Cell Cycle by Light Intensity in Chlamydomonas reinhardtii

Photosynthetic organisms coordinate their metabolism and growth with diurnal light, which can range in intensity from limiting to inhibitory. To gain a comprehensive understanding of how diurnal regulatory circuits interface with sensing and response to various light intensities, we performed a systems analysis of synchronized Chlamydomonas reinhardtii populations acclimated to low, moderate, and high diurnal light. Transcriptomic and proteomic data revealed that Chlamydomonas' rhythmic gene expression program is resilient to limiting and excess light. Although gene expression is dynamic over the diurnal cycle, Chlamydomonas populations acclimated to low and high diurnal light exhibit constitutive phenotypes with respect to photosystem abundance, thylakoid architecture, and non-photochemical quenching that persist through the night. This suggests that cells harbor a “memory” or anticipation of the daylight environment. The integrated data constitute an excellent resource for understanding gene regulatory mechanisms and photoprotection in eukaryotes under environmentally relevant conditions. Overall design: Cells were grown photoautotrophically in turbidostat mode in photobioreactors under diel cycles of 12 h light (LL 50 PFD, ML 200 PFD, or HL 1000 PFD) at 28°C and 12 h dark at 18°C for a minimum of two weeks in order to establish population synchrony and acclimate the population to the respective diurnal light intensity. Samples were collected for RNA-seq at five timepoints over the diel cycle (-2, +2, +6, +10, -10). These data are accompanied by proteomics, lipidomics, and physiological measurements. The moderate light (ML) condition served as the control, as it exhibited the highest degree of synchrony and has been reported on previously (Strenkert et al. 2019, PNAS).