Sohini Chakrabortee, Can Kayatekin, Greg A. Newby, Marc L. Mendillo, Alex Lancaster, and Susan Lindquist

Significance

Prion proteins provide the best-understood mode for protein-based molecular memory. Since their discovery in mammals, prions have been identified in diverse organisms including fungi, Aplysia, and Drosophila, but not in the plant kingdom. Applying methods we used to uncover yeast prions, we identified nearly 500 Arabidopsis proteins that harbor potential prion-like domains (PrDs). At least one of these domains, Luminidependens PrD, had some of the classical characteristics of prion proteins when tested experimentally in yeast, making it, to our knowledge, the first protein from the plant kingdom with bona fide prion attributes. Importantly, Luminidependens is involved in the process of flowering, a crucial development course that integrates several internal and external cues, including memories of winter, for its regulation.  

Abstract

Prion proteins provide a unique mode of biochemical memory through self-perpetuating changes in protein conformation and function. They have been studied in fungi and mammals, but not yet identified in plants. Using a computational model, we identified candidate prion domains (PrDs) in nearly 500 plant proteins. Plant flowering is of particular interest with respect to biological memory, because its regulation involves remembering and integrating previously experienced environmental conditions. We investigated the prion-forming capacity of three prion candidates involved in flowering using a yeast model, where prion attributes are well defined and readily tested. In yeast, prions heritably change protein functions by templating monomers into higher-order assemblies. For most yeast prions, the capacity to convert into a prion resides in a distinct prion domain. Thus, new prion-forming domains can be identified by functional complementation of a known prion domain. The prion-like domains (PrDs) of all three of the tested proteins formed higher-order oligomers. Uniquely, the Luminidependens PrD (LDPrD) fully replaced the prion-domain functions of a well-characterized yeast prion, Sup35. Our results suggest that prion-like conformational switches are evolutionarily conserved and might function in a wide variety of normal biological processes.

See: http://www.pnas.org/content/113/21/6065.full

PNAS May 24 2016; vol.111; no.21: 6065–6070

Figure 1: Characterization of the candidate Arabidopsis PrDs in S. cerevisiae. (A) HMM prediction of the cArabPrDs. The Arabidopsis proteome was searched for candidate prion domains by using the HMM. Predicted prion domains of LD, FPA, and FCA are highlighted in red. (B) Fluorescent microscopy images of yeast cells expressing the GFP-tagged Arabidopsis cPrDs. Samples were collected at 4 and 7 h. (C) Western blot analysis of a semidenaturing agarose gel of the cArabPrD-GFPs using α-GFP. Amyloid fractions are marked as high-molecular-weight fraction (HMW); small oligomers are marked as low-molecular-weight fraction (LMW). The Sup35 PrD (NM) was used as control. B, boiled fraction; NB, not boiled.