Thylakoid-determinant subunit of high molecular weight LFNRs-containing protein complexes. Component of high molecular weight thylakoid LFNRs-containing protein complexes containing LIR1, LFNR1, LFNR2, TIC62 and TROL proteins. Interacts directly with LFNR1 and LFNR2; LIR1 increases the affinity of LFNR1 and LFNR2 for TIC62 and subsequent thylakoid relocalization. Expression is controlled by light and by a circadian clock (PubMed:8499615, PubMed:26941088). Transcripts accumulate progressively during the day and fade out during the night, however, mRNA stability is enhanced during the night. Low levels during the day, accumulates during the night (at protein level). Rapidly degraded upon illumination (at protein level); this degradation coincides with the release of the LFNR from the thylakoid membrane (PubMed:26941088). May form interchain disulfide bonds with LFNR1 and LFNR2. Retarded growth. Reduced photosynthetic electron transfer. Marked decrease in the accumulation of LFNR1 and LFNR2-containing thylakoid protein complexes.