Xu Jian-Hong, Wang Ruixian, Li Xinxin, Miclaus Mihai, Messing Joachim
Institute of Crop Science, Zhejiang Key Laboratory of Crop Germplasm, Zhejiang University, Hangzhou, Zhejiang 310058, China.
National Institute of Research and Development for Biological Sciences, Cluj-Napoca, Romania.
PLoS One. 2016 Jan 7;11(1):e0146416. doi: 10.1371/journal.pone.0146416. eCollection 2016.
An interesting question in maize development is why only a single zein gene is highly expressed in each of the 19-kDa zein gene clusters (A and B types), z1A2-1 and z1B4, in the immature endosperm. For instance, epigenetic marks could provide a structural difference. Therefore, we investigated the DNA methylation of the arrays of gene copies in both promoter and gene body regions of leaf (non-expressing tissue as a control), normal endosperm, and cultured endosperm. Although we could show that expressed genes have much lower methylation levels in promoter regions than silent ones in both leaf and normal endosperm, there was surprisingly also a difference in the pattern of the z1A and z1B gene clusters. The expression of z1B gene is suppressed by increased DNA methylation and activated with reduced DNA methylation, whereas z1A gene expression is not. DNA methylation in gene coding regions is higher in leaf than in endosperm, whereas no significant difference is observed in gene bodies between expressed and non-expressed gene copies. A median CHG methylation (25-30%) appears to be optimal for gene expression. Moreover, tissue-cultured endosperm can reset the DNA methylation pattern and tissue-specific gene expression. These results reveal that DNA methylation changes of the 19-kDa zein genes is subject to plant development and tissue culture treatment, but varies in different chromosomal locations, indicating that DNA methylation changes do not apply to gene expression in a uniform fashion. Because tissue culture is used to produce transgenic plants, these studies provide new insights into variation of gene expression of integrated sequences.
玉米发育过程中一个有趣的问题是，为何在未成熟胚乳中，19-kDa醇溶蛋白基因簇（A 型和 B 型）中的每个基因簇（z1A2-1 和 z1B4）都只有一个醇溶蛋白基因高度表达。例如，表观遗传标记可能会造成结构差异。因此，我们研究了叶片（作为对照的非表达组织）、正常胚乳和培养胚乳的基因拷贝阵列在启动子区域和基因体区域的 DNA 甲基化情况。尽管我们发现，在叶片和正常胚乳中，表达的基因在启动子区域的甲基化水平均远低于沉默基因，但令人惊讶的是，z1A 和 z1B 基因簇的模式也存在差异。z1B 基因的表达会因 DNA 甲基化增加而受到抑制，因 DNA 甲基化减少而被激活，而 z1A 基因的表达则不然。叶片中基因编码区域的 DNA 甲基化高于胚乳，而在表达和未表达的基因拷贝之间，基因体中未观察到显著差异。CHG 甲基化中位数（25-30%）似乎最有利于基因表达。此外，组织培养的胚乳可以重置 DNA 甲基化模式和组织特异性基因表达。这些结果表明，19-kDa 醇溶蛋白基因的 DNA 甲基化变化受植物发育和组织培养处理的影响，但在不同染色体位置有所不同，这表明 DNA 甲基化变化并非以统一方式影响基因表达。由于组织培养用于生产转基因植物，这些研究为整合序列的基因表达变异提供了新见解。
