In plants, microRNA (miRNA) functions in the post-transcriptional repression of target mRNAs have been well explored. However, the mechanisms regulating the accumulation of miRNAs remain poorly understood. Here, we report that distinct mechanisms regulate accumulation of a monocot-specific miRNA, rice (Oryza sativa) miR528. At the transcriptional level, miR528 accumulated to higher levels in older plants than in young seedlings and exhibited aging-modulated gradual accumulation and diurnal rhythms in leaves; at the post-transcriptional level, aging also modulated miR528 levels by enhancing pri-miR528 alternative splicing. We found that miR528 promotes rice flowering under long-day conditions by targeting RED AND FAR-RED INSENSITIVE 2 (OsRFI2). Moreover, natural variations in the MIR528 promoter region caused differences in miR528 expression among rice varieties, which are correlated with their different binding affinities with the transcription factor OsSPL9 that activates the expression of miR528. Taken together, our findings reveal rice plants have evolved sophisticated modes fine-tuning miR528 levels and provide insight into the mechanisms that regulate MIRNA expression in plants.

在植物中，microRNA（miRNA）在靶标mRNA转录后抑制中的功能已经得到了很好的研究。但是，调节miRNA积累的机制仍然知之甚少。在这里，我们报道了不同的​​机制调节单子叶植物特异性miRNA，水稻（Oryza sativa）miR528的积累。在转录水平上，miR528在老龄植物中的蓄积水平高于年轻幼苗，并且在叶片中表现出衰老调节的逐步蓄积和昼夜节律。在转录后水平，衰老还通过增强pri-miR528选择性剪接来调节miR528的水平。我们发现miR528通过靶向RED和FAR-RED INSENSITIVE 2（OsRFI2）在长日照条件下促进水稻开花）。此外，MIR528启动子区域的自然变异导致水稻品种之间miR528表达的差异，这与它们与激活miR528表达的转录因子OsSPL9的不同结合亲和力有关。综上所述，我们的发现揭示了水稻植物已经进化出精细的模式来微调miR528水平，并为调节植物中MIRNA表达的机制提供了见识。