ORIGINAL PAPER Spermidine-mediated in vitro phosphorylation of transcriptional regulator OSBZ8 by SNF1-type serine/threonine protein kinase SAPK4 homolog in indica rice Bhaskar Gupta • Kamala Gupta • Dibyendu Narayan Sengupta Received: 8 October 2011 / Revised: 2 January 2012 / Accepted: 5 January 2012 Ó Franciszek Go ´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´w 2012 Abstract Plants respond to abiotic stresses such as salinity, extreme temperature and drought by the activation of complex intracellular signaling cascades that regulate acclimatory biochemical and physiological changes. Pro- tein kinases are major signal transduction factors that play a central role in mediating acclimation to environmental changes in eukaryotic organisms. It is well known that changes in abiotic conditions such as the concentration of ions, temperature and humidity lead to modulation of polyamine contents in plants. However, little is known about the relevant part these polyamines play in abiotic stress responses. Here, we address a specific role of sper- midine during high salt stress by studying its interaction with OSPDK, a sucrose nonfermenting 1-related protein kinase2 (SnRK2)-type serine/threonine protein kinase SAPK4 homolog in indica rice. In this report, we demon- strate that spermidine mediates in vitro phosphorylation of OSBZ8, a bZIP class of ABRE-binding transcription fac- tor, by OSPDK. Our results give a first-hand indication of the pivotal role played by polyamines in abiotic stress cell signaling in plants. Keywords Abiotic stress  ABRE  EMSA  Polyamine  Serine/threonine kinase  Spermidine  OSBZ8 Abbreviations ABA Abscisic acid ABRE Abscisic acid responsive element bZIP Basic leucine zipper EMSA Electrophoretic mobility shift assay GST Glutathione S-transferase MBP Myelin basic protein PA Polyamine Put Putrescine SNF-1 Sucrose non-fermenting protein 1 SnRK2 SNF1-related protein kinase 2 Spd Spermidine Spm Spermine Introduction Environmental stresses like drought, heat, cold and salinity severely affect plant growth and productivity worldwide. It has been estimated that two-thirds of the yield potential of major crops are routinely lost due to the unfavorable environmental factors (Alca ´zar et al. 2011; Gill and Tuteja 2010; Quinet et al. 2010). On the other hand, the world Communicated by R. Aroca. B. Gupta and K. Gupta contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s11738-012-0929-7) contains supplementary material, which is available to authorized users. B. Gupta  K. Gupta  D. N. Sengupta Division of Plant Biology, Bose Institute (Main Campus), 93/1 A.P.C Road, Kolkata 700009, India Present Address: B. Gupta (&) Molecular Biology Laboratory, Department of Biotechnology, Presidency University, 86/1 College Street, Kolkata 700073, India e-mail: bhaskarzoology@gmail.com Present Address: K. Gupta (&) Plant Molecular Biology Laboratory, Department of Botany, Bethune College, 181 Bidhan Sarani, Kolkata 700006, India e-mail: kamalagupta@gmail.com 123 Acta Physiol Plant DOI 10.1007/s11738-012-0929-7