Originally published as Genetics Published Articles Ahead of Print on April 15, 2007.

Genetics, Vol. 176, 829-839, June 2007, Copyright © 2007
doi:10.1534/genetics.107.072496

Multiple Trans-Sensing Interactions Affect Meiotically Heritable Epigenetic States at the Maize pl1 Locus

Department of Plant and Microbial Biology, University of California, Berkeley, California 94720

1 Corresponding author: Department of Plant and Microbial Biology, University of California, 111 Koshland Hall, Berkeley, CA 94720-3102.
E-mail: hollick{at}nature.berkeley.edu

Interactions between specific maize purple plant1 (pl1) alleles result in heritable changes of gene regulation that are manifested as differences in anthocyanin pigmentation. Transcriptionally repressed states of Pl1-Rhoades alleles (termed Pl') are remarkably stable and invariably facilitate heritable changes of highly expressed states (termed Pl-Rh) in Pl'/Pl-Rh plants. However, Pl' can revert to Pl-Rh when hemizygous, when heterozygous with pl1 alleles other than Pl1-Rhoades, or in the absence of trans-acting factors required to maintain repressed states. Cis-linked features of Pl1-Rhoades responsible for these trans-sensing behaviors remain unknown. Here, genetic tests of a pl1 allelic series identify two potentially separate cis-linked features: one facilitating repression of Pl-Rh and another stabilizing Pl' in trans. Neither function is affected in ethyl-methanesulfonate-induced Pl1-Rhoades derivatives that produce truncated PL1 peptides, indicating that PL1 is unlikely to mediate trans interactions. Both functions, however, are impaired in a spontaneous Pl1-Rhoades derivative that fails to produce detectable pl1 RNA. Pl'-like states can also repress expression of a pl1-W22 allele, but this repression is not meiotically heritable. As the Pl' state is not associated with unique small RNA species representing the pl1-coding region, the available data suggest that interactions between elements required for transcription underlie Pl1-Rhoades epigenetic behaviors.