Transcriptional responses of Arabidopsis thaliana plants to As (V) stress

Abstract

Background: Arsenic is toxic to plants and a common environmental pollutant. There is a strong chemical similarity between arsenate [As (V)] and phosphate (Pi). Whole genome oligonucleotide microarrays were employed to investigate the transcriptional responses of Arabidopsis thaliana plants to As (V) stress.

Results: Antioxidant-related genes (i.e. coding for superoxide dismutases and peroxidases) play prominent roles in response to arsenate. The microarray experiment revealed induction of chloroplast Cu/Zn superoxide dismutase (SOD) (at2g28190), Cu/Zn SOD (at1g08830), as well as an SOD copper chaperone (at1g12520). On the other hand, Fe SODs were strongly repressed in response to As (V) stress. Non-parametric rank product statistics were used to detect differentially expressed genes. Arsenate stress resulted in the repression of numerous genes known to be induced by phosphate starvation. These observations were confirmed with qRT-PCR and SOD activity assays.

Conclusion: Microarray data suggest that As (V) induces genes involved in response to oxidative stress and represses transcription of genes induced by phosphate starvation. This study implicates As (V) as a phosphate mimic in the cell by repressing genes normally induced when available phosphate is scarce. Most importantly, these data reveal that arsenate stress affects the expression of several genes with little or unknown biological functions, thereby providing new putative gene targets for future research.

Figure 1

Phenotype of arsenate stress in Arabidopsis. Representative Arabidopsis thaliana "Columbia" plants grown for 10 days on MS medium containing either (Panel A) 0 μM As (V) or (Panel B) 100 μM arsenate. C. Histogram of root length vs. As (V) concentration.

Figure 2

SOD activity in Arabidopsis thaliana 'Col' grown on medium containing 100 μM potassium arsenate. A, superoxide dismutase activity without inhibitors, B, Gels were preincubated with KCN (which inhibits CuZn SOD), C, H₂O₂ added as an inhibitor (which inhibits both CuZn SOD and Fe SOD). Lane 1, purified bovine SOD positive control. Lane 2, control plants harvested at 7 days, Lane 3, arsenate-treated plants harvested at 7 days. Lane 4, control plants harvested at 10 days, Lane 5, arsenate-treated plants harvested at 10 days. Lane 6, control plants harvested at 13 days, Lane 7, arsenate-treated plants harvested at 13 days.

Figure 3

Cluster diagram of ΔΔCt values in response to 100 μM arsenate at 3 and 10 day time points as determined by qRT-PCR. Bright green rectangles represent strongly repressed gene expression (-4-fold and lower), whereas genes strongly induced (4-fold and higher) are shown in bright red. Arabidopsis actin was used as a reference gene to calculate ΔΔCt.