Promotes both cell expansion and proliferation-dependent organ growth. Mostly expressed in young tissues such as young roots, young leaves, and seeds. Also present in stems, mature leaves, and spikelets. By auxin (e.g. NAA) and cytokinin (e.g. 6-benzylaminopurine (6-BA)). The OSR domain is sufficient to promote organ growth. Belongs to the plant organ size related (OSR) protein family.