Isolation and characterization of a rice glutathione S-transferase gene promoter regulated by herbicides and hormones.

OsGSTL2, encoding glutathione S-transferase, is a lambda class gene on chromosome 3 of rice (Oryza sativa L.). RNA blot analysis and semi-quantitative RT-PCR assays demonstrated that the transcription of OsGSTL2 in rice roots treated with chlorsulfuron increased significantly. To further understand OsGSTL2 promoter activity, a DNA fragment (GST2171) of 2,171 bp upstream of the OsGSTL2 coding region was isolated. In silico sequence analysis revealed that this fragment contains stress-regulated regulatory elements, hormone-responsive elements and three transposable elements. To define the core promoter sequence, a series of 5' truncation derivatives of GST2171 were fused to uidA gene. The chimeric genes were introduced into rice plants via Agrobacterium-mediated transformation. The expression of the GST2171::GUS transgene varied considerably. GUS staining indicated that the uidA gene is expressed in young seedlings, older leaves, flowering glumes and seeds, but not in older roots. Quantitative fluorescence assays revealed that the expression of the uidA gene is strong in young seedlings and decreases gradually over a period of 25 days. To our surprise, among the 5' truncation derivatives, the shortest promoter GST525 showed the highest GUS expression, and the second shortest promoter GST962 showed the lowest GUS expression. The uidA gene expression in the roots of transgenic rice seedlings is upregulated by chlorsulfuron, glyphosate, salicylic acid (SA) and naphthalene acetic acid (NAA). The possible roles of the repetitive elements on the OsGSTL2 promoter were discussed in terms of transcription repression and promoter induction by herbicides and hormones.