Root Growth Adaptation is Mediated by PYLs ABA Receptor‐PP2A Protein Phosphatase Complex

Abstract

Plant root architecture dynamically adapts to various environmental conditions, such as salt-containing soil. The phytohormone abscisic acid (ABA) is involved among others also in these developmental adaptations, but the underlying molecular mechanism remains elusive. Here, a novel branch of the ABA signaling pathway in Arabidopsis involving PYR/PYL/ RCAR (abbreviated as PYLs) receptor-protein phosphatase 2A (PP2A) complex that acts in parallel to the canonical PYLs-protein phosphatase 2C (PP2C) mechanism is identified. The PYLs-PP2A signaling modulates root gravitropism and lateral root formation through regulating phytohormone auxin transport. In optimal conditions, PYLs ABA receptor interacts with the catalytic subunits of PP2A, increasing their phosphatase activity and thus counteracting PINOID (PID) kinase-mediated phosphorylation of PIN-FORMED (PIN) auxin transporters. By contrast, in salt and osmotic stress conditions, ABA binds to PYLs, inhibiting the PP2A activity, which leads to increased PIN phosphorylation and consequently modulated directional auxin transport leading to adapted root architecture. This work reveals an adaptive mechanism that may flexibly adjust plant root growth to withstand saline and osmotic stresses. It occurs via the cross-talk between the stress hormone ABA and the versatile developmental regulator auxin.

Systematic analysis of specific and nonspecific auxin effects on endocytosis and trafficking

“…The potential physiological role of such auxin regulation remains unclear but may be linked to maintenance of PIN polarity, which requires constitutive PIN2 endocytosis (Dhonukshe et al, 2007;Kleine-Vehn et al, 2008cAdamowski and Friml, 2015) and auxin-mediated PIN2 degradation (Abas et al, 2006;Baster et al, 2013). Both processes have been associated with physiological responses, such as root gravitropism, phototropism, and halotropism (Abas et al, 2006;Laxmi et al, 2008;Galvan-Ampudia et al, 2013), and their regulation occurs via many endogenous signals, such as calcium (Zhang et al, 2011) and hormones like auxin (Baster et al, 2013), gibberellic acid (Löfke et al, 2013;Salanenka et al, 2018), salicylic acid (Du et al, 2013;Tan et al, 2020), abscisic acid (Li et al, 2020), or brassinosteroids (Retzer et al, 2019). These responses typically involve not only polar cellular PIN2 distribution but also asymmetric PIN2 abundance with PIN2 stabilized on one side of the root and increased degradation on the other (Abas et al, 2006;Baster et al, 2013;Galvan-Ampudia et al, 2013).…”

Effects of graphene on morphology, microstructure and transcriptomic profiling of Pinus tabuliformis Carr. roots

“…SAUR41 , which is considered as a positive regulator for cell and hypocotyl elongation, was upregulated by graphene [ 56 ]. Under abiotic stresses, such as salt stress, the PYLs (PYR/PYL/RCAR) ABA receptors are involved in root growth adaptation [ 57 ]. Mutations in PYLs promote plant growth and productivity [ 58 ].…”

Strigolactones inhibit auxin feedback on PIN-dependent auxin transport canalization

“…Notably, auxin itself appears to inhibit the process of endocytosis and antagonize the BFA effect on PIN recycling 15 . In addition to auxin effects on PINs, various other plant hormones can influence PIN-dependent auxin transport, such as cytokinins 23 , brassinosteroids 24,25 , gibberellins 26 , salicylic acid 27 , abscisic acid 28 , and strigolactones (SLs) 29 . However, much remains to be uncovered about the modes of action, by which these plant hormones regulate PINs, thereby ultimately defining plant development.…”