HOME :: CHAPTER 17 :: Essay 17.2 Diversity of Phytochrome
Chromophores Ruairidh J. H. Sawers, Department of Plant Biology,
University of Geneva, Geneva, Switzerland The first phytochrome
photoreceptors to be characterized were isolated from flowering
plants. However, recently, phytochrome and phytochrome-like
proteins have been discovered in photosynthetic and
nonphotosynthetic bacteria, in fungi, and in slime molds. Such a
distribution challenges ideas concerning the evolution of the
phytochrome receptors and the nature of their function. Are they
all photoreceptors? What was their ancestral function? It has
been suggested that the phytochrome family is derived from
proteins that evolved as bilin (linear tetrapyrrole) sensors. Of
the proteins currently known, all bind a bilin chromophore and
it is these light-absorbing prosthetic groups that confer
spectral activity. The nature of the chromophore differs among
the phytochrome-like protein family, resulting in subtle
differences in spectral properties. Howeve