Developmental epigenetic modifications in plants and animals are mostly reset during gamete formation but some are inherited from the germline. Small RNAs guide these epigenetic modifications but how inherited small RNAs are distinguished in plants and animals is unknown. Pseudouridine (Ψ) is the most abundant RNA modification but has not been explored in small RNAs. Here, we develop assays to detect Ψ in short RNA sequences, demonstrating its presence in mouse and Arabidopsis microRNAs. Germline small RNAs, namely epigenetically activated small interfering RNAs (easiRNAs) in Arabidopsis pollen and Piwi-interacting RNAs in mouse testes, are enriched for Ψ. In pollen, pseudouridylated easiRNAs are transported to sperm cells from the vegetative nucleus, and PAUSED/HEN5 (PSD), the plant homolog of Exportin-t, interacts genetically with Ψ and is required for this transport. We further show that Exportin-t is required for the triploid block: small RNA dosage-dependent seed lethality that is epigenetically inherited from pollen. Thus, Ψ has a conserved role in marking inherited small RNAs in the germline.

植物和动物的发育表观遗传修饰大多在配子形成过程中重置，但有些是从种系遗传的。小RNA指导这些表观遗传修饰，但遗传性小RNA在植物和动物中如何区分尚不清楚。假尿苷 (Ψ) 是最丰富的 RNA 修饰，但尚未在小 RNA 中进行探索。在这里，我们开发了检测短 RNA 序列中 Ψ 的方法，证明了它在小鼠和拟南芥microRNA 中的存在。种系小 RNA，即拟南芥花粉中表观遗传激活的小干扰 RNA (easiRNA) 和小鼠睾丸中的 Piwi 相互作用 RNA，富含 Ψ。在花粉中，假尿苷化 easiRNA 从营养核转运到精子细胞，而PAUSED/HEN5 (PSD) （Exportin-t 的植物同源物）与 Ψ 发生遗传相互作用，并且是这种转运所必需的。我们进一步表明，Exportin-t 对于三倍体块是必需的：小 RNA 剂量依赖性种子致死率是从花粉表观遗传的。因此，Ψ 在标记种系遗传小 RNA 方面具有保守的作用。