State transitions redistribute rather than dissipate energy between the two photosystems in Chlamydomonas

Abstract

Photosynthesis converts sunlight into biologically useful compounds, thus fuelling practically the entire biosphere. This process involves two photosystems acting in series powered by light harvesting complexes (LHCs) that dramatically increase the energy flux to the reaction centres. These complexes are the main targets of the regulatory processes that allow photosynthetic organisms to thrive across a broad range of light intensities. In microalgae, one mechanism for adjusting the flow of energy to the photosystems, state transitions, has a much larger amplitude than in terrestrial plants, whereas thermal dissipation of energy, the dominant regulatory mechanism in plants, only takes place after acclimation to high light. Here we show that, at variance with recent reports, microalgal state transitions do not dissipate light energy but redistribute it between the two photosystems, thereby allowing a well-balanced influx of excitation energy.

Light‐dependent N‐terminal phosphorylation of LHCSR3 and LHCB4 are interlinked in Chlamydomonas reinhardtii

“…The amount of mobile LHCII antenna is about 80% in C. reinhardtii (Delosme et al ., ). However, the extent of PSI antenna size increase is currently under debate as well as whether light energy is mainly dissipated or redistributed between the two photosystems (Iwai et al ., ; Nagy et al ., ; Unlu et al ., ; Nawrocki et al ., ). The process of state transitions can be reversed when LHCII proteins are de‐phosphorylated and re‐associate with PSII (state 1).…”

Changes in water color shift competition between phytoplankton species with contrasting light‐harvesting strategies

“…It has been hypothesized that PBS can dynamically move back and forth between PSII and PSI by state transitions (Mullineaux et al 1997, van Thor et al 1998), but recent research does not fully support this hypothesis (Chukhutsina et al 2015, Ranjbar Choubeh et al 2018, Calzadilla et al 2019. By contrast, the cyanobacterium Prochlorococcus, green algae, and many other eukaryotic phytoplankton (e.g., diatoms, coccolithophores, and dinoflagellates) lack PBS, but contain light-harvesting complexes consisting of chlorophylls and carotenoids that can effectively transfer light energy to both photosystems (Chisholm et al 1992, Natali and Croce 2015, Nawrocki et al 2016; Fig. 1B).…”

The function of LHCBM4/6/8 antenna proteins inChlamydomonas reinhardtii

“…Optimal use of limiting light is obtained by balancing PSII and PSI antenna sizes by transferring a subset of the LHCII from PSII to PSI whenever plastoquinone is over-reduced. Over-reduction of the plastoquinone pool activates a kinase (STT7) phosphorylating LHCII and favoring its migration to PSI (Allen and Pfannschmidt, 2000; Finazzi et al , 2002; Depège et al , 2003; Ferrante et al , 2012; Galka et al , 2012; Allorent et al , 2013; Drop et al , 2014 a , b ; Ünlü et al , 2014; Benson et al , 2015; Nawrocki et al , 2016). In Chlamydomonas reinhardtii , trimeric LHCII is encoded by nine genes called LHCBM1–LHCBM9 , with M referring to ‘major’ antenna complex (Merchant et al , 2007; Ferrante et al , 2012).…”