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Thursday, July 25, 2019 at 12:20pm
Postdoctoral Fellow, Carnegie, Department of Plant Biology
Heather received a B.A. in premedical sciences in 2011 from Sarah Lawrence College and a Ph.D. in genetics, genomics, and development in 2016 from Cornell University.
Heather initiated a pioneering scientific project to identify the molecular mechanisms that plants use to sense and respond to seasonal temperatures in order to regulate flowering time and reproduction. Timing of reproduction is critical for plant success and is particularly important with global temperature rise. This project is an interdepartmental collaboration between the Ehrhardt lab and Yixian Zheng’s lab at the Department of Embryology initiated with a Carnegie Venture Grant.
Abstract: Intrinsically disordered proteins (IDP) are promiscuous by nature. They lack stable tertiary structures, which allows them to change their shape and function under different physiological conditions. This can be highly advantageous for plants, which often use changes in their environment to trigger developmental events. For instance, some plants use exposure to winter temperatures as a cue to initiate flowering the following spring. Many of the genes involved in temperature-dependent flowering have been extensively studied in Arabidopsis thaliana, yet how plants perceive temperature changes to trigger these responses is poorly understood. Here we investigate if the IDP and flowering-time determinant, SUPPRESSOR OF FRIGIDA 4 (SUF4), undergoes temperature-dependent phase separation to regulate flowering time. IDPs are excellent environmental sensor candidates because they have been demonstrated in vitro and in vivo to be sensitive to physical conditions experienced by plants, including temperature, and a significant portion of plant proteomes are predicted to be enriched with IDPs but remain functionally uncharacterized. Using confocal microscopy, molecular genetics and biochemistry, we have discovered that SUF4 is temperature sensitive and phase separates both in vitro to form proteinaceous droplets and in vivo to promote assembly of the nucleolar cavity, an enigmatic membrane-less subdomain of the root nucleolus. Under ambient temperatures (20°C), SUF4 dynamically localizes to the nucleolar cavity and that this structure exhibits liquid-like behavior. However, when exposed to low temperatures (4°C), SUF4 is diffuse within the nucleoplasm and the cavity fails to form. Further, the disordered region of SUF4 is important for nucleolar cavity formation; plants expressing SUF4 with mutated disordered regions exhibit defects in nucleolar cavity formation and flower prematurely. Taken together, these results suggest the intriguing possibility that SUF4’s ability to undergo temperature-sensitive phase separation may be important for its function in temperature dependent flowering time, by perhaps acting through nucleolar cavity function.