A Molecular Framework for Environment Responsive Chromatin Modification in Plants

To survive in changing environments, plants have to be able to sense their surroundings and modify how they grow and develop. Furthermore, in contrast to animals, plants cannot move and so they have had to evolve different ways in which to quickly and accurately do this. One way in which both animals and plants respond to the environment is through altering their gene expression by modifying specific proteins (histones) in the protein scaffold (chromatin) that supports their DNA.

For example, a protein complex called the 'polycomb repressive complex 2' (PRC2) is involved in adding a chemical mark called methylation to histones, which causes genes to be switched off. The PRC2 is found in animals and plants, but interestingly most plants have a larger variety of the different proteins making up the complex, which means they have a broader range of potential combinations.

This means that plants have a larger 'tool kit' for controlling the specificity and timing of chromatin methylation.

The PRC2 in plants is involved in a variety of different processes, including the regulation of seed development and germination, and coordinating flowering in spring after winter. In several cases the specific genes that are methylated are known. However, we still know very little about how the PRC2 directly senses the outside world to trigger these changes only when they are needed.

We recently showed that a plant PRC2 protein called VERNALIZATION2 (VRN2) is usually very unstable, but can accumulate under certain environmental conditions, including during flooding and exposure to cold temperatures. This suggests that VRN2 might act as a 'sensor' component of the PRC2 in flowering plants that ensures methylation of certain genes is only triggered under the right environmental conditions. However, at present we still do not know much about what happens once VRN2 is stabilised.

Using a range of molecular, biochemistry, genetic and cell biology approaches in Arabidopsis (a plant model organism) we seek to address this gap in our knowledge by answering several timely questions: (1) How do increases and decreases in VRN2 affect the other PRC2 variants and shape the PRC2 landscape? (2) What are the genome-wide targets of stable VRN2-PRC2? (3) How do environment triggered increases in VRN2 translate into plant developmental changes? By answering these questions using diverse experimental approaches across three integrated work packages, we will uncover valuable new knowledge about how plants are able to coordinate chromatin methylation to modify development in response to their environment.

This work will provide a step-change in our understanding of how plants directly translate environmental changes (e.g. the seasons, or stresses such as floods) into chromatin modifications that reprogram gene expression to align growth and development with the prevailing conditions. Crucially, we previously showed that the mechanism controlling VRN2 abundance is widely conserved in flowering plants - including crop species.

As such, the fundamental new insights we uncover with this work should have longer term impact, as they will identify new molecular targets that biotechnologists and plant breeders can use to improve agriculturally important traits related to growth and stress-resilience, which is a key aim for ensuring global food security.