Meyer P, Heidmann I, Niedenhof I
Max-Delbrück-Laboratorium in der MPG, Köln, Germany.
Plant J. 1993 Jul;4(1):89-100. doi: 10.1046/j.1365-313x.1993.04010089.x.
The transgenic petunia line 17-R contains one copy of the maize A1 gene which mediates brick-red pelargonidin pigmentation of the flower. A white derivative, 17-W, was isolated from homozygous progeny of this line in which no pelargonidin pigmentation was observed. In 17-W the 35S promoter driving the A1 gene was hypermethylated, in contrast to its hypomethylated state in 17-R. Progeny plants carrying both the 17-R and 17-W allele did not show the expected A1 phenotype. Predominantly white progeny and variable plants were observed which showed a continuous change in pattern and intensity of pelargonidin pigmentation. This reduction of A1 activity argues for a semidominant effect of the 17-W allele which inhibits the activity of its homologue, 17-R. This system shows striking similarities to some paramutation phenomena in plants which represent a heritable change in gene function of a paramutable allele directed by a paramutagenic homologue. The analysis of the methylation patterns of the A1 alleles suggests that interactions between differentially methylated alleles are responsible for the paramutation-like effect which is mediated by somatic pairing. The analogy of this system to other phenomena based on homology-dependent interlocus trans-inactivation supports the assumption that those may be based on a related mechanism which includes an interaction between ectopic homologues.
转基因矮牵牛品系17-R含有一个玉米A1基因拷贝，该基因介导花朵砖红色的天竺葵色素沉着。从该品系的纯合后代中分离出一种白色衍生物17-W，在其中未观察到天竺葵色素沉着。在17-W中，驱动A1基因的35S启动子发生了高度甲基化，与其在17-R中的低甲基化状态形成对比。携带17-R和17-W等位基因的后代植株并未表现出预期的A1表型。观察到主要为白色的后代和表现出天竺葵色素沉着模式和强度持续变化的变异植株。A1活性的这种降低表明17-W等位基因具有半显性效应，它抑制了其同源物17-R的活性。该系统与植物中的一些副突变现象具有显著相似性，这些现象代表了由副突变同源物引导的副突变等位基因的基因功能的可遗传变化。对A1等位基因甲基化模式的分析表明，差异甲基化等位基因之间的相互作用是由体细胞配对介导的副突变样效应的原因。该系统与基于同源性依赖的基因座间反式失活的其他现象的类比支持了这样一种假设，即那些现象可能基于一种相关机制，该机制包括异位同源物之间的相互作用。
