Host: The Japanese Society of Plant Physiologists
Pages 0295
Four distinct isoenzymes of glutamine synthetase (GS1) are known to share their functions in maintaining ammonium assimilation in Arabidopsis root. Among them, GLN1;2 showed unique characteristics favorable for an ammonium-rich environment in root: (i) transcripts of GLN1;2 were highly accumulated by ammonium supplementation; (ii) GLN1;2 showed low substrate affinity for ammonium (Km = 2.5 mM); (iii) GLN1;2 promoter activity was localized in root epidermis and root hairs in response to ammonium supplementation, thus, it is likely that GLN1;2 is one of the most essential components in primary ammonium assimilation in roots. We further investigated the GLN1;2 promoter region responsive to ammonium supplementation using GFP as a reporter. The ammonium-responsive region was narrowed down to a 21-bp sequence which was located 3.6-kb upstream of GLN1;2 coding region and was essentially required for driving the expression of GFP in root epidermis and root hairs under ammonium-rich conditions.