Poster abstracts
Poster number 32 submitted by Oliver Marchus
A putative dsRNA-binding protein facilitates heritable, sRNA-mediated gene silencing in maize
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. Although the precise mechanism(s) responsible remain unclear, screens for genetic factors required to maintain this repression (rmr) have identified at least sixteen distinct rmr loci in maize. All known RMR proteins facilitate production of RNA polymerase IV-derived 24 nucleotide RNAs, supporting a model in which sRNAs direct establishment and maintenance of paramutations. Recent whole genome sequence analysis mapped a novel rmr locus to the x1 gene on Chr3. Phylogenetic analysis identified a family of three functionally distinct x1 orthologs in Arabidopsis which form a complex involved in the RNA-directed DNA methylation (RdDM) pathway. The complex binds specific dsRNA isoforms and facilitates de novo cytosine methylation (5mC) through recruitment of a DNA methyltransferase. One of the orthologs also shows a unique DNA binding affinity. This protein family and x1 share namesake XS and XH domains responsible for dsRNA binding and complex formation, respectively, but whether the X1 protein exhibits similar activities remains untested. Furthermore, any RdDM-based model of X1 action is complicated by the absence of a similar family of functionally distinct orthologs in maize. Thus, I will test the hypothesis that X1 facilitates paramutation by forming a dsRNA-binding complex that mediates sRNA-directed 5mC, resulting in repressive chromatin modifications and transgenerational silencing. To do so, I will investigate the effect of x1 mutation on levels of sRNA, 5mC, and histone modifications both globally and at specific regulatory sequences genetically and molecularly linked to paramutations. Furthermore, I will assess whether X1 can bind different DNA and dsRNA isoforms and the maize de novo DNA methyltransferase, as well as whether X1 can form XH domain-dependent complexes. This work will illuminate the role of a putative dsRNA binding protein in sRNA-directed transgenerational silencing and thereby enhance current understandings of RNA-mediated gene regulation.
Keywords: x1, dsRNA, sRNA