Table 2.
Selected examples of the properties, tissue-specific expression, and physiological functions of CHX transporters in plants.
| CHX isoform and plant species | Clade | Tissue expression | Membrane localization | Transport properties | Demonstrated function | References |
|---|---|---|---|---|---|---|
| In Arabidopsis thaliana | ||||||
| AtCHX1 AtCHX2 |
V | Pollen | K+? |
Sze et al., 2004; Bock et al., 2006 |
||
| AtCHX3 AtCHX4 AtCHX5 AtCHX6a AtCHX6b |
VII | Pollen | K+? |
Sze et al., 2004; Bock et al., 2006 |
||
| AtCHX8 AtCHX9 |
||||||
| AtCHX10 | VII | Pollen/Root | K+? | Downregulation by salinity. | Maathuis et al., 2003; Sze et al., 2004; Bock et al., 2006 | |
| AtCHX11 AtCHX12 |
VII | Pollen | K+? |
Sze et al., 2004; Bock et al., 2006 |
||
| AtCHX13 | VII | Pollen, root tip and elongation zone |
PM | K+ | High-affinity K+ transporter; K+ uptake under potassium deficiency. |
Zhao et al., 2008; Zhao et al., 2015 |
| AtCHX14 | VII | Pollen | PM | K+ | Low K+ affinity transporter; K+ homeostasis and K+ recirculation in plants. | Zhao et al., 2008; Zhao et al., 2015; Jia et al., 2018 |
| AtCHX15 | IV | Pollen, leaves, root | K+? | Downregulation by salinity |
Maathuis et al., 2003; Sze et al., 2004, |
|
| AtCHX16 | II | Root/leaf | ER | K+ | Chanroj et al., 2011; | |
| AtCHX17 | II | Epidermal and cortical cells of mature roots | PVC in plant, PM in plant, Golgi apparatus in plant and yeast |
K+ | pH and K+ homeostasis in Golgi cisternae; protein sorting; salt tolerance, embryo development, pollen wall formation, male fertility. |
Cellier et al., 2004; Sze et al., 2004; Maresova and Sychrova, 2006; Chanroj et al., 2011; Chanroj et al., 2013; Sun et al., 2015; Czerny et al., 2016; Padmanaban et al., 2017 |
| AtCHX18 | II | Root/Leaf | PVC | K+ | Embryo development; pH and K+ homeostasis affect pollen wall formation, male fertility. | Chanroj et al., 2011; Padmanaban et al., 2017; Jia et al., 2018 |
| AtCHX19 | II | Root, leaf | PVC | K+ | Cation/proton exchanger at an early phase of male gametogenesis. | Sze et al., 2004; Chanroj et al., 2011; Padmanaban et al., 2017 |
| AtCHX20 | III | Guard cells, root tip/cap | ER | K+ | Osmoregulation, salt stress responses; light-induced stomatal opening by regulating K+ flux and by pH modulation. |
Padmanaban et al., 2007; Chanroj et al., 2011; Padmanaban et al., 2017 |
| AtCHX21 | IV | Root endodermal cells, leaves, pollen |
PM | Na+ and K+? | Na+ transport into the xylem; pollen K+ homeostasis; salt stress responses, pollen tube navigation to the ovule. | Hall et al., 2006; Evans et al., 2012; Lu et al., 2011 |
| AtCHX23 | IV | Leaves; pollen | ER in pollen tube | K+ and Na+ | Osmotic adjustment and K+ homeostasis of pollen, pollen tube navigation to the ovule | Song et al., 2004; Sze et al., 2004; Evans et al., 2012; Lu et al., 2011 |
| AtCHX24 AtCHX25 |
VI | Pollen | K+? | Sze et al., 2004; Bock et al., 2006 | ||
| AtCHX26 AtCHX27 |
VII | Pollen | K+? | Sze et al., 2004; Bock et al., 2006 | ||
| AtCHX28 | V | Pollen | K+? |
Sze et al., 2004; Bock et al., 2006 |
||
| In Oryza sativa L. | ||||||
| OsCHX11 | III | Roots | K+ | Upregulation by salinity; salt tolerance. | Senadheera et al., 2009 | |
| OsCHX14 | II | Lodicules and the region close by throughout the flowering process | ER | K+, Rb+, Cs+ | K+ homeostasis during rice flowering. | Chen et al., 2016 |
| In Glycine max | ||||||
| GmCHX1 (GmSALT3) | III | ER | Na+, Cl-? | Salt tolerance. | Guan et al., 2014; Qi et al., 2014; Qu et al., 2020 | |
| GmST1 | III | Leaves | Na+ and K+? | Salt and drought tolerance ABA-dependent. | Ren et al., 2016 | |
| In Glycine soja | ||||||
| GsCHX19.3 | II | Root, leaf, flower | PM | K+ | K+ uptake; salt and carbonate alkaline tolerance | Jia et al., 2017 |
| In Pyrus bretschneideri | ||||||
| PbrCHX16 | IV | Pollen | PM | K+ | Pollen tube growth | Zhou et al., 2016 |
| In Physcomitrella patens | ||||||
| PpCHX1 | III | Golgi | K+ | K+ homeostasis | Mottaleb et al., 2013 | |
| PpCHX2 | III | PM, Vacuole | K+ | K+ homeostasis; transfer of K+
from the vacuole to the cytosol or from the cytosol to the external medium. |
Mottaleb et al., 2013 | |