Mechanism of gene expression of Arabidopsis glutathione S-transferase, AtGST1, and AtGST11 in response to aluminum stress

The gene expression of two Al-induced Arabidopsis glutathione S-transferase genes, AfGST1 and AtGST11, was analyzed to investigate the mechanism underlying the response to Al stress. An approximately 1-kb DNA fragment of the 5'-upstream region of each gene was fused to a beta-glucuronidase (GUS) reporter gene (pAtGST1::GUS and pAtGST11::GUS) and introduced into Arabidopsis ecotype Landsberg erecta. The constructed transgenic lines showed a time-dependent gene expression to a different degree in the root and/or leaf by Al stress. The pAtGST1::GUS gene was induced after a short Al treatment (maximum expression after a 2-h exposure), while the pAtGST11::GUS gene was induced by a longer Al treatment (approximately 8 h for maximum expression). Since the gene expression was observed in the leaf when only the root was exposed to Al stress, a signaling system between the root and shoot was suggested in Al stress. A GUS staining experiment using an adult transgenic line carrying the pAtGST11::GUS gene supported this suggestion. Furthermore, Al treatment simultaneously with various Ca depleted conditions in root region enhanced the gene expression of the pAtGST11::GUS in the shoot region. This result suggested that the degree of Al toxicity in the root reflects the gene response of pAtGST11::GUS in the shoot via the deduced signaling system. Both transgenic lines also showed an increase of GUS activity after cold stress, heat stress, metal toxicity, and oxidative damages, suggesting a common induction mechanism in response to the tested stresses including Al stress.