植物中的Dicer-like (DCL)蛋白属于第III类RNA酶，负责加工产生各种类型的小分子RNA。Phased small RNA是新近在水稻中发现的一类小分子RNA，包括21-nt和24-nt两种形式。其中24-nt长的phased small RNA在模式植物拟南芥中尚未被报道。关于该类小分子RNA的合成及作用机制，目前还不清楚。

中国科学院遗传与发育生物学研究所曹晓风实验室的研究发现，多个DCL蛋白参与了水稻phased small RNA的合成。该研究发现，OsDCL4蛋白负责产生21-nt phased small RNA；而之前功能未知的OsDCL3b负责加工产生24-nt phased small RNA。该研究证实，21-nt 和24-nt phased small RNA是分别由miR2118和miR2275两个22-nt miRNA介导产生的二级小分子RNA。这两个miRNA的合成主要依赖于OsDCL1。最后该研究还进一步揭示了这些phased small RNA主要或特异地在水稻雄蕊中表达，并且有可能是一类禾本科植物保守的小分子RNA，为下一步研究该类小分子RNA的功能指明了方向。这项工作揭示了水稻DCL蛋白在phased small RNA合成途径中的作用，提示出该类小分子RNA可能在水稻雄蕊发育过程中发挥重要的作用。研究结果已于日前在线发表于《The Plant Journal》。

论文摘要：

Higher plants have evolved multiple proteins in the RNase III family to produce and regulate different classes of small RNAs with specialized molecular functions. In rice, numerous genomic clusters are targeted by one of two miRNAs, miR2118 and miR2275, to produce secondary siRNAs of either 21- or 24-nucleotide in a phased manner. The biogenesis requirements or the functions of the phased small RNAs are completely unknown. Here we examine the rice Dicer-Like (DCL) family, including OsDCL1, 3a, 3b, and 4. By deep sequencing of small RNAs from different tissues of wild type and osdcl4-1, we revealed that the processing of 21-nucleotide siRNAs, including trans-acting siRNAs (tasiRNA) and over one thousand phased small RNA loci, was largely dependent on OsDCL4. Surprisingly, the processing of 24-nucleotide phased small RNA requires the DCL3 homolog OsDCL3b rather than OsDCL3a, suggesting functional divergence within DCL3 family. RNA ligase mediated-5′ rapid amplification of cDNA ends and parallel analysis of RNA ends (PARE)/degradome analysis confirmed that most of the 21- and 24-nucleotide phased small RNA clusters were initiated from the target sites of miR2118 and miR2275, respectively. Furthermore, the accumulation of the two triggering miRNAs requires OsDCL1 activity. Finally, we show that phased small RNAs are preferentially produced in the male reproductive organs and are likely to be conserved in monocots. Our results revealed significant roles of OsDCL4, OsDCL3b and OsDCL1 in the 21- and 24-nucleotide phased small RNA biogenesis pathway in rice.

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