ISSN 1990-519X, Cell and Tissue Biology, 2014, Vol. 8, No. 5, pp. 416–422. © Pleiades Publishing, Ltd., 2014. Original Russian Text © L.Ye. Kozeko, 2014, published in Tsitologiya, 2014, Vol. 56, No. 6, pp. 419–426. 416 Induction of heat-shock proteins (Hsp) is a funda- mental cell response to various environmental nega- tive factors common to all living organisms, including plants. Accumulation of these proteins increased cell resistance to stress, particularly, thermotolerance (Queitsch et al., 2000; Bowen et al., 2002; Sørensen et al., 2003). The main feature of Hsp family is their high conservatism in amino acid sequences and func- tions. These proteins are molecular chaperons that are involved under normal conditions in protein folding, assembly, intracellular transport. Under stress condi- tions, they ensure disaggregation of denatured pro- teins, their retention in a nonnative state, and refold- ing or degradation (Mathew and Morimoto, 1998). Elucidation of Hsp chaperone functions and regula- tion of its synthesis are mostly performed on animals and bacteria. However, there is a great deal of evidence that similar mechanisms also operate in plants (Sharova et al., 2002; Agarwal et al., 2002; Kozeko, 2010; Waters et al., 2013). Study of the mechanisms underlying Hsp synthesis revealed that the initiation of Hsp gene transcription occurred by the interaction of transcription factors (heat shock factor, Hsf) with conservative cis-regula- tory elements in the gene-promoter region, called heat-shock elements (HSE) (Pelham, 1982; Wu, 1984; Morimoto, 1998; Schöffl et al., 1998). The functionally active form of Hsf is a trimer. Under Abbreviations: GA—geldanamycin, DMSO—dimethylsulfox- ide, HSE—heat-shock element, Hsp—heat-shock protein, Hsf—heat-shock factor. unstressed conditions, Hsf pool is in the inactive form. A possible mechanism of its suppression was identified in animal cells. In Xenopus oocytes, Hsf1 was bound with cytosolic Hsp90 under physiological conditions (Ali et al., 1998). It has been proposed that stress switches the Hsp90 function, to attend to an increased amount of denatured proteins. Released Hsf produces trimers that are able to induce Hsp gene expression, including Hsp90 (Morimoto, 1998). This idea has found confirmation primarily in animals (Duncan, 2005). Recent data show that similar mechanisms also occur in plant cells. It has been shown that the Hsp90 inhibitors geldanamycin (GA) and radicycol activate gene expression in Arabidopsis thaliana seedlings. Most of these genes, including Hsp70, Hsp90, and Hsp101, contain HSE (Yamada et al., 2007). All these antibiotics have a high affinity to the ATP-binding site of the N-terminal domain of Hsp90 and, thereby, block the chaperone ATPase cycle (Prodromou et al., 1997). Hsp90-specific inhibitors make possible a more comprehensive study of this chaperone family func- tion in the regulation of stress-protein synthesis and organism stress resistance. The goal of this work was to study the effect of GA in a wide range of concentration on Hsp70 and Hsp90 synthesis, as well as thermotoler- ance of A. thaliana seedlings. Changes in Heat-Shock Protein Synthesis and Thermotolerance of Arabodopsis thaliana Seedlings Resulting from Hsp90 Inhibition by Geldanamycin L. Ye. Kozeko Institute of Botany, National Academy of Sciences of Ukraine, Kyiv, Ukraine e-mail: liudmyla.kozeko@gmail.com Received January 9, 2014 Abstract—The influence of geldanamycin (GA), a specific inhibitor of heat-shock protein Hsp90, on the synthesis of Hsp70 and Hsp90 and thermotolerance of Arabidopsis thaliana seedlings has been studied. Incu- bation of seedlings with GA under normal conditions induced synthesis of these stress proteins. Treatment of seeds with the Hsp90 inhibitor resulted in elevated constitutive levels of Hsp70 and Hsp90 in seedlings, as well as increased induction of their synthesis under heat shock. The GA effect increased with its concentration. Hsp up-regulation promoted thermotolerance of seedlings. The findings suggest autoregulation of heat- shock protein synthesis and regulation of plant tolerance by Hsp90. Keywords: heat-shock proteins, geldanamycin, stress reaction, thermotolerance, Arabidopsis thaliana DOI: 10.1134/S1990519X14050046