Genetic and Molecular Analysis of an Allelic Series of cop1 Mutants Suggests Functional Roles for the Multiple Protein Domains

Abstract

The Arabidopsis protein COP1, encoded by the constitutive photomorphogenic locus 1, is an essential regulatory molecule that plays a role in the repression of photomorphogenic development in darkness and in the ability of light-grown plants to respond to photoperiod, end-of-day far-red treatment, and ratio of red/far-red light. The COP1 protein contains three recognizable structural domains: starting from the N terminus, they are the zinc binding motif, the putative coiled-coil region, and the domain with multiple WD-40 repeats homologous to the beta subunit of trimeric G-proteins (G beta). To understand the functional implications of these structural motifs, 17 recessive mutations of the COP1 gene have been isolated based on their constitutive photomorphogenic seedling development in darkness. These mutations define three phenotypic classes: weak, strong, and lethal. The mutations that fall into the lethal class are possible null mutations of COP1. Molecular analysis of the nine mutant alleles that accumulated mutated forms of COP1 protein revealed that disruption of the G beta-protein homology domain or removal of the very C-terminal 56 amino acids are both deleterious to COP1 function. In-frame deletions or insertions of short amino acid stretches between the putative coiled-coil and G beta-protein homology domains strongly compromised COP1 function. However, a mutation resulting in a COP1 protein with only the N-terminal 282 amino acids, including both the zinc binding and the coiled-coil domains, produced a weak phenotypic defect. These results indicated that the N-terminal half of COP1 alone retains some activity and a disrupted C-terminal domain masks this remaining activity.

The Type II Transforming Growth Factor (TGF)-β Receptor-interacting Protein TRIP-1 Acts as a Modulator of the TGF-β Response

“…A mutant version of TUP-1 that lacks all of its WD40 repeats is still able to carry out many functions similarly to wild type (43,44). Also, the Arabidopsis WD40 repeat protein COP-1 was found to be very tolerant of extensive deletions, and, in fact, a mutant in which all WD40 repeats were deleted exhibited a much milder phenotype than other mutants with much less extensive mutations in the WD40 repeat sequences (20). Thus, the results from our deletion analysis of TRIP-1 resemble the results obtained with other WD40 repeat proteins, because deletion of all WD40 repeats had much less drastic effects than more restricted deletions and still allowed receptor association and inhibition of the TGF-␤ response.…”

PSEUDO RESPONSE REGULATORs stabilize CONSTANS protein to promote flowering in response to day length

“…35S:: TOC1 was crossed to SUC2 :: HA:CO and used for ChIP experiments. For cop1 mutant analyses, cop1‐4 was used (McNellis et al , 1994). For fkf1 mutant analyses, fkf1‐2 was used (Imaizumi et al , 2003).…”

The RING Finger Motif of Photomorphogenic Repressor COP1 Specifically Interacts with the RING-H2 Motif of a NovelArabidopsis Protein

“…Arabidopsis thaliana wild type and cop1-4 mutants are in Columbia (Col) background and cop1-5 mutant is in Wassilewskijce background. All other cop1 alleles and fus mutants are in Landsberg erecta background (8). The plant growth conditions were described previously (8).…”

“…All other cop1 alleles and fus mutants are in Landsberg erecta background (8). The plant growth conditions were described previously (8).…”

“…Light stimuli abrogate the nuclear localization of COP1 and allows seedlings to pursue photomorphogenic development (6). COP1 contains an N-terminal RING finger motif (7,8), which has been demonstrated to bind two zinc ions (9). The RING finger motif is followed by a coiled-coil motif, which is common among a subgroup of RING finger proteins (10) and a WD40 repeat domain in the C-terminal half.…”