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Gene Review

NPH3  -  root phototropism protein 3

Arabidopsis thaliana

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High impact information on NPH3

  • Arabidopsis NPH3: A NPH1 photoreceptor-interacting protein essential for phototropism [1].
  • The Rice COLEOPTILE PHOTOTROPISM1 gene encoding an ortholog of Arabidopsis NPH3 is required for phototropism of coleoptiles and lateral translocation of auxin [2].
  • Previous studies have shown that the proteins RPT2 (for ROOT PHOTOTROPISM2) and NPH3 (for NONPHOTOTROPIC HYPOCOTYL3) transduce signals downstream of phototropins to induce the phototropic response [3].
  • Another A. thaliana mutant, JK218, that completely lacks any phototropic responses to up to 2 h of irradiation, shows a normal level of light-induced phosphorylation at saturation [4].
  • Thus, NPH2 and NPH3 appear to act as signal carriers in a phototropism-specific pathway, whereas NPH4 is required for both phototropism and gravitropism and thus may function directly in the differential growth response [5].

Biological context of NPH3

  • Only NONPHOTOTROPIC HYPOCOTYL 3 (NPH3) and root phototropism 2, both belonging to the same family of proteins, have been previously identified as phototropin-interacting signal transducers involved in phototropism [6].
  • Surprisingly, the only significant genotype-by-environment interaction for fitness occurred during emergence: genotypes blind to dim blue light (phot1 and nph3) had poor emergence in the open, but not in the shade [7].
  • Strain JK218 exhibits no curvature to light at any fluence from 1 micromole m-2 to 2700 micromoles m-2, but shows normal gravitropism [8].

Physical interactions of NPH3

  • The PHOT1 gene product interacts with the NPH3 gene product to cause phototropic bending over a broad range of light intensity, from very weak light in the soil to stronger light in the aerial environment [7].

Analytical, diagnostic and therapeutic context of NPH3

  • A map-based cloning strategy and transgenic complementation test were applied to demonstrate that a NPH3-like gene deleted in the mutant corresponds to CPT1 [2].


  1. Arabidopsis NPH3: A NPH1 photoreceptor-interacting protein essential for phototropism. Motchoulski, A., Liscum, E. Science (1999) [Pubmed]
  2. The Rice COLEOPTILE PHOTOTROPISM1 gene encoding an ortholog of Arabidopsis NPH3 is required for phototropism of coleoptiles and lateral translocation of auxin. Haga, K., Takano, M., Neumann, R., Iino, M. Plant Cell (2005) [Pubmed]
  3. RPT2 is a signal transducer involved in phototropic response and stomatal opening by association with phototropin 1 in Arabidopsis thaliana. Inada, S., Ohgishi, M., Mayama, T., Okada, K., Sakai, T. Plant Cell (2004) [Pubmed]
  4. Light-induced phosphorylation of a membrane protein plays an early role in signal transduction for phototropism in Arabidopsis thaliana. Reymond, P., Short, T.W., Briggs, W.R., Poff, K.L. Proc. Natl. Acad. Sci. U.S.A. (1992) [Pubmed]
  5. Mutations of Arabidopsis in potential transduction and response components of the phototropic signaling pathway. Liscum, E., Briggs, W.R. Plant Physiol. (1996) [Pubmed]
  6. PHYTOCHROME KINASE SUBSTRATE 1 is a phototropin 1 binding protein required for phototropism. Lariguet, P., Schepens, I., Hodgson, D., Pedmale, U.V., Trevisan, M., Kami, C., de Carbonnel, M., Alonso, J.M., Ecker, J.R., Liscum, E., Fankhauser, C. Proc. Natl. Acad. Sci. U.S.A. (2006) [Pubmed]
  7. An experimental test of the adaptive evolution of phototropins: blue-light photoreceptors controlling phototropism in Arabidopsis thaliana. Galen, C., Huddle, J., Liscum, E. Evolution (2004) [Pubmed]
  8. Mutants of Arabidopsis thaliana with altered phototropism. Khurana, J.P., Poff, K.L. Planta (1989) [Pubmed]
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