MULTIPLE FUNCTIONS OF PROMOTER SEQUENCES INVOLVED IN ORGAN-SPECIFIC EXPRESSION AND AMMONIA REGULATION OF A CYTOSOLIC SOYBEAN GLUTAMINE-SYNTHETASE GENE IN TRANSGENIC LOTUS-CORNICULATUS

A 3.5 kbp promoter fragment fused to the reporter beta-glucuronidase (GUS) gene had previously been shown to contain the regulatory elements controlling the ammonia-stimulated transcription of GS15, a soybean gene encoding root and root nodule cytosolic glutamine synthetase (GS). Further studies using an RNase protection assay allowed detection of large amounts of GS15 transcripts in flowers and pulvinus of soybean plants, whereas in other vegetative parts of the plant, the corresponding mRNAs were expressed at low levels. A comparable GUS expression pattern was obtained in transgenic Lotus corniculatus containing the GS15-GUS construct. Histochemical localization of GUS activity revealed that the cytosolic GS gene is expressed in anther theca and pollen at a late stage of flower development. Strong GUS staining was also visible in transgenic Lotus pulvini. Progressive 5' deletion of GS15 promoter showed that regulatory elements necessary for ammonia stimulation both in roots and nodules are located between -3.5 and -1.3 kbp relative to the transcription start site. Elements involved in pulvinus-specific expression are localized between -1.3 and -0.7 kbp, whereas 240 bp are sufficient to control the expression of the GS15 gene in the anthers. It therefore appears that multiple and separate promoter sequences control the organ-specific and ammonia-regulated expression of the cytosolic GS15 gene.