Molecular evolution of duplicate copies of genes encoding cytosolic glutamine synthetase in Pisum sativum

Elsbeth L. Walker, N. F. Weeden, Crispin B. Taylor, Pamela Green, Gloria M. Coruzzi

Research output: Contribution to journalArticle

Abstract

Here, we describe two nearly identical expressed genes for cytosolic glutamine synthetase (GS3A and GS3B) in Pisum sativum L. RFLP mapping data indicates that the GS3A and GS3B genes are separate loci located on different chromosomes. DNA sequencing of the GS3A and GS3B genes revealed that the coding regions are 99% identical with only simple nucleotide substitutions resulting in three amino acid differences. Surprisingly, the non-coding regions (5′ non-coding leader, the 11 introns, and 3′ non-coding tail) all showed a high degree of identity (96%). In these non-coding regions, 25% of the observed differences between the GS3A and GS3B genes were deletions or duplications. The single difference in the 3′ non-coding regions of the GS3A and GS3B genes was a 25 bp duplication of an AU-rich element in the GS3B gene. As the GS3B mRNA accumulates to lower levels than the GS3A gene, we tested whether this sequence which resembles an mRNA instability determinant functioned as such in the context of the GS mRNA. Using the GS3B 3′ tail as part of a chimeric gene in transgenic plants, we showed that this AU-rich sequence has little effect on transgene mRNA levels. To determine whether the GS3A/GS3B genes represent a recent duplication, we examined GS3-like genes in genomic DNA of ancient relatives of P. sativum. We observed that several members of the Viceae each contain two genomic DNA fragments homologous to the GS3B gene, suggesting that this is an ancient duplication event. Gene conversion has been invoked as a possible mechanism for maintaining the high level of nucleotide similarity found between the GS3A and GS3B genes. Possible evolutionary reasons for the maintenance of these 'twin' GS genes in pea, and the general duplication of genes for cytosolic GS in all plant species are discussed.

Original languageEnglish (US)
Pages (from-to)1111-1125
Number of pages15
JournalPlant Molecular Biology
Volume29
Issue number6
DOIs
StatePublished - Dec 1995

Fingerprint

Duplicate Genes
Glutamate-Ammonia Ligase
Gene encoding
Molecular Evolution
Peas
glutamate-ammonia ligase
Pisum sativum
Genes
genes
Gene Duplication
Messenger RNA
Nucleotides
AU Rich Elements
tail
DNA
nucleotides
Gene Conversion
genomics
Genetically Modified Plants
gene conversion

Keywords

  • gene conversion
  • gene duplication
  • Glutamine synthetase
  • molecular evolution
  • multigene family

ASJC Scopus subject areas

  • Biochemistry
  • Biochemistry, Genetics and Molecular Biology(all)

Cite this

Molecular evolution of duplicate copies of genes encoding cytosolic glutamine synthetase in Pisum sativum. / Walker, Elsbeth L.; Weeden, N. F.; Taylor, Crispin B.; Green, Pamela; Coruzzi, Gloria M.

In: Plant Molecular Biology, Vol. 29, No. 6, 12.1995, p. 1111-1125.

Research output: Contribution to journalArticle

Walker, Elsbeth L. ; Weeden, N. F. ; Taylor, Crispin B. ; Green, Pamela ; Coruzzi, Gloria M. / Molecular evolution of duplicate copies of genes encoding cytosolic glutamine synthetase in Pisum sativum. In: Plant Molecular Biology. 1995 ; Vol. 29, No. 6. pp. 1111-1125.
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AB - Here, we describe two nearly identical expressed genes for cytosolic glutamine synthetase (GS3A and GS3B) in Pisum sativum L. RFLP mapping data indicates that the GS3A and GS3B genes are separate loci located on different chromosomes. DNA sequencing of the GS3A and GS3B genes revealed that the coding regions are 99% identical with only simple nucleotide substitutions resulting in three amino acid differences. Surprisingly, the non-coding regions (5′ non-coding leader, the 11 introns, and 3′ non-coding tail) all showed a high degree of identity (96%). In these non-coding regions, 25% of the observed differences between the GS3A and GS3B genes were deletions or duplications. The single difference in the 3′ non-coding regions of the GS3A and GS3B genes was a 25 bp duplication of an AU-rich element in the GS3B gene. As the GS3B mRNA accumulates to lower levels than the GS3A gene, we tested whether this sequence which resembles an mRNA instability determinant functioned as such in the context of the GS mRNA. Using the GS3B 3′ tail as part of a chimeric gene in transgenic plants, we showed that this AU-rich sequence has little effect on transgene mRNA levels. To determine whether the GS3A/GS3B genes represent a recent duplication, we examined GS3-like genes in genomic DNA of ancient relatives of P. sativum. We observed that several members of the Viceae each contain two genomic DNA fragments homologous to the GS3B gene, suggesting that this is an ancient duplication event. Gene conversion has been invoked as a possible mechanism for maintaining the high level of nucleotide similarity found between the GS3A and GS3B genes. Possible evolutionary reasons for the maintenance of these 'twin' GS genes in pea, and the general duplication of genes for cytosolic GS in all plant species are discussed.

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