Abstract
BackgroundPlants respond to low temperature through an intricately coordinated transcriptional network. The CBF/DREB-regulated network of genes has been shown to play a prominent role in freeze-tolerance of Arabidopsis through the process of cold acclimation (CA). Recent evidence also showed that the CBF/DREB regulon is not unique to CA but evolutionarily conserved between chilling-insensitive (temperate) and chilling-sensitive (warm-season) plants. In this study, the wide contrast in chilling sensitivity between indica and japonica rice was used as model to identify other regulatory clusters by integrative analysis of promoter architecture (ab initio) and gene expression profiles.ResultsTranscriptome analysis in chilling tolerant japonica rice identified a subset of 121 'early response' genes that were upregulated during the initial 24 hours at 10°C. Among this group were four transcription factors including ROS-bZIP1 and another larger sub-group with a common feature of having as1/ocs-like elements in their promoters. Cold-induction of ROS-bZIP1 preceded the induction of as1/ocs-like element-containing genes and they were also induced by exogenous H2O2 at ambient temperature. Coordinated expression patterns and similar promoter architectures among the 'early response' genes suggest that they belong to a potential regulon (ROS-bZIP – as1/ocs regulatory module) that responds to elevated levels of ROS during chilling stress. Cultivar-specific expression signatures of the candidate genes indicate a positive correlation between the activity of the putative regulon and genotypic variation in chilling tolerance.ConclusionA hypothetical model of an ROS-mediated regulon (ROS-bZIP – as1/ocs) triggered by chilling stress was assembled in rice. Based on the current results, it appears that this regulon is independent of ABA and CBF/DREB, and that its activation has an important contribution in configuring the rapid responses of rice seedlings to chilling stress.
Highlights
Plants respond to low temperature through an intricately coordinated transcriptional network
Snapshot of the cold stress early response transcriptome of rice Our previous studies showed that the cold stress library used to assemble the 5,855-feature cDNA microarray was enriched with candidate chilling-upregulated genes [23,29]
We assembled a hypothetical model of the reactive oxygen species (ROS)-mediated regulon and we propose a hypothesis on its potential relationship with other major regulon(s) involved in low temperature response of the chilling-tolerant japonica rice
Summary
Plants respond to low temperature through an intricately coordinated transcriptional network. Molecular dissection of the promoters of several COR genes of Arabidopsis (e.g., rd29A/lti78/cor, rd17/cor, cor15a, cor6.6/kin2) indicated that they are regulated in an ABA-dependent or ABA-independent pathway under cold, dehydration and high salinity conditions. Their cold-induced expression is largely through the ABA-independent pathway mediated by highly conserved promoter cis-elements that function as binding sites for transcriptional activators [6,12]. Low temperature, dehydration and high salt- inducible expression of rd29/lti78/cor requires a 9-bp sequence TA(C/ G)CGACAT called C-repeat/Dehydration-Responsive Element (CRT/DRE) that is not independently activated by ABA alone [8]. Many Arabidopsis genes with ABRE-like and CRT/DRE-like motifs in their promoters have been identified and these genes have been characterized at least in terms of their stress-responsive expression [10,13]
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