Temporal Control of Plant Organ Growth by TCP Transcription Factors

The Arabidopsis petal is a simple laminar organ whose development is largely impervious to environmental effects, making it an excellent model for dissecting the regulation of cell-cycle progression and post-mitotic cell expansion that together sculpt organ form [1, 2]. Arabidopsis petals grow via basipetal waves of cell division, followed by a phase of cell expansion [3-5]. RABBIT EARS (RBE) encodes a C2H2 zinc finger transcriptional repressor and is required for petal development [6-9]. During the early phase of petal initiation, RBE regulates a microRNA164-dependent pathway that controls cell proliferation at the petal primordium boundaries [10-12]. The effects of rbe mutations on petal lamina growth suggest that RBE is also required to regulate later developmental events during petal organogenesis [6, 12]. Here, we demonstrate that, early in petal development, RBE represses the transcription of a suite of CIN-TCP genes that in turn act to inhibit the number and duration of cell divisions; the temporal alleviation of that repression results in the transition from cell division to post-mitotic cell expansion and concomitant petal maturation.