Auxin Signaling in Maize Inflorescences

In plants, small groups of pluripotent stem cells called axillary meristems are required for the formation of the branches and flowers that eventually establish plant and inflorescence architecture. In maize inflorescences, reproductive axillary meristems initiate at the axils of suppressed bract primordia at the flanks of inflorescence meristems. To ensure their proper formation, boundary regions need to be specified. We have identified two maize genes, BARREN INFLORESCENCE1 and BARREN INFLORESCENCE4 (BIF1 and BIF4) that regulate the early steps required for inflorescence formation. BIF1 and BIF4 encode Aux/IAA proteins, key components of the auxin hormone signaling pathway that is essential for organogenesis, and regulate both suppressed bract and axillary meristem initiation in inflorescences. BIF1 and BIF4 are integral to auxin signaling modules that regulate the expression of the bHLH transcriptional regulator BARREN STALK1 (BA1) that is necessary for axillary meristem formation and shows a striking boundary expression pattern. These findings suggest that auxin signaling directly controls boundary domains during axillary meristem formation.