Cellularization is a key event in endosperm development. Polycomb group (PcG) genes, such as Fertilization-Independent Seed 2 (FIS2), are vital for the syncytium-to-cellularization transition in Arabidopsis plants. In this study, we found that OsEMF2a, a rice homolog of the Arabidopsis PcG gene Embryonic Flower2 (EMF2), plays a role similar to that of FIS2 in regard to seed development, although there is limited sequence similarity between the genes. Delayed cellularization was observed in osemf2a, associated with an unusual activation of type I MADS-box genes. The cell cycle was persistently activated in osemf2a caryopses, which was likely caused by cytokinin overproduction. However, the overaccumulation of auxin was not found to be associated with the delayed cellularization. As OsEMF2a is a maternally expressed gene in the endosperm, a paternally inherited functional allele was unable to recover the maternal defects of OsEMF2a. Many imprinted rice genes were deregulated in the defective hybrid seeds of osemf2a (♀)/9311 (♂) (m9). The paternal expression bias of some paternally expressed genes was disrupted in m9 due to either the activation of maternal alleles or the repression of paternal alleles. These findings suggest that OsEMF2a-PRC2-mediated H3K27me3 is necessary for endosperm cellularization and genomic imprinting in rice.

细胞化是胚乳发育的关键事件。多梳群 (PcG) 基因，例如与受精无关的种子 2 ( FIS2 )，对于拟南芥植物中的合胞体到细胞化的转变至关重要。在本研究中，我们发现OsEMF2a是拟南芥PcG 基因胚花 2 ( EMF2 )的水稻同源物，在种子发育方面发挥与FIS2相似的作用，尽管基因之间的序列相似性有限。在osemf2a中观察到细胞化延迟，这与 I 型 MADS-box 基因的异常激活有关。细胞周期在osemf2a caryopses，这可能是由细胞分裂素过度产生引起的。然而，没有发现生长素的过度积累与细胞化延迟有关。由于OsEMF2a是胚乳中母系表达的基因，父系遗传的功能等位基因无法恢复OsEMF2a的母系缺陷。许多印记水稻基因在osemf2a (♀)/9311 (♂) (m9)的缺陷杂交种子中失调。由于母本等位基因的激活或父本等位基因的抑制，一些父本表达基因的父本表达偏向在 m9 中被破坏。这些发现表明 OsEMF2a-PRC2 介导的 H3K27me3 是水稻胚乳细胞化和基因组印记所必需的。