DOMINANT-NEGATIVE SUPPRESSION OF ARABIDOPSIS PHOTORESPONSES BY MUTANTPHYTOCHROME-A SEQUENCES IDENTIFIES SPATIALLY DISCRETE REGULATORY DOMAINS IN THE PHOTORECEPTOR
M. Boylan et al., DOMINANT-NEGATIVE SUPPRESSION OF ARABIDOPSIS PHOTORESPONSES BY MUTANTPHYTOCHROME-A SEQUENCES IDENTIFIES SPATIALLY DISCRETE REGULATORY DOMAINS IN THE PHOTORECEPTOR, The Plant cell, 6(3), 1994, pp. 449-460
We used the exaggerated short hypocotyl phenotype induced by oat phyto
chrome A overexpression in transgenic Arabidopsis to monitor the biolo
gical activity of mutant phytochrome A derivatives. Three different mu
tations, which were generated by removing 52 amino acids from the N te
rminus (DELTAN52), the entire C-terminal domain (DELTAC617), or amino
acids 617-686 (DELTA617-686) of the oat molecule, each caused striking
dominant negative interference with the ability of endogenous Arabido
psis phytochrome A to inhibit hypocotyl growth in continuous far-red l
ight (''far-red high irradiance response'' conditions). By contrast, i
n continuous white or red light, DELTAN52 was as active as the unmutag
enized oat phytochrome A protein in suppressing hypocotyl elongation,
while DELTAC617 and DELTA617-686 continued to exhibit dominant negativ
e behavior under these conditions. These data suggest that at least th
ree spatially discrete molecular domains coordinate the photoregulator
y activities of phytochrome A in Arabidopsis seedlings. The first is t
he chromophore-bearing N-terminal domain between residues 53 and 616 t
hat is apparently sufficient for the light-induced initiation but not
the completion of productive interactions with transduction chain comp
onents. The second is the C-terminal domain between residues 617 and 1
129 that is apparently necessary for completion of productive interact
ions under all irradiation conditions. The third is the N-terminal 52
amino acids that are apparently necessary for completion of productive
interactions only under far-red high irradiance conditions and are co
mpletely dispensable under white and red light regimes.