Circadian rhythms are 24-hour biological cycles that align metabolism, physiology and development with daily environmental fluctuations. Photosynthetic processes are governed by the circadian clock in both flowering plants and cyanobacteria, but it is unclear how extensively this is conserved throughout the green lineage. We investigated the contribution of circadian regulation to photochemistry in Marchantia polymorpha, a liverwort that diverged from flowering plants early in the evolution of land plants. First, we identified in M. polymorpha the circadian regulation of several measures of photosynthetic biochemistry (delayed fluorescence, the rate of photosynthetic electron transport, and non-photochemical quenching of chlorophyll fluorescence). Second, we identified that light-dark cycles increase the robustness of the 24 h cycles of photosynthesis in M. polymorpha, which might be due to the masking of underlying circadian rhythms of photosynthesis by light-dark cycles. Finally, we used a pharmacological approach to identify that chloroplast translation might be necessary for clock control of light harvesting in M. polymorpha. We infer that the circadian regulation of photosynthesis might be well-conserved amongst terrestrial plants.
Circadian regulation of photosynthesis and transpiration from genes to ecosystems
