Reactive oxygen species trigger a regulatory module involved in the early responses of rice seedlings to cold stress

Plants respond to low temperature through an intricately coordinated transcriptional network controlled by specific groups of transcription factors. Major regulatory pathways in plants that evolved to withstand freezing by cold acclimation have been elucidated in Arabidopsis. A prominent pathway is the CBF/DREB regulon, which was also shown to be evolutionarily conserved between temperate and warm-season plants. This study exploited the wide contrast in chilling tolerance between indica and japonica rice as model to dissect the hierarchical organization of early response regulatory networks by integrative analysis of promoter architecture and gene expression profiles. Analysis of the transcriptome of japonica rice identified a group of genes that were upregulated during the initial 24 hours at 10oC. Included among the 120 ‘early response’ genes were two transcription factors (ROS-bZIP1, OsMyb4) and another larger sub-group with a common denominator of having the as1/ocs element in their promoters. ROS-bZIP1, OsMyb4 and the as1/ocs element-containing genes were also induced by exogenous H2O2 at ambient temperature, thus are likely components of a regulatory module (ROS-bZIP1-as1/ocs regulatory module) that is activated by elevated intracellular ROS induced by cold stress. Comparative analysis of the expression of ROS-bZIP1-as1/ocs regulatory module between tolerant (CT6748-8-CA-17) and intolerant (INIAP12) rice cultivars showed positive correlation of the activity of the regulon with genotypic differences in chilling tolerance. A hypothetical model of an ROS-mediate gene regulon was developed. Based on this model, it was hypothesized that the putative ROSbZIP1-as1/ocs regulatory module has a prominent role in configuring early or rapid responses to chilling in rice seedlings and that such pathway is independent of the CBF/DREB-mediated and ABA-mediated regulons. Background Keywords: Response to temperature at different time points This experiment involves the analysis of changes in gene expression in response to cold stress in a total of five time points (0.5, 2, 6, 12 and 24 hrs). Control (29C) and cold stress (10C) samples were labeled with Cy5 and Cy3, respectively. No dye swap replicate was performed in this experiment. Gene expression analysis was performed with two independent biological replicates (R1 and R2) for each time point. In each biological replicate, there were two technical replicates (T1 and T2). These technical replicates were represented by duplicate set of spots in each microarray slide.