Structural basis of abscisic acid signalling

Abstract

The phytohormone abscisic acid (ABA) mediates the adaptation of plants to environmental stresses such as drought and regulates developmental signals such as seed maturation. Within plants, the PYR/PYL/RCAR family of START proteins receives ABA to inhibit the phosphatase activity of the group-A protein phosphatases 2C (PP2Cs), which are major negative regulators in ABA signalling. Here we present the crystal structures of the ABA receptor PYL1 bound with (+)-ABA, and the complex formed by the further binding of (+)-ABA-bound PYL1 with the PP2C protein ABI1. PYL1 binds (+)-ABA using the START-protein-specific ligand-binding site, thereby forming a hydrophobic pocket on the surface of the closed lid. (+)-ABA-bound PYL1 tightly interacts with a PP2C domain of ABI1 by using the hydrophobic pocket to cover the active site of ABI1 like a plug. Our results reveal the structural basis of the mechanism of (+)-ABA-dependent inhibition of ABI1 by PYL1 in ABA signalling.

Structural insights into PYR/PYL/RCAR ABA receptors and PP2Cs

“…For instance, apoPYL1 [15], apoPYL2 [15,19], ABA-bound PYL1 [16] and ABA-bound PYL2 [15,19] structures have been resolved. In the case of PYR1, in the crystallographic asymmetric unit, there is one ABA-bound and one ABA-free subunit [17,18].…”

“…The structure of the ABA-bound forms of PYR1, PYL1 and PYL2 reveals the nature of the interactions stabilizing the hormone into the receptor binding pocket [15,16,17,18,19]. The ABA sits in a deep cavity almost completely buried from the external medium (see figure 3).…”

“…The PYR/PYL/RCAR family of ABA receptors has witnessed a rapid explosion of structural data, since five independent groups have reported structural and functional mechanisms on ABA signaling [15,16,17,18,19], and even more recently, using the seed ABA-agonist pyrabactin (Fig. 1C), the structural basis for selective activation of certain receptors and the mechanism of antagonism in other members [20,21,22].…”

ABA signalling is fine-tuned by antagonistic HAB1 variants

“…ABA binds to PYLs, promoting their interaction with PP2Cs and inhibiting their phosphatase activity [5][6][7] . Thus, SnRK2s are released from PP2C-SnRK2 complexes to phosphorylate downstream effectors and activate ABA signalling 3,5,6,[8][9][10] . Over the past several years, the structures and molecular functions of ABA receptors have received significant attention [9][10][11] .…”

“…Thus, SnRK2s are released from PP2C-SnRK2 complexes to phosphorylate downstream effectors and activate ABA signalling 3,5,6,[8][9][10] . Over the past several years, the structures and molecular functions of ABA receptors have received significant attention [9][10][11] . PP2Cs are central components of the core PYL-PP2C-SnRK2 regulatory module 1 .…”