A Molecular Framework for Auxin-Mediated Initiation of Flower Primordia

A classical role of the hormone auxin is in the formation of flowers at the periphery of the reproductive shoot apex. Mutants in regulators of polar auxin transport or in the auxin-responsive transcription factor MONOPTEROS (MP) form naked inflorescence “pins” lacking flowers. How auxin maxima and MP direct initiation of flower primordia is poorly understood. Here, we identify three genes whose expression is directly induced by auxin-activated MP that furthermore jointly regulate flower primordium initiation. These three genes encode known regulators of flower development: LEAFY (LFY), which specifies floral fate, and two AINTEGUMENTA-LIKE/PLETHORA transcription factors, key regulators of floral growth. Our study thus reveals a mechanistic link between flower primordium initiation and subsequent steps in flower morphogenesis. Finally, we uncover direct positive feedback from LFY to the auxin pathway. The auxin LFY module we describe may have been recruited during evolution to pattern other plant organ systems. [Display omitted] ► Auxin-activated MP directly induces key floral regulators LFY, ANT, and AIL6 ► The LFY promoter contains conserved biologically relevant auxin response elements ► LFY, ANT, and AIL6 have redundant roles in flower primordium initiation ► LFY feeds back to the auxin pathway at least in part by directly inducing PID Yamaguchi et al. identify three flower development regulators, including the floral fate specification factor LEAFY, as targets of the auxin-responsive transcription factor MONOPTEROS and uncover positive feedback from LEAFY to the auxin pathway. These findings elucidate a regulatory framework for flower primoridium initiation by auxin and coordination with flower morphogenesis.