Paramutation

[1] Through proper breeding, paramutation can result in siblings that have the same genetic sequence, but with drastically different phenotypes.

The gene at this locus, when actively transcribed, codes for a transcription factor that promotes anthocyanin production, resulting in kernels with a purple color.

Other, similar examples of paramutation exist at other maize loci, as well as in other plants such as the model system Arabidopsis thaliana and transgenic petunias.

[1] In the case of the r1 locus in maize, DNA methylation of a region of tandem repeats near the coding region of the gene is characteristic of the paramutagenic B’ allele, and when the paramutable B-I allele becomes paramutagenic, it too takes on the same DNA methylation pattern.

[10] In order for this methylation to be successfully transferred, a number of genes coding for RNA-dependent RNA polymerases and other components of RNA-silencing pathways are required, suggesting that paramutation is mediated via endogenous RNA-silencing pathways.

[4] In addition to the characteristic DNA methylation state changes, changes in histone modification patterns in the methylated DNA regions, and/or the requirement of histone modifying proteins to mediate paramutation have also been noted in multiple systems.

[2] The previously mentioned tandem repeat region in the r1 locus is also typical of other loci showing paramutation or paramutation-like phenomena.

[5] However, it has been noted that it is not possible to explain all occurrences and features of paramutation with what is known about RNAi-mediated transcriptional silencing, suggesting that other pathways and/or mechanisms are also at play.