The model flowering plant Aquilegia produces elongated, three-dimensional petal spurs that fill with nectar to attract pollinators. Previous studies have found that the spur develops with two major phases, firstly cell division concentrated around the incipient nectary, followed by a secondary switch to cell elongation to produce the lengthened spur. This second phase of rapid, anisotropic cell elongation determines the final length of the spur, a character which shows surprising diversity within the genus. Transcriptomic studies on the petal spur revealed the upregulation of the Aquilegia homolog of BEH4, a known response transcription factor to the plant hormone Brassinosteroid (BR). In Arabidopsis and rice, brassinosteroids have been shown to regulate a wide range of developmental processes, including cell elongation. These data suggest that BR signaling may play a critical role in the switch from cell division to cell elongation that leads to the formation and length of the petal spur in Aquilegia. In this study we are investigating the role of BR transcription factors in the Aquilegia petal spur using a combination of gene expression studies, hormone applications and gene silencing.