Biochemical characterization of Arabidopsis wild-type and mutant phytochrome B holoproteins

Plant Cell. 1997 Dec;9(12):2271-80. doi: 10.1105/tpc.9.12.2271.


Although phytochrome B (phyB) plays a particularly important role throughout the life cycle of a plant, it has not been studied in detail at the molecular level due to its low abundance. Here, we report on the expression, assembly with chromophore, and purification of epitope-tagged Arabidopsis phyB. In addition, we have reconstructed two missense mutations, phyB-4 and phyB-101, isolated in long hypocotyl screens. We show that mutant proteins phyB-4 and phyB-101 exhibit altered spectrophotometric and biochemical properties relative to the wild-type protein. In particular, we demonstrate that phyB-101 Pfr exhibits rapid nonphotochemical (dark) reversion to Pr that results in a lower photoequilibrium level of the active Pfr form. We conclude that this occurs in vivo as well because phyB-101 mutants are shown to lack an end-of-day-far-red hypocotyl elongation response that requires a stable Pfr species. We propose that this Pfr instability may be the primary molecular mechanism underlying the phyB-101 mutant phenotype.

Publication types

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

MeSH terms

  • Arabidopsis / chemistry*
  • Arabidopsis / genetics*
  • Arabidopsis / radiation effects
  • Arabidopsis Proteins
  • Base Sequence
  • DNA Primers / genetics
  • Darkness
  • Genes, Plant
  • Mutation*
  • Phenotype
  • Photochemistry
  • Photoreceptor Cells*
  • Phytochrome / chemistry*
  • Phytochrome / genetics*
  • Phytochrome / radiation effects
  • Phytochrome B
  • Plants / genetics
  • Plants / metabolism
  • Plants / radiation effects
  • Saccharomyces cerevisiae / genetics
  • Spectrophotometry
  • Transcription Factors*


  • Arabidopsis Proteins
  • DNA Primers
  • PHYB protein, Arabidopsis
  • Transcription Factors
  • Phytochrome
  • Phytochrome B