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Crosstalk between heat shock protein chapterones and heat stress transcription factors
February 2011. Exposure to high temperatures activates the cellular heat stress response (HSR), a reaction found in virtually all living organisms, from bacteria to humans. Heat stress transcription factors (Hsfs) regulate gene expression in response to such environmental stress. The Hsf network in plants is controlled at the transcriptional level by cooperation of distinct Hsf members and by interaction with chaperones. A team of scientists at the Goethe University Frankfurt found two general mechanisms of Hsf regulation by chaperones when investigating the three major Hsfs in tomato plants (A1, A2, and B1).
They observed that the heat shock proteins Hsp70 and Hsp90 regulate Hsf function by direct interactions. Hsp70 represses the activity of HsfA1, including its DNA binding, and the coactivator function of HsfB1 in the complex with HsfA2, while the DNA binding activity of HsfB1 is stimulated by Hsp90.
In addition they found that Hsp90 affects the abundance of HsfA2 and HsfB1 by modulating hsfA2 transcript degradation involved in regulation of the timing of HsfA2 synthesis. By contrast, HsfB1 binding to Hsp90 and to DNA are prerequisites for targeting this Hsf for proteasomal degradation, which also depends on a sequence element in its carboxyl-terminal domain. Thus, HsfB1 represents an Hsp90 client protein that, by interacting with the chaperone, is targeted for, rather than protected from, degradation.
Based on these findings, the scientists propose a versatile regulatory regime involving the heat shock proteins Hsp90 and Hsp70, and the three Heat stress transcription factor in the control of heat stress response.
Full paper
Crosstalk between Hsp90 and Hsp70 Chaperones and Heat Stress Transcription Factors in Tomato. 2011. Alexander Hahn, Daniela Bublak, Enrico Schleiff & Klaus-Dieter Scharf. Plant Cell Advance Online Publication. Published on February 9, 2011; 10.1105/tpc.110.076018