Abstract
Amplification of genomic DNA by endoreduplication often marks the initiation of cell differentiation in both animals and plants. The transition from the mitotic cycle to the endocycle should be developmentally programmed but how this process is regulated remains largely unknown. Here we show that the TIR1/AFB-AUX/IAA-ARF dependent auxin signal modulates the switch from the mitotic cycle to the endocycle in Arabidopsis; high levels of auxin signalling are required to repress the endocycle, thus maintaining cells in the mitotic cycle whereas lower levels of auxin signalling trigger exit from the mitotic cycle and entry into the endocycle. We further demonstrate that this auxin-mediated modulation of the mitotic-to-endocycle switch serves to retain the meristematic state in root meristem cells through the expression of core cell cycle regulators. We propose that the dose-dependent control of the two alternative DNA replication cycles is part of the mechanisms that translate the developmental gradient into the cellular differentiation.
