Variegated phenotype and developmental methylation changes of a maize allele originating from epimutation.
Two instances of genetic transmission of spontaneous epimutation of the maize P-rr gene were identified. Transmission gave rise to two similar, moderately stable alleles, designated P-pr-1 and P-pr-2, that exhibited Mendelian behavior. Both isolates of P-pr conditioned a variable and variegated phenotype, unlike the uniform pigmentation conditioned by P-rr. Extensive genomic analysis failed to reveal insertions, deletions or restriction site polymorphisms between the new allele and its progenitor. However, methylation of the P gene was increased in P-pr relative to P-rr, and was greatly reduced (though not lost) in a revertant to uniform pigmentation. Variability in pigmentation conditioned by P-pr correlated with variability in transcript levels of the P gene, and both correlated inversely with variability in its methylation. Part of the variability in methylation could be accounted for by a developmental decrease in methylation in all tissues of plants carrying P-pr. We hypothesize that the variegated phenotype results from a general epigenetic pathway which causes a progressive decrease in methylation and increase in expression potential of the P gene as a function of cell divisions in each meristem of the plant. This renders all tissues chimeric for a functional gene; chimerism is visualized as variegation only in pericarp due to the tissue specificity of P gene expression. Therefore, this allele that originates from epimutation may exemplify an epigenetic mechanism for variegation in maize.
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Waksman Institute, Rutgers University, Piscataway, New Jersey 08855-0759.
Messing
J
J
D000483:Alleles; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004251:DNA Transposable Elements; D017343:Genes, Plant; D008745:Methylation; D009154:Mutation; D010641:Phenotype; D010858:Pigmentation / Q000235:genetics; D015183:Restriction Mapping; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism
D004251:DNA Transposable Elements; D004247:DNA