A γ-glutamyl cyclotransferase protects Arabidopsis plants from heavy metal toxicity by recycling glutamate to maintain glutathione homeostasis.
Plants detoxify toxic metals through a GSH-dependent pathway. GSH homeostasis is maintained by the γ-glutamyl cycle, which involves GSH synthesis and degradation and the recycling of component amino acids. The enzyme γ-glutamyl cyclotransferase (GGCT) is involved in Glu recycling, but the gene(s) encoding GGCT has not been identified in plants. Here, we report that an Arabidopsis thaliana protein with a cation transport regulator-like domain, hereafter referred to as GGCT2;1, functions as γ-glutamyl cyclotransferase. Heterologous expression of GGCT2;1 in Saccharomyces cerevisiae produced phenotypes that were consistent with decreased GSH content attributable to either GSH degradation or the diversion of γ-glutamyl peptides to produce 5-oxoproline (5-OP). 5-OP levels were further increased by the addition of arsenite and GSH to the medium, indicating that GGCT2;1 participates in the cellular response to arsenic (As) via GSH degradation. Recombinant GGCT2;1 converted both GSH and γ-glutamyl Ala to 5-OP in vitro. GGCT2;1 transcripts were upregulated in As-treated Arabidopsis, and ggct2;1 knockout mutants were more tolerant to As and cadmium than the wild type. Overexpression of GGCT2;1 in Arabidopsis resulted in the accumulation of 5-OP. Under As toxicity, the overexpression lines showed minimal changes in de novo Glu synthesis, while the ggct2;1 mutant increased nitrogen assimilation by severalfold, resulting in a very low As/N ratio in tissue. Thus, our results suggest that GGCT2;1 ensures sufficient GSH turnover during abiotic stress by recycling Glu.
Stockbridge School of Agriculture, University of Massachusetts, Amherst, Massachusetts 01003.
Bibin
B
Paulose
Sudesh
S
Chhikara
Joshua
J
Coomey
Ha-Il
HI
Jung
Olena
O
Vatamaniuk
Om Parkash
OP
Dhankher
D017360:Arabidopsis / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D018053:Arsenites / Q000633:toxicity; D002104:Cadmium / Q000633:toxicity; D004269:DNA, Bacterial; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018698:Glutamic Acid / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism*; D006706:Homeostasis / Q000187:drug effects; D008658:Inactivation, Metabolic; D019216:Metals, Heavy / Q000633:toxicity*; D016254:Mutagenesis, Insertional; D009584:Nitrogen / Q000378:metabolism; D030821:Plants, Genetically Modified; D011761:Pyrrolidonecarboxylic Acid / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics; D005722:gamma-Glutamylcyclotransferase / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D018053:Arsenites; D004269:DNA, Bacterial; D019216:Metals, Heavy; C036483:T-DNA; D002104:Cadmium; D018698:Glutamic Acid; D005722:gamma-Glutamylcyclotransferase; D005978:Glutathione; D009584:Nitrogen; D011761:Pyrrolidonecarboxylic Acid