The plant Mediator and its role in noncoding RNA production

doi:10.1007/s11515-011-1133-7

Front Biol

2011, Vol. 6

Issue (2) : 125-132 https://doi.org/10.1007/s11515-011-1133-7

REVIEW

The plant Mediator and its role in noncoding RNA production

Yun Ju KIM, Xuemei CHEN(

)

Department of Botany and Plant Sciences and Institute of Integrative Genome Biology, University of California, Riverside, CA 92521, USA

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Abstract

Mediator, a conserved multiprotein complex in animals, plants, and fungi, is a cofactor of RNA polymerase II (Pol II). It is known to promote basal Pol II-mediated transcription as well as bridge sequence-specific transcriptional regulators and Pol II to integrate regulatory information. Pol II transcribes not only protein-coding genes but also intergenic regions to generate noncoding RNAs such as small RNAs (microRNAs and small interfering RNAs) and long noncoding RNAs. Intriguingly, two plant-specific polymerases, Pol IV and Pol V, have evolved from Pol II and play a role in the production of small interfering RNAs and long noncoding RNAs at heterochromatic regions to maintain genome stability through transcriptional gene silencing (TGS). Recent studies have defined the composition of the plant Mediator and evaluated its role in noncoding RNA production in relationship to Pol II, Pol IV and Pol V. Here, we review the functions of Mediator and that of noncoding RNAs generated by Pol II, Pol IV and Pol V in plants, and discuss a role of Mediator in epigenetic regulation via noncoding RNA production.

Keywords small RNA noncoding RNA Mediator Pol II Pol IV Pol V

Corresponding Author(s): CHEN Xuemei,Email:xuemei.chen@ucr.edu

Issue Date: 01 April 2011

Cite this article:

Yun Ju KIM,Xuemei CHEN. The plant Mediator and its role in noncoding RNA production[J]. Front Biol, 2011, 6(2): 125-132.

URL:

https://academic.hep.com.cn/fib/EN/10.1007/s11515-011-1133-7
https://academic.hep.com.cn/fib/EN/Y2011/V6/I2/125

Tab.1 Mediator composition from diverse eukaryotes

Fig.1 Roles of Mediator in noncoding RNA production in plants. (A) A diagram of the miRNA biogenesis pathway in . Mediator recruits Pol II to promoters of microRNA genes to promote the transcription of genes possibly by bridging the interaction between transcription factors and Pol II. A gene is transcribed by Pol II into a capped and polyadenylated primary precursor, which undergoes processing to give rise to a small RNA duplex containing the miRNA and the antisense miRNA*. The duplex is methylated on the 2′ OH of the 3′ terminal nucleotides, and the miRNA strand is bound by AGO1, the miRNA effector protein. Known factors in miRNA biogenesis are indicated. TF, transcription factor; CBC, cap binding complex; DDL, DAWDLE; DCL1, DICER-LIKE1; HYL1, HYPONASTIC LEAVES1; SE, SERRATE; HEN1, HUA ENHANCER1; AGO1, ARGONAUTE1. (B) A diagram of siRNA biogenesis and siRNA-mediated transcriptional gene silencing at repeats and transposable elements. The black rectangle represents a repeats- or transposable element-containing locus that harbors DNA methylation (CH). Pol IV presumably transcribes the locus into a single-stranded noncoding RNA, which eventually gives rise to 24 nt siRNAs through the activities of RNA-dependent RNA polymerase 2 (RDR2), DICER-LIKE3 (DCL3), and HEN1. The siRNAs are bound by AGO4, a major siRNA effector protein. The AGO4/siRNA complexes are thought to be recruited back to homologous chromatin by noncoding scaffold transcripts produced by Pol V, and at some loci, Pol II. It is not known whether Mediator assists Pol V in the production of noncoding RNAs, but it is required for noncoding RNA production by Pol II. The small black dots in (A) and (B) indicate the methyl group on the 3′ terminal ribose of small RNAs.

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