High salt-induced PSI-supercomplex is associated with high CEF and attenuation of state-transitions

Abstract

Abstract While PSI-driven cyclic electron flow (CEF) and assembly of thylakoid supercomplexes have been described in model organisms like Chlamydomonas reinhardtii, open questions remain regarding their contributions to survival under long term stress. The Antarctic halophyte, C. priscuii UWO241 (UWO241), possesses constitutive high CEF rates and a stable PSI-supercomplex as a consequence of adaptation to permanent low temperatures and high salinity. To understand whether CEF represents a common strategy in long-term stress acclimation, we compared high salt acclimation in the halotolerant UWO241 with a salt-sensitive model, C. reinhardtii, as well as a moderately halotolerant Antarctic green alga, C. sp. ICE-MDV (ICE-MDV). CEF was activated under high salt and associated with increased non-photochemical quenching in C. reinhardtii and ICE-MDV. Furthermore, high salt acclimated cells of either strain formed a PSI-supercomplex, while state transition capacity was attenuated. How the CEF-associated PSI-supercomplex interferes with state transition response is not yet known. We present a model for interaction between PSI-supercomplex formation, state transitions and the essential role of CEF for survival during long-term exposure to high salt.