Tethering of ferredoxin:NADP+ oxidoreductase to thylakoid membranes is mediated by novel chloroplast protein TROL

Working in tandem, two photosystems in the chloroplast thylakoid membranes produce a linear electron flow from H₂O to NADP⁺. Final electron transfer from ferredoxin to NADP⁺ is accomplished by a flavoenzyme ferredoxin:NADP⁺ oxidoreductase (FNR). Here we describe TROL (t hylakoid r ho danese‐l ike protein), a nuclear‐encoded component of thylakoid membranes that is required for tethering of FNR and sustaining efficient linear electron flow (LEF) in vascular plants. TROL consists of two distinct modules; a centrally positioned rhodanese‐like domain and a C‐terminal hydrophobic FNR binding region. Analysis of Arabidopsis mutant lines indicates that, in the absence of TROL, relative electron transport rates at high‐light intensities are severely lowered accompanied with significant increase in non‐photochemical quenching (NPQ). Thus, TROL might represent a missing thylakoid membrane docking site for a complex between FNR, ferredoxin and NADP⁺. Such association might be necessary for maintaining photosynthetic redox poise and enhancement of the NPQ.