CONSTANS and the CCAAT box binding complex share a functionally important domain and interact to regulate flowering of Arabidopsis.
The CCT (for CONSTANS, CONSTANS-LIKE, TOC1) domain is found in 45 Arabidopsis thaliana proteins involved in processes such as photoperiodic flowering, light signaling, and regulation of circadian rhythms. We show that this domain exhibits similarities to yeast HEME ACTIVATOR PROTEIN2 (HAP2), which is a subunit of the HAP2/HAP3/HAP5 trimeric complex that binds to CCAAT boxes in eukaryotic promoters. Moreover, we demonstrate that CONSTANS (CO), which promotes Arabidopsis flowering, interacts with At HAP3 and At HAP5 in yeast, in vitro, and in planta. Mutations in CO that delay flowering affect residues highly conserved between CCT and the DNA binding domain of HAP2. Taken together, these data suggest that CO might replace At HAP2 in the HAP complex to form a trimeric CO/At HAP3/At HAP5 complex. Flowering was delayed by overexpression of At HAP2 or At HAP3 throughout the plant or in phloem companion cells, where CO is expressed. This phenotype was correlated with reduced abundance of FLOWERING LOCUS T (FT) mRNA and no change in CO mRNA levels. At HAP2 or At HAP3 overexpression may therefore impair formation of a CO/At HAP3/At HAP5 complex leading to reduced expression of FT. During plant evolution, the number of genes encoding HAP proteins was greatly amplified, and these proteins may have acquired novel functions, such as mediating the effect of CCT domain proteins on gene expression.
Wenkel
Stephan
S
Max Planck Institute for Plant Breeding Research, D-50829 Cologne, Germany.
Turck
Franziska
F
Singer
Kamy
K
Gissot
Lionel
L
Le Gourrierec
José
J
Samach
Alon
A
Coupland
George
G
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D023081:CCAAT-Binding Factor / Q000378:metabolism*; D002940:Circadian Rhythm / Q000502:physiology; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D035264:Flowers / Q000166:cytology / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D009842:Oligopeptides; D010455:Peptides; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D016415:Sequence Alignment; D017385:Sequence Homology; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D023081:CCAAT-Binding Factor; C092776:CONSTANS protein, Arabidopsis; D004268:DNA-Binding Proteins; C121183:GI protein, Arabidopsis; C491932:At5g12840 protein, Arabidopsis; C491930:HAP3a protein, Arabidopsis; C491935:HAP5a protein, Arabidopsis; D009842:Oligopeptides; D010455:Peptides; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C085706:FLAG peptide