Poster: Posttranscriptional Regulation

Abs # 1082: The 3’ untranslated region of a cytosolic glutamine synthetase gene from soybean mediates the nitrogen-dependent abundance of the transcript and polypeptide

Presenter:	Sengupta-Gopalan, Champa , csgopala@nmsu.edu
Authors	Sengupta-Gopalan, Champa  (A)   Moguel-Esponda, Salvador  (A)   Ortega, Jose L (A)
Affiliations:	(A): New Mexico State University

Glutamine synthetase (GS) catalyzes the ATP dependent condensation of ammonia with glutamate to yield glutamine. There are two major isoforms in plants, a cytosolic form (GS₁) and a chloroplastic form (GS₂). Analysis of alfalfa plants transformed with a GS₁ transgene driven by the CaMV 35S promoter has shown that GS₁ in alfalfa is regulated at the level of transcript turnover and polypeptide accumulation. We investigated the function of the 3’ untranslated region (3’UTR) of a soybean GS₁ gene in transgenic alfalfa with regards to nitrogen-dependent accumulation of the corresponding GS₁ RNA and protein. Several independent alfalfa transformants with the soybean GS₁ gene, with or without its 3’UTR (pGS53 and pGS50, respectively), were analyzed for the accumulation of the transgene transcript by quantitative RT PCR and northern blot analysis, and for the protein by SDS PAGE and native gel electrophoresis followed by immunoblot analysis. The pGS50 transformants showed higher levels of transgene transcript accumulation compared to the pGS53 transformants. Experiments using RNA synthesis inhibitors have shown that the enhancement in the level of accumulation of the transgene transcript is due to reduced turnover and not due to increased synthesis. Nitrate feeding showed a drop in the transgene transcript level in the leaves of the pGS53 plants but not in the pGS50 plants suggesting that nitrate or an assimilation product is involved in the 3’UTR mediated turnover of the transcript. The pGS53 transformants showed no accumulation of the transgene polypeptide when grown in the presence or absence of nitrate while the pGS50 transformants showed a significant increase in the level of accumulation of the polypeptide indicating that the 3’UTR acts as a translation repressor.