Spliceosome disassembly factors ILP1 and NTR1 promote microRNA biogenesis in Arabidopsis

A battery of spliceosome-associated proteins has been identified in microRNA (miRNA) biogenesis; however, the underlying mechanisms remain elusive. The intron lariat spliceosome (ILS) complex is highly conserved among eukaryotes and its disassembly marks the end of a canonical splicing cycle. In this study, we show that two conserved disassembly factors of the ILS complex, ILP1 and NTR1, positively regulate microRNA biogenesis through facilitating transcriptional elongation in Arabidopsis. ILP1 and NTR1 form a stable complex and co-regulate alternative splicing of more than a hundred genes across the genome including the core circadian gene LHY and some pri-miRNAs. Dysfunction in either ILP1 or NTR1 result in reduced RNA polymerase II occupancy at elongated regions of MIR chromatins, without affecting MIR promoter activity, pri-miRNA decay and DCL1 processing. Our results provide insights into the molecular mechanisms of spliceosomal machineries in non-coding RNA regulation.

已有研究在微小RNA（miRNA）的生物发生过程中鉴定出一系列与剪接体相关的蛋白质，但其背后的分子机制仍不明晰。内含子套索剪接体（ILS）复合物在真核生物中高度保守，其解离标志着经典剪接循环的终结。本研究表明，ILS复合物的两个保守解离因子ILP1与NTR1，可通过促进拟南芥的转录延伸，正向调控微小RNA的生物发生。ILP1与NTR1形成稳定复合物，共同调控基因组中百余个基因的可变剪接，其中包括核心生物钟基因LHY以及部分初级微小RNA（pri-miRNA）。ILP1或NTR1功能失常，会导致RNA聚合酶II在MIR染色质的延伸区域的富集量降低，但不会影响MIR的启动子活性、初级微小RNA的降解以及DCL1的加工过程。本研究结果为剪接体机器在非编码RNA调控中的分子机制提供了新的见解。