OsbZIP76 interacts with OsNF-YBs and regulates endosperm cellularization in rice (Oryza sativa)

Following double fertilization, plant endosperm nuclei undergo syncytial divisions, followed by synchronous cellularization. Cellularization is a key event during endosperm development, but our understanding of its regulation is limited toArabidopsis. In this study we show thatOsbZIP76regulates cellularization in rice (Oryza sativa). Activation ofOsbZIP76coincided with the initiation of cellularization, and its knockdown or knockout mutants exhibited precocious cellularization. Genes involved in endosperm development or starch biosynthesis were prematurely activated in theosbzip76caryopsis. As a putative transcription factor, OsbZIP76 alone lacked transcriptional activation activity; however, it interacted with the nuclear factor Y (NF-Y) family transcription factors OsNF-YB9 and OsNF-YB1 in yeast andin planta. OsbZIP76andOsNF-YB9were predominantly expressed in the endosperm and the proteins colocalized. Seeds ofosnf-yb1andosbzip76mutants showed reduced size and reduced apparent amylose content. The parent-of-origin-dependent expression ofOsbZIP76is variable in different rice accessions. In summary,OsbZIP76is an endosperm-expressed imprinted gene that regulates endosperm development in rice.