Arabidopsis 2010: Defining the Role of Nurse Cells in the Propagation of Transposable Element Epigenetic Silencing

Ohio State University, The, Columbus OH

Investigators

Abstract

The DNA in multicellular organisms does not exclusively code for genes. Rather, most organisms' genome, including humans, is also composed of ancient viruses and other parasites call 'jumping genes' or transposable elements (TEs). TEs are fragments of DNA that have the ability to move from one location to another in the genome. When active, TEs have the potential to jump into genes and generate mutations, chromosome breakage and genomic instability. To inhibit the formation of new mutations associated with active TEs, plants, animals and fungi possess a mechanism to suppress and silence TE activity. This mechanism is based on degradation of TE RNA transcripts into TE small RNAs. These TE small RNAs result in the marking of the TE DNA with a molecular flag (such as DNA methylation or post-translational histone modification) that tells the cell to silence the TE. This ?flag? or gene regulatory information on the DNA can be passed through cell division without being reset in an event termed epigenetic inheritance. In plants (and in some cases animals), this information can also be inherited from one generation to the next, helping offspring determine what protein coding regions of DNA are genes and should be expressed, and which are TEs and should be silenced. This project aims to determine how epigenetic information is passed from one generation to the next. In flowering plants, each pollen grain consists of sperm cells and a non-germinal nurse cell termed the pollen vegetative cell. The sperm cells depend on the pollen vegetative cell for delivery to the female egg, but only the DNA of the sperm cells is passed on to the next generation. The nucleus of the pollen vegetative cell undergoes a loss of epigenetic silencing of TEs, resulting in an increase in TE RNA and some new TE small RNAs. In the model flowering plant Arabidopsis thaliana, investigation will focus on 1) whether TE reactivation in the pollen vegetative cell influences the silenced state of sperm cell TEs, and 2) if the increased TE small RNAs in the pollen grain help to reinforce TE silencing in the next generation. 3) Research will focus on how heritable information is physically passed from the non-germinal pollen vegetative cell to the germinal sperm cells. This research has the potential to shift the understanding of parental nourishment, and how multicellular organisms pass heritable information to their offspring. Broader Impacts This project will impact the education, training and enrichment of students at each academic level from middle school to post-doctoral. An educational outreach course is taught annually to middle school students from The Ohio State Young Scholars Program, which specializes in providing academic enrichment and career exploration experiences to racial and ethic minorities under represented in STEM fields. High school students will perform senior research projects in the laboratory in collaboration with The Metro School, part of The Ohio State University STEM Learning Network. Undergraduate students will gain summer educational enrichment and exposure to science as a career option through The Ohio State Research Experience for Undergraduates. Through collaborations with outreach organizations at the middle school and high school levels, as well as diversity programs for undergraduate, graduate and post-doctoral students, this project will serve as an educational tool for the development of new scientists.