Evolutionary insights into photoregulation of the cell cycle in the green lineage

• Photosynthesis and photoreceptors mediate light regulation of the cell cycle.
• The photosynthetic pathway evolved to act non-cell-autonomously in sink tissues.
• Photoreceptor pathways have been prone to rewiring during evolution.
• Light-dependent cell-cycle re-entry involves global transcriptional reprogramming.
• Cytokinin links the light signal to cell-cycle progression at least in some cases.

Plant growth depends solely on light energy, which drives photosynthesis. Thus, linking growth control to light signals during certain developmental events, such as seed or spore germination and organ formation, is a crucial feature that plants evolved to use energy efficiently. How light controls the cell cycle depends on growth habitats, body plans (unicellular vs. multicellular), and photosensors. For example, the photosensors mediating light signaling to promote cell division appear to differ between green algae and land plants. In this review, we focus on cell-cycle regulation by light and discuss the transition of its molecular mechanisms during evolution. Recent advances show that light-dependent cell-cycle control involves global changes in transcription of cell-cycle genes, and is mediated by auxin and cytokinin.