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.

Many proteins fold through intermediates that are populated in the submillisecond time regime. To monitor directly the formation of these kinetic intermediates, we have developed a simple, robust, easy to assemble continuous flow mixer for studying folding reactions in the $35–1000\mu \mathrm{s}$ time regime. The mixer is constructed by laser-machining $75\text{-}\mu \mathrm{m}$ channels in a $127\text{-}\mu \mathrm{m}$ -thick polyimide or polyetheretherketone polymer wafer. Mixing times of $\sim 25\text{to}\sim 50\mu \mathrm{s}$ can be achieved for a $1∕10$ dilution reaction of $8\mathrm{M}$ urea with flow rates of $10–20\mathrm{mL}∕\min$ . CCD-based steady-state and time-correlated single-photon-counting-based fluorescence detection strategies are described. Preliminary results on the early events in the refolding of cytochrome c are presented.