PGRL1-mediated cyclic electron flow is crucial for acclimation to anoxia and complementary to non-photochemical quenching in stress adaptation.

Kukuczka B, Magneschi L, Petroutsos D, Steinbeck J, Bald T, Powikrowska M, Fufezan C, Finazzi G, Hippler M

Zusammenfassung

To investigate the functional importance of PGRL1 for photosynthetic performances in the moss Physcomitrella patens, we generated a pgrl1 knockout mutant. Functional analysis revealed diminished non-photochemical quenching (NPQ) as well as decreased capacity for cyclic electron flow (CEF) in pgrl1. Under anoxia, where CEF is induced, quantitative proteomics evidenced severe down regulation of photosystems but up regulation of the chloroplast NDH complex, plastocyanin and CAS in the mutant, indicating that the absence of PGRL1 triggered mechanism compensatory for diminished CEF. On the other hand, proteins required for NPQ, such as LHCSR1, VDE and PSBS, remained stable. To further investigate the interrelation between CEF and NPQ, we generated a pgrl1 npq4 double mutant in the green alga Chlamydomonas reinhardtii lacking both PGRL1 and LHCSR3 expression. Phenotypic comparative analyses of this double mutant together with the single knockout strains and with the Physcomitrella pgrl1 demonstrated that PGRL1 is crucial for acclimation to high light (HL) and anoxia in both organisms. Moreover the data generated for the Chlamydomonas double mutant clearly showed a complementary role of PGRL1 and LHCSR3 in managing HL stress response. We conclude that both proteins are needed for photo-protection and for survival under low oxygen, underpinning a tight link between CEF and NPQ in oxygenic photosynthesis. Given the complementarity of qE and PGRL1-mediated CEF, we suggest that PGRL1 is a capacitor linked to the evolution of PSBS-dependent qE in terrestrial plants.