Autophagy Is Involved in the Viability of Overexpressing Thioredoxin o 1 Tobacco BY-2 Cells under Oxidative Conditions.

Autophagy is an essential process for the degradation of non-useful components, although the mechanism involved in its regulation is less known in plants than in animal systems. Redox regulation of autophagy components is emerging as a possible key mechanism with thioredoxins (TRXs) proposed as involved candidates. In this work, using overexpressing PsTRX o 1 tobacco cells (OEX), which present higher viability than non-overexpressing cells after H 2 O 2 treatment, we examine the functional interaction of autophagy and PsTRX o 1 in a collaborative response. OEX cells present higher gene expression of the ATG (Autophagy related) marker ATG4 and higher protein content of ATG4, ATG8, and lipidated ATG8 as well as higher ATG4 activity than control cells, supporting the involvement of autophagy in their response to H 2 O 2 . In this oxidative situation, autophagy occurs in OEX cells as is evident from an accumulation of autolysosomes and ATG8 immunolocalization when the E-64d autophagy inhibitor is used. Interestingly, cell viability decreases in the presence of the inhibitor, pointing to autophagy as being involved in cell survival. The in vitro interaction of ATG4 and PsTRX o 1 proteins is confirmed by dot-blot and co-immunoprecipitation assays as well as the redox regulation of ATG4 activity by PsTRX o 1. These findings extend the role of TRXs in mediating the redox regulation of the autophagy process in plant cells.