Table II. Functions of CHX and NHX in Arabidopsis and other plants.
In or It, Morning glory; Pp, Physcomitrella patens. Reference groups are as follows: (1) Yokoi et al. (2002); Venema et al. (2002); Leidi et al. (2010); Bassil et al. (2011b); Barragán et al. (2012); Andrés et al. (2014). (2) Venema et al. (2003); Bassil et al. (2011a). (3) Wu et al. (1996); Shi et al. (2002). (4) An et al. (2007). (5) Fukada-Tanaka et al. (2000); Yamaguchi et al. (2001); Yoshida et al. (2005). (6) Zhao et al. (2008, 2015. (7) Chanroj (2011); Chanroj et al. (2013). (8) Chanroj et al. (2011, 2013,Padmanaban et al. (2017). (9) Chen et al. (2016). (10) Padmanaban et al. (2007). (11a) Guan et al. (2014). (11b) Qi et al. (2014). (12) Mottaleb et al. (2013). (13) Lu et al. (2011); Evans et al. (2012).
| Plant Transporter | Tissue Expression | Membrane Location | Transport Mode | Main Function or Mutant Phenotype | References |
|---|---|---|---|---|---|
| NHX | |||||
| AtNHX1, NHX2 | Ubiquitous | Tonoplast | K+(Na)/H+ | K+ uptake into vacuolar compartments for cell expansion; vacuole biogenesis; vacuole alkalinization; guard cell movement | 1 |
| AtNHX5, NHX6, LeNHX2 | Ubiquitous | Golgi, TGN | K+(Na)/H+ | pH homeostasis in TGN/PVC affects cargo sorting to vacuole and vacuole biogenesis | 2 |
| AtSOS1/NHX7 | Root, stem, and leaf xylem | PM | Na+/H+ | sos1 mutant is hypersensitive to Na+ and Li+, cannot grow on low K+; extrudes Na+ out of the cell | 3 |
| AtNHX8 | Ubiquitous | PM | Li+/H+ | nhx8 mutant is hypersensitive to Li; extrudes Li+ out of the cell. | 4 |
| InNHX1 or ItNHX1 | Flower petal | Tonoplast | K+(Na)/H+ | Vacuole alkalinization turns morning glory petals blue | 5 |
| CHX | |||||
| AtCHX13 | Pollen, root tip | PM | K+ | chx13 mutant is sensitive to K+ deficiency | 6 |
| AtCHX14 | Pollen, root, shoot vascular | PM | K+ efflux | Overexpressing plant is sensitive to low K+ | |
| AtCHX16 | Root | ER, PVC, PM | K+ | chx16 chx17 chx18 chx19 mutant shows lower seed set; poor plant growth on hydroponic medium | 7 |
| AtCHX17 | Root, pollen | PVC, PM | K+/nH+ (predicted from core residues) K+ (Rb) | Triple chx17 chx18 chx19 mutant shows disorganized pollen wall; reduced male fertility; impaired fertilization, reduced seed set | 8 |
| AtCHX18 | Hydathode, vascular, sperm | PVC, PM | |||
| AtCHX19 | Pollen | PVC, PM | |||
| OsCHX14 | Flower | Endomembrane, ER | K+ (Rb) | Jasmonic acid (JA) signaling and flower opening; K+, Rb transport in oocyte | 9 |
| AtCHX20 | Guard cell, root cap | Reticulate, ER | K+ | Participates in stomatal opening, guard cell movement | 10 |
| GmSALT3 | Root, vascular | ER | Confers salt tolerance in wild soybean | 11a | |
| Gm/GsCHX1 | K+ | 11b | |||
| PpCHX1,2 | Protonema | Punctate, PM | K+ efflux? | No phenotype yet | 12 |
| AtCHX23 (CHX21) | Pollen, tube | ER | K+ | Involved in pollen tube targeting of ovule | 13 |