The foxtail millet Si69 gene is a Wali7 (wheat aluminum-induced protein 7) homologue and may function in aluminum tolerance

We isolated a clone, named Si69, from a foxtail millet immature seed cDNA library. The protein encoded by Si69 contains a conserved Wali7 (wheat aluminum induced protein 7) domain and shares high-level homology with aluminum-induced proteins from other species including rice and Arabidopsis. The Si69 gene presents as a single locus in foxtail millet genome and is globally expressed in all tissues examined. Its expression is up-regulated by aluminum. The sequence feature and expression pattern suggest that the Si69 gene is involved in aluminum tolerance or detoxification. To confirm its biological functions, Si69 controlled by the CaMV35S promoter was introduced into Arabidopsis. Transgenic plants did not show any visible morphological changes compared to wild-type plants under normal growth conditions. However, when treated with 20 or 50 μmol/L Aluminum (Al), the root apices of wild-type plants were heavily stained by hematoxylin, whereas those of Si69 transgenic plants were not stained when treated with 20 μmol/L Al and slightly stained when treated with 50 μmol/L Al. Scanning electron microscopy (SEM) results further demonstrated that the damage of the root apices was severer in wild-type plants than in transgenic plants. Inhibition of root growth and accumulation of malondialdehyde (MDA), an indicator of lipid peroxidation, were lower in transgenic plants than in wild-type plants. The results show that overexpression of Si69 may increase Al tolerance in transgenic plants, indicating that a series of Wali7-containing genes may play similar roles in Al tolerance/detoxification.