PYL8 mediates ABA perception in the root through non-cell-autonomous and ligand-stabilization-based mechanisms

[EN] The phytohormone abscisic acid (ABA) plays a key role regulating root growth, root system architecture, and root adaptive responses, such as hydrotropism. The molecular and cellular mechanisms that regulate the action of core ABA signaling components in roots are not fully understood. ABA is perceived through receptors from the PYR/PYL/RCAR family and PP2C coreceptors. PYL8/RCAR3 plays a nonredundant role in regulating primary and lateral root growth. Here we demonstrate that ABA specifically stabilizes PYL8 compared with other ABA receptors and induces accumulation of PYL8 in root nuclei. This requires ABA perception by PYL8 and leads to diminished ubiquitination of PYL8 in roots. The ABA agonist quinabactin, which promotes root ABA signaling through dimeric receptors, fails to stabilize the monomeric receptor PYL8. Moreover, a PYL8 mutant unable to bind ABA and inhibit PP2C is not stabilized by the ligand, whereas a PYL85KR mutant is more stable than PYL8 at endogenous ABA concentrations. The PYL8 transcript was detected in the epidermis and stele of the root meristem; however, the PYL8 protein was also detected in adjacent tissues. Expression of PYL8 driven by tissue-specific promoters revealed movement to adjacent tissues. Hence both inter- and intracellular trafficking of PYL8 appears to occur in the root apical meristem. Our findings reveal a non-cell-autonomous mechanism for hormone receptors and help explain the nonredundant role of PYL8-mediated root ABA signaling. Work in the P.L.R. and F.M. laboratories was supported by the Ministerio de Ciencia e Innovacion, Fondo Europeo de Desarrollo Regional and Consejo Superior de Investigaciones Cientificas Grants BIO2014-52537-R and BIO2017-82503-R (to P.L.R.) and BIO2015-64307-R (to F.M.). J.L.-J. was supported by a Juan de la Cierva contract from Ministerio de Economia y Competitividad (MINECO) and by the Marie Sklodowska-Curie Action H2020-MSCA-IF-2015-707477. B.B.-P. was funded by Programa VALi+d GVA APOSTD/2017/039. J.J. was supported by a FPI contract from MINECO and M.A.F. by a Formacion de Profesorado Universitario contract from MINECO. D.D. and M.J.B. were supported by Biotechnology and Biological Sciences Research Council Grant BB/M002136/1 and Leverhulme Trust Grant RPG-2016-409. Belda-Palazón, B.; Gonzalez-Garcia, M.; Lozano Juste, J.; Coego Gonzalez, A.; Antoni-Alandes, R.; Julian-Valenzuela, J.; Peirats-Llobet, M... (2018). PYL8 mediates ABA perception in the root through non-cell-auton