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近日，植物學頂級期刊Plant Cell在線發表題為「Transcriptome-Wide Mapping of RNA 5-Methylcytosine in Arabidopsis mRNAs and Noncoding RNAs」 的研究論文，利用BS-seq甲基化測序技術對擬南芥RNA進行全轉錄組的甲基化測序，並繪製了首張擬南芥RNA的m5C甲基化圖譜。
Figure 1. Transcriptome-Wide Mapping of m5C Using bsRNA-Seq in Arabidopsis.
RNA作為一種最古老而又非常重要的遺傳物質，目前已發現其存在100餘種不同的化學修飾形式，這些不同的化學修飾以甲基化為主。RNA的胞嘧啶(C)在轉錄後進行甲基化修飾形成 5-甲基胞嘧啶(m5C)，植物中RNA的m5C作為一種重要的修飾具有多種重要功能，例如調控植物對於脅迫的響應、參與幹細胞增殖以及RNA代謝等。該研究團隊利用BS-seq甲基化測序檢測了模式植物擬南芥(Arabidopsis thaliana) RNA全轉錄組中的m5C甲基化修飾，研究發現在擬南芥幼苗地上部和根部以及角果組織中的mRNA、lncRNA及其它非編碼RNA中存在上千個m5C修飾位點，這三種不同組織中m5C修飾位點數量上的差異暗示了m5C調控的組織特異性。幹擾RNA m5C甲基轉移酶 TRM4B導致mRNA和ncRNA上大量m5C的丟失，並且影響tRNA的穩定性。該研究同時還證明了m5C在植物發育過程中的重要性，如：擬南芥trm4b突變體的主根長度與野生型相比明顯縮短，同時根尖分生組織(RAM)的細胞分裂活性也降低，另外trm4b突變體對於氧化脅迫更加敏感，並且非甲基化的tRNA的穩定性降低。該研究從全基因組水平上提供了擬南芥RNA的m5C甲基化修飾圖譜，並且將這種修飾與其調控的生物學功能相結合。
Transcriptome-Wide Mapping of RNA 5-Methylcytosine in Arabidopsis mRNAs and Noncoding RNAs
Rakesh David, Alice Burgess, Brian Parker, Jun Li,a Kalinya Pulsford, Tennille Sibbritt, Thomas Preiss and Iain Robert Searlea
Posttranscriptional methylation of RNA cytosine residues to 5-methylcytosine (m5C) is an important modification with diverse roles, such as regulating stress responses, stem cell proliferation, and RNA metabolism. Here, we used RNA bisulfite sequencing for transcriptome-wide quantitative mapping of m5C in the model plant Arabidopsis thaliana. We discovered more than a thousand m5C sites in Arabidopsis mRNAs, long noncoding RNAs, and other noncoding RNAs across three tissue types (siliques, seedling shoots, and roots) and validated a number of these sites. Quantitative differences in methylated sites between these three tissues suggest tissue-specific regulation of m5C. Perturbing the RNA m5C methyltransferase TRM4B resulted in the loss of m5C sites on mRNAs and noncoding RNAs and reduced the stability of tRNAAsp(GTC). We also demonstrate the importance of m5C in plant development, as trm4b mutants have shorter primary roots than the wild type due to reduced cell division in the root apical meristem. In addition, trm4b mutants show increased sensitivity to oxidative stress. Finally, we provide insights into the targeting mechanism of TRM4B by demonstrating that a 50-nucleotide sequence flanking m5C C3349 in MAIGO5 mRNA is sufficient to confer methylation of a transgene reporter in Nicotiana benthamiana.
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