Epigenetic allelic states of a maize transcriptional regulatory locus exhibit overdominant gene action.
Using alleles of the maize purple plant locus (pl), which encodes a transcriptional regulator of anthocyanin pigment synthesis, we describe a case of single-locus heterosis, or overdominance, where the heterozygote displays a phenotype that is greater than either homozygote. The Pl-Rhoades (Pl-Rh) allele is subject to epigenetic changes in gene expression, resulting in quantitatively distinct expression states. Allelic states with low-expression levels, designated Pl'-mahogany (Pl'-mah), are dominant to the high-expression state of Pl-Rh. Pl'-mah states retain low-expression levels in subsequent generations when homozygous or heterozygous with Pl-Rh. However, Pl'-mah alleles frequently exhibit higher expression levels when heterozygous with other pl alleles; illustrating an overdominant allelic relationship. Higher expression levels are also observed when Pl'-mah is hemizygous. These results suggest that persistent allelic interactions between Pl'-mah and Pl-Rh are required to maintain the low-expression state and that other pl alleles are missing sequences required for this interaction. The Pl-Rh state can be sexually transmitted from Pl'-mah/pl heterozygotes, but not from Pl'-mah hemizygotes, suggesting that fixation of the high-expression state may involve synapsis. The existence of such allele-dependent regulatory mechanisms implicates a novel importance of allele polymorphisms in the genesis and maintenance of genetic variation.
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229, USA.
J B
JB
Hollick
V L
VL
Chandler
D000483:Alleles; D000872:Anthocyanins / Q000096:biosynthesis; D003433:Crosses, Genetic; D018628:Gene Dosage; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D005799:Genes, Dominant / Q000235:genetics*; D017343:Genes, Plant / Q000235:genetics; D005809:Genes, Regulator / Q000235:genetics*; D006579:Heterozygote; D006720:Homozygote; D003313:Zea mays / Q000235:genetics*
D000872:Anthocyanins