not only growth retardation under normal growth conditions but also improved tolerance to drought, high-salt and low-temperature stresses like the transgenic Arabidopsis plants overexpressing OsDREB1 or DREB1. We also detected elevated contents of osmoprotectants such as free proline and various soluble sugars in the transgenic rice as in the transgenic Arabidopsis plants. We identified target stress-inducible genes of OsDREB1A in the transgenic rice using microarray and RNA gel blot analyses. These genes encode proteins that are thought to function in stress tolerance in the plants. These results indicate that the DREB1/CBF cold-responsive pathway is conserved in rice and the DREB1-type genes are quite useful for improvement of stress tolerance to environmental stresses in various kinds of transgenic plants including rice.
Recently, a major transcription system that controls abscisic-acid-independent gene expression in response to dehydration and low temperature has been identified. The system includes the DRE/CRT ...(dehydration-responsive element/C-repeat) cis-acting element and its DNA-binding protein, DREB/CBF (DRE-binding protein/C-repeat binding factor), which has an AP2 domain. DREB/CBF contains two subclasses, DREB1/CBF and DREB2, which are induced by cold and dehydration, respectively, and control the expression of various genes involved in stress tolerance. Recent studies are providing evidence of differences between dehydration-signaling and cold-stress-signaling cascades, and of cross-talk between them.
ABSTRACT
To characterize the genes for enzymes involved in the biosynthesis of polyamines (PAs), their expression profiles were investigated and the levels of PAs in Arabidopsis thaliana quantified. ...In the Arabidopsis genome, eight genes involved in PAs biosynthesis were identified and the expression profiles of these genes were analysed, not only under abiotic stress to determine whether they were stress‐inducible, constitutive, or stress‐repressible, but also in various organs to show their tissue specificity. AtADC2 and AtSPMS mRNAs, encoding arginine decarboxylase and spermine synthase, clearly increased in response to NaCl and dehydration and abscisic acid treatments. Stress‐inducible accumulation of AtADC2 mRNA correlated with putrescine (Put) accumulation under NaCl and dehydration treatments. In a cold condition, AtSAMDC2 mRNA increased significantly. AtADC2 and AtSAMDC2 mRNA were expressed in sexual organs such as flowers, buds and immature siliques. PAs also accumulated in sexual organs. These results suggest that the transcripts of eight genes involved in PA biosynthesis show different profiles of expression not only in response to environmental stress but also during plant development.
Molecular and genomic studies have shown that several genes with various functions are induced by drought and cold stresses, and that various transcription factors are involved in the regulation of ...stress-inducible genes. The products of stress-inducible genes function not only in stress tolerance but also in stress response. Genetic studies have identified many factors that modify the regulation of stress responses. Recent progress has been made in analyzing the complex cascades of gene expression in drought and cold stress responses, especially in identifying specificity and crosstalk in stress signaling.
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