Physiological characterization of Physcomitrium patens lines with different level of expression of flavodiiron proteins

Photosynthetic organisms are constantly exposed to light stress and, to avoid photodamage, they evolved several strategies to sidestep electrons accumulation. Indeed, electrons excited at photosystem II (PSII) and photosystem I (PSI) level can follow the linear electron flow (LEF) to the Calvin-Benson cycle (CBC) or the alternative electron pathways. Cyclic electron transports (CET) and pseudo-cyclic electron transports (PCET) constitute the most conserved ones. While CETs recycle electrons from PSI back to the plastoquinone pool, PCETs use electrons to reduce molecular oxygen into water. FLVs proteins represent the major electron sink among the PCETs resulting indispensable in the dark-to-light transition and under fluctuating light exposure. Homologous sequences of FLVs have been highly conserved during evolution, but they have been lost in angiosperm. Physcomitrium patens is a bryophyte widespread used as a model organism and different alternative electron flow co-exist in it, including the heterodimer FlvA/FlvB. In this study, P.patens double knock-out mutans have been transformed with WT FLVA and FLVB genes. Molecular and physiological analysis allowed to analyse the effect of the overexpression of one or both flavodiiron proteins, with a focus on the impact on the efficiency of the two photosystems and on the level of photodamage.