Epigenomic Consequences of Increased Heterochromatin Load in Maize

Wendte Jered M, Athens GA

Investigators

Abstract

This action funds an NSF National Plant Genome Initiative Postdoctoral Research Fellowship in Biology for FY 2018. The fellowship supports a research and training plan in a host laboratory for the Fellow who also presents a plan to broaden participation in biology. The title of the research and training plan for this fellowship to Dr. Jered M. Wendte is "The Epigenomic Consequences of Increased Heterochromatin Load in Maize". The host institution for the fellowship is the University of Georgia and the sponsoring scientist is Dr. Robert J. Schmitz. A major problem facing humanity is the production of an adequate food supply for an exponentially increasing population. One promising strategy to address this problem is the modification of crop plant genomes to produce crop varieties with higher yields and desirable traits through genome engineering. Plant genomes are comprised of several long stretches of DNA, termed chromosomes. Each chromosome encodes thousands of genes, which provide the blueprint of an organism. This project will advance genome engineering technologies in the important cereal crop, maize, by evaluating two potential genome engineering strategies. The first involves the possibility of adding entirely new chromosomes to maize as a means to introduce desirable traits that are encoded by multiple genes. The second involves adding genes that encode proteins that chemically modify DNA to maize as a means to increase trait diversity in maize, which can then be selected on for desirable traits, such as drought or disease resistance. Training objectives include genomics, bioinformatics, and science communication. Broader impacts include participation in existing programs directed at introducing Hispanic and Native American communities to opportunities in plant genomics sciences. Epigenetic modification of chromatin plays a critical role in the maintenance of genomic stability by targeting repetitive sequences, such as transposable elements (TEs), for heterochromatin formation and transcriptional silencing. In plants, which are characterized by relatively large genomes mostly comprised of TEs that are targeted for heterochromatin formation, heterochromatin also plays an important role in phenotypic diversity. Between plant species, there is remarkable variation in the amount and distribution heterochromatin modifications within genomes. Also, within species, heritable changes in chromatin state, or epialleles, account for an important source of phenotypic variability. However, mechanistic explanations for these phenomena, including factors that influence variation in overall heterochromatin capacity and the initiating events that lead to epiallele formation, are currently lacking. Using advanced genomics techniques and novel genetic resources in maize, this project will address these knowledge gaps by 1) determining if a cell?s capacity for heterochromatin is limited, and what factors could be rate limiting by assessing the impacts of the introduction of large, multi-megabase quantities of genetic material in the form of supernumerary B chromosomes on maize heterochromatin structure; and 2) identifying the determinates of methyltransferase targeting and their role in the initiating events of epiallele formation by assessing the heterologous expression of DNA methyltransferases in maize. All data will be made available through public repositories including NCBI (https://www.ncbi.nlm.nih.gov/) and the host laboratory website (http://schmitzlab.genetics.uga.edu/data). If successful, this project will provide new important information that can be applied to help guide crop genome engineering design strategies for artificial chromosomes that have minimal detrimental impacts on heterochromatin regulatory pathways. Project outcomes will also help assess the potential of strategies for modulation of the epigenome to induce phenotypic variability that can be selected on for desirable traits. Keywords: maize, epigenetics, DNA methylation, heterochromatin, artificial chromosomes, genome engineering This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.