46.アブシジン酸受容体PYR/PYL/RCARファミリーを介したアブシジン酸情報伝達機構(口頭発表)

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Abscisic acid (ABA) regulates physiologically important stress and developmental responses. ABI1 encodes a protein phosphatase 2C that functions early in the ABA signaling cascade. To address the mechanism of ABI1-mediated ABA signaling, we generated tagged ABI1 Arabidopsis expression lines and performed affinity column purification of ABI1-associated proteins. Interestingly, the most robust in planta ABI1-interacting proteins in all LC-MS/MS experiments were nine START domain proteins. The major in vivo ABI1 interactors correspond to PYR/PYL/RCAR proteins, which were recently reported as ABA-binding signal transduction proteins, demonstrating in vivo PYR/PYL/RCAR interactions with ABI1 in Arabidopsis. To investigate the biological relevance of the PYR/PYLs, we analyzed pyr1pyl1pyl2pyl4 quadruple mutant plants and found strong insensitivities in ABA-induced stomatal closure and ABA-inhibition of stomatal opening. We investigated the structural mechanisms by which PYR/PYL/RCAR proteins mediate signaling. PYR1 crystallographic structures reveal an α/β helix-grip fold and homodimeric assembly. The homodimeric assembly was verified in planta by co-immunoprecipitation. ABA binding within a large internal cavity switches structural motifs distinguishing ABA-free "open-lid" from ABA-bound "closed-lid" conformations. Site-directed PYR1 mutants designed to disrupt hormone binding lose ABA-triggered interactions with ABI1 in planta.
2010-10-01