The AP2 transcription factor BARE RECEPTACLE regulates floral organogenesis via auxin pathways in woodland strawberry

During flower development, different floral organs are formed to ensure fertilization and fruit set. Although the genetic networks underlying flower development are increasingly well understood, less is known about the mechanistic basis in different species. Here, we identified a mutant of woodland strawberry (Fragaria vesca), bare receptacle (bre), which produces flowers with greatly reduced carpels and other floral organs. Genetic analysis revealed that BRE encodes an APETALA2 (AP2) transcription factor. BRE was highly expressed in floral meristems and floral organ primordia. BRE could directly bind the GCC-box motif in the YUCCA (YUC) auxin biosynthesis genes FveYUC4 and FveYUC2 and promote their expression. The yuc4 mutant had fewer floral organs, and the bre yuc4 double mutant had similar numbers of petals and carpels to bre. Auxin homeostasis and distribution were severely disrupted in bre. Although auxin application or FveYUC4 overexpression did not rescue the bre phenotypes, bre was hypersensitive to treatment with the polar auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). In addition, BRE was able to directly bind and regulate the expression of five other auxin pathway genes. Overall, these results demonstrate that BRE is required for floral organogenesis, particularly carpel initiation, and acts through the auxin pathway in strawberry.