PT  - JOURNAL ARTICLE
AU  - Nikkanen, Lauri
AU  - Toivola, Jouni
AU  - Trotta, Andrea
AU  - Diaz, Manuel Guinea
AU  - Tikkanen, Mikko
AU  - Aro, Eva-Mari
AU  - Rintamäki, Eevi
TI  - Regulation of chloroplast NADH dehydrogenase-like complex by NADPH-dependent thioredoxin system
AID  - 10.1101/261560
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 261560
4099  - http://biorxiv.org/content/early/2018/02/07/261560.short
4100  - http://biorxiv.org/content/early/2018/02/07/261560.full
AB  - Linear electron transport in the thylakoid membrane drives both photosynthetic NADPH and ATP production, while cyclic electron flow (CEF) around photosystem I only promotes the translocation of protons from stroma to thylakoid lumen. The chloroplast NADH-dehydrogenase-like complex (NDH) participates in one CEF route transferring electrons from ferredoxin back to the plastoquinone pool with concomitant proton pumping to the lumen. CEF has been proposed to balance the ratio of ATP/NADPH production and to control the redox poise particularly in fluctuating light conditions, but the mechanisms regulating the NDH complex remain unknown. We have investigated the regulation of the CEF pathways by the chloroplast NADPH-thioredoxin reductase (NTRC) in vivo by using an Arabidopsis knockout line of NTRC as well as lines overexpressing NTRC. Here we present biochemical and biophysical evidence showing that NTRC activates the NDH-dependent CEF and regulates the generation of proton motive force, thylakoid conductivity to protons and redox homeostasis between the thylakoid electron transfer chain and the stroma during changes in light conditions. Further, protein-protein interaction assays suggest a putative TRX-target site in close proximity to the ferredoxin binding domain of NDH, thus providing a plausible mechanism for regulation of the NDH ferredoxin:plastoquinone oxidoreductase activity by NTRC.