Poster abstracts
Poster number 99 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 that result in meiotically heritable gene silencing. In maize, paramutations occur between specific alleles at both the purple plant1 (pl1) and booster1 (b1) loci which encode transcription factors regulating anthocyanin biosynthesis. Relative to the highly expressed Pl-Rh and B-I reference states, the paramutant derivatives (Pl′ and B′ ) confer weak plant color and are exclusively transmitted from respective 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 have defined at least sixteen loci. 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 analysis putatively maps rmr17 to the x1 gene encoding the founding member of a plant-specific protein family with namesake XS domains responsible for binding 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 the SWI3B nucleosome remodeler, and 3) help recruit the DRM2 de novo cytosine methyltransferase. Our findings thus support a role for X1 in paramutation by recognizing 24nt RNA-lncRNA duplexes and recruiting proteins that facilitate meiotically-heritable repressive chromatin modifications.
Keywords: x1, paramutation