| Aspect | Key findings | Evidence type/assays | Key citations with year & URL |
|---|---|---|---|
| Identity verified | Arabidopsis thaliana NHX7 is the same protein as SOS1/At2g01980 (UniProt Q9LKW9), a plasma-membrane Na+/H+ antiporter in the CPA1 family with a long regulatory C-terminus; this distinguishes it from vacuolar NHX proteins and similarly named genes in other species. | Gene cloning/annotation synthesis; comparative structural/domain analysis | Xie et al., 2022, Front Plant Sci, https://doi.org/10.3389/fpls.2022.866265 (pqac-00000003, pqac-00000007) |
| Transport function and coupling | SOS1/NHX7 mediates active Na+ efflux from the cytosol in exchange for H+, lowering cytosolic Na+ during salt stress. Transport is driven by the proton electrochemical gradient generated by the plasma-membrane H+-ATPase. | Genetics, heterologous yeast complementation, pathway reconstitution, physiological transport analyses | Xie et al., 2022, https://doi.org/10.3389/fpls.2022.866265; Zhang et al., 2025 review summarizing Arabidopsis work, https://doi.org/10.3389/fpls.2025.1527952 (pqac-00000003, pqac-00000001) |
| Localization and expression domains | SOS1 is plasma-membrane localized and strongly associated with root epidermis and xylem-associated parenchyma; expression is also reported in stems and leaves and is induced by salt stress. | GFP localization, promoter-GUS, expression analyses, mutant phenotypes | Xie et al., 2022, https://doi.org/10.3389/fpls.2022.866265; Ferrandi, 2023 summary of Arabidopsis literature (unknown journal) (pqac-00000006, pqac-00000014) |
| Physiological role in salt tolerance | sos1 loss-of-function mutants are highly salt sensitive. SOS1 supports root Na+ extrusion and contributes to long-distance Na+ transport/xylem ion handling, with context-dependent effects on shoot Na+ accumulation under mild versus severe salinity. | Mutant phenotyping, shoot/root ion measurements, xylem sap analyses | Xie et al., 2022, https://doi.org/10.3389/fpls.2022.866265; Ferrandi, 2023 summary (pqac-00000006, pqac-00000014) |
| Core SOS pathway: SOS3/CBL4 → SOS2/CIPK24 → SOS1 | Salt-induced cytosolic Ca2+ is sensed by SOS3/CBL4, which recruits/activates SOS2/CIPK24 at the plasma membrane; SOS2 then phosphorylates the C-terminal inhibitory region of SOS1 to activate Na+ export. | Genetic epistasis, kinase-substrate studies, protein interaction assays, yeast reconstitution | Xie et al., 2022, https://doi.org/10.3389/fpls.2022.866265; Li & Yang, 2023, https://doi.org/10.3389/fpls.2023.1217193; Zhang et al., 2025, https://doi.org/10.3389/fpls.2025.1527952 (pqac-00000004, pqac-00000013, pqac-00000002) |
| CBL10/SCaBP8 branch | SCaBP8/CBL10 also binds SOS2 and recruits it to the plasma membrane, functioning especially in shoots; recent reviews further note that SCaBP8 relieves inhibition of SOS1 by repressing PP2C.D phosphatases. | Protein interaction, phosphorylation studies, review synthesis of recent Arabidopsis work | Zhang et al., 2025, https://doi.org/10.3389/fpls.2025.1527952; Li & Yang, 2023, https://doi.org/10.3389/fpls.2023.1217193; Fu & Yang, 2023, https://doi.org/10.3390/cimb45070374 (pqac-00000002, pqac-00000013) |
| Regulatory domains/residues: S3BD | A SOS3-binding domain (S3BD) in SOS1 was mapped to K460-L482. SOS3 binds this region directly; deleting S3BD abolishes SOS3 binding and prevents complementation of sos1-1 in planta, although basal transporter activity can increase in yeast. | BiFC, co-IP, fluorescence titration, structure-guided modeling, yeast complementation, plant complementation | Gámez-Arjona et al., 2024, PNAS, https://doi.org/10.1073/pnas.2320657121 (pqac-00000010, pqac-00000011, pqac-00000008) |
| Regulatory domains/residues: autoinhibitory region | The C-terminal autoinhibitory region around L1005-L1047 keeps SOS1 inactive under non-stress conditions; deletion of the C-terminus causes constitutive activation. | Domain deletion/mutagenesis, heterologous functional assays, structural modeling/review synthesis | Gámez-Arjona et al., 2024, https://doi.org/10.1073/pnas.2320657121; Xie et al., 2022, https://doi.org/10.3389/fpls.2022.866265 (pqac-00000010, pqac-00000004) |
| Regulatory phosphorylation sites | SOS2/CIPK24 phosphorylates conserved serines S1136/S1138 in the self-inhibitory domain, relieving autoinhibition and activating SOS1; Ser→Ala substitutions reduce salt tolerance, while phosphomimic mutations increase SOS2 binding. | Site-directed mutagenesis, kinase regulation studies, salt-tolerance assays | Xie et al., 2022, https://doi.org/10.3389/fpls.2022.866265 (pqac-00000004) |
| 2024 PNAS: SOS3-dependent PM recruitment of SOS1 | Under 50 mM NaCl, SOS1:GFP is recruited to the plasma membrane over 1-3 days in wild-type roots, but in sos3 mutants it redistributes to intracellular compartments/vacuoles. Imaging was quantified from at least 70 cells and at least 7 plants. | Confocal microscopy of SOS1:GFP in roots under salt treatment | Gámez-Arjona et al., 2024, PNAS, https://doi.org/10.1073/pnas.2320657121 (pqac-00000011, pqac-00000012, pqac-00000016) |
| 2024 PNAS: inverse regulation of HKT1;1 | SOS3 also binds HKT1;1 and promotes its salt- and Ca2+-dependent proteasomal degradation, shifting Na+ handling away from root retention toward SOS1-mediated efflux/xylem loading under acute salinity. Coexpression of SOS3 did not alter HKT1;1 currents in oocytes, supporting regulation via localization/stability rather than channel gating. | BiFC, co-IP, degradation assays, Xenopus oocyte electrophysiology | Gámez-Arjona et al., 2024, PNAS, https://doi.org/10.1073/pnas.2320657121 (pqac-00000008, pqac-00000012) |
| 2024 PNAS: MG132 evidence | HKT1;1 protein abundance declines over 24 h of salt treatment, and this degradation is blocked by the 26S proteasome inhibitor MG132; similar effects are induced by 3 mM CaCl2, and the degradation response is absent in sos3-1. | Immunoblot/protein stability assays with MG132 and Ca2+ treatments | Gámez-Arjona et al., 2024, PNAS, https://doi.org/10.1073/pnas.2320657121 (pqac-00000012, pqac-00000017) |
| Structural state of the field | Recent Arabidopsis work cites a cryo-EM structure of SOS1 consistent with the topology of the pore domain and C-terminal autoinhibitory/helical-cytosolic regions, strengthening current models of activation, though the detailed structural paper itself was not directly available in retrieved full text. | Structure-guided interpretation cited by recent primary literature | Gámez-Arjona et al., 2024, https://doi.org/10.1073/pnas.2320657121 (pqac-00000010) |


*Table: This table summarizes verified identity, transport function, localization, regulation, and recent 2024 mechanistic findings for Arabidopsis SOS1/NHX7. It is useful as a compact evidence map linking each major claim to the assays and citations supporting it.*