Revisiting cyanobacterial state transitions: balancing photosystem activities

CALZADILLA P.I.; ZHAN, JIAO; SÉTIF, PIERRE; LEMAIRE, CLAIRE; SOLYMOSI, DANIEL; BATTCHIKOVA, NATALIA; WANG, QIANG; KIRILOVSKY, DIANA

Boulder

Workshop; 13th Workshop on Cyanobacteria; 2019

Photosynthetic organisms need to sense and respond to fluctuating environmentalconditions to avoid the formation of dangerous reactive oxygen species. The excitationenergy arriving at each photosystem permanently changes due to variations of intensityand spectral properties of the absorbed light. Cyanobacteria, like plants and algae, havedeveloped a mechanism, named state transitions, that sense and respond to thesefluctuating conditions. In this work, we characterize the role of the cytochrome b6f andphosphorylation reactions in cyanobacterial state transitions using Synechococcuselongatus PCC 7942 and Synechocystis PCC 6803. A large Photosystem II fluorescencequenching was observed in State II which seems not to be related to spillover. Thismembrane-associated process was inhibited by betaine, sucrose and high concentrationsof phosphate. Then, using different chemicals affecting the PQ pool redox state and theactivity of the cytochrome b6f, we demonstrated that this complex is not involved in S.elongatus and Synechocystis PCC6803 state transitions. Finally, by constructing andcharacterizing 21 kinase and phosphatase mutants and using chemical inhibitors, it wasclearly shown that phosphorylation reactions are not essential in cyanobacterial statetransitions. Thus, signal transduction is completely different in cyanobacteria and plant(green alga) state transitions.