ABA Receptors: Prospects for Enhancing Biotic and Abiotic Stress Tolerance of Crops

Abstract

The plant stress hormone abscisic acid (ABA) regulates myriad of plant developmental programs such as germination, root development, vegetative growth, seed development, dormancy, and seed desiccation tolerance. ABA, the master controller of transpiration, regulates ion channels and gene expression that are necessary for abiotic stress tolerance of plants and hence popularly called as the plant stress hormone. In the past one decade, the role of ABA in regulation of biotic stress tolerance is emerging. In response to low leaf water status as well as pathogen-associated molecular pattern (PAMP) signaling, ABA induces closure of stomata, which are major gateways of pathogens entry into plant cells. Salicylic acid (SA) promotes systemic acquired resistance (SAR) to biotrophic lifestyle, while jasmonic acid (JA) and ethylene positively regulate induced systemic resistance (ISR) against necrotrophic pathogens and insects. In addition to its role in PAMP-mediated stomatal closure, ABA interacts synergistically or antagonistically with SA, JA, and ethylene to regulate disease resistance pathway. Intense efforts made since 1980s have unraveled the molecular details of ABA signaling, culminating with the breakthrough discovery of the START domain proteins PYR/PYL/RCAR as ABA receptors (ABAR) and identifi cation of core components of ABA signaling in 2009. Recent studies have also revealed the critical role of ABA receptors in plant processes such as fruit ripening and secondary metabolite accumulation. Genetic manipulation of ABA signaling is envisaged as a potential tool for enhancing plant development and biotic and abiotic stress tolerance of crops. This chapter focuses on molecular and structural basis of ABA signaling. Further, it explores the potential of genetic engineering of core components, protein engineering to develop orthogonal receptor, and development of novel synthetic agonists of ABARs for improving crop yield, quality, and stress tolerance.

ABA-mediated responses to water deficit separate grapevine genotypes by their genetic background

“…SnRK2 proteins belong to a family of plant-specific serine/threonine kinases that are involved in abiotic and ABA responses [ 6 ]. From the SnRK2 genes identified in the grapevine genome [ 39 ], the abundance of VviSnRK2.1 was increased by water deficit in leaves and roots, while VviSnRK2.6 was not significantly modified in the roots supporting a similar response as reported for Arabidopsis SnRK genes [ 34 ].…”

“…The ABA signalling pathway involves a cascade of receptors, phosphatases, kinases and transcription factors (TFs), which have been well characterized [ 5 , 6 , 32 – 35 ]. The key components of this system are the protein receptor complex PYR/PYL/RCAR (PYRABACTIN RESISTANCE1)/(PYR1-LIKE)/(REGULATORY COMPONENTS OF ABA RECEPTORS), PP2Cs (PROTEIN PHOSPHATASE 2C) and SnRK2s (SUCROSE NON-FERMENTING-RELATED KINASE 2).…”

“…The binding of ABA to PYR/PYL/RCAR leads to a conformational change in the receptor enabling its interaction with PP2Cs and thereby activating the SnRK2s. The SnRK2s released from PP2C inhibition are then able to activate (via phosphorylation) downstream transcription factors (TF) and ABA-responsive element binding factors (ABFs or AREBs), leading to the induction of ABA-responsive genes [ 5 , 6 , 34 , 36 ]. Most of the components of the ABA signal transduction pathway have been identified in the V. vinifera genome [ 37 – 39 ].…”

PYR/PYL/RCAR Receptors Play a Vital Role in the Abscisic-Acid-Dependent Responses of Plants to External or Internal Stimuli

“…They form loops with a conserved amino acid sequence, capable of ABA binding and initiation of the signaling cascade [66,67]. The most important sections are the gate loop between β3 and β4 (preserved GLPA amino acid sequence) and the latch loop between β6 and β7 (preserved HRL amino acid sequence) [72]. Thus, the correct receptor pocket is present between the α-helix of the C-terminus of the protein and the loops.…”

Drought and heat stress-related proteins: an update about their functional relevance in imparting stress tolerance in agricultural crops

“…In 2009, discovery of chief ABA signaling components and the identification of START domain proteins PYR/PYL/RCAR as ABA receptors (ABAR) provided knowledge regarding molecular aspects of ABA signaling (Ma et al 2009;Park et al 2009). Major signaling components include ABAR (initially known as PYRABACTIN RESISTANCE [PYR]/ PYR1-LIKE [PYL], which belongs to START protein superfamily, group-A protein phosphatases 2C (PP2C), and subclass III sucrose non-fermenting1 (SNF1)-related protein kinase 2 (SnRK2, also named SRK2) (Dalal and Chinnusamy 2015). Stress-induced increase in cellular ABA is first recognized by the START domain of PYL/ RCAR (pyrabactin resistance-like/regulatory) component of ABA receptors protein family (Ma et al 2009).…”