Epigenetic reprogramming of FLC

The Dean laboratory has been investigating what controls the timing of flowering. We are using a model plant Arabidopsis thaliana to identify genes involved in controlling flowering as in this plant it is easy to clone genes based on a mutant phenotype. Over the years we have shown that a key player in the regulation of flowering is a protein called FLC. FLC prevents flowering by stopping the activation of a set of genes needed to make flowers. FLC expression levels are reduced by prolonged cold and then remain stably off through the rest of the life-cycle of that plant. This stable repression is caused by chromatin silencing of the FLC gene through a conserved mechanism involving Polycomb group proteins. Before the next generation the levels of this gene need to be reset to ensure the progeny also need vernalization for flowering. This process may have many parallels with epigenetic reprogramming in mammals / the process that went wrong in the cloned sheep Dolly. We have mutations that disrupt the reprogramming of FLC and wish to exploit these to identify the molecular mechanisms involved. We will explore any parallels between FLC resetting and the epigenetic reprogramming that occurs in the mouse germline through a collaboration with Prof. Azim Surani in Cambridge. Our work on FLC epigenetic reprogramming is likely to produce concepts relevant to gene regulation throughout biology.

At a certain stage in their life-cycle plants undergo the transition from vegetative to reproductive development. The correct timing of this transition, flowering, is crucial for reproductive success so multiple environmental and endogenous signals are integrated to judge when to flower. The Dean laboratory is studying the importance of prolonged cold or winter for flowering, a process known as vernalization. The need for vernalization ensures plants overwinter vegetatively and flower in the favourable conditions of spring. Vernalization involves cold-induced and stable repression of a floral repressor, FLC by a Polycomb-mediated chromatin silencing mechanism. Unlike animals, the germ line in plant cells originates from somatic tissues of the flower so, after vernalization, FLC expression needs to be reset to ensure a vernalization requirement in the next generation. Recently, our lab in collaboration with others has shown using an FLC-GUS translational fusion that FLC levels are restored after vernalization, at different stages through male reproductive development and in early stages of embryo development. We have now used a Landsberg erecta line carrying an FLC-luciferase translational fusion to identify mutations disrupting the resetting of FLC expression. In this proposal we will utilize these mutations to further define the FLC reprogramming process, using two complementary approaches: (i) characterization of molecular signatures that define the resetting process; (ii) identification of factors that regulate or are directly involved in this process, to explore the molecular mechanisms involved. The results obtained from this work will help us to understand epigenetic reprogramming of Polycomb targets in plants and other organisms.