The Arabidopsis transcription factor AINTEGUMENTA orchestrates patterning genes and auxin signaling in the establishment of floral growth and form.

Understanding how flowers form is an important problem in plant biology, as the human food supply depends on flower and seed production. Flower development also provides an excellent model for understanding how cell division, expansion and differentiation are coordinated during organogenesis. In the model plant Arabidopsis thaliana, floral organogenesis requires AINTEGUMENTA (ANT) and AINTEGUMENTA-LIKE6 (AIL6)/PLETHORA3 (PLT3), two members of the Arabidopsis AINTEGUMENTA-LIKE/PLETHORA (AIL/PLT) transcription factor family. Together, ANT and AIL6/PLT3 regulate aspects of floral organogenesis including floral organ initiation, growth, identity specification, and patterning. Previously, we used RNA-Seq to identify thousands of genes with disrupted expression in ant ail6 mutant flowers, indicating that ANT and AIL6/PLT3 influence a vast transcriptional network. However, the immediate downstream targets of ANT and AIL6/PLT3 in flowers are unknown. To identify direct targets of ANT regulation, we performed a RNA-Seq time course experiment in which we induced ANT activity in transgenic plants bearing an ANT-glucocorticoid receptor fusion construct. In addition, we performed a ChIP-Seq experiment that identified ANT binding sites in developing flowers. These experiments identified 200 potential ANT target genes based on their proximity to ANT binding sites and differential expression in response to ANT. These 200 candidate target genes were involved in functions such as polarity specification, floral organ development, meristem development and auxin signaling. In addition, we identified several genes associated with lateral organ growth that may mediate ANT's role in organ size control. These results reveal new features of the ANT transcriptional network by linking ANT to previously unknown regulatory targets.