The ApcD mutant do not impair state transitions in Synechococcus elongatus

CALZADILLA P.I; MUZZOPAPPA, FERNANDO; SÉTIF, PIERRE; KIRILOVSKY, DIANA

Paris

Jornada; Sfphi2018 : Journées de la Société Française de Photosynthèse; 2018

Société Française de Photosynthèse

Photosynthetic organisms adapt to a changing light environment through different mechanisms. In particular, ?state transitions? is one of these processes, controlling the relative extent of energy transfer from antennae to photosystems. Two ?States? are defined: State II is characterized by relative low PSII to PSI fluorescence ratio, and State I by high PSII to PSI fluorescence ratio. In cyanobacteria, light is absorbed by large protein complexes on the surface of the thylakoid membrane called phycobilisomes (PBS), constituted by phycobiliproteins organized in a core from which rods radiate. Within the core, three proteins are ascribed as relevant in energy transfer: apcD, apcF and apcE. The apcD mutant of Synechocystis PCC 6803 and Synechococcus PCC 7002 lack state transitions, although the reason is still controversial. In this work, we further investigate state transitions by characterizing the apcD and apcF Synechococcus elongatus (PCC7942) mutants. Comparison with Synechocystis wt and apcD were also done. Unexpectedly, the apcD S. elongatus mutant presented ?normal? state transitions. Moreover, alterations in energy transfer to PSI were shown in this strain, but no effect in energy transfer to neither of both photosystems were observed in apcF. Large changes in Chl PSII related fluorescence were observed in S. elongatus between State I and II, while in Synechocystis changes at the level of PBS fluorescence seemed to be more significant. These results suggest that the preponderance of the mechanisms involved in state transitions could be different between the S. elongatus and Synechocystis strains.