HCG: Epihybridity in Zea Mays

Ohio State University, The, Columbus OH

Investigators

Abstract

PI: Jay Hollick (Ohio State University) CoPI: William F. Tracy (University of Wisconsin - Madison) The general observation that hybrid offspring, in some manner or another, are larger than their parents is referred to as "hybrid vigor". Although this behavior serves to support much of the world's food supply, the biology behind this breeding behavior has remained remarkably intransient and the subject of much debate. The primary models accounting for hybrid vigor, and the reciprocal behavior of inbreeding depression, are based on the principles of Mendelian genetics. This project tests a novel model in which a form of non-Mendelian epigenetic inheritance contributes to these breeding behaviors. Epigenetic refers to heritable information that is adjunct to DNA, the widely recognized molecule of genetic transmission. "Epihybridity" is used here to describe that component of hybrid vigor attributable to dynamic changes in epigenetic sources of genomic, or epigenomic, variation. Field-based yield trials will be used to compare the extents of hybrid vigor and inbreeding depression occurring in normal corn (Zea mays) varieties versus derivatives in which the function of a specific molecule (RMR1) responsible for an RNA-based form of epigenetic inheritance is compromised. Primary studies indicate that RMR1 both enhances inbreeding depression and conditions parental genomes in ways that affect hybrid progeny traits. Using a high-resolution RNA sequencing approach, this project tests the idea that individual plants maintain unique RMR1-dependent small RNA populations and that hybrid progeny contain novel small RNA profiles that may specify gene expression patterns having complementary properties to growth and development. This project further uses an experimentally tractable example of hybrid vigor occurring at a single chromosome region responsible for producing plant pigments to identify specific DNA features that interface with this small RNA-based repression system. Understanding the nature of these features and this particular mechanism of eukaryotic genetics provides a novel perspective of RNA-based inheritance promising transformative impacts to the future of agriculture and human health. This project combines research groups from the Universities of Wisconsin (UW) and California (UCB), fostering scientific outreach across broad disciplines (epigenetics, genomics, and plant breeding) and providing education, scientific training and research experiences for a UCB graduate student, UW and UCB undergraduates, and high school students from the East Bay area. Minorities traditionally underrepresented in the sciences are engaged in these research activities through the support of existing high school and undergraduate programs promoting ethnic and socioeconomic diversity. The project will generate maize seed resources of potential interest to the hybrid seed industry [available from the project leader (hollick@nature.berkeley.edu) and from American Tissue Culture Collection (ATCC)], and academic researchers [available from the project leader and from the Maize Genetics Cooperation Stock Center (http://www.uiuc.edu/ph/www/maize)]. Nucleic acid sequence resources including small RNA profiles and limited genomic DNA sequence from an A619 inbred line will be generated and available for download from NCBI (http://www.ncbi.nlm.nih.gov/) or through a genome browser interface provided by MaizeGDB (http://www.maizegdb.org/). Data from the field trials will be made available through MaizeGDB. A BAC library representing the A619 inbred line will be constructed and available for community dissemination at cost by contacting the project leader. This BAC resource will likely provide material for an eventual genome resequencing project.