Identification of biochemical association of phycobilisome with photosystems in cyanobacterial state transition.

State transition is a short-term balance mechanism of energy distribution between photosystem II (PSII) and PSI. Although light-induced state transition in cyanobacteria has been suggested to depend completely on the phycobilisome (PBS) movement between PSII and PSI, the biochemical evidence has not been clearly shown. In this study, we locked the association of PBS with PSII or PSI using glycinebetaine when cells attain State 1 or 2 by exposure to light of blue or green, respectively. Subsequently, the PBS-reaction centers were resolved by blue native polyacrylamide gel electrophoresis and two-dimensional electrophoresis, and then identified by western blot analysis. The results showed that in wild-type (WT) Synechocystis sp. strain PCC 6803, the PBS core always co-migrates with the PSII dimer during light-induced State 1-State 2 transition, but its rod leaves the PSII dimer in State 2 regardless of its co-migration in State 1. In the light-induced State 2, the co-migration of PBS rod with PSI trimer was observed in WT, but not in ΔndhB (M55), a State-2-transition-deficient mutant. This study first provided the biochemical evidence for the association of PBS with photosystems during cyanobacterial state transition.