Rice shoot branching requires an ATP-binding cassette subfamily G protein.

• Shoot branching is important for the establishment of plant architecture and productivity. * Here, characterization of rice (Oryza sativa) reduced culm number 1 (rcn1) mutants revealed that Rcn1 positively controls shoot branching by promoting the outgrowth of lateral shoots. Molecular studies revealed that Rcn1 encodes a novel member of ATP-binding cassette protein subfamily G (ABCG subfamily), also known as the white-brown complex (WBC) subfamily, and is designated OsABCG5. * Rcn1 is expressed in leaf primordia of main and axillary shoots, and in the vascular cells and leaf epidermis of older leaves. In addition, Rcn1 is expressed in the crown root primordia, endodermis, pericycle and stele in the root. No effect on Rcn1 expression in shoots or roots was seen when the roots were treated with auxins. Phenotypic analyses of rcn1 and tillering dwarf 3 (d3) double mutants at the seedling stage clarified that Rcn1 works independently of D3 in the branching inhibitor pathway. * Rcn1 is the first functionally defined plant ABCG protein gene that controls shoot branching and could thus be significant in future breeding for high-yielding rice.