Tiller development is an important agronomic trait in plant architecture and grain yield. Many plant hormones regulate axillary meristem formation, including bud outgrowth for shoot branching. However, the molecular mechanism underlying the brassinosteroid (BR) in tiller development is not yet well known. Therefore, in this study, we identified and characterized two novel T-DNA insertion mutants, osgras19 and osgras32, which showed the typical BR-deficient phenotype, such as fewer tiller numbers, dark-green leaves, and semi-dwarf phenotypes. Double knockout mutants, osgras19 osgras32, were then generated by crossing, and they showed similar phenotypic traits of each single mutant. Both OsGRAS19 and OsGRAS32 encoded the GRAS family proteins and were localized in the nucleus. We also confirmed that OsGRAS19 and OsGRAS32 did not directly interact with each other; however, OsGRAS19 interacted with MOC1 and SMALL ORGAN SIZE1 (SMOS1), an auxin-regulated APETALA2-type transcription factor, in yeast. Thus, we proposed OsGRAS19 as a component of the complex on the auxin-BR signaling pathway and plays role in the tiller development in rice.

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