The Robert H. Smith
Institute of Plant Sciences and Genetics in Agriculture, Israel
“The Evolution of ABA Signaling”
The evolution of desiccation tolerance enabled the colonization of land by an aquatic algal ancestor. In land plants, this critical adaptation relies on abscisic acid (ABA), a regulator of responses to abiotic stress. In the seminar, I provide evidence of a progressive assembly of the ABA signaling over the course of 600 million years of evolution. Evidence from the streptophyte alga Zygnema suggests that ABA biosynthetic enzymes are already present and functional before the onset of terrestrialization. In algae, ABA levels remain low, likely reflecting a role as a metabolic intermediate rather than a dedicated signaling molecule. In parallel, PYL-like receptors exhibit ABA-independent inhibition of PP2Cs, suggesting that hormone perception evolved from a preexisting, ligand-insensitive regulatory module. This system was further refined in mosses through substitution within otherwise conserved domains, which suppressed basal activity and enabled ligand-dependent signaling, an example of convergent evolution toward enhanced ABA responsiveness. This strategy differs from angiosperms, where dimeric PYL receptors undergo dissociation to facilitate strict ABA-dependent PP2C inhibition, highlighting distinct adaptations in receptor evolution. Together, these findings support a stepwise evolutionary model in which ABA transitioned from a metabolic byproduct to a bona fide signaling molecule through the co-option of ancestral signaling components and progressive tuning of receptor properties. Please find attached a recent paper.
Short bio
Assaf received a PhD in Plant Sciences from Tel Aviv University, where his research focused on moss development and the regulation of reproductive product formation by the Polycomb complex. He then conducted postdoctoral research with Prof. Sean Cutler, working on engineering abscisic acid (ABA) receptors to respond to alternative ligands. Since 2014, Assaf is a faculty member at the Hebrew University’s Faculty of Agriculture. Assaf studies the natural and synthetic evolution of ABA signaling molecules. His group study how ABA signaling emerged from algae and diversified across plant lineages, and leverages these proteins to engineer novel enzymatic activities with agricultural applications.
If anyone is interested in meeting with the speaker, please contact Jorge Lozano (lojujo@ibmcp.upv.es)
