Genetic and Epigenetic Regulation of Gametophyte Development and Transposon Expression in Maize

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

PI: Matthew M. S. Evans (Carnegie Institution of Washington) CoPIs: Donald L. Auger (South Dakota State University), John E. Fowler (Oregon State University), R. Keith Slotkin (The Ohio State University) and Erik W. Volbrecht (Iowa State University) Senior Collaborators: Allison Phillips (Wisconsin Lutheran College) and Jennifer Eustaquio (Stanford University) This project comprises foundational research on epigenetics and gene expression, and thus may have broad implications for the manifestation of important plant traits, particularly in crops with large numbers of transposons in their genomes. More specifically, gametophytes are central to plant reproduction; thus this project is directly relevant to several agricultural objectives (e.g., controlling pollen fertility, limiting pollen-mediated transgene flow, inducing apomixis), particularly given the project's focus on a crucial crop plant, maize. Additionally, the project will provide a data framework for other researchers to determine how gametophytes function and how they can be manipulated to generate improved crop plants. This project will train a number of undergraduate, graduate and post-graduate scientists in an interdisciplinary fashion through frequent exchanges between the partnering laboratories. Undergraduates will gain experience in modern laboratory techniques as well as computational analysis of large-scale data sets. Undergraduate students will simultaneously be trained as researchers and educators through Stanford University's Science in Service Program. Undergraduates learn to be Science Mentors for high school students and develop laboratory curricula that are then performed by local high school programs under the supervision of the undergraduate mentors. As part of the project, students from the high school programs also participate in the project, getting exposure to genetics and image analysis. Within the floral tissues of flowering plants, multicellular haploid female and male gametophytes produce the gametes that undergo fertilization to produce seeds. Although gametophytes are small and undergo few cell divisions, they are crucial for producing the next generation, and execute diverse biological processes. Plant seed formation and reproduction, and thus global agriculture, are dependent on gametophyte function. In spite of their critical role in plant reproduction, gametophyte function and development has largely been overlooked due to their small size and imbedded location within the parental tissue. The maize genome, like many crop plant genomes, harbors a large number of mobile DNA elements, called transposons, and control of these elements, often through regulation of epigenetic states, is critical for maintenance of gene function and genome structure. Gametophytes help set epigenetic states in the next generation, however little is known, especially in the female gametophyte, about how transposon expression is regulated, and how that control impacts the concurrent expression of protein-coding genes. This project will use tissue micro-dissection techniques and whole genome analysis to understand the mechanisms that underlie developmental regulation of epigenetic states and cellular functions in the gametophytes of both sexes in maize. This project will screen for new mutants and genes that function in gametophyte development; perform genome-wide analysis of expression of genes, transposons, and different classes of RNAs with cellular detail; generate visual reporters for transposon activity; and characterize transposon expression in developing gametophytes. This project will determine the spatial and temporal expression pattern for genes and transposons in developing gametophytes, as well as define how they function to program gametophyte development. The effect of relevant mutants on transposon expression is expected to increase understanding of the interaction between basic gametophyte development and control of transposon activity in the important crop plant, maize. The sequence gene expression data generated from this project will be widely accessible through the project website (www.maizegametophyte.org) and the National Center for Biotechnology Information Gene Expression Omnibus (www.ncbi.nlm.nih.gov/geo), and the Maize Genetics and Genomics Database (maizegdb.org). Seed stocks will be deposited with the Maize Genetics Cooperation Stock Center.