High levels of boron (B) induce DNA double-strand breaks (DSBs) in eukaryotes, including plants. Here we show a molecular pathway of high B-induced DSBs by characterizing Arabidopsis thaliana hypersensitive to excess boron mutants. Molecular analysis of the mutants revealed that degradation of a SWItch/Sucrose Non-Fermentable subunit, BRAHMA (BRM), by a 26S proteasome (26SP) with specific subunits is a key process for ameliorating high-B-induced DSBs. We also found that high-B treatment induces histone hyperacetylation, which increases susceptibility to DSBs. BRM binds to acetylated histone residues and opens chromatin. Accordingly, we propose that the 26SP limits chromatin opening by BRM in conjunction with histone hyperacetylation to maintain chromatin stability and avoid DSB formation under high-B conditions. Interestingly, a positive correlation between the extent of histone acetylation and DSB formation is evident in human cultured cells, suggesting that the mechanism of DSB induction is also valid in animals.

Harnessing plant metabolites and biomass not only for food, feed, and medicines, but also for feedstock for biofuels and industrial materials, appears promising as a strategy to provide sustainable and renewable resources. Biochemical compositions, yield, and yield stability of these plant materials are subject to transcriptional regulation of a diverse array of genes involved in regulatory networks of many metabolic pathways, growth and differentiation, and response to environmental stimuli. Since transcription factors control gene expression by binding directly or indirectly to the promoters of target genes in a sequence-specific manner to either activate or repress the transcription of downstream target genes, they naturally act as master regulators of many biological processes that are associated with quality and quantity of plant metabolites and biomass. Several pioneering studies demonstrated the potential of transcription factors for the manipulation of complex metabolic pathways in plants (Broun 2004). Therefore, understanding of function of transcription factors is an important step towards to develop the transcription factor-based technology for improvement of value and productivity of the plant materials (Broun 2004;Century et al. 2008;Grotewold 2008).With the completion of the Arabidopsis sequences, it became possible to identify putative genes for Abstract The Dof (DNA-binding with one finger) genes are members of a family of plant-specific transcription factors that have a highly conserved DNA-binding domain, namely, Dof domain. The Dof domain is a particular class of zinc finger domain that has been demonstrated to bind specifically to DNA sequences with a T/AAAAG core. In the Arabidopsis genomic database, 36 Dof genes have been identified, whereas the functions of most of the members still remain to be studied. Therefore, we attempted to comprehensively and systematically investigate functions of Arabidopsis Dof genes. As the first step, we isolated cDNAs of all the Arabidopsis Dof genes based on the coding sequences identified on the genomic database. Then, we selected genes, which are subjected to further functional analysis, through a phylogenetic analysis, and transformed Arabidopsis cultured cells (line T87) using cDNAs corresponding to the selected genes. After that, we examined transcriptional profiles in the Dof gene-overexpressed calli using an Arabidopsis DNA microarray. From the results, possible involvements of the Dof genes in regulation of metabolic pathways are discussed. Functional genomics of the Dof transcription factor family genes in suspension-cultured cells of Arabidopsis thalianaKey words: Arabidopsis thaliana, cultured cells, Dof family, metabolic regulation, microarray, transcription factors, transgenic callus.Plant Biotechnology 26, 15-28 (2009) Original PaperAbbreviations: CaMV35S, cauliflower mosaic virus 35S; CDS, coding sequence; Dof, DNA-binding with one finger; exGUS, callus ectopically expressing GUS; GUS, b-galacturonidase; LC/PDA/MS, liquid chromatography/ph...

Ethylene-responsive transcription factor (ERF) family genes, which are involved in regulation of metabolic pathways and/or are useful for metabolic engineering, were investigated in the cultured cells of Arabidopsis thaliana. The pectin content in the gelatinous precipitates after the ethanol precipitation of extracts derived from calli of a transgenic cell line, A17, overexpressing an ERF gene (At1g44830), increased in comparison with the control. Expression of genes involved in pectin biosynthesis was up-regulated in the A17 calli. Overexpression of the ERF gene coordinately activates the pectin biosynthetic pathway genes and increases the content of pectin. These results therefore will be useful as a genetic resource for engineering pectin biosynthesis in plants.