The phytohormone abscisic acid (ABA) regulates the expression of many genes in plants; it has critical functions in stress resistance and in growth and development1,2,3,4,5,6,7. Several proteins have been reported to function as ABA receptors8,9,10,11,12,13, and many more are known to be involved in ABA signalling3,4,14. However, the identities of ABA receptors remain controversial and the mechanism of signalling from perception to downstream gene expression is unclear15,16. Here we show that by combining the recently identified ABA receptor PYR1 with the type 2C protein phosphatase (PP2C) ABI1, the serine/threonine protein kinase SnRK2.6/OST1 and the transcription factor ABF2/AREB1, we can reconstitute ABA-triggered phosphorylation of the transcription factor in vitro. Introduction of these four components into plant protoplasts results in ABA-responsive gene expression. Protoplast and test-tube reconstitution assays were used to test the function of various members of the receptor, protein phosphatase and kinase families. Our results suggest that the default state of the SnRK2 kinases is an autophosphorylated, active state and that the SnRK2 kinases are kept inactive by the PP2Cs through physical interaction and dephosphorylation. We found that in the presence of ABA, the PYR/PYL (pyrabactin resistance 1/PYR1-like) receptor proteins can disrupt the interaction between the SnRK2s and PP2Cs, thus preventing the PP2C-mediated dephosphorylation of the SnRK2s and resulting in the activation of the SnRK2 kinases. Our results reveal new insights into ABA signalling mechanisms and define a minimal set of core components of a complete major ABA signalling pathway.
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We thank R. Bressan for helpful discussions and for editing of the manuscript. This work was supported by National Institutes of Health grants (J.-K.Z.) and MICIIN and CSIC fellowships (S.R. and R.A.).
Author Contributions H.F. contributed Figs 2a–c, e, 3, 4a–c and Supplementary Fig. 4. V.C. contributed Fig. 1a–d and Supplementary Fig. 1a, b. A.R., S.R., R.A. and P.L.R. contributed Fig. 2d and Supplementary Figs 2 and 3. S.-Y.P. and S.R.C. assisted with the generation of recombinant proteins, and S.R.C. helped edit the manuscript. J.S. assisted with protoplast assays. J.-K.Z. designed the experiments, and wrote the paper together with V.C. and H.F.
This file contains Supplementary Figures 1-4 with Legends.
About this article
Horticulture Research (2019)