Compartmentation of photosynthesis gene expression in C4 maize depends on time of day

C₄ photosynthesis involves the compartmentalization of the photosynthetic reactions across bundle sheath and mesophyll cells, which requires cell-specific gene expression; however, we do not fully understand how this occurs or how photoperiod impacts it. Here maize (Zea mays) was grown in constant light/temperature conditions, and chlorophyll fluorescence and carbon assimilation were measured over 14-hours. The carbon assimilation rate increased from 0 to 10 hours reaching its maximum 10 hours after dawn, whereas maximal photosystem II efficiency occurred 2 hours after dawn. The lack of synchronization between the maximal carbon assimilation rate and photosystem II efficiency might be due to the saturation level of the carbon concentration mechanism, or which decarboxylase is functioning. To further investigate cell specific gene expression, the authors extracted and sequenced RNA from mesophyll and bundle sheath cells over 24-hours. A principal component analysis revealed that both the time of day and cell type affect transcript levels. The largest differences occurred when carbon fixation was at its maximum, 6-10 hrs after dawn, with over 12,000 differentially expressed transcripts. Therefore, this work sheds insight into how the time-of-day influences cell specific gene expression in C₄ maize. (Summary by Rose McNelly @Rose_McN) Plant Physiol.  10.1093/plphys/kiad447