蛋白質(zhì)是生物體結(jié)構(gòu)與功能的基本單位,，是所有生命活動(dòng)的物質(zhì)基礎(chǔ)和生理功能的重要執(zhí)行者,。蛋白質(zhì)翻譯后修飾是調(diào)節(jié)蛋白質(zhì)生物學(xué)功能的關(guān)鍵步驟之一。作為基因產(chǎn)物,，幾乎所有的蛋白質(zhì)都要經(jīng)過翻譯后的剪切修飾才能成為成熟蛋白質(zhì),。
目前已發(fā)現(xiàn)的蛋白質(zhì)翻譯后修飾形式已經(jīng)多達(dá)100種以上，其中蛋白質(zhì)精氨酸甲基化是一種非常重要的蛋白翻譯后共價(jià)修飾,，參與調(diào)控細(xì)胞的多種重要的生命過程,。蛋白質(zhì)精氨酸甲基化由一類被稱為蛋白質(zhì)精氨酸甲基轉(zhuǎn)移酶（PRMT）的蛋白家族催化完成，主要分為非對(duì)稱性雙甲基化（I型）和對(duì)稱性雙甲基化（II型）,。AtPRMT5是擬南芥中一個(gè)主要的II型蛋白精氨酸甲基轉(zhuǎn)移酶,，能夠催化組蛋白和非組蛋白的對(duì)稱性雙甲基化，參與調(diào)控植物生長(zhǎng)發(fā)育的各個(gè)過程,，包括葉片形態(tài),、生長(zhǎng)速率，并且通過下調(diào)開花抑制基因FLC的表達(dá)而促進(jìn)開花等過程,。但是目前，對(duì)于AtPRMT5參與植物生長(zhǎng)發(fā)育的分子機(jī)制的認(rèn)識(shí)還非常有限,。
中國(guó)科學(xué)院遺傳與發(fā)育生物學(xué)研究所曹曉風(fēng)實(shí)驗(yàn)室以模式植物擬南芥為材料,，結(jié)合蛋白組學(xué)、轉(zhuǎn)錄組學(xué)和遺傳學(xué)等研究手段,，揭示了對(duì)稱性雙甲基化在mRNA前體拼接過程中的重要作用,，闡釋了AtPRMT5參與調(diào)控植物生長(zhǎng)發(fā)育過程的分子機(jī)制。曹曉風(fēng)研究員及其研究團(tuán)隊(duì)利用蛋白組學(xué)手段,，鑒定了AtPRMT5的體內(nèi)非組蛋白底物,，其中包括一些與RNA代謝相關(guān)的蛋白。隨后,，他們利用高通量轉(zhuǎn)錄組測(cè)序技術(shù)（RNA-seq）來檢測(cè)RNA代謝的變化,。
研究結(jié)果表明,，AtPRMT5的缺失會(huì)導(dǎo)致大量的mRNA前體的拼接出現(xiàn)異常，而這些mRNA參與植物生長(zhǎng)發(fā)育的多個(gè)過程,，如非生物刺激響應(yīng),，光合作用，溫度響應(yīng)等,。以開花時(shí)間調(diào)節(jié)為例,，在atprmt5突變體中，開花調(diào)節(jié)基因FLK的異常拼接會(huì)導(dǎo)致其正常功能轉(zhuǎn)錄本的減少和蛋白水平的下降,，從而造成FLC的上調(diào)以及晚花的表型,。由此可知，AtPRMT5通過調(diào)控植物生命周期各個(gè)階段中mRNA前體的正確加工,，保證了植物正常的生長(zhǎng)發(fā)育過程,。
擬南芥精氨酸甲基轉(zhuǎn)移酶AtPRMT5的功能研究，為AtPRMT5介導(dǎo)的對(duì)稱性雙甲基化參與調(diào)節(jié)mRNA前體拼接提供了體內(nèi)的直接證據(jù),，同時(shí)為深入開展PRMT5的研究提供了全新的思路,，將其功能從轉(zhuǎn)錄調(diào)節(jié)水平擴(kuò)展到了轉(zhuǎn)錄后調(diào)節(jié)水平，具有重要的參考意義,。
上述研究成果在線發(fā)表于國(guó)際知名期刊Proceedings of the National Academy of Sciences USA上,。該論文的兩位評(píng)審專家均對(duì)本研究給予了高度的評(píng)價(jià)：“作者優(yōu)秀的研究工作揭示了精氨酸甲基化與mRNA前體拼接的重要關(guān)系，同時(shí)為停滯了很久的FLK基因的研究提供了一個(gè)很好的切入點(diǎn)”,。
此項(xiàng)研究得到了重大研究計(jì)劃,、973和國(guó)家自然科學(xué)基金項(xiàng)目的資助。（生物谷Bioon.com）
生物谷推薦英文摘要：
PNAS doi: 10.1073/pnas.1009669107
Arginine methylation mediated by the Arabidopsis homolog of PRMT5 is essential for proper pre-mRNA splicing
Xian Denga,b,1, Lianfeng Gua,b,1, Chunyan Liua,1, Tiancong Lua,b,c,1, Falong Lua,b, Zhike Lua, Peng Cuid, Yanxi Peia,e, Baichen Wangc, Songnian Hud, and Xiaofeng Caoa,2
aState Key Laboratory of Plant Genomics and National Center for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China;
bGraduate School of the Chinese Academy of Sciences, Beijing 100039, China;
cNortheast Forestry University, Harbin 150040, China;
dBeijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100029, China; and
eCollege of Life Science and Technology, Shanxi University, Taiyuan 030006, China
Protein arginine methylation, one of the most abundant and important posttranslational modifications, is involved in a multitude of biological processes in eukaryotes, such as transcriptional regulation and RNA processing. Symmetric arginine dimethylation is required for snRNP biogenesis and is assumed to be essential for pre-mRNA splicing; however, except for in vitro evidence, whether it affects splicing in vivo remains elusive. Mutation in an Arabidopsis symmetric arginine dimethyltransferase, AtPRMT5, causes pleiotropic developmental defects, including late flowering, but the underlying molecular mechanism is largely unknown. Here we show that AtPRMT5 methylates a wide spectrum of substrates, including some RNA binding or processing factors and U snRNP AtSmD1, D3, and AtLSm4 proteins, which are involved in RNA metabolism. RNA-seq analyses reveal that AtPRMT5 deficiency causes splicing defects in hundreds of genes involved in multiple biological processes. The splicing defects are identified in transcripts of several RNA processing factors involved in regulating flowering time. In particular, splicing defects at the flowering regulator FLOWERING LOCUS KH DOMAIN (FLK) in atprmt5 mutants reduce its functional transcript and protein levels, resulting in the up-regulation of a flowering repressor FLOWERING LOCUS C (FLC) and consequently late flowering. Taken together, our findings uncover an essential role for arginine methylation in proper pre-mRNA splicing that impacts diverse developmental processes.
