Fertilization Independent Endosperm (FIE) is an essential member of Polycomb Repressive Complex 2 (PRC2) that plays important roles in the developmental regulation of plants. OsFIE1 and OsFIE2 are two FIE homologs in the rice genome. Here, we showed that OsFIE1 probably duplicated from OsFIE2 after the origin of the tribe Oryzeae, but has a specific expression pattern and methylation landscape. During evolution, OsFIE1 underwent a less intensive purifying selection than did OsFIE2. The mutant osfie1 produced smaller seeds and displayed reduced dormancy, indicating that OsFIE1 predominantly functions in late seed development. Ectopic expression of OsFIE1, but not OsFIE2, was deleterious to vegetative growth in a dose‐dependent manner. The newly evolved N‐terminal tail of OsFIE1 was probably not the cause of the adverse effects on vegetative growth. The CRISPR/Cas9‐derived mutant osfie2 exhibited impaired cellularization of the endosperm, which suggested that OsFIE2 is indispensable for early seed development as a positive regulator of cellularization. Autonomous endosperm was observed in both OsFIE2⁺⁻ and osfie1/OsFIE2⁺⁻ but at a very low frequency. Although OsFIE1‐PRC2 exhibited H3K27me3 methyltransferase ability in plants, OsFIE1‐PRC2 is likely to be less important for development in rice than is OsFIE2‐PRC2. Our findings revealed the functional divergence of OsFIE1 and OsFIE2 and shed light on their distinct evolution following duplication.

中文翻译：

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水稻中两个重复的不依赖受精的胚乳基因在种子发育方面的功能差异

受精非胚乳（FIE）是Polycomb Repressive Complex 2（PRC2）的重要组成部分，在植物的发育调控中起着重要作用。OsFIE1和OsFIE2是水稻基因组中的两个FIE同源物。在这里，我们表明OsFIE1可能是在Oryzeae部落起源后从OsFIE2复制的，但具有特定的表达模式和甲基化态势。在进化过程中，OsFIE1的纯化选择比OsFIE2少。突变体osfie1产生了较小的种子，并显示出降低的休眠状态，表明OsFIE1主要在后期种子发育中起作用。OsFIE1的异位表达，而不是OsFIE2的异位表达，对植物生长具有剂量依赖性。OsFIE1的新进化的N末端尾巴可能不是造成营养生长的不利原因。源自CRISPR / Cas9的突变体osfie2表现出胚乳细胞化受损，这表明OsFIE2作为细胞化的积极调节剂对于早期种子发育是必不可少的。在OsFIE2 ^+-和osfie1 / OsFIE2 ^+-中均观察到自主胚乳但频率很低。尽管OsFIE1-PRC2在植物中表现出H3K27me3甲基转移酶功能，但是OsFIE1-PRC2对水稻的发育可能不如OsFIE2-PRC2重要。我们的发现揭示了OsFIE1和OsFIE2的功能差异，并阐明了复制后它们的独特进化。