Functional analysis of a nitrite reductase promoter from birch in transgenic tobacco

Nitrate assimilation is a highly regulated process in higher plants, and th e regulatory cues governing gene expression in this pathway include both ex ternal and internal factors. In birch (Betula pendula Roth) the expression of nitrate reductase (NR) and nitrite reductase (NiR) genes is co-regulated by light and nitrate at the transcriptional level. In order to identify ci s-acting DNA-elements involved in light and nitrate induction of the birch NIR gene, a 0.9 kb 5' flanking region of the NiR gene was isolated, analyse d on the DNA level, and the transcription start site was determined. Deleti on analysis of the birch NiR promoter region fused to the GUS reporter gene (uidA) in transgenic tobacco (Nicotiana tabacum) revealed the presence of light- and nitrate-responsive promoter fragments. The responsive fragments showed different activities in leaves and roots. Further, gel mobility shif t assays using nuclear proteins from leaves detected a specific DNA-binding activity to the sequence between - 146 and - 267 bp that was induced in da rkness and disappeared in the light. The deletion analysis has shown that t his region is critical for light inducibility of the birch NiR gene in leav es. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.