Low ABA concentration promotes root growth and hydrotropism through relief of ABA INSENSITIVE 1-mediated inhibition of plasma membrane H+-ATPase 2

[EN] The hab1-1abi1-2abi2-2pp2ca-1 quadruple mutant (Qabi2-2) seedlings lacking key negative regulators of ABA signaling, namely, clade A protein phosphatases type 2C (PP2Cs), show more apoplastic H+ efflux in roots and display an enhanced root growth under normal medium or water stress medium compared to the wild type. The presence of low ABA concentration (0.1 micromolar), inhibiting PP2C activity via monomeric ABA receptors, enhances root apoplastic H+ efflux and growth of the wild type, resembling the Qabi2-2 phenotype in normal medium. Qabi2-2 seedlings also demonstrate increased hydrotropism compared to the wild type in obliquely-oriented hydrotropic experimental system, and asymmetric H+ efflux in root elongation zone is crucial for root hydrotropism. Moreover, we reveal that Arabidopsis ABA-insensitive 1, a key PP2C in ABA signaling, interacts directly with the C terminus of Arabidopsis plasma membrane H+-dependent adenosine triphosphatase 2 (AHA2) and dephosphorylates its penultimate threonine residue (Thr(947)), whose dephosphorylation negatively regulates AHA2.We are grateful for grant support from the National Key R&D Program of China (2017YFE0118100 and 2018YFD02003025), National Natural Science Foundation of China (nos. 31600209, 31761130073, and 31872169), a Newton Advanced Fellowship (NSFC-RS: NA160430), Fujian Province Education Department Funding (JK2017015), and Research Grant of FAFU (KXGH17005). Work in the laboratory of P.L.R. was supported by the Ministerio de Ciencia, Innovacion y Universidades (MICIU), grant BIO2017-82503-R.Miao, R.; Yuan, W.; Wang, Y.; Garcia-Maquilon, I.; Dang, X.; Li, Y.; Zhang, J.... (2021). Low ABA concentration promotes root growth and hydrotropism through relief of ABA INSENSITIVE 1-mediated inhibition of plasma membrane H+-ATPase 2. Science Advances. 7(12):1-14. https://doi.org/10.1126/sciadv.abd411311471