ABA activated SnRK2 kinases: an emerging role in plant growth and physiology

Abstract

Members of the SNF1-related protein kinase 2 (SnRK2) family are plant-specific serine or threonine kinases that play a pivotal role in the response of plants to abiotic stresses. Members of this plant-specific kinase family have included a critical regulator (SnRK2) of abscisic acid (ABA) response in plants. Plant organ development is governed substantially by the interaction of the SnRK2 and the phytohormone abscisic acid (ABA). Recent research has revealed a synergistic link between SnRK2 and ABA signaling in a plant's response to stress such as drought and shoot growth. SnRK2 kinases play a dual role in the control of SnRK1 and the development of a plant. The dual role of SnRK2 kinases promotes plant growth under optimal conditions and in the absence of ABA while inhibiting the growth of plants in response to ABA. In this review, we have uncovered the roles of ABA-activated SnRK2 kinases in plants, as well as their physiological mechanisms.

Keywords: Abiotic stress; land plants; phosphorylation; phytohormone; protein kinases; stomatal closure.

Figure 1.

The simple pathway SnRK2s pathways involved in plant response to abiotic stress and SnRK2 kinases perform dual functions in plants adapted from Belda-Palazón et al. (2020). SnRK2s boost growth under optimal conditions. SnRK2s are involved in the formation of SnRK1 repressor complexes which also contain PP2Cs in the lack of ABA. SnRK1 sequestration in these complexes is critical for preventing SnRK1 from interacting with TOR and thus allowing growth while conditions are suitable. SnRK2s prevent the growth in response to stress. SnRK2 and PP2C-containing SnRK1 repressor complexes dismantle in the involvement of ABA via classical ABA signaling, which involves the sequestration of PP2Cs by ABA-bound PYR/PYL receptors.SnRK2s and SnRK1 are released when the complexes are disassembled, triggering stress responses and inhibiting growth. This is achieved in part through direct TOR suppression by SnRK1, but it is also possible that SnRK2 kinases are involved in the process.Inactive components are spotlighted in white, whereas active components are displayed in other colors.