Variegated Phenotype and Developmental Methylation Changes of a Maize Allele Originating From Epimutation

• Published in: Genetics (Austin) Vol. 136; no. 3; pp. 1121 - 1141
• Main Authors: Das, O. P, Messing, J
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Genetics Soc America 01-03-1994; Genetics Society of America
• Subjects: Alleles; Biological and medical sciences; Classical genetics, quantitative genetics, hybrids; Corn; DNA - genetics; DNA - metabolism; DNA Transposable Elements; Fundamental and applied biological sciences. Psychology; Genes; Genes, Plant; Genetics; Genetics of eukaryotes. Biological and molecular evolution; Investigations; Methylation; Mutation; Phenotype; Pigmentation - genetics; Pteridophyta, spermatophyta; Restriction Mapping; Transcription, Genetic; Vegetals; Zea mays; Zea mays - genetics; Zea mays - growth & development; Zea mays - metabolism; Monocotyledones; Allele; Genetic inheritance; Variegation; Zea mays; Gramineae; Angiospermae; Epigenetics; Spermatophyta; Mutation; Methylation; Pigmentation
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1093/genetics/136.3.1121

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.