The regulation of gene expression by transcription factors drives cell fate specification during development. In Arabidopsis, transcription factors encoded by four classes of homeotic genes control floral organ identity. The A-class gene APETALA2 (AP2) promotes sepal and petal identity and restricts expression of the C-class gene AGAMOUS (AG), which specifies stamen and carpel identity, but how does AP2 perform these functions? On p. 1978, Xuemei Chen and co-workers report that AP2 recognises and acts through an AT-rich sequence element. The researchers show that AP2R2 (one of two DNA-binding domains in AP2) binds a non-canonical AT-rich target sequence in vitro and that the presence of this sequence in the second intron of AG is important for the restriction of AG expression in vivo. Other experiments indicate that AP2 directly regulates AG expression in young flowers through this sequence element, which is highly conserved in Brassicaceae. Together, these findings shed light on the molecular mechanism underlying AP2 action and provide a missing link in the mechanisms controlling flower development.

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