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Structural insights into the mechanism of abscisic acid signaling by PYL proteins


Abscisic acid (ABA) is an important phytohormone that regulates plant stress responses. Proteins from the PYR-PYL-RCAR family were recently identified as ABA receptors. Upon binding to ABA, a PYL protein associates with type 2C protein phosphatases (PP2Cs) such as ABI1 and ABI2, inhibiting their activity; the molecular mechanisms by which PYLs mediate ABA signaling remain unknown, however. Here we report three crystal structures: apo-PYL2, (+)-ABA-bound PYL2 and (+)-ABA-bound PYL1 in complex with phosphatase ABI1. Apo-PYL2 contains a pocket surrounded by four highly conserved surface loops. In response to ABA binding, loop CL2 closes onto the pocket, creating a surface that recognizes ABI1. In the ternary complex, the CL2 loop is located near the active site of ABI1, blocking the entry of substrate proteins. Together, our data reveal the mechanisms by which ABA regulates PYL-mediated inhibition of PP2Cs.

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Figure 1: Structure of ABA-free PYL2.
Figure 2: Structure of (+)-ABA bound PYL2.
Figure 3: Structural comparison between (+)-ABA–free and (+)-ABA –bound PYL2.
Figure 4: Structural comparison of (+)-ABA–free and (+)-ABA –bound PYL2 homodimers.
Figure 5: Structure of the (+)-ABA–bound PYL1 in complex with ABI1.
Figure 6: Recognition and inhibition of ABI1 by the (+)-ABA–bound PYL1.
Figure 7: A working model for ABA-dependent recognition and inhibition of PP2Cs by PYLs.

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We thank D. Zhang for providing the A. thaliana cDNA library; N. Shimizu, S. Baba and T. Kumasaka at the Spring-8 beamline BL41XU for on-site assistance; J. He and S. Huang for crystal screening at Shanghai Synchrotron Radiation Facility (SSRF); and Y. Shi for critical reading of the manuscript. This work was supported by funds from the China Ministry of Science and Technology (grant 2009CB918802), Tsinghua University 985 Phase II funds, Yuyuan Foundation and Li's Foundation.

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P.Y., H.F., Q.H., X.Y., D.W., Y.P. and W.L. performed experiments and analyzed data. C.Y., J.W. and N.Y. analyzed data. N.Y. wrote the manuscript.

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Correspondence to Nieng Yan.

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Yin, P., Fan, H., Hao, Q. et al. Structural insights into the mechanism of abscisic acid signaling by PYL proteins. Nat Struct Mol Biol 16, 1230–1236 (2009).

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