Phenotypes are determined by both genetic (i.e. DNA sequence-dependent) and epigenetic factors (i.e. reversible, DNA sequence-independent modifications of chromatin). Sequence-based information is essential to define phenotypic outcome, but depends on the establishment of a proper chromatin environment (the epigenome), which determines the transcriptional competence of genes. Given their role in gene expression, epigenetic factors are of great interest for fundamental as well as translational research, and understanding the interplay between genetic and epigenetic factors is an important, open question in plant biology.
Owing to its relative simplicity as an experimental model, Arabidopsis thaliana has thus far provided the bulk of our current understanding of epigenetic regulations in plants. It is however a rather unusual plant species with a small genome size and a low proportion of repetitive elements, in sharp contrast to the genome of most crops. In addition, altering the epigenome in crops, particularly in maize, has profound developmental consequences. By contrast, Arabidopsis is highly resilient to epigenomic instability.
Reproductive development is of course central to plant breeding, yield, and food security. In contrast to animal models, however, where the relation between epigenetics and reproduction is a major theme of research, our understanding of the mechanisms controlling epigenome dynamics during plant reproduction remains rudimentary. However, published data indicate that, at many crop species, alterations of key enzymes controlling chromatin states results in altered reproductive development, including sterility, but also intriguing phenomena such as clear tendencies for clonal reproduction through seeds (a process known as apomixis in plants), or formation of unreduced gametes, both of which represent potentially very useful tools in plant breeding.
In this proposal, we proposed a dedicated effort to elucidate the role of chromatin regulation on reproduction in a crop species, using maize as our primary experimental model. Maize is a essential crop in both the US, where the host lab is located, and Europe. It is also an exceptional model to address the interplay between genetic and epigenetic factors, owing to a long history of epigenetic research, collections of mutants affecting epigenetic determinants, and, as far as this project is concerned, an exceptional cytology. The project relies on a unique collection of (mostly unpublished) maize mutants affecting chromatin factors acting during reproduction, and on the strong experience of the participants in both the construction of epigenetic maps, and the analysis of plant reproductive development. We hope to harness this expertise to assess the functional importance of key epigenetic pathways in shaping maize reproductive outcomes, and derive novel tools for plant breeding, as described below.
