Hypomethylation and transcriptional reactivation of retrotransposon-like sequences in ddm1 transgenic plants of Brassica rapa
Hypomethylation and transcriptional reactivation of retrotransposon-like sequences in ddm1 transgenic plants of Brassica rapa
复制标题
DOI：
10.1007/s11103-007-9285-1
复制
发表时间：
2008-03-01
影响因子：
5.1
通讯作者：
Nishio, Takeshi
中科院分区：
文献类型：
--
作者：
Fujimoto, Ryo;Sasaki, Taku;Nishio, Takeshi
DNA甲基化和组蛋白修饰在基因表达调控中起着重要作用。拟南芥中DDM1基因（AtDDM1）是维持DNA甲基化水平和组蛋白H3甲基化模式所必需的。我们从油菜、BrDDM1a和BrDDM1b中分离出DDM1同源基因，它们与AtDDM1的氨基酸序列同源性分别为84.4%和84.1%。BrDDM1a和BrDDM1b基因均在营养组织和生殖组织中表达。BrDDM1a/BrDDM1b表达水平降低的B. rapa ddm1-RNAi转基因植株表现出全基因组和非组织特异性的去甲基化。这些结果表明，BrDDM1a和BrDDM1b基因是AtDDM1的同源基因，并且与AtDDM1一样是维持DNA甲基化所必需的。尽管进行了全基因组去甲基化，但在ddm1-RNAi转基因植物中未发现发育异常。BrDDM1低表达不影响油菜S杂合子SP11/SCR等位基因的显性关系，而SP11/SCR等位基因是油菜自交不亲和花粉识别特异性的决定因素。在ddm1-RNAi转基因植物中观察到逆转录转座子样序列的转录再激活，表明BrDDM1a和BrDDM1b参与了逆转录转座子的沉默。ddm1-RNAi转基因植株的低甲基化状态可以遗传给下一代植株，甚至是由于分离而失去RNAi构建体的植株。在少数后代中观察到再甲基化。在没有RNAi构建的后代中，18S rDNA、BoSTF12a/15a和BrTto1序列的再甲基化效率不同。
DNA methylation and histone modification play important roles in regulating gene expression. The DDM1 gene in Arabidopsis thaliana (AtDDM1) is required for the maintenance of DNA methylation level and histone H3 methylation pattern. We isolated DDM1 homologs of Brassica rapa, BrDDM1a and BrDDM1b, which have 84.4% and 84.1% deduced amino acid sequence identities with AtDDM1, respectively. Both the BrDDM1a and BrDDM1b genes were found to be expressed in vegetative and reproductive tissues. B. rapa ddm1-RNAi transgenic plants with reduced levels of BrDDM1a/BrDDM1b expression showed genome-wide and non-tissue-specific demethylation. These results suggest that the BrDDM1a and BrDDM1b genes are orthologs of AtDDM1 and are required for the maintenance of DNA methylation as is AtDDM1. Despite genome-wide demethylation, developmental abnormalities were not found in the ddm1-RNAi transgenic plants. Dominance relationships of SP11/SCR alleles, the determinant of pollen recognition specificity in Brassica self-incompatibility, in S heterozygotes in B. rapa were not influenced by the low level of the BrDDM1 expression. Transcriptional reactivation of retrotransposon-like sequences observed in the ddm1-RNAi transgenic plants indicates that BrDDM1a and BrDDM1b participate in silencing of retrotransposons. Hypomethylation states of the ddm1-RNAi transgenic plants were inherited by plants of the next generation even by plants which had lost the RNAi construct by segregation. Remethylation was observed in a few progenies. Efficiencies of remethylation in the progenies without the RNAi construct were different between 18S rDNA, BoSTF12a/15a, and BrTto1 sequences.