中文摘要：

DNA甲基化模式和水平取决于DNA甲基转移酶和去甲基化酶的作用，而DNA去甲基化酶在DNA主动去甲基化过程中起到关键作用。文章以已知的10个DNA去甲基化酶基因为参照，鉴定出两种单子叶植物（水稻和高粱）、两种双子叶植物（拟南芥和毛果杨）中所有的DNA去甲基化酶同源基因，其中新鉴定出两类DNA去甲基化酶类似基因DML4和DML5。基于保守的糖苷酶结构域序列的系统进化分析以及基因在染色体上的位置分析表明，植物中DNA去甲基化酶基因存在串联复制、染色体区段复制和全基因组复制而导致基因的新功能化和亚功能化。文章还进一步分析了DNA去甲基化酶基因在不同组织中的表达情况，旨在理解DNA去甲基化酶基因的功能与进化的关系，以期为DNA去甲基化酶基因在植物中的利用提供参考。

英文摘要：

The DNA methylation patterns and levels are depended on the function of DNA methyltransferase and DNA demethylase, and DNA demethylase plays a critical role in active DNA demethylation. In this paper, all homologous DNA demethylase gene copies were identified in monocots （O. sativa and S. bicolor） and dicotyledon （A.thaliana and P trichocarpa） based on ten known DNA demethylase genes from rice and Arabidopsis. Two types of new DNA demethylase-like genes （DML4 and DML5） were identified. Tandem duplication, segmental duplication and whole genome duplication exist in DNA demethylase gene family in plants, which result in neo izatin and subfuncfionalization upon the phylogeny of conserved glycosylase domains and chromosomal locations of genes. Furthermore, the expression of DNA demethylase genes was investigated in different tissues. This study will facilitate our understanding of the relationship between function and evolution of DNA demethylase, and utilizing the DNA demethylase genes in plants.