Microarray expression of genes in Arabidopsis Col-0 and Ws-2 plants exposed to As stress. (a) Venn diagram of regulated As-responsive genes extracted by comparing microarray probe sets of the 2 Arabidopsis accessions. The number of overlapping and non-overlapping genes early (1.5 to 3 h) after treatment with 100 or 200 μM As is shown. The probe sets were selected on the basis of an adjusted P-value of <0.05 and a >2-fold change in gene expression. The area of the diagram is proportional to the number of genes that are up- or downregulated in response to As stress. To clearly differentiate As-regulated genes in Col-0 from that in Ws-2, the Col-0-specific set contains only those genes with both >2-fold change in abundance (compared with control treatment) in Col-0 and <1.4-fold change in Ws-2. Likewise, the Ws-2-specific set contains genes with both > 2-fold change in abundance in Ws-2 and < 1.4-fold change in Col-0. The general As-regulated gene set contains genes displaying > 2-fold change in abundance in Col-0 or Ws-2 and >1.4-fold change in another accession. (b) Displayed are genes associated with ubiquitin pathways and abiotic stress responses using MapMan software. Both sets of material were harvested from roots tissues treated with or without As stress (100 and 200 μM for Ws-2 and Col-0, respectively). Red and blue signals represent a decrease and increase in transcript abundance, respectively, relative to water-treated control samples. The scale used for coloration of signals (log2 ratios) is presented. (c) Validation of representative As-induced genes by semi-quantitative RT-PCR analysis. Total RNA was extracted from root tissues of Arabidopsis plants with different accessions with As treatment. The As-treated roots were harvested at 1 and 3 h. The samples were pooled together. The transcript level of actin served as an equal loading control.