Most colored-seed alleles of the maize R gene are metastable. Pigmentation is reduced heritably by heterozygosity with certain alleles (paramutation) and increased heritably in still other combinations. The changes are cumulative over generations. Exploratory tests using restriction enzymes whose action is sensitive to cytosine methylation indicate hypermethylation in the R region of DNA from paramutant R alleles. We propose to characterize this change in the least complex alleles that undergo paramutation, utilizing a graded series of pigmentation levels that includes enhanced as well as reduced states. Other phenomena of R action to be characterized in terms of DNA modification include: a marked influence of alkylating agents on R paramutation, differences in R pigmentation level following transmission through pollen and ovule, and the dependence of paramutation of R plant pigmentation on presence of seed-color component in the allelic complex. Components responsible for inducing paramutation that have been mapped genetically in the R- stippled allele are to be characterized molecularly. Paramutation is a genetic phenomena for which there is as yet no molecular explanation. In this system the best understood example of paramutation in any organism, indications are that methylation of the DNA is involved. Results from this study should provide further insight into the mechanisms involved in gene expression and may enhance commercial applications of genetic engineering.
