Irish Erin E, McMurray Douglas
Department of Biological Sciences, The University of Iowa, Iowa City, IA 52242, USA.
Plant Mol Biol. 2006 Mar;60(5):747-58. doi: 10.1007/s11103-005-5620-6.
Cytosine methylation provides an attractive epigenetic modification for the global maintenance of phases in plant development; however, there are few known examples of specific genes whose methylation status changes in a developmentally regulated manner. Pl-Blotched, an allele of purple plant1 (pl1), which encodes a myb-like transcription factor that regulates anthocyanin production in maize, is one such gene: certain cytosines at the 3' end of this allele are hypomethylated in seedlings, become hypermethylated in organs formed in the adult phase, and are hypomethylated again in the next generation. We tested whether this developmental pattern of low juvenile cytosine methylation followed by higher methylation in adult tissues could also be observed in plants "rejuvenated" via shoot apex culture. We found that cytosine methylation patterns at Pl-Blotched were indeed recapitulated in culture-rejuvenated plants, showing hypomethylation in leaves with juvenile patterns of differentiation (even though they were made by an old meristem) followed by hypermethylation in later-formed leaves. Our results show that methylation status at that locus is determined by the developmental phase of the shoot, rather than by the age of the meristem forming it. These results support the hypothesis that DNA methylation is employed by the plant to maintain an epigenetic state.
胞嘧啶甲基化为植物发育阶段的整体维持提供了一种引人注目的表观遗传修饰；然而，很少有已知的特定基因的例子，其甲基化状态以发育调控的方式发生变化。Pl-Blotched是紫色植物1（pl1）的一个等位基因，它编码一种调控玉米花青素产生的类myb转录因子，就是这样一个基因：该等位基因3'端的某些胞嘧啶在幼苗中低甲基化，在成年期形成的器官中高甲基化，而在下一代中又低甲基化。我们测试了这种在幼年时胞嘧啶甲基化水平低，随后在成年组织中甲基化水平更高的发育模式，是否也能在通过茎尖培养“复壮”的植物中观察到。我们发现，在通过培养复壮的植物中，Pl-Blotched位点的胞嘧啶甲基化模式确实得以重现，在具有幼年分化模式的叶片中表现为低甲基化（尽管它们是由老的分生组织形成的），随后在后期形成的叶片中高甲基化。我们的结果表明，该位点的甲基化状态是由茎的发育阶段决定的，而不是由形成它的分生组织的年龄决定的。这些结果支持了植物利用DNA甲基化来维持表观遗传状态这一假说。
