Disease relevance of RML1

• The derived amino acid sequence constitutes a polypeptide of 59.9 kDa and shows only 44-48% similarity with previously published sequences of rat kidney, human liver, yeast, and E. coli gamma-ECS [1].
• The ch1 mutants defective in a light-harvesting antenna in photosystem II showed reduced GSH levels with accumulation of the GSH precursor cysteine, and introduction of the gamma-ECS gene GSH1 under the control of the cauliflower mosaic virus 35S promoter (35S-GSH1) into the ch1 mutant altered the GSH level in response to the gamma-ECS mRNA level [2].
• A few possible mechanisms for gamma-ECS-enhanced arsenic and mercury resistance and cadmium hypersensitivity are discussed [3].

High impact information on RML1

• Mapping revealed that rax1-1 is an allele of gamma-GLUTAMYLCYSTEINE SYNTHETASE 1 (GSH1), which encodes chloroplastic gamma-glutamylcysteine synthetase, the controlling step of glutathione biosynthesis [4].
• By comparison of rax1-1 with the GSH1 mutant cadmium hypersensitive 2, the expression of 32 stress-responsive genes was shown to be responsive to changed glutathione metabolism [4].
• The phenotype of the rml1 mutant, which was also evident in the roots of wild-type Arabidopsis and tobacco treated with an inhibitor of GSH biosynthesis, could be relieved by applying GSH to rml1 seedlings [5].
• Arabidopsis plants treated with cadmium or copper responded by increasing transcription of the genes for glutathione synthesis, gamma-glutamylcysteine synthetase and glutathione synthetase, as well as glutathione reductase [6].
• AtCAD2, 3, as well as AtCAD7 and 8 (highest homology to sinapyl alcohol dehydrogenase) were catalytically less active overall by at least an order of magnitude, due to increased K(m) and lower k(cat) values [7].

Biological context of RML1

• Complementation tests identified two RML loci; RML1 maps to chromosome IV and RML2 maps to chromosome III [8].
• RML1 and RML2, Arabidopsis genes required for cell proliferation at the root tip [8].
• A new cadmium-sensitive mutant affected at a second locus, cad2, has been identified using this phenotype [9].
• Both root growth and GCS activity of the cad2-1 mutant was less sensitive than the wild-type to inhibition by BSO, indicating that the mutation may alter the affinity of the inhibitor binding site [10].
• Transient transformation experiments with reporter gene fusions, bearing long or short 5'-UTRs, indicated an exclusive targeting of GSH1 to the plastids [11].

Associations of RML1 with chemical compounds

• The glutathione-deficient, cadmium-sensitive mutant, cad2-1, of Arabidopsis thaliana is deficient in gamma-glutamylcysteine synthetase [10].
• The mutant accumulates a substrate of GCS, cysteine, and is deficient in the product, gamma-glutamylcysteine [10].
• Confocal imaging of GSH in isolated mutant and wild-type embryos after fluorescent labeling with monochlorobimane detected residual amounts of GSH in rml1 embryos [12].
• However, ars1 plants produce phytochelatin levels similar to levels produced by the wild type, and the enhanced resistance of ars1 is not abolished by the gamma-glutamylcysteine synthetase inhibitor l-buthionine sulfoxime (BSO) [13].
• Whereas growth, chlorophyll content, and photosynthetic quantum yield were very similar to wild type in vte1, vtc1, cad2, or vte1vtc1, they were reduced in vte1cad2, indicating that the simultaneous loss of tocopherol and glutathione results in moderate oxidative stress that affects the stability and the efficiency of the photosynthetic apparatus [14].
• The thiol-based regulation of GCL provides a posttranslational mechanism for modulating enzyme activity in response to in vivo redox environment and suggests a role for oxidative signaling in the maintenance of glutathione homeostasis in plants [15].

Other interactions of RML1

• A Cu-sensitive mutant, cup1-1, of Arabidopsis thaliana has a pattern of heavy-metal sensitivity different from that of the cad1 and cad2 mutants, which are deficient in phytochelatin biosynthesis [16].
• In vitro enzyme assays showed that the cad2-1 mutant has 40% of wild-type levels of GCS activity but is unchanged in the activity of the second enzyme in the pathway, GSH synthetase [10].
• Identification of PAD2 as a gamma-glutamylcysteine synthetase highlights the importance of glutathione in disease resistance of Arabidopsis [17].

Analytical, diagnostic and therapeutic context of RML1

• We report the molecular cloning of the RML1 gene, which encodes the first enzyme of glutathione (GSH) biosynthesis, gamma-glutamylcysteine synthetase, and which is allelic to CADMIUM SENSITIVE2 [5].
• Finally, the plastidic GSH1 localization was confirmed by immunocytochemistry [11].
• Moreover, immunofluorescence localization studies with antibacterial gamma-glutamyl cysteine synthetase and antiglutathione synthetase antibodies demonstrated that these immune reagents reacted strongly with their respective target proteins in chemically fixed cells from transgenic plants [18].
• Enzyme-linked immunosorbent assays and western blots with the recombinant proteins in crude extracts demonstrated that the monoclonal antibodies produced to synthetic peptides were highly specific for the different target proteins, gamma-glutamyl cysteine synthetase, glutathione synthetase, and phytochelatin synthase [18].
• For the heavy metal accumulator Brassica juncea L. a partial gamma-ECS cDNA was cloned by RT-PCR [19].

References