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Mailing Address:
The Robert H. Smith Institute of
Plant Sciences and Genetics
in Agriculture
POB 12, Rehovot 76100, Israel

Administrator: Neomi Maimon 
Tel: 972-8-948-9251,
Fax: 972-8-948-9899,

Director: Prof. David Weiss
Tel: 972-8-948-9436
Fax: 972-8-948-9899


A ligand-independent origin of abscisic acid perception


Sun, Y. ; Harpazi, B. ; Wijerathna-Yapa, A. ; Merilo, E. ; de Vries, J. ; Michaeli, D. ; Gal, M. ; Cuming, A. C. ; Kollist, H. ; Mosquna, A. A ligand-independent origin of abscisic acid perception. Proceedings of the National Academy of Sciences of the United States of America 2019, 116, 24892-24899.


Land plants are considered monophyletic, descending from a single successful colonization of land by an aquatic algal ancestor. The ability to survive dehydration to the point of desiccation is a key adaptive trait enabling terrestrialization. In extant land plants, desiccation tolerance depends on the action of the hormone abscisic acid (ABA) that acts through a receptor-signal transduction pathway comprising a PYRABACTIN RESISTANCE 1-like (PYL)–PROTEIN PHOSPHATASE 2C (PP2C)–SNF1-RELATED PROTEIN KINASE 2 (SnRK2) module. Early-diverging aeroterrestrial algae mount a dehydration response that is similar to that of land plants, but that does not depend on ABA: Although ABA synthesis is widespread among algal species, ABA-dependent responses are not detected, and algae lack an ABA-binding PYL homolog. This raises the key question of how ABA signaling arose in the earliest land plants. Here, we systematically characterized ABA receptor-like proteins from major land plant lineages, including a protein found in the algal sister lineage of land plants. We found that the algal PYL-homolog encoded by Zygnema circumcarinatum has basal, ligand-independent activity of PP2C repression, suggesting this to be an ancestral function. Similarly, a liverwort receptor possesses basal activity, but it is further activated by ABA. We propose that co-option of ABA to control a preexisting PP2C-SnRK2-dependent desiccation-tolerance pathway enabled transition from an all-or-nothing survival strategy to a hormone-modulated, competitive strategy by enabling continued growth of anatomically diversifying vascular plants in dehydrative conditions, enabling them to exploit their new environment more efficiently. © 2019 National Academy of Sciences. All rights reserved.