Zinc Finger Homeobox Transcription Factors OsMIF1 and OsMIF2 Regulate Grain Size and Panicle Development in Rice

Mini zinc finger (MIF) proteins are plant-specific zinc finger-homeodomain (ZF-HD) transcription factors lacking a homeodomain, and its biological functions are critical for normal plant development and the response to environmental stress. Here, CRISPR-Cas9 approach was used to engineer null alleles of rice OsMIF1 and OsMIF2, and the resulting OsMIF1 and OsMIF2 edited lines were used to identify the biological roles of OsMIF1 and OsMIF2. The results suggest that OsMIF proteins regulate grain size by controlling the size of epidermal cells and the length and branching of rice panicles. RNA-seq analysis of OsMIF-knockout cells revealed altered expression of genes involved in development, the response to environmental stress and grain size. In addition, 10 protein-interacting partners of OsMIF1 were identified using a yeast two-hybrid screen: these proteins play roles in diverse developmental, hormonal, stress response, and metabolic processes. The results support the involvement of OsMIF1 and OsMIF2 in the regulation of panicle and grain development and suggest that they may be associated with diverse biological pathways through interactions with multiple regulatory proteins.