PHYTOCHROME KINASE SUBSTRATE 1 is a phototropin 1 binding protein required for phototropism

Proc Natl Acad Sci U S A. 2006 Jun 27;103(26):10134-9. doi: 10.1073/pnas.0603799103. Epub 2006 Jun 15.


Phototropism, or plant growth in response to unidirectional light, is an adaptive response of crucial importance. Lateral differences in low fluence rates of blue light are detected by phototropin 1 (phot1) in Arabidopsis. 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. PHYTOCHROME KINASE SUBSTRATE (PKS) 1 and PKS2 are two phytochrome signaling components belonging to a small gene family in Arabidopsis (PKS1-PKS4). The strong enhancement of PKS1 expression by blue light and its light induction in the elongation zone of the hypocotyl prompted us to study the function of this gene family during phototropism. Photobiological experiments show that the PKS proteins are critical for hypocotyl phototropism. Furthermore, PKS1 interacts with phot1 and NPH3 in vivo at the plasma membrane and in vitro, indicating that the PKS proteins may function directly with phot1 and NPH3 to mediate phototropism. The phytochromes are known to influence phototropism but the mechanism involved is still unclear. We show that PKS1 induction by a pulse of blue light is phytochrome A-dependent, suggesting that the PKS proteins may provide a molecular link between these two photoreceptor families.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / physiology*
  • Arabidopsis Proteins / analysis
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Cell Membrane / chemistry
  • Cell Membrane / metabolism
  • Intracellular Signaling Peptides and Proteins / analysis
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Membrane Proteins / analysis
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Phosphoproteins / analysis
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism*
  • Phototropism / genetics*
  • Phytochrome A / metabolism
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism


  • Arabidopsis Proteins
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • NPH3 protein, Arabidopsis
  • PKS1 protein, Arabidopsis
  • PKS2 protein, Arabidopsis
  • Phosphoproteins
  • Phytochrome A
  • NPH1 protein, Arabidopsis
  • PKS4 protein, Arabidopsis
  • Protein Serine-Threonine Kinases