Table I. Plant NHX and CHX members show distinct roles in yeast growth.
Plant (At for Arabidopsis and Le for tomato) or yeast (Sc for S. cerevisiae) genes or vector only (None) were expressed in various mutants that were unable to grow under limiting conditions I to IV. The yeast strain is shown in parentheses. Growth was scored as none (−), no or low (−/+), low (+), medium (++), or high (+++). Blank spaces, Not determined. Localization refers to GFP-tagged protein in yeast cells only. Results are taken from Chanroj et al. (2011) unless indicated otherwise in the footnotes. Note that, in experiment I, AtNHX activity was assayed using the AXT3 (ena1-4, nha1, nhx1) strain (Yokoi et al., 2002) or with nhx1 (Gaxiola et al., 1999). CHX activity was tested in the KTA40-2 strain at pH 5. High K+/Na+ varied from 50 to 400 mm. The KTA40-2 (ena1-4, nha1, nhx1, kha1) strain was used to test conditions II and IV (Chanroj et al., 2011). LMM04 (ena1-4, nha1, kha1, trk1,2, tok1) was used to test condition III. LMB01 (ena1-4, nha1, kha1) has wild-type ScNhx1. (See Fig. 1B legend for gene names.)
| Transporter Gene | Localization | Relative Yeast Growth | |||
|---|---|---|---|---|---|
| I. High K+/Na+, pH ∼ 5 | II. Low K+ at pH 7.5 | III. Low K+ at pH 7.5 | IV. HygB at pH 5.6 | ||
| Plant (At or Le) or yeast (Sc) | In yeast only | (AXT3) | (KTA40-2) | (LMM04) | (KTA40-2) |
| None | − | −/+ | −/+ | − | |
| AtNHX1 and NHX2a | Vacuole, endosome | +++ | + | − | +++ |
| AtNHX5, NHX6, and LeNHX2b | Endomembrane, post-Golgi | ++ | +++b | ||
| ScNhx1 | PVC, endosomef | +++c (KTA40-2) | − (LMB01) | +++ (LMB01) | |
| AtCHX20d | Golgi, ERESe | − | ++ | −/+ | − |
| AtCHX17, AtCHX18, and AtCHX19 | Golgi | − | +++ | +++ | + |
| ScKha1 | Golgie | − (AXT3) | +++ (AXT3) | ++ (AXT3) | |
References are as follows: Gaxiola et al. (1999); Quintero et al. (2000); Yokoi et al. (2002).
References are as follows: Yokoi et al. (2002), AtNHX5; Venema et al. (2003), LeNhx2.
Brett et al. (2005) tested the wild type and nhx1 with 0.6 m KCl at pH 4.
AtCHX20-GFP fluorescence in yeast resembled ER exit site (ERES) markers. Fluorescence patterns of CHX17-GFP and ScKHA1-GFP in yeast were similar (Chanroj et al., 2011; Wu et al., 2016).