Inflorescence branching is a major yield trait in crop plants controlled by the developmental fate of axillary shoot meristems1. Variations in branching patterns lead to diversity in flower-bearing architectures (inflorescences) and affect crop yield by influencing seed number or harvesting ability2,3. Several growth regulators such as auxins, cytokinins and carotenoid derivatives regulate branching architectures4. Inflorescence branching in maize is regulated by three RAMOSA genes5. 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)5. 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.
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We thank C. Carson and E. Coe for initial molecular mapping of RA3; S. Hake for the fea1-Mu line; N. Inada, E. Irish, J. Linder and E. Vollbrecht for ra3 alleles; T. Mulligan for plant care; J. Andersen, N. Kobayashi-Simorowski and N. Tonks for help with phosphatase assays; V. Koroth Edavana for suggestions about the Mycobacterium TPP clone; P. Dahl, D. Goto, K. Noma and T. Phelps-Durr for suggestions for the yeast complementation test; J. Kossuth for help with DNA sequencing; and E. Kellogg, W. Lukowitz, J. Simorowski, E. Vollbrecht, and members of the Jackson laboratory for comments on the manuscript. Funding was provided by the National Science Foundation, Plant Genome Research Program, and the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service (to D.J.). Author Contributions N.S.-N. performed the SEM analyses, RA3 mapping, RT–PCRs, in situ hybridizations, double-mutant analyses, phosphatase assay and yeast complementation test. N.N. helped with RA3 mapping and provided the material for RT–PCR in rice. S.M. performed phylogenetic analyses and in situ hybridizations in rice. H.S. organized the collaboration. D.J. supervised the research and wrote the paper. All authors discussed the results and commented on the manuscript.
This file contains Supplementary Figures 1–4, Supplementary Tables 1 and 2, Supplementary Methods and additional references.