Inflorescence branching is a major yield trait in crop plants controlled by the developmental fate of axillary shoot meristems. Variations in branching patterns lead to diversity in flower-bearing architectures (inflorescences) and affect crop yield by influencing seed number or harvesting ability. Several growth regulators such as auxins, cytokinins and carotenoid derivatives regulate branching architectures. Inflorescence branching in maize is regulated by three RAMOSA genes. Here we show that one of these genes, RAMOSA3 (RA3), encodes a trehalose-6-phosphate phosphatase expressed in discrete domains subtending axillary inflorescence meristems. Genetic and molecular data indicate that RA3 functions through the predicted transcriptional regulator RAMOSA1 (RA1). We propose that RA3 regulates inflorescence branching by modification of a sugar signal that moves into axillary meristems. Alternatively, the fact that RA3 acts upstream of RA1 supports a hypothesis that RA3 itself may have a transcriptional regulatory function.