Doris Wagner, University of Pennsylvania, USA
Claudia Köhler
Lecture hall A281, Uppsala BioCentre, Ultuna
14:00 - 15:00
A hormone-dependent chromatin switch in control of flower primordium initiation

My lab is interested in the question how multicellular eukaryotes can switch from an existing developmental program to an entirely different one in a controlled and reproducible manner. Reprogramming of cell identities during development frequently depends on chromatin state changes. A key question is how these changes are restricted to the correct cell populations. We have uncovered a hormone-dependent chromatin switch that directs reprogramming from transit amplifying to primordium founder cell fate in Arabidopsis inflorescence meristems. In response to the hormone auxin, the MONOPTEROS transcription factor recruits SWI/SNF chromatin remodeling ATPases to activate expression of key regulators of flower primordium initiation.  SWI/SNF ATPase activity is required for the transcriptional changes and for the cell fate switch to occur. In the absence of the hormonal cue, Aux/IAA proteins associate with the MONOPTEROS transcription factor to block recruitment of the SWI/SNF chromatin remodeling ATPases and to instead recruit a histone deacetylase to MONOPTEROS target loci, thus preventing their expression. The uncovered auxin-mediated chromatin state switch is ideally suited for spatiotemporal control of flower primordium initiation. It may moreover underpins additional developmental cell fate transitions triggered by this morphogenetic plant hormone and represent an ancient regulatory module in land plants