Antag0onistic histone modifiers coordinate flooding stress tolerance and memory in plants

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Flooding is an increasing problem around the world. In addition to having devastating effects on people's homes and businesses, it severely impacts livestock and crop survival, which can ultimately affect farmer's livelihoods and food production. Many of the key crops we grow (wheat, rice, potatoes) are particularly susceptible to floods, which cause plant death by limiting oxygen availability. If we want to develop new improved crop varieties that have a better chance at withstanding floods, then we first need to understand how plants sense and respond to flooding stress at the molecular and genetic level. Lab based experiments on model plant species, such as Arabidopsis (a common weed), can help to identify the underlying biological principles that control flooding (and other) stress responses, which can then be the focus of more targeted breeding and biotechnology approaches in crops.An emerging phenomenon in plant stress biology is the concept that plants can sense and "remember" previous stresses by chemically modifying genes (referred to as epigenetics). We recently showed that a conserved plant protein called VRN2, which helps to establish this type of environmental epigenetic memory by switching off gene expression, increases in response to flooding stress. Therefore, we predicted it might be involved in promoting a memory of floods. We have now shown that Arabidopsis plants that were previous exposed to a flood have better survival rates than plants that did not receive this prior stress, and that this is dependent on VRN2. We have also identified a second protein, called REF6, that targets flood-associated genes. Interestingly, REF6 is also an epigenetic regulator, but works in the opposite way to VRN2 by activating gene expression. We propose that these antagonistic memory proteins are part of a previously uncharacterised network of flood-responsive regulators that is important or controlling short- and long-term gene expression changes that promote flooding resilience and provide plants with a positive memory of stress. With this grant, we will explore this concept in more detail, with particular focus on characterising the REF6 component.To achieve this, we will use a range of molecular, genetic, biochemistry and physiological experiments in Arabidopsis to answer the following questions: (1) What are flood-responsive gene targets of REF6? (2) How is REF6 targeted to these genes during floods? (3) What are the shared and distinct gene targets of REF6 and VRN2? (4) How does the combined activity of these proteins coordinate global gene expression to promote flooding stress tolerance and memory? By answering these questions, our work will reveal how flooding stress signals are directly converted into epigenetic changes, providing fundamental new and detailed insight into how plants can sense, respond, and adapt to stresses in their environment. Whilst Arabidopsis is not a crop, it is hoped that the results of this project will provide plant breeders and biotechnologists with new information that could help them to develop improved varieties of important crops that are better able to withstand floods, and which will help to improve global food security.