Redox regulation by the CDSP32 thioredoxin of ATP-synthase activity and enzymatic antioxidant network in Solanum tuberosum

Plant thioredoxins (TRXs) form a complex family involved in numerous metabolic and signalling pathways, such as the regulation of photosynthetic metabolism in relation with light conditions. The atypical CDSP32, chloroplastic drought-induced stress protein of 32 kDa, TRX includes two TRX-fold domains, one of which has an atypical redox-active HCGPC motif, and has been initially reported to participate in responses to oxidative stress as an electron donor to peroxiredoxins and methionine sulfoxide reductases. Here, we further characterized potato lines modified for CDSP32 expression to clarify the physiological roles of the TRX. Upon high salt treatments, modified lines displayed changes in the abundance and redox status of CDSP32 antioxidant partners, and exhibited sensitivity to NaHCO ₃ , but not to NaCl. In non-stressed plants overexpressing CDSP32, a lower abundance of photosystem II PsbO and D1 subunits and ATP-synthase γ subunit was noticed. The CDSP32 co-suppressed line showed altered chlorophyll a fluorescence induction and modified regulation of the plastidial ATP-synthase activity during dark/light and light/dark transitions, revealing the involvement of CDSP32 in the control of the photosynthetic machinery. In agreement with the previously reported interaction in planta between CDSP32 and the ATP-synthase γ subunit, our data show that CDSP32 participates in the regulation of the transthylakoid membrane potential. Consistently, modeling of protein complex 3-D structure indicates that the CDSP32 TRX constitutes a suitable partner of ATP-synthase γ subunit. We discuss the roles of CDSP32 in chloroplast redox homeostasis through the regulation of both photosynthetic activity and enzymatic antioxidant network.