蓖麻DNA甲基转移酶序列与基因表达分析

Sequence and Gene Expression Analysis of DNA Methyltransferase in Castor Bean(Ricinus communis L.)

植物DNA甲基化是与调控基因表达、保护基因组免受逆境胁迫等相关的表观遗传现象,其中关键酶DNA甲基转移酶催化DNA序列维持甲基化和从头甲基化。本研究基于蓖麻全基因组、利用生物信息学分析方法、结合转录组数据和RT-PCR半定量表达分析,鉴别出蓖麻DNA甲基转移酶氨基酸序列的结构特征、系统发生和表达形式。结果如下:通过同源序列BLAST从蓖麻基因组数据库中获得8个DNA甲基转移酶基因;系统进化分析将8个蛋白分为4个亚家族:2个MET同源蛋白、2个CMT同源蛋白、3个DRM同源蛋白和1个DNMT2同源蛋白,进一步发现DNA甲基转移酶在系统进化上较为保守,分化发生在单双子叶植物分化之后;亚细胞定位分析发现8个DNA甲基转移酶都定位在细胞核中;蛋白结构域比对结果显示8个蛋白的C端催化结构域都有6个保守motif参与甲基化修饰催化功能,表明蛋白具有基本的催化甲基化功能,而N端调节功能域的差异将蛋白分为四类,其中Rc DNMT2缺少N端调节结构域;结合转录组数据和RT-PCR半定量表达分析发现蓖麻DNA甲基转移酶基因(除Rc DRM2外)在发育胚乳中相对其他检测组织高表达,推测是该时期的胚乳低甲基化诱导甲基化基因高表达。该结果有助于全面了解蓖麻DNA甲基转移酶特征及为从表观遗传深入开展蓖麻品种改良具有重要理论指导作用。

DNA methylation, which can protect plant genome from adversity stress and regulate gene expression, is one of epigenetic modification. DNA methyltransferase is key enzyme for maintaining DNA methylation and de novo methylation. In this research, 8 putative genes encoding DNA methyltransferase were identified and characterized from castor bean （Ricinus communis） genome. These genes have been classified into MET, CMT, DRM and DNMT2 subfamilies based on phylogenetic relationship and domain organization, and their structures, conserved domains, and subcellular locations were also characterized. In addition, the gene expression was inspected through the high-throughput transcriptional sequencing data and RT-PCR methods. Results showed these proteins encoded by 8 genes were located at nucleus, and catalytic C-terminal domain with 6 conserved motifs have common methylation function, while the N-terminal domain of these proteins showed diverse structural features between different subfamilies, meanwhile, the lacking N-terminal domain presented in the RcDNMT2. Phylogenetically, the MET, CMT, DRM and DNMT2 were conservative and differentiated after mono- and dicot-cotyledon. The expression level of all genes in developing endosperm was higher than other detective tissues except RcDRM2, and hypothesized that endosperm hypomethylation can induce the high expression of these DNA methyltransferase genes during this period. These results contribute to understanding castor bean DNA methyltransferase comprehensively and provide a guidline for epigenetics breeding.