The 3' untranslated region of a soybean cytosolic glutamine synthetase (GS1) affects transcript stability and protein accumulation in transgenic alfalfa.
Higher plants assimilate nitrogen in the form of ammonia through the concerted activity of glutamine synthetase (GS) and glutamate synthase (GOGAT). The GS enzyme is either located in the cytoplasm (GS1) or in the chloroplast (GS2). Glutamine synthetase 1 is regulated in different plants at the transcriptional level and there are some reports of regulation at the level of protein stability. Here we present data that clearly establish that GS1 in plants is also regulated at the level of transcript turnover and at the translational level. Using a Glycine max (soybean) GS1 transgene, with and without its 3' untranslated region (UTR), driven by the constitutive CaMV 35S promoter in Medicago sativa (alfalfa) and Nicotiana tabacum (tobacco), we show that the 3' UTR plays a major role in both transcript turnover and translation repression in both the leaves and the nodules. Our data suggest that the 3' UTR mediated turnover of the transcript is regulated by a nitrogen metabolite or carbon/nitrogen ratios. We also show that the 3' UTR of the gene for the soybean GS1 confers post-transcriptional regulation on a reporter gene. Our dissection of post-transcriptional and translational levels of regulation of GS in plants shows that the situation in plants strongly resembles that in other organisms where GS is regulated at almost all levels. Multistep regulation of GS shows the high priority given by organisms to regulating and ensuring optimal control of nitrogen substrates and preventing overproduction of glutamine and drainage of the glutamate pool.
Ortega
Jose L
JL
Department of Agronomy and Horticulture, New Mexico State University, Las Cruces, NM 88003, USA.
Moguel-Esponda
Salvador
S
Potenza
Carol
C
Conklin
Cristina F
CF
Quintana
Anita
A
Sengupta-Gopalan
Champa
C
D020413:3' Untranslated Regions / Q000502:physiology*; D017930:Genes, Reporter; D005966:Glucuronidase / Q000235:genetics; D005974:Glutamate-Ammonia Ligase / Q000235:genetics* / Q000378:metabolism; D000455:Medicago sativa / Q000235:genetics / Q000502:physiology*; D009566:Nitrates / Q000378:metabolism / Q000494:pharmacology; D009584:Nitrogen / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000502:physiology; D014176:Protein Biosynthesis; D012323:RNA Processing, Post-Transcriptional / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013025:Glycine max / Q000235:genetics; D014026:Nicotiana; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D020413:3' Untranslated Regions; D009566:Nitrates; D011993:Recombinant Fusion Proteins; D005966:Glucuronidase; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen