Progressive DNA demethylation in epigenetic hybrids between parental plants with and without methylation of the transgene promoter.

Abstract

Crosses of parents that differ in their DNA methylation states leads to progressive demethylation in the F1 hybrids. In plant breeding research, hybrid vigor in F1 hybrids is known to be a very important phenomenon. Hybrid vigor, or heterosis, refers to the fact that F1 hybrids from crosses with a certain combination of parents have traits that are superior to those of the parents. In addition, DNA methylation is an important factor that affects gene expression in plant genomes and contributes to hybrid vigor. We introduced the 35S promoter sequence into the cucumber mosaic virus (CMV)-based vector and inoculated the GFP-expressing transgenic Nicotiana benthamiana line 16c with the recombinant virus specifically to induce DNA methylation on the 35S promoter. For plants that had transcriptional gene silencing (TGS) of GFP established by methylation of the 35S promoter (35S-TGS), TGS was fully maintained in their later self-pollinated generations. When the 35S-TGS plants were crossed with 16c, which does not contain DNA methylation in the 35S promoter, the F1 hybrids unexpectedly became progressively DNA demethylated as the plants grew. We hypothesis that in F1 hybrids that are produced by a cross between parents with extremely different gene methylation states, the methylation state of the genes in question may shift more and more to hypomethylation as the plants grow. This progressive demethylation phenomenon observed in this study may be important in plant breeding to reactivate the genes which were silenced by DNA methylation.