DNA甲基化是重要的表观遗传修饰之一, 参与调控植物基因组稳定性、发育及胁迫响应等过程。DNA甲基转移酶是DNA甲基化的关键酶。为了解铁甲秋海棠(Begonia masoniana) DNA甲基转移酶的功能, 采用生物信息学方法从铁甲秋海棠基因组中鉴定出5个编码DNA甲基转移酶的基因。根据序列特征将其分为CMT、MET和DRM三类。不同类别成员的基因序列长度和内含子数量存在明显差异, 但同类成员的基因结构和保守结构域具有高度保守性。这些蛋白均定位于细胞核, 且基因启动子含有大量的光响应、MYB结合及植物激素响应等元件。激素响应模式分析表明, CMT3类在GA、SA和NAA处理下基因表达显著降低, CMT2类在MeJA和NAA处理下基因表达显著降低, 而MET类和DRM类分别在GA和ABA处理下基因表达显著升高。此外, 组织特异性分析发现, 叶片中BmaCMT2-5和BmaDRM2-2的表达量明显高于其它组织器官, 且这2个酶的编码基因与BmaMET1-15在叶片红色部分的表达高于绿叶部分, 推测这3个DNA甲基转移酶可能在叶斑形成过程中发挥重要作用。

INTRODUCTION: DNA methylation is one of the important epigenetic modifications involved in the regulation of plant genome stability, development and stress responses. DNA methylation introduces methylation groups into DNA molecules, thereby altering the activity of DNA segments. DNA methylation is catalyzed by DNA methyltransferase, a process by which methyl groups formed from S-adenosyl-L-methionine are transferred via covalent links to specific locations in the DNA sequence to form N4-methylcytosine, 5-methylcytosine, N6-methyladenine, or 7-methylguanine. However, there are few reports about the effects of DNA methyltransferase on leaf variegation formation and stress response of Begonia.
RATIONALE: Studies have shown that DNA methylation is involved in regulating the formation of leaf color, flower color and leaf variegation, as well as responses to stresses and hormones. As an endemic species of Begonia, Begonia masoniana has unique and beautiful leaf markings, pink, dark green and light green in different developmental stages. It has high ornamental value and is an excellent foliage plant. Therefore, based on the genomic data, this study conducted genome-wide identification and expression pattern analysis of DNA methyltransferase genes, aiming to explore the genetic resources that regulate the formation of leaf variegation.
RESULTS: To investigate whether DNA methyltransferase is involved in the regulation of leaf variegation formation and stress response in B. masoniana, bioinformatics analysis was used to identify the genes encoding DNA methyltransferase. Five genes were obtained from the genome of B. masoniana. According to the protein structural characteristics, their encoded proteins were divided into three categories including CMT, MET and DRM. The sequence length and intron number of these genes were significantly categorized into different subgroups, but their structure and conserved domains in the same subgroup were highly conserved. In addition, all the encoded proteins were predicted to locate in the nucleus. The promoters of these genes contain a large number of cis-acting elements such as light response, MYB binding, and plant hormone response elements. Analysis of hormone response patterns showed that the gene expression of CMT3 was significantly decreased under GA, SA and NAA, and the gene expression of CMT2 was significantly decreased under MeJA and NAA, while MET-type and DRM-type genes displayed significantly increased expression under GA and ABA treatments. In addition, tissue specific analysis showed that the expression levels of BmaCMT2-5 and BmaDRM2-2 in leaves were significantly higher than those of other tissues, while the expressions of these two genes and BmaMET1-15 in red part of leaves were significantly higher than that of green part, implying that these three genes may be involved in regulating the formation of leaf variegation.
CONCLUSION: The structure and function of DNA methyltransferase genes vary significantly across different categories in B. masoniana. However, within each category, members display high conservation in gene structure, conserved domains, motifs, and evolutionary patterns. These genes are likely to play crucial roles in the growth and development of diverse tissues and organs, as well as in responding to various biological and abiotic stresses. Moreover, based on the differential expression patterns of BmaCMT2-5, BmaMET1-15, and BmaDRM2-2 genes between leaf variegation and non-variegation areas, coupled with the abundance of MYB regulatory elements related to anthocyanin synthesis in their promoters, it is hypothesized that these genes may contribute to the formation of leaf variegation. As the current understanding of the functional roles of these methyltransferase genes is largely speculative, future research should focus on their functional validation, which will involve utilizing reverse genetics techniques coupled with phenotypic observations to determine their involvement in specific biological processes. Additionally, physiological, biochemical, and molecular biological methods should be employed to elucidate the precise mechanisms of their actions.

Relative expression levels of DNA methyltransferase genes in different tissues and organs of Begonia masoniana