Stable complex formation of thylakoidal processing peptidase and PGRL1

• The two thylakoidal processing peptidase isoforms are present in distinct complexes.
• Plsp1 and PGRL1 form a stable complex.
• The complex with PGRL is dispensable for the known functions of Plsp1in vivo.

The thylakoid-transfer signal is required for energy-dependent translocation of preproteins into the thylakoid lumen and is removed by the thylakoidal processing peptidase (TPP). PGRL1 is an essential component of antimycin A-sensitive photosynthetic cyclic electron flow in chloroplasts. Here we report that one of the TPP isoforms, Plsp1, forms a stable complex with PGRL1. Genetic data demonstrate that PGRL1 is not essential for Plsp1 activity in vivo, leading to a possibility that PGRL1 may act as a regulator of TPP.