The Presence of GSI-Like Genes in Higher Plants: Support for the Paralogous Evolution of GSI and GSII Genes |
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Authors: | René Mathis Pascal Gamas Yves Meyer Julie V Cullimore |
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Institution: | (1) Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, Institut National de la Recherche Agronomique—Centre National de la Recherche Scientifique UMR215, 31326 Castanet-Tolosan Cedex, France, FR;(2) Laboratoire de Physiologie et Biologie Moléculaire des Plantes, Université/Centre National de la Recherche Scientifique URA 565, 66860 Perpignan Cedex, France, FR |
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Abstract: | Glutamine synthetase type I (GSI) genes have previously been described only in prokaryotes except that the fungus Emericella nidulans contains a gene (fluG) which encodes a protein with a large N-terminal domain linked to a C-terminal GSI-like domain. Eukaryotes generally contain
the type II (GSII) genes which have been shown to occur also in some prokaryotes. The question of whether GSI and GSII genes
are orthologues or paralogues remains a point of controversy. In this article we show that GSI-like genes are widespread in
higher plants and have characterized one of the genes from the legume Medicago truncatula. This gene is part of a small gene family and is expressed in many organs of the plant. It encodes a protein similar in size
and with between 36 and 46% amino acid sequence similarity to prokaryotic GS proteins used in the analyses, whereas it is
larger and with less than 25% similarity to GSII proteins, including those from the same plant species. Phylogenetic analyses
suggest that this protein is most similar to putative proteins encoded by expressed sequence tags of other higher plant species
(including dicots and a monocot) and forms a cluster with FluG as the most divergent of the GSI sequences. The discovery of
GSI-like genes in higher plants supports the paralogous evolution of GSI and GSII genes, which has implications for the use
of GS in molecular studies on evolution.
Received: 4 May 1999 / Accepted: 17 September 1999 |
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Keywords: | : Gene families — Glutamine synthetase — Medicago truncatula— Phylogeny |
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