Regulation and function of heat stress transcription factors and molecular chaperones in protein homeostasis
(Klaus-Dieter Scharf, Sotirios Fragkostefanakis, Daniela Bublak, Sascha Röth, Puneet Paul, Yangjie Hu, Anida Mesihovic, Asmaa El-Shershaby)
Molecular chaperones form a network of proteins involved in the control of the cellular protein homeostasis under normal and stressful growth conditions. In plants they are encoded by several multigene families of an unusually high complexity. This can only partially be explained by specific developmental and stress-induced expression patterns of individual members in each family and/or by differences in the subcellular distribution of the corresponding proteins.
Molecular chaperones like heat shock proteins (Hsps) are important components of the general heat stress response (HSR), a highly conserved response system among different organisms, which in plants shows a remarkable complexity and unique features. The transcriptional reprogramming under elevated temperatures is mediated by the activity of the heat stress transcription factors (Hsfs). Hsfs are subjected to different regulatory mechanisms from transcriptional to post-translational level, including cell-type dependent feedback regulation through physical and functional interactions with members of the Hsp90, Hsp70 and small Hsp families. Apart from their importance for HSR and thermotolerance Hsf/chaperone networks are assumed to be involved in other stresses and in various developmental processes. In this direction, the maintenance of the cellular homeostasis is a prerequisite to ensure the robustness of developmental programs under stressful climate conditions. As pollen development is most sensitive to high temperatures in many plant cultivars, the contribution of Hsf and chaperone functions to pollen thermotolerance is addressed in individual research projects associated with the Marie-Curie-International Training Network on "Solanaceae pollen thermotolerance and crop fertility" (SPOT-ITN).
To unravel the regulation and function of Hsfs and chaperones we utilize various approaches including plant physiology, cell and molecular biology, genetics and biochemistry. We have established in vitro and in vivo test systems to analyze the functional contribution of chaperones in protein distribution and in sensing and signaling of disturbed protein homeostasis in different cellular compartments including plastids and mitochondria.
The research on heat stress motivated us to develop HEATSTER, a central platform for the work with Hsfs. Currently the platform provides a manually curated database that includes more than 500 plant Hsf sequences, which are covering the Hsf gene families of more than 20 fully sequenced plant genomes and an annotation tool that allows the automatic identification and classification of Hsfs.