Diurnal Light Transitions in Chlamydomonas reinhardtii

For the model alga Chlamydomonas, acclimation to diurnal low light (LL) or high light (HL) results in changes in photosynthetic complexes, chlorophyll content, thylakoid membrane architecture, and nonphotochemical quenching capacity that are maintained through the intervening night phases. To determine how diurnal photoacclimation influences algal fitness and document the molecular events during reacclimation upon a change in daylight intensity, we transitioned LL-acclimated populations to diurnal HL and HL-acclimated populations to diurnal LL and performed an RNA-Seq timecourse over two diurnal periods. Overall design: Cells were grown photoautotrophically in turbidostat photobioreactors under diurnal cycles of 12 h light at 28°C and 12 h dark at 18°C for a minimum of two weeks in order to establish population synchrony and acclimate them to either LL (50 PFD) or HL (1000 PFD). Then, the LL-acclimated populations were subjected to diurnal HL conditions, and the HL-acclimated populations were subjected to diurnal LL conditions. Cell physiology (cell number, size, pigments, photosynthetic parameters), the transcriptome, and the proteome were monitored for two diurnal periods. Samples were collected for RNA-Seq every 2 h.