Role of the intrinsically disordered protein PIR in Polycomb silencing and environmental responses in Arabidopsis

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The goal of this project is to uncover the molecular basis for plant survival under harsh conditions, such as drought. When plants experience a dry spell, subsets of genes in the genome are turned off, or silenced, by a protein regulator called Polycomb. This silencing helps the plant conserve crucial resources to survive the drought. Some aspects of how Polycomb works to silence genes is understood, but exactly how Polycomb targets the correct genes to silence in response to drought is still a mystery. Following up on clues obtained from recent studies, this project will study a newly identified protein called PIR, which may provide the missing link between drought and Polycomb action. Understanding this connection could have broad impacts for agriculture, as the findings would help plant breeders develop crop varieties that can grow better in dry environments. The project will also have educational impact by improving structured active learning activities in classroom settings, in both introductory and advanced biology courses. In addition, we will develop and disseminate research laboratory modules for engaging high school students in authentic research experiences. The educational activities are aimed at enhancing the success and retention of diverse groups of students in science and are expected to contribute to preparation of a future STEM workforce.In plants and animals, Polycomb protein complexes have long been recognized as key developmental regulators and much is known about how they repress gene expression by histone modification and chromatin compaction. In contrast, less is understood about how these regulators control gene expression in response to exogenous cues. This project will use the model plant Arabidopsis thaliana to study how drought stress influences silencing through interaction of the Polycomb Repressive Complex 2 (PRC2) with another protein, called Polycomb Interacting Repressor (PIR). Preliminary results provided evidence that PIR is linked to drought stress response and that it interacts genetically and physically with PRC2. These observations will be followed up to explore: how drought stress influences recruitment and activity of PIR/PRC2 complexes on chromatin; whether PIR functions as a non-stoichiometric auxiliary PRC2 component; and whether drought leads PIR, which is an intrinsically disordered protein, to form membrane-less phase-separated nuclear condensates, known as polycomb bodies. Together, the results should provide new mechanistic links between drought response and chromatin-based regulation. This award was co-funded by the Genetic Mechanisms Program (Division of Molecular and Cellular Biosciences) and by the Plant Genome Research Program and the Physiological Mechanisms and Biomechanics Program (Division of Integrative Organismal Systems), all in the Directorate for Biological Sciences.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.