Multiple functions of promoter sequences involved in organ‐specific expression and ammonia regulation of a cytosolic soybean glutamine synthetase gene in transgenic Lotus corniculatus

Abstract

SummaryA 3.5 kbp promoter fragment fused to the reporter p-glucuronidase (GUS) gene had previously been shown to contain the regulatory elements controlling the ammonia-stimulated transcription of GSf5, a soybean gene encoding root and root nodule CytosoIic glutamine synthetase (GS). Further studies using an RNase protection assay allowed detection of large amounts of GSldtranscripts 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 comiculatus 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 GUSstaining 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 GSf5 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.

Asparaginase gene expression is regulated in a complex spatial and temporal pattern in nitrogen‐sink tissues

“…Although no direct effect of exogenous asparagine on asparaginase transcription has been demonstrated, the correlation between patterns of GUS expression and known locations of high asparagine concentration suggests that a plausible mechanism for the transcriptional contol of this asparaginase gene involves the influence of local asparagine levels. Increased expression of a glutamine synthetase gene in roots in response to exogenous ammonia has been demonstrated (Hire1 et a/ ., 1987;Marsolier et a/., 1993), but glutamine synthetase expression in fix pea nodules was unaltered, indicating ammonia production was not required in this tissue (Walker and Coruzzi, 1989). No evidence has been found for metabolite regulation of pea asparagine synthase although its transcription is regulated by light and developmental conditions (Tsai and Coruzzi, 1990 (Balconi eta/., 1993).…”

Identification of several soybean cytosolic glutamine synthetase transcripts highly or specifically expressed in nodules: expression studies using one of the corresponding genes in transgenic Lotus corniculatus

“…We have previously characterized a GS gene (GS 15) that is highly expressed in roots and root nodules and the transcription of which was shown to be controlled by the availability of ammonia. Moreover, we have demonstrated that the promoter of this gene, when fused to the coding region for GUS, directs ammonia-responsive and organspecific expression of the reporter gene in transgenic Lotus corniculatus plants [29,31].…”

“…The expression of these cytosolic GS genes was studied either by measuring the level of transcripts in their native environment or by analysing their promoter activity in transgenic plants using the E. coli/%glucuronidase (GUS) reporter gene [6,14,16,19,31 ]. These approaches have helped identify the physiological roles of the various GS isoforms in plant nitrogen metabolism, including their function in generating glutamine for nitrogen transport [6,14,16,29].…”

Actinorhizal, mycorhizal and rhizobial symbioses: how much do we know?

“…Furthermore, promoter analysis of a cytosolic soybean glutamine synthetase gene GS15 showed that regulatory elements necessary for ammonia stimulation in nodules are located between -3.5 and -1.3 kbp (Marsolier et al, 1993).…”