Poster: Epigenetics & gene silencing

Abs # 835: Post-transcriptional silencing of cytosolic glutamine synthetase in transgenic alfalfa

Presenter:	Ortega Carranza, Jose L, jortegac@nmsu.edu
Authors	Ortega Carranza, Jose L (A)   Moguel Esponda, Salvador  (B)   Conklin, Cristina  (C)   Sengupta-Gopalan, Champa  (A)
Affiliations:	(A): Department of Agronomy and Horticulture. New Mexico State University (B): Molecular Biology Graduate Program. New Mexico State University (C): MARC Program. New Mexico State University

Glutamine synthetase (GS) catalyzes the synthesis of glutamine through the condensation of ammonia and glutamate. It represents a crossing point between the carbon and nitrogen metabolism. GS occurs as different isoforms located either in the cytosol (GS₁) or chloroplast (GS₂) that perform non-overlapping roles in the assimilation of ammonia produced by different physiological processes. Since GS has a key role in plant metabolism we introduced a soybean GS₁ gene as a 35S-GS₁ construct into alfalfa in order to over express the GS₁. Our results show that in the transgenic alfalfa the GS₁ is controlled at the level of transcript stability and translatability of the mRNA. Nitrogen availability has an effect on the acumulation of the GS₁ transcript corresponding to the transgene suggesting that a product of nitrogen assimilation has a role in the turnover of the GS₁ transcript. Regulation of the GS₁ at the transcript stability and translatability levels is mediated by the 3' untranslated region (UTR). Removal of the 3' UTR of the soybean GS₁ transgene results in higher accumulation of the GS₁ transcript and reverts the inhibition of the translation of the GS₁ mRNA. To assert the role of the GS₁ 3'UTR in the stability and translatability of the messenger and the mechanisms involved in these processes, we have introduced this regulatory region behind the GUS reporter gene driven by the CaMV 35S promoter. The chimeric gene constructs will be assayed in a transient expression system under different nitrogen conditions.