Heterotrimeric G Protein-Regulated Ca2+ Influx and PIN2 Asymmetric Distribution Are Involved in Arabidopsis thaliana Roots' Avoidance Response to Extracellular ATP

Abstract

Extracellular ATP (eATP) has been reported to be involved in plant growth as a primary messenger in the apoplast. Here, roots of Arabidopsis thaliana seedlings growing in jointed medium bent upon contact with ATP-containing medium to keep away from eATP, showing a marked avoidance response. Roots responded similarly to ADP and bz-ATP but did not respond to AMP and GTP. The eATP avoidance response was reduced in loss-of-function mutants of heterotrimeric G protein α subunit (Gα) (gpa1-1 and gpa1-2) and enhanced in Gα-over-expression (OE) lines (wGα and cGα). Ethylenebis(oxyethylenenitrilo) tetraacetic acid (EGTA) and Gd3+ remarkably suppressed eATP-induced root bending. ATP-stimulated Ca2+ influx was impaired in Gα null mutants and increased in its OE lines. DR5-GFP and PIN2 were asymmetrically distributed in ATP-stimulated root tips, this effect was strongly suppressed by EGTA and diminished in Gα null mutants. In addition, some eATP-induced genes' expression was also impaired in Gα null mutants. Based on these results, we propose that heterotrimeric Gα-regulated Ca2+ influx and PIN2 distribution may be key signaling events in eATP sensing and avoidance response in Arabidopsis thaliana roots.

Early Extracellular ATP Signaling in Arabidopsis Root Epidermis: A Multi-Conductance Process

“…This HACC may contribute to the net Ca 2+ influx reported for this root zone (Demidchik et al, 2009; Shang et al, 2009; Dark et al, 2011; Demidchik et al, 2011). Patch clamping has also implicated the heterotrimeric G protein α subunit in eATP activation of the PM HACC conductance of apical root cells (Zhu et al, 2017). Furthermore, patch clamping of elongation zone epidermal PM has revealed a small HACC-like conductance (which also permits K + influx) and a K + efflux conductance (in 44 out of 113 protoplasts) that not only are activated by eATP but also lie downstream of P2K1 (Wang et al, 2018).…”

New Insight into Plant Signaling: Extracellular ATP and Uncommon Nucleotides

“…It was a result of the heterotrimeric G-protein G α subunit activation followed by the opening of a plasma-membrane Ca 2+ channel. This finding suggests new, P2K1-independent responses to eATP, involved among others in the root-bending mechanism [39]. Moreover DORN1 could underpin several calcium-related responses but it may not be the only receptor for eATP in Arabidopsis thaliana [40].…”

“…Recently, the existence of another, unidentified, non-P2K1 receptor with affinity to eATP was suggested [39]. It was reported that Arabidopsis thaliana dorn1 null mutants demonstrated an increased level of cytosolic Ca 2+ under the exogenously applied ATP.…”

Arabidopsis ERF109 regulates auxin transport-related genes in root development

“…PIN1 primarily regulates plant meristem tissue and organ development process at the rootward faces of the stele (Huang et al , 2010; O’Connor et al , 2017; Paponov et al , 2005; Xi et al , 2016). PIN2 is observed on the shootward faces of epidermal cells, and regulates root gravitropism through the redistribution of auxin among root tissue (Mendez-Bravo et al , 2019; Muller et al , 1998; Vieten et al , 2005; Zhu et al , 2017). PIN3 concentrates on the basal side of vascular cells as well as the lateral side of pericycle cells in the elongation zone, whose main function is to modulate differential growth and regulate tropic growth (Chen et al , 2015; Friml et al , 2002b; Petrasek and Friml, 2009; Zhang et al , 2013).…”