Plant cell proliferation is affected by microgravity during spaceflight, but involved molecular mechanisms, key for space agronomy goals, remain unclear. To investigate transcriptomic changes in cell cycle phases caused by simulated microgravity, an Arabidopsis immobilized synchronous suspension culture was incubated in a Random Positioning Machine. After simulation, a transcriptomic analysis was performed with two subpopulations of cells (G2/M and G1 phases enriched) and an asynchronous culture sample. Differential expression was found at cell proliferation, energy/redox and stress responses, plus unknown biological processes gene ontology groups. Overall expression inhibition was a common response to simulated microgravity, but differences peak at the G2/M phase and stress response components change dramatically from G2/M to the G1 subpopulation suggesting a differential adaptation response to simulated microgravity through the cell cycle. Cell cycle adaptation using both known stress mechanisms and unknown function genes may cope with reduced gravity as an evolutionary novel environment.