Transcription activator that plays a role in the regulation of meristematic function in leaves, stems and inflorescences (PubMed:24532604). Transcription activator that plays a regulatory role in grain development (PubMed:26187814, PubMed:27250747, PubMed:27250749, PubMed:26936408, PubMed:27107174). Positively regulates grain size by promoting cell division and expansion, leading to increased grain length and width (PubMed:26187814, PubMed:27250747, PubMed:27250749, PubMed:26936408, PubMed:27107174). Positively regulates the expression of genes promoting cell proliferation (PubMed:26187814, PubMed:26936408). Activates the expression of expansin genes to promote cell expansion and grain size (PubMed:27250747). May promote grain size by activating brassinosteroid responses (PubMed:27250747). Component of a network formed by the microRNA396 (miRNA396), the GRFs and their interacting factors (GIFs) acting in the regulation of meristem function, at least partially through the control of cell proliferation (Probable). Component of the miRNA396c-GRF4-GIF1 regulatory module that plays an important role in grain size determination (Probable) (PubMed:27250747, PubMed:27250749, PubMed:27107174). Transactivation activity is repressed by GSK2. Interacts with GIF1 (PubMed:27250747, PubMed:27250749, PubMed:27107174). Interacts with GSK2 (PubMed:27250747). Expressed in stems (PubMed:27107174). Expressed in panicles (PubMed:26187814, PubMed:27250747, PubMed:27250749, PubMed:27107174). The microRNA396c negatively regulates GRF4 at the transcriptional level. The QLQ domain and WRC domain may be involved in protein-protein interaction and DNA-binding, respectively (Probable). The C-terminal region downstream of the QLQ and WRC domains is necessary for transactivation activity (PubMed:26187814, PubMed:27250747, PubMed:27107174). A two nucleotide mutation at the miRNA396c target site results in elevated transcript levels of GRF4, and the accumulation of GRF4 leads to enlarged cell size and increased cell number, which in turn results in enhanced grain weight and yield. Plants over-expressing GRF4 exhibit increased grain length, width and weight (PubMed:27107174). Plants silencing GRF4 exhibit dwarfism, delayed growth and inflorescence formation (PubMed:24532604). Belongs to the GRF family.