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INVESTIGATOR: Robbins, M.; Chopra, S.

PERFORMING INSTITUTION:
PENNSYLVANIA STATE UNIVERSITY
208 MUELLER LABORATORY
UNIVERSITY PARK, PENNSYLVANIA 16802

IDENTIFICATION AND CHARACTERIZATION OF STRESS-INDUCED EPIALLELES IN MAIZE

NON-TECHNICAL SUMMARY: Global climate change models forecast elevated temperatures and severe food scarcity if a greater yield is not achieved by enhancing the stress tolerance of crops. The current rate of crop yield increases pales in comparison to the amount needed to meet the needs of future generations. In fact, the most impoverished areas in the world currently facing these problems would be decimated if science cannot provide a solution for obtaining higher crop yields under suboptimal conditions. A typical molecular breeding approach is to map genes associated with tolerance to specific stresses and subsequently introgressing these beneficial alleles into local varieties. These traditional approaches will continue to modestly improve crops over time; however, other unique avenues that manipulate a plant's natural response to physiological conditions by adjusting its epigenetic gene regulation will have to be implemented to keep up with demand. Recent evidence shows that plants challenged with stress produce progeny that can be more fit when challenged with the same stress. However, this beneficial effect has thus far only been shown to happen in the immediate generation following stress application. The epigenetic modifications responsible for the benefits of prior stress exposure were not stable. We have therefore decided to focus on a phenotypic marker for stress that is maintained over generations in the absence of the inducing high-temperature stress. This will allow us to isolate novel stress-induced epialleles that may function in transgenerational adaptation to stress. The feasibility of using stress-induced epialleles in breeding programs will be tested by examining the transcriptional and epigenetic state of epialleles during the initial phase of introgression. We aim to learn how progeny of stressed plants could be a genetic source in breeding programs to improve stress tolerance.

OBJECTIVES: Stress threshold tests show that plants exposed to environmental stress produce progeny that can be more tolerant when treated with the same stress. The initial stresses produce global epigenetic changes that are correlated with the meiotic heritability of the resistance response. However, very little is known about which loci are heritably epigenetically modified to result in changed expression and a heightened stress response. Moreover, a limited number of previous studies have suggested that after one generation, the benefits of parental stress treatments were no longer observed. This is likely due to the instability of gene expression changes at affected loci. This project aims to identify meiotically-heritable stress-induced epialleles. Since epigenetic modifications are often variable and unstable, this research employs a marker gene with a conspicuous phenotype that is maintained for multiple generations after stress induction. The marker gene is epigenetically-silenced and the level of silencing is modulated by temperature-stress. We will use global transcriptional approaches to identify other epialleles that are modified by temperature in a transgenerational manner similar to our marker gene. We will then profile the epigenetic state of the top candidate genes generated by transcriptional profiling. Once stress-induced epialleles are identified, we aim to test the stability of their epigenetic state during the initial phase of introgression. From this research we hope to learn if stress-induced epialleles can be used in breeding programs to potentially protect plants against abiotic stress. If successful, pre-stressed plants could be a genetic source in breeding programs to improve stress tolerance.