Cis-Regulatory Elements Occurrence In Promoters of Antioxidant Signaling Network Genes up-Regulated In Rice Under Iron Stress Toxicity.

This work aimed to identify cis-regulatory elements (CRE) in promoters of up-regulated genes belonging to network signaling cascades in response to oxidative stress under iron toxicity conditions. A microarray approach was utilized to identify differentially expressed genes in rice leaves (Oryza sativa L. ssp. japonica cv. Nipponbare) of seedlings grown in iron excess (7mM FeSO₄7H₂O) and control solutions. Three biological replicates of each condition (control and iron excess) were hybridized with the Rice transposome array v.2.0 microarray (Roche/NimbleGen technology). Data set of gene expression was analyzed by the Bayesian t test and the BH adjustment method. Gene annotation, gene ontology and download of sequences 1kb upstream of genes were obtained in RAP-DB (Rice Annotation Project Database) and to find the significant occurrence of CRE, a Z test was performed (P≤0.05). A total of 167 up-regulated genes related to network signaling cascades of response to oxidative stress and scavengers of reactive oxygen species were analyzed, these genes include 90 for protein kinases, 19 WRKY transcription factor, 13 heat shock protein transcription factors, 10 genes for glutathione transferase, and another 35 related genes. We found 250 CREs occurring significant (P≤0.05), its occurrence in the promoters was divided into 3 groups: <5 CREs in promoter (one gene), ≤5 and ≥10 (43 genes) and >10 (123 genes). Occurrence of each CRE in the different promoter genes were divided into three classes: class I <10 promoter genes (157 CREs); class II ≥10 and ≤25 promoter genes (82 CREs) and class III >25 (11 CREs). The 11 CRE class III occur in 158 of 167 analyzed genes, and are binding sites of transcription factors, ARF1 (1), bZIP (6) and MYB2 (1) GT/trihelix (1) and AP2 (1).