Regulatory network of gene expression in the drought and cold stress responses
Introduction
Environmental stresses, such as drought, high salinity and low temperature, have adverse effects on plant growth and seed production. Plants respond and adapt to these stresses through various biochemical and physiological processes, thereby acquiring stress tolerance. Many genes respond to drought, salt and/or cold stress at the transcriptional level, and the products of these genes function in the stress response and tolerance 1., 2., 3.. Transcriptome analyses using microarray technology 4., 5., 6. have identified several genes that are induced by abiotic stresses, and these genes have been classified into two major groups 1., 2., 3.. One group encodes products that directly protect plant cells against stresses, whereas the products of the other group regulate gene expression and signal transduction in abiotic stress responses. Molecular and genomic analyses have shown that several different transcriptional regulatory systems are involved in stress-responsive gene induction. Several different sets of cis- and trans-acting factors are known to be involved in stress-responsive transcription. Some of them are controlled by abscisic acid (ABA) but others are not, indicating the involvement of both ABA-dependent and -independent regulatory systems for stress-responsive gene expression 1., 2., 3., 7.•. Many genes are induced by both drought and cold stress, suggesting the existence of crosstalk between the drought and cold-stress signaling pathways. The use of mutants isolated from transgenic Arabidopsis that contain promoter::luciferase (LUC) constructs provides a powerful method for the analysis of stress signaling pathways 7.•, 8.. In this short review, we highlight recent progress in understanding the regulation of gene expression in response to drought and/or cold stress, and in revealing complex gene networks for specificity and crosstalk in abiotic-stress-responsive gene expression.
Section snippets
Transcriptome analysis of stress-inducible gene expression using microarray technology
Microarray technology using cDNAs or oligonucleotides has become a powerful and useful tool for analyzing the gene expression profiles of plants that are exposed to abiotic stresses, such as drought, cold and high salinity, or to ABA treatment 4., 5., 9., 10.••, 11.•, 12., 13.•, 14.•, 15.•. Potential cis-acting DNA elements have been analyzed by comparing their expression profiles with those of the promoter sequences of stress-inducible genes 9., 10.••, 11.•, 13.•. Microarray technology is also
Systems that regulate gene expression in response to drought and cold stress: identification of cis-acting elements and their DNA-binding proteins in ABA-independent pathways
The cis-acting elements of some genes that have a typical stress-inducible expression profile and the transcription factors that affect the expression of these genes have been analyzed precisely 1., 2., 3.. Promoter analyses of drought- and/or cold-inducible genes have provided at least four independent regulatory systems for gene expression [2].
The promoter of a drought-, high-salinity- and cold-inducible gene, RESPONSIVE TO DEHYDRATION29A (RD29A)/COLD-REGULATED78 (COR78)/
Cis-acting elements and transcription factors involved in ABA-dependent gene expression
ABA is synthesized de novo mainly in response to drought and high-salinity stress but not in response to cold stress. Many stress-inducible genes are regulated by the endogenous ABA that accumulates during drought and high-salinity stress 1., 2.. Recently, genes that are involved in ABA biosynthesis have been identified through genetic and genomics analyses 7.•, 31.. Several of these genes are induced by drought and high salinity but not by cold stress. This indicates important roles for ABA in
Genetic analysis of drought and cold-stress signaling pathways
A unique mutant screening system using transgenic Arabidopsis plants with a firefly LUC reporter gene under the control of the RD29A promoter has been developed to screen mutants that have defects in their abiotic-stress signal transduction pathways [45]. Using this system, many Arabidopsis mutants have been isolated that have altered induction of stress-responsive genes by drought, high-salinity, cold and ABA. These mutants exhibited altered expression of the RD29A::LUC gene at a constitutive (
Complexity of stress-responsive gene networks: specificity and crosstalk
Four transcriptional regulatory systems have been reported, two of them are ABA-independent whereas two are ABA-dependent. Crosstalk between these regulatory systems has, however, been suggested by genetic and molecular analyses. Genomic analyses of stress-inducible genes using microarrays have recently revealed crosstalk in stress-responsive gene expression 10.••, 11.•, 15.•. Most drought-inducible genes are also induced by high-salinity stress, and many drought-inducible genes are also
Conclusions and perspectives
Molecular and genomic analyses have revealed many genes that are induced by abiotic stress and their functions in stress-responsive gene expression and stress tolerance. The many stress-inducible genes include those that encode signaling molecules, such as enzymes involved in phospholipid metabolism and various protein kinases including mitogen-activated protein (MAP) kinases, calcium-dependent protein kinases (CDPKs), receptor-like kinases and histidine kinases 2., 7.•, 8.. Transgenic plants
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
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of special interest
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of outstanding interest
Acknowledgements
This work was supported in part by a grant for Genome Research from RIKEN, by the Special Coordination Fund of the Science and Technology Agency and by a Grant-in-Aid from the Ministry of Education, Culture, Sports, Science and Technology of Japan (MECSST) to KS. KS and KY-S are also recipients of a grant from the Program for the Promotion of Basic Research Activities for Innovative Biosciences. The work was also supported in part by a Grant-in-Aid for Scientific Research on Priority Areas (C)
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