ABSTRACT
BRCA1 is a well-known tumor suppressor protein in mammals, involved in multiple cellular processes such as DNA repair, chromosome segregation and chromatin remodeling. Interestingly, homologs of BRCA1 and several of its complex partners are also found in plants. As the respective mutants are viable, in contrast to mammalian mutants, detailed analyses of their biological role is possible. Here we demonstrate that the model plant Arabidopsis thaliana harbors two homologs of the mammalian BRCA1 interaction partner BRCC36, AtBRCC36A and AtBRCC36B. Mutants of both genes as well as the double mutants are fully fertile and show no defects in development. We were able to show that mutation of one of the homologs, AtBRCC36A, leads to a severe defect in intra- and interchromosomal homologous recombination (HR). A HR defect is also apparent in Atbrca1 mutants. As the Atbrcc36a/Atbrca1 double mutant behaves like the single mutants of AtBRCA1 and AtBRCC36A both proteins seem to be involved in a common pathway in the regulation of HR. AtBRCC36 is also epistatic to AtBRCA1 in DNA crosslink repair. Upon genotoxic stress, AtBRCC36A is transferred into the nucleus.
Subject(s)
Arabidopsis Proteins/physiology , BRCA1 Protein/physiology , DNA Repair , Epistasis, Genetic , Recombination, Genetic , Amino Acid Sequence , Arabidopsis/genetics , Arabidopsis/growth & development , Arabidopsis/metabolism , Arabidopsis Proteins/chemistry , Arabidopsis Proteins/genetics , BRCA1 Protein/genetics , Bleomycin/toxicity , Molecular Sequence Data , Nuclear Proteins/analysis , Sequence Homology, Amino AcidABSTRACT
hBRCA1 and hBARD1 are tumor suppressor proteins that are involved as heterodimer via ubiquitinylation in many cellular processes, such as DNA repair. Loss of BRCA1 or BARD1 results in early embryonic lethality and chromosomal instability. The Arabidopsis genome carries a BRCA1 homologue, and we were able to identify a BARD1 homologue. AtBRCA1 and the putative AtBARD1 protein are able to interact with each other as indicated by in vitro and in planta experiments. We have identified T-DNA insertion mutants for both genes, which show no visible phenotype under standard growth conditions and are fully fertile. Thus, in contrast to animals, both genes have no indispensable role during development and meiosis in plants. The two single as well as the double mutant are to a similar extent sensitive to mitomycin C, indicating an epistatic interaction in DNA crosslink repair. We could further demonstrate that in Arabidopsis BARD1 plays a prominent role in the regulation of homologous DNA repair in somatic cells.
Subject(s)
Arabidopsis/genetics , DNA Repair/genetics , Genes, Plant , Tumor Suppressor Proteins/genetics , Ubiquitin-Protein Ligases/genetics , Amino Acid Sequence , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Base Sequence , Breast Neoplasms/genetics , DNA, Bacterial/genetics , DNA, Plant/genetics , DNA, Plant/metabolism , Epistasis, Genetic , Female , Genes, BRCA1 , Humans , Meiosis , Mitomycin/pharmacology , Molecular Sequence Data , Mutagenesis, Insertional , Phenotype , Plants, Genetically Modified , Sequence Homology, Amino AcidABSTRACT
Iron mobilization responses are induced by low iron supply at transcriptional level. In tomato, the basic helix-loop-helix gene FER is required for induction of iron mobilization. Using molecular-genetic techniques, we analyzed the function of BHLH029, named FRU (FER-like regulator of iron uptake), the Arabidopsis thaliana homolog of the tomato FER gene. The FRU gene was mainly expressed in roots in a cell-specific pattern and induced by iron deficiency. FRU mutant plants were chlorotic, and the FRU gene was found necessary for induction of the essential iron mobilization genes FRO2 (ferric chelate reductase gene) and IRT1 (iron-regulated transporter gene). Overexpression of FRU resulted in an increase of iron mobilization responses at low iron supply. Thus, the FRU gene is a mediator in induction of iron mobilization responses in Arabidopsis, indicating that regulation of iron uptake is conserved in dicot species.
Subject(s)
Arabidopsis/genetics , Gene Expression Regulation, Plant , Genes, Plant , Genes, Regulator , Iron/metabolism , Amino Acid Sequence , Arabidopsis/growth & development , Arabidopsis Proteins/chemistry , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Basic Helix-Loop-Helix Transcription Factors , Conserved Sequence , Genetic Techniques , Helix-Loop-Helix Motifs/genetics , Iron Deficiencies , Molecular Biology/methods , Molecular Sequence Data , Mutation , Plant Roots/cytology , Plant Roots/genetics , Plant Roots/metabolism , Plants, Genetically Modified , Promoter Regions, Genetic , Protein Structure, Tertiary , Reverse Transcriptase Polymerase Chain Reaction , Sequence Homology, Amino Acid , Transcription Factors/chemistry , Transcription Factors/genetics , Transcription Factors/metabolism , Up-RegulationABSTRACT
In Arabidopsis thaliana (L.) Heynh. the seed-specific transcription factors ABI3 and FUS3 have key regulatory functions during the development of mature seeds. The highly conserved RY motif [DNA motif CATGCA(TG)], present in many seed-specific promoters, is an essential target of both regulators. Here we show that, in vitro, the full-length ABI3 protein, as well as FUS3 protein, is able to bind to RY-DNA and that the B3 domains of both transcription factors are necessary and sufficient for the specific interaction with the RY element. Flanking sequences of the RY motif modulate the binding, but the presence of an RY sequence alone allows the specific interaction of ABI3 and FUS3 with the target in vitro. Transcriptional activity of ABI3 and FUS3, measured by transient promoter activation, requires the B3 DNA-binding domain and an activation domain. In addition to the known N-terminal-located activation domain, a second transcription activation domain was found in the B1 region of ABI3.
