Charting the protein modifications systems that underpin submergence tolerance in rice

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Climate change models predict that large areas of Northern Europe and Asia is likely to experience flooding in the next 50 years. Currently flooding affects rice cultivation across 20 million hectares in Asia. To stabilize crop yields it is imperative to increase the capacity of cereal and vegetable crops to endure partial to complete submergence. This has been feasible for rice, due to the identification of the SUBMERGENCE 1A gene (SUB1A, (encoding a group VII ETHYLENE RESPONSE FACTOR [ERFVII] transcription factor) providing tolerance to complete submergence for over 7 days. The molecular characterization of SUB1A has begun to provide new insights into molecular, physiological and developmental processes that underlie an effective submergence survival strategy in plants. While SUB1A is important to ensure rice productivity in vast flood prone areas of the world, recent increases in frequency and magnitude of submergence due to extreme flooding events across Asia has negatively impacted SUB1A efficacy. New knowledge and resources are urgently needed that can boost SUB1A efficacy in mediating flooding tolerance. Recent evidence indicates that a difference in levels of flooding tolerance of SUB1A introgressed lines may be due to either transcriptional or post-transcriptional mechanisms that affect SUB1A activity. Our preliminary evidence suggests that the stability of the SUB1A protein is likely to be critical in mediated prolonged submergence tolerance in rice.The project partners have discovered that SUB1A protein stability (and therefore activity) is affected by two major post-translational mechanisms, ubiquitylation and SUMOylation. By exploiting this new knowledge we aim to pave the way to develop new rice varieties in which the SUB1A protein is more stable and active during prolonged flooding, generates enhanced submergence tolerance and therefore greater stability of yield. This proposal also aims to exploit the project partners unique insight and world leads into post-translational mechanisms (PTMs), including N-end rule based Ubiquitylation and SUMOylation, to identify new molecular regulators that control submergence response in plants. This could lead the development of a new generation of flooding tolerant crop varieties.Overarching hypotheses of the proposal: 1. Manipulating protein modifications that govern SUB1A stability can lead to extended flooding tolerance in rice. 2. Protein modification systems can be exploited to identify new regulators of submergence tolerance in rice.These 2 hypotheses will be tested by 3 main objectives within the 3 year project.1. To investigate the interaction between the molecular and environmental factors that affect SUB1A stability and posttranslational state. 2. To test for submergence tolerance and (time permitting) cross-tolerance to multiple abiotic stresses in transgenic rice plants that manipulate the regulatory components of SUB1A stability. 3. Discover novel regulators of flooding tolerance by exploiting preliminary data that indicates the presence of new targets that affects plant survival and undergo both N-end rule mediated Ubiquitylation and SUMOylation during submergence induced hypoxia.Timeliness: Our preliminary observations demonstrating that posttranslational modifications are essential for SUB1A function provide a highly novel molecular explanation and conduit to enhanced flooding tolerance in rice. Characterization of the role of the PTMs in controlling SUB1A and definition of new regulators of submergence with solved molecular mechanisms will offer novel approaches for delivery of plants with robust flooding and wider abiotic stress tolerance.