Ferredoxin-plastoquinone reductase involved in cyclic electron flow (CEF) around photosystem I. The homodimer is probably not involved in CEF. Inhibited by antimycin A. Homodimer and heterodimer with PGR5. Interacts with PGR5, FD2, petC, psaD1, LFNR1 and LFNR2. Interacts also with a Fe-containing cofactor (FCC). Predominantly located in the appressed regions of the thylakoids and less abundant in the stroma lamellae. Up-regulated by drought stress. The C-terminal loop (258-324) is required for ferredoxin binding. Disulfide bonds; Cys-300 and Cys-303 are probably involved in the formation of disulfide bridges with 'Cys-11' and 'Cys-105' of PGR5 while Cys-272 and Cys-275 are probably involved in the binding of a Fe-containing cofactor (FCC). No visible phenotype; due to the redundancy with PGRL1B. Pgrl1a and pgrl1b double mutant grows slowly and has pale green leaves. Thioredoxins prevent homodimerization. Belongs to the PGR5 family.