Research Article

Timing Mechanism Dependent on Cell Division Is Invoked by Polycomb Eviction in Plant Stem Cells

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Science  31 Jan 2014:
Vol. 343, Issue 6170, 1248559
DOI: 10.1126/science.1248559

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A Matter of Timing

Plants flower only when their developmental programs give the go-ahead; otherwise floral genes remain repressed. Sun et al. (10.1126/science.1248559; see the Perspective by Zhang) analyzed the regulatory program that controls expression of the transcription factor KNUCKLES (KNU), which is required in the control of floral genes. KNU expression was silenced by the presence of Polycomb group (PcG) proteins. The floral homeotic protein AGAMOUS competed for control of KNU and activated its expression, but with a 2-day lag time. Thus, eviction of PcG by activating DNA binding proteins can insert a lag time before a switch in gene expression takes place.