Identification of a calmodulin‐regulated autoinhibited Ca²⁺‐ATPase (ACA11) that is localized to vacuole membranes in Arabidopsis

Abstract

In plant cells, the vacuole functions as a major calcium store. Although a calmodulin-regulated Ca 2+ -ATPase (ACA4) is known to be present in prevacuolar compartments, the presence of an ACA-type Ca 2+ -ATPase in the mature vacuole of a plant cell has not been verified. Here we provide evidence that ACA11 localizes to the vacuole membrane. ACA11 tagged with GFP was expressed in stable transgenic plants, and visualized in root cells and protoplasts by confocal microscopy. A Ca 2+ -ATPase function for ACA11 was confirmed by complementation of yeast mutants. A calmodulin binding domain was identified within the first 37 residues of the N-terminal autoinhibitory region. Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.

A P IIB -type Ca 2+ -ATPase is essential for stress adaptation in Physcomitrella patens

“…We therefore propose that PCA1 is required to restore the [Ca 2+ ] cyt for the generation of a stimulus- specific transient increase in [Ca 2+ ] cyt (3,47) PCA1 was localized in membranes of small vacuolar compartments, which is consistent with the localization of the Arabidopsis P IIB -type Ca 2+ -ATPase ACA4 (16). The additional subcellular localization sites of plant P IIB -type Ca 2+ -ATPases in the plasma membrane (17,36), the ER (37), and the central vacuole (38) point to functional diversities within the plasma membrane and the endomembrane system in relation to Ca 2+ homeostasis and Ca 2+ signaling. Besides Ca 2+ -ATPases, Ca 2+ /H + exchangers control Ca 2+ homeostasis under stress conditions as Arabidopsis T-DNA mutants of the CAX1 Ca 2+ /H + antiporter displayed an enhanced freezing tolerance that was correlated with an elevated expression of CBF/DREB1 genes and their corresponding targets (48).…”

“…Exploring the intracellular localization of Ca 2+ -ATPases may provide insights into the subcellular compartments that are involved in the maintenance of low [Ca 2+ ] cyt . Previous studies indicated a diverse localization of plant P IIB -type Ca 2+ -ATPases in the plasma membrane (17,36), the endoplasmic reticulum (ER) (37), small vacuoles (16), and the central vacuole (38). To analyze the localization of PCA1, we fused the cDNA of the GFP to the 3′ end of the PCA1 coding region under the control of the cauliflower mosaic virus 35S promoter and transfected the construct into Physcomitrella protoplasts that were analyzed by confocal laser scanning microscopy 48 h after the transformation.…”

Cell-Specific Vacuolar Calcium Storage Mediated by CAX1 Regulates Apoplastic Calcium Concentration, Gas Exchange, and Plant Productivity in Arabidopsis

“…In addition to CAX1, other vacuolar Ca 2+ transporters, notably, ACA4 and ACA11, were preferentially expressed in the mesophyll of Arabidopsis leaves (Figure 2A), but a metadata analysis of publicly available ionomic and expression data from various Arabidopsis ecotypes revealed a positive correlation for Ca accumulation with only CAX1 expression ( Figure 2D). Furthermore, when compared with other plant tissues, CAX1 has greatest expression in the leaf, whereas CAX3 is more abundant in roots, and both ACA4 and ACA11 have comparable expression elsewhere in the plant (Geisler et al, 2000a, Cheng et al, 2005Lee et al, 2007). Taken together, these observations highlight the importance of CAX1 as the dominant mechanism in Ca accumulation in the leaf.…”

“…Members of the (autoinhibited) type-P 2A Ca 2+ -ATPases (ACA) family are high-affinity Ca 2+ pumps that are stimulated by calmodulin and are implicated in adjusting cytosolic [Ca 2+ ] ([Ca 2+ ] cyt ) within the nanomolar range (Harper et al, 1998). Of the 10 members in Arabidopsis, only ACA4 and ACA11 have been shown to be both expressed in the leaf and localized on the tonoplast; however, the specific roles of these proteins and the regulation of their expression or activity are not currently well defined (Geisler et al, 2000b;Baxter et al, 2003;Bolte et al, 2004;Lee et al, 2007;see Discussion). The Ca 2+ /H + antiporters (CAX) have lower transport affinities for Ca 2+ than ACA proteins (CAX1, K m = 10 to 15 mM; Hirschi et al, 1996), possess an N-terminal autoinhibitory domain, and use the proton-motive force across the tonoplast to remove Ca 2+ from the cytosol when free [Ca 2+ ] cyt is significantly above resting levels.…”

Fluorescence Resonance Energy Transfer-Sensitized Emission of Yellow Cameleon 3.60 Reveals Root Zone-Specific Calcium Signatures in Arabidopsis in Response to Aluminum and Other Trivalent Cations

“…The on switches depend on membrane-localized Ca 2+ channels that control the entry of Ca 2+ into the cytosol Tester, 1995, 1997;Thion et al, 1998;Kiegle et al, 2000a;White et al, 2000;Demidchik et al, 2002;Miedema et al, 2008). On the other hand, the off switches consist of a family of Ca 2+ -ATPases and Ca 2+ /H + exchangers in the plasma membrane or endomembrane that remove Ca 2+ from the cytosol, bringing the [Ca 2+ ] cyt down to the initial resting level (Lee et al, 2007;Li et al, 2008).…”