Abstract
To assess potential physical interactions of type I phyA with the type II phyB-phyE phytochromes in vivo, transgenes expressing fusion gene forms of phyA were introduced into the Arabidopsis phyA mutant background. When a single c-Myc (myc) epitope is added to either the N- or C-terminus of phyA, the constructs completely complement phyA mutant phenotypes. However, addition of larger tags, such as six consecutive myc epitopes or the yellow fluorescent protein sequence, result in fusion proteins that show reduced activity. All the tagged phyA proteins migrate as dimers on native gels and co-immunoprecipitation reveals no binding interaction of phyA to any of the type II phys in the dark or under continuous far-red light. Dimers of the phyA 1–615 amino acid N-terminal photosensory domain (NphyA), generated in vivo with a yeast GAL4 dimerization domain and attached to a constitutive nuclear localization sequence, are expressed at a low level and, although they cause a cop phenotype in darkness and mediate a very low fluence response to pulses of FR, have no activity under continuous FR. It is concluded that type I phyA in its Pr form is present in plants predominantly or exclusively as a homodimer and does not stably interact with type II phys in a dimer-to-dimer manner. In addition, its activity in mediating response to continuous FR is sensitive to modification of its N- or C-terminus.
Highlights
The presence of light triggers developmental programs in plants that result in gene expression and growth patterns adapted for harvesting solar energy, competing with neighboring vegetation, and engaging in photoautotrophic metabolism
It has previously been observed that the phyA-GFP or phyA-YFP protein fusions expressed from the CaMV 35S promoter are biologically active in transgenic tobacco and Arabidopsis plants [36,37,38]
Seeds were stratified, induced to germinate with a pulse of R (30 μmol m-2 s-1), and incubated at 22 ̊C for 4 days in darkness or for one day in the dark followed by 3 days under FR. (C) FR fluence response curve showing the lack of effect of continuous FR on the mild cop phenotype of N-terminal photosensory domain (NphyA)-GAL #116 lines
Summary
The presence of light triggers developmental programs in plants that result in gene expression and growth patterns adapted for harvesting solar energy, competing with neighboring vegetation, and engaging in photoautotrophic metabolism. These light-induced changes in morphology, physiology, and metabolism are referred to as photomorphogenesis. The environmental light signals that trigger photomorphogenesis are sensed by discrete classes of photoreceptor molecules, which are responsive to UV, blue, red, and far-red wavelengths [1,2,3,4]. Phytochromes (phy) are dimeric chromoproteins that function as red(R)/far-red(FR) photoreceptors in plants, algae, and bacteria [5,6,7,8].
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