Tomato heat stress transcription factor HsfB1 represents a novel type of general transcription coactivator with a histone-like motif interacting with the plant CREB binding protein ortholog HAC1

• Published in: The Plant cell 2004-06, Vol.16 (6), p.1521-1535
• Main Authors: Bharti, K, Koskull-Doring, P. von, Bharti, S, Kumar, P, Tintschl-Korbitzer, A, Treuter, E, Nover, L
• Format: Article
• Language: English
• Subjects: Amino Acid Motifs; Amino Acid Sequence; amino acid sequences; Amino acids; Animals; Arabidopsis - cytology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins; Arabidopsis thaliana; beta-glucuronidase; binding capacity; binding sites; Cauliflower mosaic virus; COS Cells; CREB-Binding Protein; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Drug Synergism; Gene Expression Regulation, Plant; Genes; Genes, Plant - genetics; Genes, Reporter - genetics; Heat Shock Transcription Factors; heat stress; Heat stress disorders; Heat tolerance; Heat-Shock Proteins; histones; Histones - chemistry; Housekeeping; Journalism; luciferase; Lycopersicon esculentum - genetics; Lycopersicon esculentum - metabolism; Macromolecular Substances; Molecular Sequence Data; Nicotiana benthamiana; Nicotiana tabacum; Nuclear Proteins - metabolism; Plant cells; Plant Proteins - chemistry; Plant Proteins - genetics; Plant Proteins - metabolism; Plasmids; promoter regions; Promoter Regions, Genetic - genetics; Protein Binding; protein-protein interactions; Protoplasts; Protoplasts - cytology; Protoplasts - metabolism; Reporter genes; Repressor Proteins - genetics; Repressor Proteins - metabolism; Solanum peruvianum; tobacco; Tomatoes; Trans-Activators - metabolism; transcription (genetics); Transcription factors; Transcription Factors - chemistry; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic - genetics; transcriptional activation; transgenic plants
• ISSN: 1040-4651; 1532-298X; 1532-298X
• DOI: 10.1105/tpc.019927

In contrast with the class A heat stress transcription factors (HSFs) of plants, a considerable number of HSFs assigned to classes B and C have no evident function as transcription activators on their own. However, in the following article, we provide evidence that tomato (Lycopersicon peruvianum) HsfB1 represents a novel type of coactivator cooperating with class A HSFs (e.g., with tomato HsfA1). Provided the appropriate promoter architecture, the two HSFs assemble into an enhanceosome-like complex, resulting in strong synergistic activation of reporter gene expression. Moreover, HsfB1 also cooperates in a similar manner with other activators, for example, with the ASF1/2 enhancer binding proteins of the 35S promoter of Cauliflower mosaic virus or with yet unidentified activators controlling housekeeping gene expression. By these effects, HsfB1 may help to maintain and/or restore expression of certain viral or housekeeping genes during ongoing heat stress. The coactivator function of HsfB1 depends on a histone-like motif in its C-terminal domain with an indispensable Lys residue in the center (GRGKMMK). This motif is required for recruitment of the plant CREB binding protein (CBP) ortholog HAC1. HsfA1, HsfB1, and HAC1/CBP form ternary complexes in vitro and in vivo with markedly enhanced efficiency in promoter recognition and transcription activation in plant and mammalian (COS7) cells. Using small interfering RNA-mediated knock down of HAC1 expression in Arabidopsis thaliana mesophyll protoplasts, the crucial role for the coactivator function of HsfB1 was confirmed.