Small nucleolar RNAs (snoRNAs) are noncoding RNAs (ncRNAs) that guide chemical modifications of structural RNAs, which are essential for ribosome assembly and function in eukaryotes. Although numerous snoRNAs have been identified in plants by high-throughput sequencing, the biological functions of most of these snoRNAs remain unclear. Here, we identified box C/D SnoR28.1s as important regulators of plant growth and development by screening a CRISPR/Cas9-generated ncRNA deletion mutant library in Arabidopsis thaliana. Deletion of the SnoR28.1 locus, which contains a cluster of three genes producing SnoR28.1s, resulted in defects in root and shoot growth. SnoR28.1s guide 2'-O-ribose methylation of 25S rRNA at G2396. SnoR28.1s facilitate proper and efficient pre-rRNA processing, as the SnoR28.1 deletion mutants also showed impaired ribosome assembly and function, which may account for the growth defects. SnoR28 contains a 7-bp antisense box, which is required for 2'-O-ribose methylation of 25S rRNA at G2396, and an 8-bp extra box that is complementary to a nearby rRNA methylation site and is partially responsible for methylation of G2396. Both of these motifs are required for proper and efficient pre-rRNA processing. Finally, we show that SnoR28.1s genetically interact with HIDDEN TREASURE2 and NUCLEOLIN1. Our results advance our understanding of the roles of snoRNAs in Arabidopsis.

中文翻译：

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小核仁 RNA SnoR28 通过指导 rRNA 成熟来调节植物生长和发育。

小核仁 RNA (snoRNA) 是指导结构 RNA 化学修饰的非编码 RNA (ncRNA)，这对于真核生物中核糖体的组装和功能至关重要。尽管通过高通量测序在植物中鉴定出了许多 snoRNA，但大多数 snoRNA 的生物学功能仍不清楚。在这里，我们通过筛选拟南芥中 CRISPR/Cas9 生成的 ncRNA 缺失突变体文库，确定了 Box C/D SnoR28.1s 作为植物生长和发育的重要调节因子。SnoR28.1 基因座包含三个产生 SnoR28.1 的基因簇，其缺失会导致根和芽生长缺陷。SnoR28.1s 指导 25S rRNA G2396 处的 2'-O-核糖甲基化。SnoR28.1 促进正确且有效的前 rRNA 加工，因为 SnoR28.1 缺失突变体还显示出核糖体组装和功能受损，这可能是生长缺陷的原因。SnoR28 包含一个 7 bp 反义盒（G2396 处 25S rRNA 的 2'-O-核糖甲基化所需）和一个 8 bp 额外盒（与附近的 rRNA 甲基化位点互补，部分负责 G2396 甲基化） 。这两个基序都是正确且有效的 rRNA 前处理所必需的。最后，我们证明 SnoR28.1 与 HIDDEN TREASURE2 和 NUCLEOLIN1 存在遗传相互作用。我们的结果增进了我们对拟南芥中 snoRNA 作用的理解。