Table 1.
Description of mutant alleles exhibiting de-regulated iron (Fe) signaling.
| Organism/ Gene (allele) |
Function | Cellular localization/tissue expression | Expression of FRO2/IRT1 | Fe concentration in the mutant vs. wild-type | Treatments that rescue Fe deficiency symptoms | Reference |
|---|---|---|---|---|---|---|
|
Arabidopsis thaliana /FRD3 (frd3) |
Citrate efflux | Plasma membrane/ Root pericycle |
Constitutive expression of FRO2 and IRT1 | High Fe accumulation in apoplast and vasculature, but less Fe in cytosol | Foliar application of Fe; grafting frd3 shoots onto Wt roots; citrate addition to growth media | Rogers and Guerinot, 2002; Green and Rogers, 2004; Garcia et al., 2013 |
|
A. thaliana /NAS1, NAS2 NAS3, NAS4 (nas4x-1, nas4x-2) |
nicotianamine (NA) synthesis | Cytosol/ Roots (NAS1/2) and shoots (NAS1/2/3/4) |
Elevated expression of FRO2, IRT1, and FIT in Fe-sufficient plants in the nas4x-1 | Elevated Fe concentration in the whole rosette of the nas4x-1 mutant compared at the reproductive but not at the vegetative stage. Higher Fe in older leaves vs. younger leaves in the nas4x-1 mutant | Foliar application of Fe or NA rescues interveinal leaf chlorosis of nas4x-2 | Bauer et al., 2004; Klatte et al., 2009; Schuler et al., 2012 |
|
A. thaliana /OPT3 (opt3-2 and opt3-3) |
Fe influx | Plasma membrane/ Phloem companion cells |
Constitutive expression of FRO2 and IRT1 | High Fe accumulation in shoots Higher Fe in older leaves vs. younger leaves |
Grafting Wt shoots onto opt3 roots Expression of OPT3 in leaves of the opt3-2 |
Stacey et al., 2008; Mendoza-Cozatl et al., 2014; Zhai et al., 2014 |
|
A. thaliana /YSL1, YSL2, YSL3(ysl1,ysl2 ysl1ysl3) |
Fe–NA transport | Plasma membrane/ Vascular parenchyma cells (YSL1 and YSL3), xylem parenchyma cells in roots (YSL2) |
Lower or wild-type FRO2 activity in ysl1ysl3 mutants, not tested in ysl1 or ysl2 mutants | No difference in ysl2-1 mutant Less Fe in seeds of ysl1 single mutant Less Fe in roots and shoots of ysl1ysl3 double mutants |
Foliar application of Fe increasing Fe in growth media for detached roots |
DiDonato et al., 2004; Jean et al., 2005; Waters et al., 2006; Chu et al., 2010 |
| Solanum lycopersicon NAS (chln) | NA synthesis | Cytosol/ Roots and shoots |
Constitutive expression of SlFRO1 and SlIRT1 | High Fe accumulation in shoots Higher Fe in older leaves vs. younger leaves |
Foliar application of Fe or NA | Scholz et al., 1985; Garcia et al., 2013 |
| Unknown (brz) | Unknown | Unknown | Constitutive expression of PsFRO1 and PsIRT1 | High Fe accumulation in shoots Higher Fe in older leaves vs. younger leaves |
Foliar application of Fe | Kneen et al., 1990; Garcia et al., 2013 |
| Unknown (dgl) | Unknown | Unknown | Constitutive expression of PsFRO1 and PsIRT1 | High Fe accumulation in older leaves | Grafting Wt shoots onto dgl roots | Grusak and Pezeshgi, 1996; Garcia et al., 2013 |