Poster abstracts
Poster number 25 submitted by Oliver Marchus
pl1 paramutation requires an SNF2-type ATPase encoded by the rmr13 locus
Oliver Marchus (Department of Molecular Genetics and Centers for Applied Plant Sciences and RNA Biology, The Ohio State University, Columbus, OH, 43210), Mowei Li (Department of Molecular Genetics and Centers for Applied Plant Sciences and RNA Biology, The Ohio State University, Columbus, OH, 43210), Jay Hollick (Department of Molecular Genetics and Centers for Applied Plant Sciences and RNA Biology, The Ohio State University, Columbus, OH, 43210)
Abstract:
Paramutations are defined by trans-homolog interactions that result in meiotically heritable changes in gene regulation. While the mechanism(s) responsible remain unclear, an RNA-directed DNA methylation (RdDM) pathway provides a working model. In maize, one example of paramutation occurs at the purple plant1 (pl1) Pl1-Rhoades (Pl1-Rh) allele which encodes a regulator of anthocyanin production. Relative to the highly expressed reference state (Pl-Rh), a paramutant derivative (Pl′ ) confers weak anther color and is exclusively transmitted from Pl′ / Pl-Rh heterozygotes in apparent violation of Mendelian segregation. In a screen for genetic factors required to maintain repression (rmr) of Pl′ states, ethyl methanesulfonate (EMS)-induced recessive mutations have defined at least sixteen distinct rmr loci. All known RMR proteins, except RMR12, are involved in RNA polymerase IV-derived 24 nucleotide sRNA biogenesis. Curiously, no RdDM-like sRNA effector proteins have been identified. Here we characterize mutations defining a novel locus (rmr13), which genetic tests show is necessary for both the establishment and maintenance of Pl′ repression. Analysis of whole genome sequence from independently-derived rmr13 mutants identified two transition-type nonsense mutations in the same 4L gene model. Phylogenetic analysis of this putative rmr13-encoded protein places it in a family of SNF2 ATPases containing RING finger domains associated with E3 ubiquitin ligase activity. Intriguingly, the closest rice ortholog, BIT-responsive Histone-interacting SNF2 ATPase 1 (BRHIS1), suppresses rice innate immunity through binding to monoubiquitinated H2A and H2B variants. The closest Arabidopsis ortholog, SNF2-ring-helicase-like2 (FRG2), also suppresses the immune response and functions downstream of sRNA biogenesis in RdDM. These findings support a role for rmr13 in establishment and maintenance of Pl′ repression through chromatin remodeling and variant histone ubiquitination. RMR13 thus represents the first possible sRNA effector central to the pl1 paramutation mechanism.
Keywords: Paramutation, rmr13