Table 2.

Proton-involved transporters and protein factors regulate chloroplast stromal pH.

Locus	Protein	Subcellular localization	Proposed function(s)	References
At1g01790	KEA1	Chloroplast envelope membrane	K+/H+ specific antiporters Regulation of K+-induced stromal alkalization upon dark-to-light transition. Regulation of neutralization of stromal pH upon light-to-dark transition.	Aranda-Sicilia et al., 2012 Kunz et al., 2014 Aranda Sicilia et al., 2021
At4g00630	KEA2	Chloroplast envelope membrane (distinct spots)*
At4g13590	PAM71-HL BICAT2	Chloroplast envelope membrane	Putative Ca2+/H+ antiporter Mn2+, Ca2+, and pH homeostasis in chloroplasts Bivalent cation transporter	Schneider et al., 2016 Frank et al., 2019
At3g19490	NHD1	Chloroplast envelope membrane	A putative Na+/H+ antiporter Generation of a sodium gradient across the envelope membrane for activating Na+-dependent metabolite transporter Balancing between Na+ influxes and effluxes in chloroplasts	Furumoto et al., 2011 Kunz et al., 2014
–	P-type H+-ATPase(s)	Chloroplast envelope membrane	Generation of ΔpH across the chloroplast envelope Stabilization of alkaline pH in chloroplast stroma upon light illumination	Berkowitz and Peters, 1993 Shingles and McCarty, 1994 Peters and Berkowitz, 1998
At4g31040	DLDG1	Chloroplast envelope membrane	NPQ control Chloroplast pH homeostasis controller A putative K+(Ca2+)/H+ antiporter or a K+(Ca2+)/H+ antiport regulator	Harada et al., 2019
Atcg00530	Ycf10	Chloroplast envelope inner membrane	Ci transport candidate or regulator of HCO3− and CO2 uptake♠ Regulation of light-induced H+ extrusion♦ NPQ control♣	Rolland et al., 1997 Sasaki et al., 1993 Sonoda et al., 1998 Trinh et al., 2021

^*Distinct spots were proposed as the thylakoid biogenesis center.

^♠A study in Chlamydomonas.

^♦A study of Ycf10 ortholog (pxcA or CotA) in cyanobacteria.

^♣A study in tobacco.