Molecular regulation of plant endoreduplication: core mechanisms and their upstream control.

Endoreduplication, or the endocycle, is a widespread developmental program in plants, in which cells repeatedly replicate their nuclear genome without cell division, leading to endopolyploidy. Unlike endomitosis or chemically induced polyploidization, this process arises from an intrinsic reconfiguration of the cell cycle machinery that uncouples G1/S progression from M-phase entry. A useful conceptual framework for this regulation is the "endocycle oscillator", a periodic control logic that supports repeated rounds of DNA replication while bypassing mitosis. Studies in animal systems, particularly Drosophila, have helped define this logic, whereas how far comparable principles apply in plants remains less clear. This review integrates current understanding of the plant endocycle, progressing from the operational logic of endocycle control to regulatory networks characterized in angiosperms. It specifically addresses how current findings in plants can be organized in terms of repeated S-phase entry and mitotic suppression. Available evidence points to important roles for licensing-related pathways in repeated genome duplication and for cyclin-CDKB complexes in the control of mitotic entry. Diverse upstream signals, such as light, phytohormones, and DNA damage responses, converge on this core machinery to modulate ploidy levels during organogenesis and stress adaptation. In this context, endoreduplication is increasingly recognized as a flexible mechanism that supports developmental plasticity. Identifying feedback loops that generate periodicity within the plant endocycle oscillator and advancing from static ploidy assessments to dynamic, system-level analyses will be essential for clarifying how plants deploy this cell cycle variant.