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Arabidopsis γ‐glutamylcyclotransferase affects glutathione content and root system architecture during sulfur starvation

Joshi, Naveen C., Meyer, Andreas J., Bangash, Sajid A. K., Zheng, Zhi‐Liang, Leustek, Thomas
Thenew phytologist 2019 v.221 no.3 pp. 1387-1397
Arabidopsis thaliana, acyltransferases, cysteine, gene expression regulation, genes, glutamic acid, glutathione, mutants, root growth, root systems, root tips, seedlings, sulfates, sulfur, tissues, transcription (genetics)
γ‐Glutamylcyclotransferase initiates glutathione degradation to component amino acids l‐glutamate, l‐cysteine and l‐glycine. The enzyme is encoded by three genes in Arabidopsis thaliana, one of which (GGCT2;1) is transcriptionally upregulated by starvation for the essential macronutrient sulfur (S). Regulation by S‐starvation suggests that GGCT2;1 mobilizes l‐cysteine from glutathione when there is insufficient sulfate for de novo l‐cysteine synthesis. The response of wild‐type seedlings to S‐starvation was compared to ggct2;1 null mutants. S‐starvation causes glutathione depletion in S‐starved wild‐type seedlings, but higher glutathione is maintained in the primary root tip than in other seedling tissues. Although GGCT2;1 is induced throughout seedlings, its expression is concentrated in the primary root tip where it activates the γ‐glutamyl cycle. S‐starved wild‐type plants also produce longer primary roots, and lateral root growth is suppressed. While glutathione is also rapidly depleted in ggct2;1 null seedlings, much higher glutathione is maintained in the primary root tip compared to the wild‐type. S‐starved ggct2;1 primary roots grow longer than the wild‐type, and lateral root growth is not suppressed. These results point to a role for GGCT2;1 in S‐starvation‐response changes to root system architecture through activity of the γ‐glutamyl cycle in the primary root tip. l‐Cysteine mobilization from glutathione is not solely a function of GGCT2;1.