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Gene Review

SOS3  -  calcineurin B-like protein 4

Arabidopsis thaliana

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Disease relevance of SOS3


High impact information on SOS3

  • 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 [2].
  • 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].
  • Gel mobility shift and (45)Ca(2)+ overlay assays demonstrated that SOS3 is a unique calcium binding protein and that the sos3-1 mutation substantially reduced the capacity of SOS3 to bind calcium [4].
  • Expression of the myristoylated but not the nonmyristoylated SOS3 complemented the salt-hypersensitive phenotype of sos3-1 plants [4].

Biological context of SOS3

  • The mutation is recessive and is in a nuclear gene that maps to chromosome V. The sos3 mutation also renders the plant unable to grow on low K+ [5].
  • Also, mutations that alter the NaCl sensitivity of sos3-1 were screened for potential genetic suppressors or enhancers of salt-stress responses mediated by SOS3 [6].
  • Targeted mutagenesis of the N-terminal glycine-2 to alanine prevented the myristoylation of SOS3 [4].
  • 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 [7].
  • The SOS2/SOS3 kinase complex promoted the phosphorylation of SOS1 [8].

Anatomical context of SOS3


Associations of SOS3 with chemical compounds


Physical interactions of SOS3

  • We report here the identification of a SOS3 binding motif in SOS2 that also serves as the kinase autoinhibitory domain [3].

Other interactions of SOS3

  • Coexpression of SOS3 with SOS2 forms that retained the FISL motif resulted in more dramatic increases in salt tolerance [2].
  • Based on these results, a genetic model for salt tolerance mechanisms in Arabidopsis is presented in which SOS1, SOS2, and SOS3 are postulated to encode regulatory components controlling plant K+ nutrition that in turn is essential for salt tolerance [12].
  • CIPKs/PKS are a group of Ser/Thr protein kinases associated with the AtCBL/SOS3-like calcium-binding proteins (SCaBP) [13].
  • In each of these yeast assays, the activation of CAX1 by SOS2 was SOS3-independent [9].

Analytical, diagnostic and therapeutic context of SOS3


  1. SOS3 (salt overly sensitive 3) from Arabidopsis thaliana: expression, purification, crystallization and preliminary X-ray analysis. Sánchez-Barrena, M.J., Martínez-Ripoll, M., Zhu, J.K., Albert, A. Acta Crystallogr. D Biol. Crystallogr. (2004) [Pubmed]
  2. 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]
  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. SOS3 function in plant salt tolerance requires N-myristoylation and calcium binding. Ishitani, M., Liu, J., Halfter, U., Kim, C.S., Shi, W., Zhu, J.K. Plant Cell (2000) [Pubmed]
  5. An arabidopsis mutant that requires increased calcium for potassium nutrition and salt tolerance. Liu, J., Zhu, J.K. Proc. Natl. Acad. Sci. U.S.A. (1997) [Pubmed]
  6. Identification of plant stress-responsive determinants in arabidopsis by large-scale forward genetic screens. Koiwa, H., Bressan, R.A., Hasegawa, P.M. J. Exp. Bot. (2006) [Pubmed]
  7. 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]
  8. 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]
  9. 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]
  10. The structure of the Arabidopsis thaliana SOS3: molecular mechanism of sensing calcium for salt stress response. Sánchez-Barrena, M.J., Martínez-Ripoll, M., Zhu, J.K., Albert, A. J. Mol. Biol. (2005) [Pubmed]
  11. 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]
  12. 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]
  13. 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]
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