Plants might use prions to form memories
A. thaliana. Image courtesy of Peggy Greb (US Department of Agriculture).
Every spring, plants bloom depending on factors such as hydration, temperature, and vernalization, a process that helps form a memory of experienced winter. However, the molecular mechanism underlying such memory remains incompletely understood. Because prions have been implicated in neuronal synapse maintenance in fruit flies and sea slugs, Sohini Chakrabortee et al. (pp. 6065–6070) sifted through the sequences of the entire set of proteins in Arabidopsis thaliana using an algorithm tailored to detect prion-like protein domains in yeast. The authors identified 474 candidate proteins, narrowed the analysis to three proteins implicated in flowering-associated gene expression, and tested the proteins’ prion-like properties using established methods in yeast. Among these proteins, Luminidependens (LD) met the defining criteria for a prion: the ability to maintain an oligomeric self-replicating state that can consistently and heritably alter the function of an associated yeast protein domain in lab experiments. Further, when grafted onto the yeast prion Sup35, the LD prion domain functionally replaced the yeast prion domain, suggesting that LD might be a bona fide prion and likely the first prion to be reported in plants. According to the authors, plants’ ability to distinguish winter from unseasonably cold spells might be tied to proteins such as LD, which might help trigger or mediate epigenetic changes associated with vernalization and flowering. — P.N.
Gene duplication and gene output in Drosophila
Gene duplication represents a primary driver of evolution in all organisms. When two copies of a gene exist, one copy is free to acquire a novel function, but little is known about the short-term consequences of single gene duplication. To test a hypothesis that gene expression is doubled when two copies exist, David Loehlin and Sean Carroll (pp. 5988–5992) examined the Alcohol dehydrogenase (Adh) gene in fruit flies. The authors found that naturally occurring tandem duplications of this gene result in 2.6-fold increased expression of the gene, and the tandem duplication yields more gene product than two copies of Adh found on different chromosomes, suggesting that the tandem arrangement enhances activity more than copy number alone. Further, the authors constructed tandem duplications of the unrelated synthetic reporter gene vgQ-lacZ in fruit flies and measured gene output at various positions on the genome. At all sites tested, this duplication resulted in 2.3- to 5.1-fold increased activity, compared with the singleton gene. According to the authors, the findings suggest that nonlinear gene enhancement may be a general property of tandem gene duplication. — T.J.