Arabidopsis thaliana Oxoprolinase 1 (AtOXP1) maintains glutamate homeostasis, promotes arsenite and mercury tolerance, and reduces accumulation in plants.

SUMMARY: Glutathione (GSH) plays a crucial role in cellular redox regulation and enhancing plant survival under heavy metal toxicity. In plants, GSH homeostasis is managed through the γ‐glutamyl cycle, though the genes involved in GSH degradation and recycling are not fully understood. Here, we have characterized the Arabidopsis oxoprolinase 1 (AtOXP1) gene for its role in providing tolerance to arsenite (AsIII) and mercury (Hg) stress. The oxp1 T‐DNA mutants showed severe sensitivity to Hg, with significantly lower shoot (~40%) and root (~86%) biomass compared with WT. The mutants accumulated ~45% higher arsenic and Hg accumulation in shoots. The oxp1 mutants also had elevated GSH (2.3–4.0 folds) and oxoproline (5‐OP) levels (96%–265%) compared with Col‐0 under control and stress conditions. The mutants showed significantly (15%–78%) lower glutamate levels than Col‐0 under metal stress. Conversely, relative to WT, AtOXP1 overexpression (OE) lines had significantly higher biomass (18%–43% more) and reduced As (40%) and Hg (19%–35%) accumulation in the shoots. Compared with Col‐6, the AtOXP1 OE lines had significantly (44%–57%) lower buildup of GSH levels under both AsIII and Hg treatment. Isotopic analysis revealed that the oxp1 mutants had 29% higher 15N‐Glu/Total Glu compared to WT, while OE lines were similar to WT. Additionally, OE lines had significantly higher shoot (15%–22%) and root (~77%) biomass under low nitrogen conditions. The results demonstrate that OXP1 is involved in Glu recycling via GSH degradation and holds the potential to improve plant productivity and reduce toxic metal(loid)s accumulation for food safety. [ABSTRACT FROM AUTHOR]