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Regulatory mechanism of abscisic acid signaling

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ABSTRACT

Abscisic acid (ABA) is a major phytohormone that mediates the adaptation of plants to environmental stresses such as drought and regulates developmental signals such as seed maturation. Studies on ABA signaling have progressed rapidly since the recent discovery of PYR/PYL receptor proteins as soluble ABA receptors. In plant cells, the receptor receives ABA to inhibit the phosphatase activity of type 2C protein phosphatase (PP2C), which is the major negative regulator in ABA signaling. SNF1-related protein kinase 2 (SnRK2) is then released from negative regulation by PP2C, turning on ABA signals by the phosphorylation of downstream factors. Insights into the regulation of PYR/PYL receptor proteins is therefore required in order to control drought-stress tolerance in plants. This article reviews the regulatory mechanism of the ABA receptor by ABA and its selective agonist. Structural analyses of PYR/PYL receptors have clearly elucidated the mechanism of ABA perception of the receptor or the mechanism of interaction with PP2C that leads to inhibition of its phosphatase activity. Moreover, the structures of PYR/PYL receptors complexed with pyrabactin, a selective ABA agonist, have provided the structural basis of ABA agonism and antagonism.

No MeSH data available.


Open-to-closed gating mechanism of PYL1. Structures of apo- (green and orange) and ABA-bound (magenta and blue) states are superposed on each other. The gate and latch loops move to a closed conformation upon ABA binding, as shown by arrows. Two closed loops form a hydrogen bond, which is represented by a dashed line. This figure was created using the PDB coordinates of apo-PYL1 (3KAY) and ABA-bound PYL1 (3JRS).
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f3-7_123: Open-to-closed gating mechanism of PYL1. Structures of apo- (green and orange) and ABA-bound (magenta and blue) states are superposed on each other. The gate and latch loops move to a closed conformation upon ABA binding, as shown by arrows. Two closed loops form a hydrogen bond, which is represented by a dashed line. This figure was created using the PDB coordinates of apo-PYL1 (3KAY) and ABA-bound PYL1 (3JRS).

Mentions: ABA perception by a PYR/PYL receptor induces structural changes essential for ABA signal transduction. Superposition of the apo- and ABA-bound structures of PYL1 shows the conformational differences in the two conserved loops (Fig. 3)9,10. One of the two loops connects β-strand 3 with β-strand 4 (referred to as the gate loop), and the other loop connects β-strand 5 with β-strand 6 (referred to as the latch loop). Upon ABA binding, P115 on the gate loop moves toward the 2,6,6-trimethyl-cyclohexene ring of ABA to close the gate on the cavity, whereas S112 is flipped out of the ABA-occupied cavity. In addition, H142 on the latch loop turns into the cavity to form van der Waals contacts with ABA. The latch loop locks the closed gate loop by a hydrogen bond and van der Waals contacts. Multiple conformations of these loops are observed in the ABA-bound structures of the receptors. Most residues on these loops very weakly contribute to ABA binding10. Hence, the closed conformations of the gate and latch loops are expected to be insufficiently stabilized even if ABA is trapped in the cavities of its receptors9,10.


Regulatory mechanism of abscisic acid signaling
Open-to-closed gating mechanism of PYL1. Structures of apo- (green and orange) and ABA-bound (magenta and blue) states are superposed on each other. The gate and latch loops move to a closed conformation upon ABA binding, as shown by arrows. Two closed loops form a hydrogen bond, which is represented by a dashed line. This figure was created using the PDB coordinates of apo-PYL1 (3KAY) and ABA-bound PYL1 (3JRS).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC5036775&req=5

f3-7_123: Open-to-closed gating mechanism of PYL1. Structures of apo- (green and orange) and ABA-bound (magenta and blue) states are superposed on each other. The gate and latch loops move to a closed conformation upon ABA binding, as shown by arrows. Two closed loops form a hydrogen bond, which is represented by a dashed line. This figure was created using the PDB coordinates of apo-PYL1 (3KAY) and ABA-bound PYL1 (3JRS).
Mentions: ABA perception by a PYR/PYL receptor induces structural changes essential for ABA signal transduction. Superposition of the apo- and ABA-bound structures of PYL1 shows the conformational differences in the two conserved loops (Fig. 3)9,10. One of the two loops connects β-strand 3 with β-strand 4 (referred to as the gate loop), and the other loop connects β-strand 5 with β-strand 6 (referred to as the latch loop). Upon ABA binding, P115 on the gate loop moves toward the 2,6,6-trimethyl-cyclohexene ring of ABA to close the gate on the cavity, whereas S112 is flipped out of the ABA-occupied cavity. In addition, H142 on the latch loop turns into the cavity to form van der Waals contacts with ABA. The latch loop locks the closed gate loop by a hydrogen bond and van der Waals contacts. Multiple conformations of these loops are observed in the ABA-bound structures of the receptors. Most residues on these loops very weakly contribute to ABA binding10. Hence, the closed conformations of the gate and latch loops are expected to be insufficiently stabilized even if ABA is trapped in the cavities of its receptors9,10.

View Article: PubMed Central - PubMed

ABSTRACT

Abscisic acid (ABA) is a major phytohormone that mediates the adaptation of plants to environmental stresses such as drought and regulates developmental signals such as seed maturation. Studies on ABA signaling have progressed rapidly since the recent discovery of PYR/PYL receptor proteins as soluble ABA receptors. In plant cells, the receptor receives ABA to inhibit the phosphatase activity of type 2C protein phosphatase (PP2C), which is the major negative regulator in ABA signaling. SNF1-related protein kinase 2 (SnRK2) is then released from negative regulation by PP2C, turning on ABA signals by the phosphorylation of downstream factors. Insights into the regulation of PYR/PYL receptor proteins is therefore required in order to control drought-stress tolerance in plants. This article reviews the regulatory mechanism of the ABA receptor by ABA and its selective agonist. Structural analyses of PYR/PYL receptors have clearly elucidated the mechanism of ABA perception of the receptor or the mechanism of interaction with PP2C that leads to inhibition of its phosphatase activity. Moreover, the structures of PYR/PYL receptors complexed with pyrabactin, a selective ABA agonist, have provided the structural basis of ABA agonism and antagonism.

No MeSH data available.