Loss of function mutations in the rice chromomethylase OsCMT3a cause a burst of transposition
Loss of function mutations in the rice chromomethylase OsCMT3a cause a burst of transposition
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DOI：
10.1111/tpj.12952
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发表时间：
2015-09-01
期刊：
影响因子：
7.2
通讯作者：
Hirochika, Hirohiko
中科院分区：
文献类型：
--
作者：
Cheng, Chaoyang;Tarutani, Yoshiaki;Hirochika, Hirohiko
植物的甲基化模式是独特的，因为除了在哺乳动物中发生的CG二核苷酸处的甲基化之外，甲基化也发生在非CG位点处。基因在CG位点被甲基化，但转座因子（TE）在CG和非CG位点都被甲基化。目前，非CG甲基化在TE转录沉默中的作用正在被广泛研究，但当非CG甲基化机制受损时，只有非常罕见的转座被报道。为了了解非CG甲基化在TE抑制和植物发育中的作用，我们表征了水稻突变体中的染色质甲基化酶基因OsCMT 3a的变化。oscmt 3a突变体表现出CHG甲基化急剧下降、一些基因和TE表达的变化以及多效性发育异常。基因组重测序确定了8个TE家庭在正常繁殖过程中在osmt 3a动员。这些TE包括组织培养激活的copia逆转录转座子Tos 17和Tos 19（Lullaby），一个着丝粒周围成簇的高拷贝数非自主吉普赛逆转录转座子Dasheng，两个copia逆转录转座子Osr 4和Osr 13，一个hAT-tip 100转座子DaiZ，一个MITE转座子mPing，和LINE元件LINE 1 -6_OS。我们通过聚合酶链反应（PCR）和/或Southern印迹分析证实了这些TE的转座，并显示转座依赖于OSCMT 3A突变。这些结果表明，OsCMT 3a介导的非CG DNA甲基化在发育和抑制广谱TE中起关键作用。这些在植物体内的移动的转座酶对于研究转座酶与宿主基因组的相互作用以及水稻功能基因组学研究具有重要意义。
Methylation patterns of plants are unique as, in addition to the methylation at CG dinucleotides that occurs in mammals, methylation also occurs at non-CG sites. Genes are methylated at CG sites, but transposable elements (TEs) are methylated at both CG and non-CG sites. The role of non-CG methylation in transcriptional silencing of TEs is being extensively studied at this time, but only very rare transpositions have been reported when non-CG methylation machineries have been compromised. To understand the role of non-CG methylation in TE suppression and in plant development, we characterized rice mutants with changes in the chromomethylase gene, OsCMT3a. oscmt3a mutants exhibited a dramatic decrease in CHG methylation, changes in the expression of some genes and TEs, and pleiotropic developmental abnormalities. Genome resequencing identified eight TE families mobilized in oscmt3a during normal propagation. These TEs included tissue culture-activated copia retrotransposons Tos17 and Tos19 (Lullaby), a pericentromeric clustered high-copy-number non-autonomous gypsy retrotransposon Dasheng, two copia retrotransposons Osr4 and Osr13, a hAT-tip100 transposon DaiZ, a MITE transposon mPing, and a LINE element LINE1-6_OS. We confirmed the transposition of these TEs by polymerase chain reaction (PCR) and/or Southern blot analysis, and showed that transposition was dependent on the oscmt3a mutation. These results demonstrated that OsCMT3a-mediated non-CG DNA methylation plays a critical role in development and in the suppression of a wide spectrum of TEs. These in planta mobile TEs are important for studying the interaction between TEs and the host genome, and for rice functional genomics.