Impact of energy limitations on function and resilience in long-wavelength photosystem II

Stefania Viola (1) , William Roseby (1) , Stefano Santabarabara (2) , Dennis Nürnberg (3) , Ricardo Assunção (3) , Holger Dau (3) , Julien Sellés (4) , Alain Boussac (5) , Andrea Fantuzzi (1) , A. William Rutherford (1)

1 Department of Life Sciences
2 CNR - Consiglio Nazionale delle Ricerche [Milano]
3 Freie Universität Berlin
4 Biologie du chloroplaste et perception de la lumière chez les micro-algues
5 I2BC - Institut de Biologie Intégrative de la Cellule

Photosystem II (PSII) uses the energy from red light to split water and reduce quinone, an energy-demanding process based on chlorophyll a (Chl-a) photochemistry. Two kinds of cyanobacterial PSII can use Chl-d and Chl-f to perform the same reactions using lower energy, far-red light. PSII from $Acaryochloris\ marina$ has Chl-d replacing all but one of its 35 Chl-a, while PSII from $Chroococcidiopsis\ thermalis$ , a facultative far-red species, has just 4 Chl-f and 1 Chl-d and 30 Chl-a. From bioenergetic considerations, the far-red PSII were predicted to lose photochemical efficiency and/or resilience to photodamage. Here, we compare enzyme turnover efficiency, forward electron transfer, back-reactions and photodamage in Chl-f-PSII, Chl-d-PSII and Chl-a-PSII. We show that: i) all types of PSII have a comparable efficiency in enzyme turnover; ii) the modified energy gaps on the acceptor side of Chl-d-PSII favor recombination via P$_{D1}$$^+$ Phe$^-$ repopulation, leading to increased singlet oxygen production and greater sensitivity to high-light damage compared to Chl-a-PSII and Chl-f-PSII; ii) the acceptor-side energy gaps in Chl-f-PSII are tuned to avoid harmful back reactions, favoring resilience to photodamage over efficiency of light usage. The results are explained by the differences in the redox tuning of the electron transfer cofactors Phe and Q$_A$ and in the number and layout of the chlorophylls that share the excitation energy with the primary electron donor. PSII has adapted to lower energy in two distinct ways, each appropriate for its specific environment but with different functional penalties.

Domaines: Sciences du Vivant [q-bio]

Stefania Viola, William Roseby, Stefano Santabarabara, Dennis Nürnberg, Ricardo Assunção, et al.. Impact of energy limitations on function and resilience in long-wavelength photosystem II. eLife, 2022, 11, pp.e79890. ⟨10.7554/eLife.79890⟩. ⟨hal-03795541⟩