title: Repercussion of mesophyll-specific overexpression of a soybean cytosolic glutamine synthetase gene in alfalfa (Medicago sativaL.) and tobacco (Nicotiana tabaccumL.).
abstract: Glutamine synthetase (GS) plays a central role in plant nitrogen metabolism. Plant GS occurs as a number of isoenzymes present in either the cytosol (GS1) or chloroplast/plastid (GS2). There are several reports of improved performance in transgenic plants overexpressing GS1transgenes driven by the constitutive CaMV35S promoter. Improvement has been attributed to the GS1transgene product functioning to enhance re-assimilation of NH4+released by photorespiration or protein degradation. In this paper, alfalfa and tobacco transformants expressing a soybean gene driven by a photosynthetic cell-specific promoter have been compared to transformants with the same transgene driven by the stronger CaMV35S promoter. The two classes of alfalfa and tobacco transformants showed differences in the level of GS1transcript and GS1protein accumulation, but the difference in the total GS activity was small. The discrepancy in the transgene expression level and GS activity has been attributed to posttranslational regulation at the level of holoprotein stability. Both classes of transformants exhibited similar level of improvement in soluble protein and in the rates of photosynthesis and photorespiration. The data supports the hypothesis that GS1made in the mesophyll cells is involved in the re-assimilation of NH4+released via photorespiration and/or protein degradation.
authors: Graduate Program in Molecular Biology, New Mexico State University, 945 College Ave, MSC-3Q, Las Cruces, NM 88003 USA.
authors: Mark
authors: M
authors: Seger
authors: Department of Plant and Environmental Sciences, New Mexico State University, 945 College Ave, MSC-3Q, Las Cruces, NM 88003 USA.
authors: Jose Luis
authors: JL
authors: Ortega
authors: Department of Plant and Environmental Sciences, New Mexico State University, 945 College Ave, MSC-3Q, Las Cruces, NM 88003 USA.
authors: Suman
authors: S
authors: Bagga
authors: Graduate Program in Molecular Biology, New Mexico State University, 945 College Ave, MSC-3Q, Las Cruces, NM 88003 USA ; Department of Plant and Environmental Sciences, New Mexico State University, 945 College Ave, MSC-3Q, Las Cruces, NM 88003 USA.
authors: Champa-Sengupta
authors: CS
authors: Gopalan
keywords: Glutamine synthetase; mesophyll-specific overexpression; nitrogen assimilation; photorespiratory ammonium; transgenic alfalfa