Microarray Analysis of Arabidopsis Genome Response to Aluminum Stress

To better understand the mechanisms involved in aluminum (Al) toxicity and tolerance in plants, microarray technology was used to evaluate changes in gene expression in Arabidopsis thaliana under Al stress. With the use of Affymetrix Arabidopsis ATH1 Genechip, a comparison of RNA expression profiles was made between control and Al-treated Arabidopsis seedlings. A total of 256 genes were identified as Al-responsive. Ninety-four genes were shown to be up-regulated and 162 were down-regulated; comprising 1.1% of the 24,000 Arabidopsis genes. Real-time RT-PCR was used to confirm the microarray data. RNAs associated with known protein functions were classified into categories. The analysis showed that a large number of transcription factors and several putative signaling components were up-regulated by aluminum. Chloroplast structural and photosynthetic genes were, in general, down-regulated. A number of previously identified Al-responsive genes showed similar expression pattern changes in this study. For example, GST, Auxin-regulated, Peroxidase, and Chitinase, were found to be up-regulated by Al-stress, whereas, genes such as Wali 3 and Wali 4, were down-regulated. We also identified several up-regulated genes involved in vacuolar signaling, sorting and docking. Three genes were also up-regulated by Al-stress, Ras GTP-binding protein, ABC-cassette binding, and the AtELP1 receptor genes, have previously been documented as responsive to drought and/or oxidative stress and may play important roles the detoxification of Al ions by transportation and storage into root vacuoles. Ultrastructural changes in the roots tips cells of Arabidopsis were evaluated using TEM and EDXMA with SEM. Results using combined TEM and SEM-EDXMA showed that Al accumulattion in the root tip of Arabidopsis was detectable. The coupling these techniques can be useful for measuring Al in situ in cellular and sub cellular section of plant roots.

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