New role for thioredoxins in plants: Implication of TRXo1 in protein depersulfidation

Persulfidation, a posttranslational modification of cysteines to persulfides, is the best characterized molecular mechanism of H₂S signaling. This study is focused on new functions for thioredoxins (TRXs) in plants beyond those of thiol disulfide (S-S) exchange, including the regulation of protein persulfidation as it has been described in animal systems. To elucidate the impact of TRXo1 deficiency on the protein persulfidation pattern in plants of Arabidopsis thaliana L. wild type (WT) and two Attrxo1 T-DNA insertion mutants grown under non stress conditions, a quantitative proteomic approach was performed. The proteomic analysis revealed a higher number of proteins that were more persulfidated in the mutants compared to WT plants, suggesting a role for TRXo1 in protein depersulfidation. Interestingly, most of the differentially persulfidated proteins were located in the chloroplast, implying a coordination between chloroplast H₂S-dependent persulfidation and mitochondrial TRXo1 depersulfidation. Among the differentially persulfidated proteins located in mitochondria, the antioxidant enzymes sAPX, DHAR1 and MDAR6 were selected for further studies. The effect of H₂S-dependent persulfidation on their enzymatic activities and its reversibility by the NADPH/thioredoxin reductase (NTRB)/TRXo1 system was analyzed, as well as their persulfidation levels were quantified. Sulfide treatment brought about increases in the activity levels of the enzymes, that match with a raise on the persulfidation levels. Interestingly, both activations declining after treatment with the thioredoxin system, indicate the regulation of their persulfidation by TRXo1. These results point to a positive effect of persulfidation on the enzymatic activities and also to a new depersulfidase activity for TRXo1. All together these results give a new insight of the mechanism of elimination of -SSH groups in plants exerted by TRXo1, and the involvement of a redox regulation on the protein persulfidation.