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A New Component in Regulating Plant DNA Methylation Identified

Apr 20, 2016     Email"> PrintText Size

Argonaute (AGO) proteins play key roles in plant small RNA mediated epigenetic regulations. They recruit 21–24-nucleotide (nt) small RNAs (sRNAs) to constitute RNA-induced silencing complexes (RISCs) to regulate gene expression at transcriptional or post-transcriptional levels. Model plant Arabidopsis thaliana encodes nine functional AGO proteins. These proteins are classified into three clusters, AGO1/5/10, AGO2/3/7 and AGO4/6/9, according to their sequence similarity, functional redundancy, as well as the species and features of their associated sRNAs. Although some AGO proteins in Arabidopsis, such as AGO1 and AGO4, have been well studied, the sRNA selection feature and functions of AGO3 are still unknown.
A team led by WANG Xiujie of the Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology (IGDB), Chinese Academy of Sciences, cooperated with ZHANG Xiuren’s team at Texas A & M University, recently reported the function and associated sRNA features of Arabidopsis AGO3.
They found that AGO3 could not complement the function of AGO2, the closest genetic paralog of AGO3, in regulating host antiviral defense. Bioinformatic analysis shows that AGO2 mainly bound 21-nt sRNAs, whereas AGO3 predominantly bound 24-nt sRNAs, and the spectrum of AGO3-associated sRNAs was more similar to those bound to AGO4, with over 60% of AGO3-associated 24-nt sRNA-enriched loci were identical to those of AGO4. In addition, expression of AGO3 driven by the AGO4 promoter partially complemented AGO4 function and rescued a DNA methylation defect in the ago4-1 background plant.
Together, this finding identified that AGO3, similarly to AGO4, functions in epigenetic modification through regulating DNA methylation.
The work entitled “Arabidopsis AGO3 predominantly recruits 24-nt small RNAs to regulate epigenetic silencing” was published in Nature Plants on April 18, 2016 (doi:10.1038/nplants.2016.49).
This research was supported by the grants from the National Natural Science Foundation of China. 
Figure. Small RNA binding preference and downstream functions of Arabidopsis AGO proteins (Image by ZHANG Zhonghui et al.)

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(Editor: YUAN Linlin)

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