Poster: Epigenetics & gene silencing

Abs # 832: Rmr6 functions in paramutation and developmental epigenetics

Presenter:	Parkinson, Susan E., sep@uclink.berkeley.edu
Authors	Parkinson, Susan E. (A)   Hollick, Jay B. (A)
Affiliations:	(A): Department of Plant and Microbial Biology, UC Berkeley

The rmr6 (required to maintain repression6) locus encodes a trans-acting factor required to maintain paramutation-induced silencing at the purple plant1 (pl1) locus. The pl1 gene encodes a transcriptional regulator of genes required for anthocyanin biosynthesis. The Pl-Rhoades (Pl-Rh) allele can adopt various epigenetic expression states that are reflected by levels of pigmentation. Strong expression states (Pl) undergo transcriptional repression when coupled in a heterozygote with weak expression states (Pl’), an example of paramutation. Pl-Rh alleles segregating from a Pl/Pl’ heterozygote remain repressed and direct silencing of naïve Pl states in subsequent progeny. Molecular and genetic analyses indicate that RMR6 is necessary for the maintenance of Pl’ repression. Pl’/Pl’ plants with an rmr6 mutant genotype have high levels of anthocyanin pigmentation, increased pl1 transcription rates and pl1 transcript levels, relative to non-mutant siblings. Many Pl’ alleles transmitted from rmr6 mutant genotypes lose the capacity to repress Pl states. In addition to maintaining epigenetic repression of Pl’, RMR6 also ensures proper internode elongation, abaxial/adaxial polarity, floral organ identity, and lateral meristem repression. RMR6 also contributes to proper expression patterns of specific regulatory factors. Double mutant analysis suggests that RMR6 restricts sk1 (silkless1) expression from the apical inflorescence. Similarly, RMR6 appears to restrict pl1 expression from aleurone tissues, a site where the paralogous colorless1 (c1) factor is expressed. The action of RMR6 in pl1 paramutation and its role in developmental progression supports the hypothesis that the epigenetic regulation of paramutation is related to normal mechanisms of developmental gene regulation.