Abstract
Phenotypic variations are often caused by epigenetics. The recessive spontaneous mutation pearly-v in the morning glory (I. tricorol), conferring flower variegation, is caused by the insertion of a Mutator-like transposon, ItMULE1, within the promoter region of the DFR-B gene for anthocyanin biosynthesis. It is well known that the flower variegations are caused by recurrent somatic mutations due to the excision of integrated transposons from pigmentation genes. However, no excisions of ItMULE1 could be observed in the variegated flowers. We found that cytosine methylation within the 100 to 150 region upstream of the DFR-B transcription initiation site was associated with repression of the flower pigmentation. The 50-bp promoter region was hypermethylated in the non-pigmented cells, whereas it was hypomethylated in the pigmented cells of the variegated flowers. The results suggested that the flower variegation is due to high frequent changes of DNA methylation of the DFR-B promoter rather than to excision of ItMULE1.
