Transcription coactivator that plays a role in the regulation of meristematic function in leaves, stems and inflorescences (PubMed:29051769, PubMed:29567670). May regulate leaf size, length of stem internodes, and seed size by promoting cell expansion (PubMed:29051769) (Probable). Transcription coactivator that plays a role in the regulation of grain size (PubMed:27107174, PubMed:29051769, PubMed:29567670). 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 (PubMed:27107174). Interacts with GRF4. Localizes predominantly in the nucleus. Highly expressed in internodes, nodes, developing spikelets and developing anthers (PubMed:29051769). Expressed at low levels in roots and mature glumes (PubMed:29051769). Reduced plant height, and short and narrow leaves. Plants over-expressing GIF1 exhibit increased size of multiple organs, such as leaves, stems, panicles and grains. 'Makiba' means 'pasture land' in Japanese. Belongs to the SS18 family.