Table 1.

Examples of identified endomembrane transporters with demonstrated roles in modulation of Ca²⁺ _cyt or organellar Ca²⁺.

Intracellular sources and sinks with demonstrated roles in regulating Ca2+ cyt
Compartment membrane	Transporters	Ca2+ cyt impact	Physiological process	References
Tonoplast	PIIB ATPase PCA1	↓	Physcomitrium salinity/osmotic signalling	Qudeimat et al., 2008
	TPC1?	↑ ↑	Arabidopsis long-distance signalling. Stomatal closure in response to external Ca2+ and ROS.	Cho et al., 2012; Islam et al., 2010; Kiep et al., 2015; Peiter et al., 2005
	AtACA4, ACA11	↓	Arabidopsis response to flg22 and maintenance of resting Ca2+ cyt.	Frei et al., 2012; Hilleary et al., 2020
	AtPIEZO (AtPZO1) PpPIEZO	↑ ↑	Mechanotransduction in root cells. Ca2+ cyt oscillations in Physcomitrium	Mousavi et al., 2021 Radin et al., 2021
	AtCAX2	↓	Flooding and hypoxia Ca2+ cyt response modulation	Bakshi et al., 2023
	AtCCX2	↕?	Salt and osmotic responses	Corso et al., 2018
ER	AtECA1 AtACA1,2,7 NbCA1 AtCCX2	↓ ↓ ↓	Asymmetric Ca2+ cyt elevation in root bending and hydrotropic response. Arabidopsis response to flg and maintenance of resting Ca2+ cyt. Responses to cryptogenic. Regulation of ER-cytosol Ca2+ exchange.	Shkolnik et al., 2018 Ishka et al., 2021 Corso et al., 2018
Intracellular organelle-specific Ca2+ cyt elevations
Compartment membrane	Transporters	Organelle Ca2+ impact	Physiological process	References
Mitochondria	AtMCU1–3 AtMICU	↑ ↓	A major route for fast mitochondrial Ca2+ uptake. Required for jasmonic acid signalling and thigmomorphogenesis Modulates mitochondrial Ca2+ uptake by MCU and shapes mitochondrial Ca2+ signatures.	Ruberti et al., 2022; Teardo et al., 2017 Wagner et al., 2015
Chloroplast	AtMCU AtBICAT2 AtBICAT1	↑ ↑ ↓	Stromal Ca2+ accumulation in response to hyperosmotic shock. Imports Ca2+ across the chloroplast envelope. Underlies stromal Ca2+ increase in response to light–dark transition Transports Ca2+ into the thylakoid lumen. Modulates BICAT2-mediated stromal Ca2+ increase	Teardo et al., 2019 Frank et al., 2019
Nucleus	MtCNGC15/MtDMI1	↑	Nuclear envelope-ER localized channels coordinately mediate nuclear Ca2+ cyt oscillations in response to root nodulation factors	Liu et al., 2022 Charpentier et al., 2016