Extended: Auxin dynamics and symmetry breaking in Mimulus floral meristem (view live broadcast from main session)

Bilaterally symmetric flowers exhibit only one plane of symmetry along the dorsal-ventral (D-V) axis and is one of the most common floral forms. The developmental programs governing differential organ elaboration along the D-V axis in many taxa have been known since the early 1990s, but how are the D-V domains specified at the earliest stage of the floral meristem (FM) remains elusive. Previous studies indicated that auxin dynamic is crucial for D-V domain establishment, while the mechanism of which is unknown. Using the monkey flower species Mimulus parishii as a model system, we conducted quantitative high-resolution live-imaging of auxin-maxima reporter DR5 in both wild-type and transgenic mutants with either dorsalized or ventralized flowers. We observed striking auxin dynamics during the earliest developmental stages of the FM, during which the auxin maxima first appear at the center of the FM, then move to the dorsal most region, and subsequently the D-V domains are separated by a band of auxin depletion zone. Our results provide the first line of evidence of how the spatiotemporal dynamics of auxin can be associated with the symmetry-breaking mechanism in the FM and the putative genes controlling this process.