Molecular analysis of the pathway for the synthesis of thiol tripeptides in the model legume Lotus japonicus.
The thiol tripeptides, glutathione (GSH) and homoglutathione (hGSH), perform multiple roles in legumes, including protection against toxicity of free radicals and heavy metals. The three genes involved in the synthesis of GSH and hGSH in the model legume, Lotus japonicus, have been fully characterized and appear to be present as single copies in the genome. The gamma-glutamylcysteine synthetase (gamma(ecs)) gene was mapped on the long arm of chromosome 4 (70.0 centimorgans [cM]) and consists of 15 exons, whereas the glutathione synthetase (gshs) and homoglutathione synthetase (hgshs) genes were mapped on the long arm of chromosome 1 (81.3 cM) and found to be arranged in tandem with a separation of approximately 8 kb. Both genes consist of 12 exons of exactly the same size (except exon 1, which is similar). Two types of transcripts were detected for the gshs gene, which putatively encode proteins localized in the plastids and cytosol. Promoter regions contain cis-acting regulatory elements that may be involved in the plant's response to light, hormones, and stress. Determination of transcript levels, enzyme activities, and thiol contents in nodules, roots, and leaves revealed that gamma(ecs) and hgshs are expressed in all three plant organs, whereas gshs is significantly functional only in nodules. This strongly suggests an important role of GSH in the rhizobia-legume symbiosis.
Department of Botany, University of Queensland, Brisbane, Australia.
Manuel A
MA
Matamoros
Maria R
MR
Clemente
Shusei
S
Sato
Erika
E
Asamizu
Satoshi
S
Tabata
Javier
J
Ramos
Jose F
JF
Moran
Jiri
J
Stiller
Peter M
PM
Gresshoff
Manuel
M
Becana
D001483:Base Sequence; D017931:DNA Primers; D007887:Fabaceae / Q000235:genetics / Q000378:metabolism; D005721:Glutamate-Cysteine Ligase / Q000235:genetics; D005978:Glutathione / Q000096:biosynthesis / Q000235:genetics; D005981:Glutathione Synthase / Q000235:genetics; D000070116:Lotus / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis*; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013438:Sulfhydryl Compounds
D017931:DNA Primers; D009842:Oligopeptides; D013438:Sulfhydryl Compounds; D005721:Glutamate-Cysteine Ligase; D005981:Glutathione Synthase; D005978:Glutathione