How an individual's genes are activated or silenced is an essential question impacting all fields of biology. Gene expression patterns, i.e. which genes are on and which are off in different tissues and during development, are highly reproducible among individuals of each species and those patterns are efficiently reset every generation. One exception to these genetic rules is paramutation in maize. Paramutation leads to certain genes becoming silenced and that silencing is retained when the genes are transmitted to offspring. Depending on which genes are silenced dramatic changes in the plant's growth and development can be observed. Prior work has demonstrated that these heritable changes in gene expression are mediated by RNA, demonstrating RNA is not just a vehicle for DNA's commands; it is able to issue its own commands that alter how genes are expressed in the next generation. This project is to characterize a gene that is required for paramutation, mop3 (mediator of paramutation3). Initial research has demonstrated that mop3 acts at a distinct step in RNA mediated gene silencing relative to other previously characterized genes required for paramutation. Thus, new mechanistic insights should be gained from further study of mop3 as well as from the isolation and characterization of additional genes required for paramutation, another major goal of this project. Understanding mechanisms for heritable changes in gene expression will provide new insights into how plants might mediate adaptive responses to a changing environment.
Broader Impacts: The investigators for this project have had a long standing commitment to training and outreach. During the past 12 years, 5 postdoctoral fellows, 8 graduate students, 45 undergraduate students, 10 high school students and 5 high school teachers have participated in the research efforts that generated the data that formed the basis for this project. The current research project will provide training for two undergraduate students each year and a high school teacher and her students. The high school teacher will participate in a summer internship each year that will involve direct participation in the experiments and designing curriculum to engage the high school students during the academic year. The teacher will participate in a broad network with other teachers so that each person's curriculum innovation can be shared and thus, contribute to an increase in the science literacy of a larger number of students.
How an individual’s genes are activated or silenced is an essential question impacting all fields of biology. Usually gene expression patterns, i.e. which genes are on and which are off in different tissues and during development, are highly reproducible and those patterns are efficiently reset in the next generation of progeny. Paramutation, which we study, represents an exception to these genetic rules, in that for certain genes the silencing that is established in an individual is efficiently transmitted to their progeny. Importantly, in these subsequent generations the silenced gene continues to silence other active versions of that gene. Our prior work demonstrated that these heritable gene expression changes are not accompanied by changes in DNA sequence, therefore they are mediate by control mechanisms superimposed on the DNA sequence. It is highly unusual for non-DNA changes in gene expression to be efficiently transmitted to subsequent generations. Our research took a genetic approach to uncover the underlying mechanism. We succeeded in isolating and characterizing a number of mutations in genes that are required for paramutation. Identifying what these genes are revealed hypotheses for how they function to mediate heritable gene silencing. We have shown that the multiple, closely related, plant-specific RNA olymerases, the enzymes that produce RNA from either DNA or RNA templates, are mediating gene silencing through specific DNA sequences associated with the silenced genes. Results from our experiments suggest testable models for the role of these polymerases in multiple gene silencing processes. Interestingly our data also suggest that these enzymes have diverged functions in maize relative to the other plant species that has been well studied. Understanding mechanisms for heritable changes in gene expression has major implications for researchers studying complex traits with eventual applications in improving agricultural species’ responses to environmental changes and tackling diseases in animals, plants and humans. Our data and interpretations have been published in peer-reviewed journals and the maize stocks have been deposited in a public repository, the Maize Genetics Stock Center. We mentored one high school teacher, two high school students, a minority undergraduate student, and two faculty members from a community college. All summer interns were involved in all stages of mutant isolation and characterization in the field and laboratory settings. While an intern in the laboratory, one of the high school teachers developed a plan for remodeling her high school classroom into a biotech teaching laboratory. She used the practical experience gained during her internships to design the laboratory, order equipment, establish safety protocols, and develop laboratory teaching plan, which included the latest genomics methods.
