ABA
Phytohormone ABA is a major plant stress hormone that regulates growth, development, stomatal closure, seed germination, osmotic regulation, and environmental stress responses[1]. Mechanistically, ABA binds PYR/PYL/RCAR receptors, promotes receptor interaction with PP2C phosphatases, and inhibits PP2C activity at the apex of ABA signaling[2][3]. This inhibition releases ABA-activated SnRK2 protein kinases from PP2C repression, supporting ABA-responsive phosphorylation and gene regulation in water-stress models[4]. In drought-related experimental systems, ABA signaling connects guard-cell closure with reduced water loss and improved drought tolerance in Arabidopsis and soybean models[5]. Compared with related receptor isoforms, pyrabactin activates PYR1 and PYL1 but antagonizes PYL2, showing that ABA receptor ligands can produce isoform-selective activation or inhibition[6]. For research applications, quinabactin activates dimeric ABA receptors and induces guard-cell closure, whereas opabactin was designed as an ABA mimic with higher receptor affinity and stronger in vivo activity than ABA[5][7].
References:
- [1]. Chen K, et al. Abscisic acid dynamics, signaling, and functions in plants. J Integr Plant Biol. 2020 Jan;62(1):25-54. [Content Brief]
- [2]. Park SY, et al. Abscisic acid inhibits type 2C protein phosphatases via the PYR/PYL family of START proteins. Science. 2009 May 22;324(5930):1068-71. [Content Brief]
- [3]. Ma Y, et al. Regulators of PP2C phosphatase activity function as abscisic acid sensors. Science. 2009 May 22;324(5930):1064-8. [Content Brief]
- [4]. Umezawa T, et al. Type 2C protein phosphatases directly regulate abscisic acid-activated protein kinases in Arabidopsis. Proc Natl Acad Sci U S A. 2009 Oct 13;106(41):17588-93. [Content Brief]
- [5]. Okamoto M, et al. Activation of dimeric ABA receptors elicits guard cell closure, ABA-regulated gene expression, and drought tolerance. Proc Natl Acad Sci U S A. 2013 Jul 16;110(29):12132-7. [Content Brief]
- [6]. Melcher K, et al. Identification and mechanism of ABA receptor antagonism. Nat Struct Mol Biol. 2010 Sep;17(9):1102-8. [Content Brief]
- [7]. Vaidya AS, et al. Dynamic control of plant water use using designed ABA receptor agonists. Science. 2019 Oct 25;366(6464):eaaw8848. [Content Brief]
