Ca2+-dependent phosphoregulation of the plasma membrane Ca2+-ATPase ACA8 modulates stimulus-induced calcium signatures.

Maria Ida De Michelis,Sonia Giacometti,Jörg Kudla,Kenji Hashimoto,Claudia Adriana Marrano,Alex Costa,Laura Luoni,Philipp Köster,Maria Cristina Bonza

doi:10.1093/jxb/erx162

Maria Ida De Michelis, Sonia Giacometti + Show 7 more

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https://doi.org/10.1093/jxb/erx162

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Abstract

Ca2+ signals are transient, hence, upon a stimulus-induced increase in cytosolic Ca2+ concentration, cells have to re-establish resting Ca2+ levels. Ca2+ extrusion is operated by a wealth of transporters, such as Ca2+ pumps and Ca2+/H+ antiporters, which often require a rise in Ca2+ concentration to be activated. Here, we report a regulatory fine-tuning mechanism of the Arabidopsis thaliana plasma membrane-localized Ca2+-ATPase isoform ACA8 that is mediated by calcineurin B-like protein (CBL) and CBL-interacting protein kinase (CIPK) complexes. We show that two CIPKs (CIPK9 and CIPK14) are able to interact with ACA8 in vivo and phosphorylate it in vitro. Transient co-overexpression of ACA8 with CIPK9 and the plasma membrane Ca2+ sensor CBL1 in tobacco leaf cells influences nuclear Ca2+ dynamics, specifically reducing the height of the second peak of the wound-induced Ca2+ transient. Stimulus-induced Ca2+ transients in mature leaves and seedlings of an aca8 T-DNA insertion line exhibit altered dynamics when compared with the wild type. Altogether our results identify ACA8 as a prominent in vivo regulator of cellular Ca2+ dynamics and reveal the existence of a Ca2+-dependent CBL-CIPK-mediated regulatory feedback mechanism, which crucially functions in the termination of Ca2+ signals.

Highlights

In all eukaryotes, calcium ions are involved in many biological processes, regulating a variety of essential cell functions
Combinations of both CIPK9 and CIPK14 with the empty vector used as negative control clearly showed no growth (Fig. 1), excluding the possibility that the growth of the two co-transformants could depend on transactivation due to the presence of the kinases themselves
Despite the functional overlap of plasma membrane (PM)-localized Ca2+ATPase isoforms (Bonza and De Michelis, 2011; Bose et al, 2011), our complementary analyses combining overexpression in N. benthamiana and investigation of an Arabidopsis loss-offunction mutant allowed us to identify ACA8 as a prominent pump involved in the termination of Ca2+ signals in response to wounding and extracellular ATP (eATP) application

Summary

Introduction

Calcium ions are involved in many biological processes, regulating a variety of essential cell functions. Perception of signals generates elevations in cytosolic Ca2+ concentration triggered by the opening of Ca2+ channels, while active Ca2+ transporters (Ca2+/H+ exchangers and Ca2+ pumps) determine the recovery of the basal pre-stimulus cytosolic free Ca2+ concentration ([Ca2+]cyt) (Sanders et al, 2002; Berridge et al, 2003; McAinsh and Pittman, 2009; Dodd et al, 2010; Kudla et al., 2010; Steinhorst and Kudla, 2013).

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