One factor, many systems: the floral homeotic protein AGAMOUS and its epigenetic regulatory mechanisms.

Tissue-specific transcription factors allow cells to specify new fates by exerting control over gene regulatory networks and the epigenetic landscape of a cell. However, our knowledge of the molecular mechanisms underlying cell fate decisions is limited. In Arabidopsis, the MADS-box transcription factor AGAMOUS (AG) plays a central role in regulating reproductive organ identity and meristem determinacy during flower development. During the vegetative phase, AG transcription is repressed by Polycomb complexes and intronic noncoding RNA. Once AG is transcribed in a spatiotemporally regulated manner during the reproductive phase, AG functions with chromatin regulators to change the chromatin structure at key target gene loci. The concerted actions of AG and the transcription factors functioning downstream of AG recruit general transcription machinery for proper cell fate decision. In this review, we describe progress in AG research that has provided important insights into the regulatory and epigenetic mechanisms underlying cell fate determination in plants.