Enhancing stress tolerance using a phase-dependent stress response

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Climate change threatens global crop production. These threats vary in frequency, type and severity depending on geographic location. As a consequence, crops grown across latitudinal zones require diverse coping strategies. To ensure the future of crop production, this project will apply an imaginative model for crop improvement based on the plant’s circadian clock, an internal timekeeper that enables plants to coordinate growth with the environment in accordance with the daylength. This internal oscillator, much like the human circadian clock, controls when physiological and metabolic changes occur throughout the day. As a result, plants under stress turn on and off certain genes at specific times of day to modulate physiological responses. The energy cost associated with a stress response is high and while turning these genes on indefinitely can provide stress tolerance it often leads to a significant reduction in yield. This project will test whether cold stress tolerance can be achieved by modifying the timing of the response through fine-tuning when these genes are turned on and off and monitoring the physiological impact on growth. These tests will be performed in the model plant Arabidopsis and crop Brassica rapa, a diverse crop that includes Chinese cabbage, turnip, oilseed and leafy vegetable varieties that have a wide range of cold tolerance traits to be studied. The methods and tools used to create these modifications will be made available to the scientific community to allow for implementation in other crop systems against a variety of stresses to improve yield throughout the U.S.Current models for abiotic stress improvement often rely on over-expression of identified transcription factors (TFs) that confer improved stress response but come at a cost to overall growth and yield. As a central integrator of environmental signals, the circadian clock provides a unique target for optimizing responses to the environment while maintaining proper physiological processes. This project incorporates time dependent transcriptome and physiological cold stress datasets from diverse B. rapa and Arabidopsis genotypes into temporal gene regulatory networks (GRNs). These GRNs will be used to identify Temporal Stress Regulator (TSR) TFs that are associated with cold tolerant genotypes. TSRs showing altered temporal responses between tolerant and sensitive genotypes will be selected for phase-dependent TSR synthetic constructs. CRISPR/Cas9 techniques will be used to adjust the expression of the native TSR in the sensitive genotype to mimic the pattern observed in the tolerant genotype. These phase-altered TSRs that are integrated into the circadian and/or diel networks will be tested for improved stress tolerance using physiological measures of PSII efficiency, growth rate, flowering time and biomass. Transcriptome profiling of successfully altered genotypes will be performed with temporal resolution to identify the degree of GRN reorganization and improve future model predictions. In addition to providing data analysis tools and techniques for applying this method to other crops, a plant stress education module will be introduced to middle school students to introduce them to plant biology and help prepare them for STEM-based careers.This award was co-funded by the Plant Genome Research Program and the Physiological Mechanisms and Biomechanics Program in the Division of Integrative Organismal Systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.