Dolata Jakub, Taube Michał, Bajczyk Mateusz, Jarmolowski Artur, Szweykowska-Kulinska Zofia, Bielewicz Dawid
Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University in Poznan, Poznan, Poland.
Front Plant Sci. 2018 Jun 5;9:753. doi: 10.3389/fpls.2018.00753. eCollection 2018.
MicroRNAs are small molecules (∼21 nucleotides long) that are key regulators of gene expression. They originate from long stem-loop RNAs as a product of cleavage by a protein complex called Microprocessor. The core components of the plant Microprocessor are the RNase type III enzyme Dicer-Like 1 (DCL1), the zinc finger protein Serrate (SE), and the double-stranded RNA binding protein Hyponastic Leaves 1 (HYL1). Microprocessor assembly and its processing of microRNA precursors have been reported to occur in discrete nuclear bodies called Dicing bodies. The accessibility of and modifications to Microprocessor components affect microRNA levels and may have dramatic consequences in plant development. Currently, numerous lines of evidence indicate that plant Microprocessor activity is tightly regulated. The cellular localization of HYL1 is dependent on a specific KETCH1 importin, and the E3 ubiquitin ligase COP1 indirectly protects HYL1 from degradation in a light-dependent manner. Furthermore, proper localization of HYL1 in Dicing bodies is regulated by MOS2. On the other hand, the Dicing body localization of DCL1 is regulated by NOT2b, which also interacts with SE in the nucleus. Post-translational modifications are substantial factors that contribute to protein functional diversity and provide a fine-tuning system for the regulation of protein activity. The phosphorylation status of HYL1 is crucial for its activity/stability and is a result of the interplay between kinases (MPK3 and SnRK2) and phosphatases (CPL1 and PP4). Additionally, MPK3 and SnRK2 are known to phosphorylate SE. Several other proteins (e.g., TGH, CDF2, SIC, and RCF3) that interact with Microprocessor have been found to influence its RNA-binding and processing activities. In this minireview, recent findings on the various modes of Microprocessor activity regulation are discussed.
微小RNA是小分子（约21个核苷酸长），是基因表达的关键调节因子。它们源自长茎环RNA，是一种名为微处理器的蛋白质复合物切割的产物。植物微处理器的核心成分是III型核糖核酸酶类Dicer-Like 1（DCL1）、锌指蛋白锯齿状（SE）和双链RNA结合蛋白下弯叶1（HYL1）。据报道，微处理器的组装及其对微小RNA前体的加工发生在称为切割体的离散核小体中。微处理器成分的可及性和修饰会影响微小RNA水平，并可能在植物发育中产生重大影响。目前，大量证据表明植物微处理器的活性受到严格调控。HYL1的细胞定位依赖于特定的KETCH1输入蛋白，E3泛素连接酶COP1以光依赖的方式间接保护HYL1不被降解。此外，HYL1在切割体中的正确定位由MOS2调控。另一方面，DCL1在切割体中的定位由NOT2b调控，NOT2b也在细胞核中与SE相互作用。翻译后修饰是导致蛋白质功能多样性的重要因素，并为蛋白质活性的调节提供了一个微调系统。HYL1的磷酸化状态对其活性/稳定性至关重要，是激酶（MPK3和SnRK2）和磷酸酶（CPL1和PP4）相互作用的结果。此外，已知MPK3和SnRK2会使SE磷酸化。已发现其他几种与微处理器相互作用的蛋白质（如TGH、CDF2、SIC和RCF3）会影响其RNA结合和加工活性。在这篇小型综述中，讨论了微处理器活性调控的各种模式的最新发现。
