2014 OSU Molecular Life Sciences
Interdisciplinary Graduate Programs Symposium

 

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Poster number 6 submitted by Janelle Gabriel

DICER-LIKE3 is Required for 24nt Small RNA Biogenesis and Paramutation in Zea mays

Janelle M. Gabriel (Department of Molecular Genetics, The Ohio State University), Joy-El R. B. Talbot (Department of Molecular Genetics, The Ohio State University; Department of Plant and Microbial Biology, University of California, Berkeley), Ankur Narain, Irene T. Liao, Glenna Kong (Department of Plant and Microbial Biology, University of California, Berkeley), Stacey A. Simon, Blake C. Meyers (Delaware Biotechnology Institute, University of Delaware), Jay B. Hollick (Department of Molecular Genetics, The Ohio State University; Department of Plant and Microbial Biology, University of California, Berkeley)

Abstract:
Paramutation refers to a meiotically heritable epigenetic change in gene regulation involving allelic interactions1. Paramutations are influenced by trans-homolog interactions that are potentially mediated by small RNAs (sRNAs) as part of an RNA-directed DNA methylation pathway (RdDM)2. In Zea mays (maize), paramutation has been detected among alleles of the purple plant1 (pl1) and booster1 (b1) loci, both of which encode transcription factors necessary for anthocyanin pigment production. Paramutation can be affected by mutations in genes encoding presumed RdDM components3. A genetic screen for factors required to maintain repression of a paramutant pl1 allele identified four separate EMS-induced mutant alleles defining the rmr5 locus. Genetic tests show that rmr5 function is required to establish repressed paramutant states at the b1 locus. Fine-scale mapping identified a candidate gene model encoding a DICER-LIKE3 (DCL3) protein having a likely role in RdDM. In plants, specific DCL proteins process distinct sized sRNAs from double-stranded RNA precursors. Sequencing this dcl3 candidate gene, we identified single transition-type lesions predicting protein dysfunction in all four mutant rmr5 alleles. We also found sRNA profiles of rmr5 mutants replete of 24¬ nucleotide (nt) RNAs, strongly indicating that rmr5 encodes DCL3. Unlike in the eudicot Arabidopsis thaliana, DCL3 is required for normal maize growth and development consistent with a potentially broader role for RdDM in the grasses. Additionally, comparisons of 5’-methylcytosine profiles at various positions in the maize genome show that DCL3-derived 24 nt RNAs are not required for DNA methylation typical of RdDM. Our analyses indicate that loss of 24 nt RNAs can be compensated by alternate, yet RdDM effective, small RNA size classes. These findings point to a specific role of the 24nt RNAs in affecting paramutations.

References:
1. Hollick, J.B. and Erhard, K. F. (2011). Paramutation: a Process for Acquiring trans-Generational Regulatory Stress, Curr Opin Plant Biol, 14, 1-7.
2. Bond, D.M. and Baulcombe, D.C. (2014) Small RNAs and Heritable Epigenetic Variation in Plants, Trends Cell Biol, 24, 100-107.
3. Hollick, J.B. (2012). Paramutation: a trans-homolog interaction affecting heritable gene regulation, Curr Opin Plant Biol, 15, 536-543.

Keywords: RdDM, DCL3