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Gene Review

SOS2  -  CBL-interacting serine/threonine-protein...

Arabidopsis thaliana

Synonyms: ATSOS2, CBL-INTERACTING PROTEIN KINASE 24, CIPK24, K21B8.3, K21B8_3, ...
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Disease relevance of SOS2

  • In planta assays showed that the Thr(168)-to-Asp-activated mutant SOS2 partially rescued the salt hypersensitivity in sos2 and sos3 mutant plants [1].
  • To determine its biochemical properties, we expressed and isolated a number of active and inactive SOS2 mutants as glutathione S-transferase fusion proteins in Escherichia coli [2].

High impact information on SOS2

  • In Arabidopsis thaliana, the calcium binding protein Salt Overly Sensitive3 (SOS3) interacts with and activates the protein kinase SOS2, which in turn activates the plasma membrane Na(+)/H(+) antiporter SOS1 to bring about sodium ion homeostasis and salt tolerance [1].
  • These studies demonstrate that the protein kinase activity of SOS2 is partially sufficient for activation of SOS1 and for salt tolerance in vivo and in planta and that the kinase activity of SOS2 is limiting for plant salt tolerance [1].
  • Constitutively active alleles of SOS2 can be constructed in vitro by changing Thr(168) to Asp in the activation loop of the kinase catalytic domain and/or by removing the autoinhibitory FISL motif from the C-terminal regulatory domain [1].
  • The SOS3 (for SALT OVERLY SENSITIVE3) calcium binding protein and SOS2 protein kinase are required for sodium and potassium ion homeostasis and salt tolerance in Arabidopsis [3].
  • Constitutively active SOS2 that is SOS3 independent also was produced by changing Thr(168) to Asp in the activation loop of the SOS2 kinase domain [3].

Biological context of SOS2

  • Deletion analysis led to the discovery of a novel protein domain of 37 amino acid residues, designated as the protein phosphatase interaction (PPI) motif, of SOS2 that is necessary and sufficient for interaction with ABI2 [4].
  • These findings suggest multiple functions for SOS2 and provide a mechanistic link between Ca(2+) and Na(+) homeostasis in plants [5].
  • The sos2 mutations, which are recessive, were mapped to the lower arm of chromosome V, approximately 2.3 centimorgans away from the marker PHYC [6].
  • The SOS2/SOS3 kinase complex promoted the phosphorylation of SOS1 [7].
  • SOS3 is an EF hand type calcium-binding protein having sequence similarities with animal neuronal calcium sensors and the yeast calcineurin B. SOS2 is a serine/threonine protein kinase in the SNF1/AMPK family [8].

Anatomical context of SOS2

  • Although vesicles of sos2 and sos3 plants had reduced plasma membrane Na(+)/H(+)-exchange activity, transport activity in both increased with the addition of activated SOS2 protein [9].
  • Vacuolar membranes from CAX1-expressing cells were made to be H(+)/Ca(2+)-competent by the addition of SOS2 protein in a dose-dependent manner [5].

Associations of SOS2 with chemical compounds


Physical interactions of SOS2


Regulatory relationships of SOS2

  • Here we demonstrate that SOS2 regulates the vacuolar H(+)/Ca(2+) antiporter CAX1 [5].
  • CAX1-like chimeric transporters were activated by SOS2 if the chimeric proteins contained the N terminus of CAX1 [5].

Other interactions of SOS2

  • Our search yielded 28 new alleles of sos1, nine mutant alleles of a newly identified locus, SOS2, and one allele of a third salt tolerance locus, SOS3 [6].
  • Mutations in the conserved amino acid residues in the PPI motif abolish the interaction of SOS2 with ABI2 [4].
  • However, the addition of activated SOS2 did not have any stimulatory effect on the exchange activity in sos1 plants [9].
  • Our results establish the PPI motif and the protein kinase interaction domain as novel protein interaction domains that mediate the binding between the SOS2 family of protein kinases and the ABI1/2 family of protein phosphatases [4].
  • In each of these yeast assays, the activation of CAX1 by SOS2 was SOS3-independent [5].

Analytical, diagnostic and therapeutic context of SOS2


  1. Transgenic evaluation of activated mutant alleles of SOS2 reveals a critical requirement for its kinase activity and C-terminal regulatory domain for salt tolerance in Arabidopsis thaliana. Guo, Y., Qiu, Q.S., Quintero, F.J., Pardo, J.M., Ohta, M., Zhang, C., Schumaker, K.S., Zhu, J.K. Plant Cell (2004) [Pubmed]
  2. Biochemical characterization of the Arabidopsis protein kinase SOS2 that functions in salt tolerance. Gong, D., Guo, Y., Jagendorf, A.T., Zhu, J.K. Plant Physiol. (2002) [Pubmed]
  3. Molecular characterization of functional domains in the protein kinase SOS2 that is required for plant salt tolerance. Guo, Y., Halfter, U., Ishitani, M., Zhu, J.K. Plant Cell (2001) [Pubmed]
  4. A novel domain in the protein kinase SOS2 mediates interaction with the protein phosphatase 2C ABI2. Ohta, M., Guo, Y., Halfter, U., Zhu, J.K. Proc. Natl. Acad. Sci. U.S.A. (2003) [Pubmed]
  5. The protein kinase SOS2 activates the Arabidopsis H(+)/Ca(2+) antiporter CAX1 to integrate calcium transport and salt tolerance. Cheng, N.H., Pittman, J.K., Zhu, J.K., Hirschi, K.D. J. Biol. Chem. (2004) [Pubmed]
  6. Genetic analysis of salt tolerance in arabidopsis. Evidence for a critical role of potassium nutrition. Zhu, J.K., Liu, J., Xiong, L. Plant Cell (1998) [Pubmed]
  7. Reconstitution in yeast of the Arabidopsis SOS signaling pathway for Na+ homeostasis. Quintero, F.J., Ohta, M., Shi, H., Zhu, J.K., Pardo, J.M. Proc. Natl. Acad. Sci. U.S.A. (2002) [Pubmed]
  8. The Arabidopsis SOS2 protein kinase physically interacts with and is activated by the calcium-binding protein SOS3. Halfter, U., Ishitani, M., Zhu, J.K. Proc. Natl. Acad. Sci. U.S.A. (2000) [Pubmed]
  9. Regulation of SOS1, a plasma membrane Na+/H+ exchanger in Arabidopsis thaliana, by SOS2 and SOS3. Qiu, Q.S., Guo, Y., Dietrich, M.A., Schumaker, K.S., Zhu, J.K. Proc. Natl. Acad. Sci. U.S.A. (2002) [Pubmed]
  10. Isolation and characterization of a novel rice Ca2+-regulated protein kinase gene involved in responses to diverse signals including cold, light, cytokinins, sugars and salts. Kim, K.N., Lee, J.S., Han, H., Choi, S.A., Go, S.J., Yoon, I.S. Plant Mol. Biol. (2003) [Pubmed]
  11. The Arabidopsis thaliana SOS2 gene encodes a protein kinase that is required for salt tolerance. Liu, J., Ishitani, M., Halfter, U., Kim, C.S., Zhu, J.K. Proc. Natl. Acad. Sci. U.S.A. (2000) [Pubmed]
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