Sustained but not transient phytochrome A signaling targets a region of an Lhcb1*2 promoter not necessary for phytochrome B action.
Current evidence is inconclusive regarding the point of signaling convergence downstream from different members of the phytochrome family. In transgenic Arabidopsis, the activity of a reporter enzyme under the control of the -453 to +67 fragment of an Lhcb1*2 promoter shows very low fluence responses (VLFRs) and high-irradiance responses (HIRs) mediated by phytochrome A and low-fluence responses (LFRs) mediated by phytochrome B. A 5' deletion of the promoter to -134 abolished the HIR without affecting VLFR or LFR. In transgenic tobacco, VLFR and LFR were observed for the -176 to -31 or -134 to -31 fragments of Lhcb1*2 fused to 35S cauliflower mosaic virus minimal promoters, but only the largest fragment showed HIR. We propose that sustained activation of phytochrome A with far-red light initiates a signaling cascade that deviates from phytochrome B signaling and transient phytochrome A signaling and that this divergence extends as far as the Lhcb1*2 promoter.
Cerdán
P D
PD
Instituto de Investigaciones Bioquímicas Fundación Campomar, Buenos Aires, Argentina.
Staneloni
R J
RJ
Ortega
J
J
Bunge
M M
MM
Rodriguez-Batiller
M J
MJ
Sánchez
R A
RA
Casal
J J
JJ
D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins; D001483:Base Sequence; D017796:Caulimovirus / Q000235:genetics; D017931:DNA Primers; D010786:Photoreceptor Cells; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D010834:Phytochrome / Q000378:metabolism*; D051942:Phytochrome A; D051939:Phytochrome B; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D014157:Transcription Factors
D029681:Arabidopsis Proteins; D017931:DNA Primers; C497973:PHYA protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D051942:Phytochrome A; D014157:Transcription Factors; D010834:Phytochrome; D051939:Phytochrome B