Cryptogam phytochromes

Abstract

ABSTRACTPhytochrome responses in cryptogams are well characterized. However, the properties of cryptogam phytochromes are not well understood, because of the difficulty in obtaining suitable material. Recent advances in molecular biology offer the possibility of studying cryptogam phytochromes at the molecular level. The functional domains in cryptogam phytochromes have been predicted from the homology of the deduced amino acid sequences to known sequences of different functional proteins. Cryptogam phytochrome gene families are highly variable in size and composition. The most structurally unusual cryptogam phytochrome, found in the moss Ceratodon and the fern Adiantum, has a protein kinase catalytic domain in the C‐terminal half, although the N‐terminal half is homologous to conventional phytochromes. In conventional phytochrome, modules homologous to the bacterial two‐component (transmitter) protein kinase have also been found in the C‐terminal ends. While phytochromes lack membrane‐spanning sequences, some types may have microtubule attachment sequences. The relationship of these to dichroic phytochrome is discussed. Phytochrome mRNA and proteins are also discussed, as well as the use of mutants in elucidating signal transduction pathways.