Poster abstracts
Poster number 176 submitted by Oliver Marchus
x1 encodes a putative RNA-binding protein required for paramutation
Oliver J. Marchus (Department of Molecular Genetics and Centers for Applied Plant Sciences and RNA Biology, The Ohio State University, Columbus, OH, 43210), Jay B. 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 resulting in meiotically heritable changes in gene regulation. In maize, paramutations occur between specific alleles at both the purple plant1 (pl1) and booster1 (b1) loci, which encode transcription factors facilitating anthocyanin biosynthesis. Relative to the highly expressed Pl-Rh and B-I reference states, paramutant derivatives (Pl′ and B′ ) confer weak color and transmit exclusively from Pl-Rh / Pl′ and B-I / B′ heterozygotes in apparent violation of Mendelian segregation. While the nature of these interactions remains unclear, an Arabidopsis thaliana (A.t.)-based RNA-directed DNA methylation (RdDM)-like mechanism provides a working model. In forward genetic screens for factors required to maintain repression (rmr) of Pl′ states, ems-induced mutations define at least sixteen loci. Consistent with an RdDM-type model, all seven known RMR proteins facilitate RNA polymerase IV-derived 24 nucleotide (nt) RNA biogenesis, yet no RdDM-like 24nt RNA effector proteins have been identified. Here, we show the rmr17 locus is required to establish both pl1 and b1 paramutations. Bulk-segregant and SNP analyses map the rmr17-1 mutation to a gene (x1) encoding the founding member of a plant-specific protein family with namesake XS domains that bind double-stranded (ds) RNA. In A.t., three non-redundant X1-like proteins form heteromeric complexes required for RdDM. These complexes 1) bind 24nt RNA and RNA polymerase V-derived long non-coding RNA (lncRNA) duplexes, 2) interact with a SWI/SNF-type subunit (SWI3B), and 3) help recruit a de novo cytosine methyltransferase (DRM2). mRNA level differences in rmr17-1 mutants significantly overlap those of other rmr mutants, including affecting the maize ortholog of a known A.t. RdDM target (ros1). These findings support an RdDM-like mechanism for X1 in paramutation by recognizing 24nt RNA-lncRNA duplexes and recruiting factors to facilitate meiotically heritable repressive chromatin modifications.
Keywords: x1, paramutation