N-terminal region of rice polycomb group protein OsEZ1 is required for OsEZ1–OsFIE2 protein interaction

Polycomb group (PcG) proteins form Polycomb Repressive Complex 2 (PRC2), which regulates seed development by the epigenetic control of gene expression. Interaction assay among Arabidopsis Fertilization-independent-seed2 (FIS) class PcG proteins showed that Fertilization-independent endosperm (FIE) interacts with Medea (MEA), a SET-domain polycomb protein, of which N-terminal region is crucial for the interaction. In this study, rice SET-domain PcG protein OsEZ1, also known as OsiEZ1 in indica rice, was analyzed to identify an interacting domain of OsEZ1 required for OsEZ1–OsFIE2 protein interaction. A series of OsEZ1 deletions were generated and used to determine an interacting domain of OsEZ1 with OsFIE2 using the yeast two-hybrid system. Among OsEZ1 deletions, only OsEZ1∆2 and OsEZ1∆3 interacted with OsFIE2, indicating that the 155K–169R or N-proximal region of OsEZ1 is crucial for OsFIE2–OsEZ1 interaction. To examine the physiological roles of OsEZ1, 35S:OsEZ1 Arabidopsis lines were generated. OsEZ1 overexpressors exhibited altered seedling growth and seed size, implying that OsEZ1 may play important roles in seedling and seed development.