The Rice Light-Regulated Gene RA68 Encodes a Novel Protein Interacting with Oxygen-Evolving Complex PsbO Mature Protein

The oxygen-evolving complex (OEC), which is located on the luminal side of photosystem II, plays an important role in water oxidation. It is generally considered that OEC consists of the Mn₄Ca cluster and three extrinsic proteins, PsbO, PsbP, and PsbQ. In this study, we report that a novel rice protein RA68 interacts with PsbO. RA68 is expressed preferentially in seedlings and encodes a novel protein without significant homology with any other proteins. Northern analysis demonstrates that RA68 is a light-regulated gene with a diurnal oscillation pattern under different light conditions. Yeast two-hybrid screening reveals that RA68 interacts with PsbO and PsbP. Further experiments demonstrate that RA68 has specific interaction with PsbO mature protein rather than its precursor form. Moreover, in situ hybridization shows that RA68 and PsbO have similar expression patterns in seedlings.