Calcium/calmodulin-dependent and -independent phytochrome signal transduction pathways

Cell. 1993 Jun 4;73(5):937-52. doi: 10.1016/0092-8674(93)90272-r.


Phytochrome is a well-characterized plant photoreceptor, able to modulate many morphological, physiological, and biochemical events through as yet undefined mechanisms. By developing single-cell assays to visualize phytochrome responses, we have studied the effects of microinjecting putative signaling intermediates into phytochrome-deficient tomato cells. We demonstrate that phytochrome phototransduction initially involves the activation of one or more G proteins that are coupled to at least two different pathways; one pathway requires calcium and activated calmodulin and can stimulate expression of a photoregulated cab-GUS reporter gene together with the synthesis and assembly of some, but not all, of the photosynthetic complexes. The other pathway, controlling anthocyanin biosynthesis, does not require calcium. Furthermore, our results reveal that phytochrome signaling is cell autonomous and is not likely to require any light-activated steps downstream of the G protein.

Publication types

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

MeSH terms

  • ATP Synthetase Complexes
  • Anthocyanins / biosynthesis
  • Calcium / physiology*
  • Calmodulin / physiology*
  • Chloroplasts / ultrastructure
  • Fluorescent Antibody Technique
  • GTP-Binding Proteins / physiology
  • Gene Expression Regulation
  • Light
  • Microinjections
  • Multienzyme Complexes / biosynthesis
  • Phosphotransferases / biosynthesis
  • Photosynthetic Reaction Center Complex Proteins / biosynthesis
  • Photosynthetic Reaction Center Complex Proteins / genetics
  • Phytochrome*
  • Ribulose-Bisphosphate Carboxylase / biosynthesis
  • Signal Transduction


  • Anthocyanins
  • Calmodulin
  • Multienzyme Complexes
  • Photosynthetic Reaction Center Complex Proteins
  • Phytochrome
  • Phosphotransferases
  • ATP Synthetase Complexes
  • GTP-Binding Proteins
  • Ribulose-Bisphosphate Carboxylase
  • Calcium