RESEARCH PAPER Two sunflower 17.6HSP genes, arranged in tandem and highly homologous, are induced differently by various elicitors P. Rampino 1 , G. Mita 2 , E. Assab 1 , M. De Pascali 1 , E. Giangrande 1 , A. S. Treglia 1 & C. Perrotta 1 1 Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Universita ` del Salento, Lecce, Italy 2 ISPA-CNR Unita ` di Lecce, Lecce, Italy INTRODUCTION Heat stress is one of the main environmental factors to which living organisms are subjected. At cellular level, it is responsible for a rapid, specific and highly conserved response known as the ‘heat shock response’. This response is mediated by the activation of heat shock (HS) genes that are considered an optimal model system to study the coordinate regulation of gene expression and cell response to environmental stresses (Scho ¨ffl et al. 1998). At the molecular level, there is a transient re-pro- gramming of cellular activities characterized by the cessa- tion of normal protein synthesis concomitant with the synthesis of HS proteins (HSPs). A common feature of HSPs is their accumulation, in a dose-dependent manner, to reach levels sufficient to protect cells. A peculiar feature of the HS response in plants is the synthesis of abundant small HSPs (sHSPs), ranging in size from 15 to 30 kDa, forming a heterogeneous family related to a-crystallins of the vertebrates (Waters et al. 1996, 2008). These proteins are coded by nuclear genes and, in Arabidopsis (Siddique et al. 2008), are classified into 12 different subfamilies on the basis of their amino acid sequences and homology, and of their intracellular localization. Seven are cytoplasmic ⁄ nuclear subfamilies, class I to class VII (CI–CVII); another three subfamilies are localized, respectively, in plastids (P), in the endoplas- mic reticulum (ER) and in peroxisomes (Po); and the last two are located in mitochondria (MI and MII). CI is the largest subfamily, where A. thaliana has six CI gene mem- bers (Sun et al. 2002; Siddique et al. 2008). These genes are induced by heat stress as well as by other abiotic stresses such as heavy metals, chilling, oxidative stress, etc. (Sun et al. 2002; Gullı` et al. 2005). Their transcrip- tion is also induced by development in pollen, seeds, fruits and flowers (Rojas et al. 2002; Volkov et al. 2005). The expression of HSPs is primarily controlled at the transcriptional level and requires interaction of the tran- scription machinery with specific transcription factors, the heat stress factors (HSFs), which play a key role in Keywords Abiotic stresses; gene expression; heat shock proteins; Helianthus annuus L. Correspondence C. Perrotta, Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Universita ` del Salento, via Prov.le Monteroni, 73100 Lecce, Italy. E-mail: carla.perrotta@unile.it Editor J. Whelan Received: 1 December 2008; Accepted: 15 January 2009 doi:10.1111/j.1438-8677.2009.00200.x ABSTRACT Plants respond to environmental stimuli, such as heat shock, by re-program- ming cellular activity through differential gene expression, mainly controlled at the transcription level. The current study refers to two sunflower small heat shock protein (sHSP) genes arranged in tandem in head-to-head orien- tation and linked by a 3809 bp region. These genes exhibit only slight struc- tural differences in the coding portion. They code for cytosolic class I sHSPs and are named HaHSP17.6a and HaHSP17.6b according to the molecular weight of the putative proteins. The genomic organization of these genes is consistent with the idea that many HSP genes originate from duplication events; in this case, probably an inversion and duplication occurred. The HaHSP17.6a and HaHSP17.6b genes are characterized by different expres- sion levels under various heat stress conditions; moreover, their expression is differently induced by various elicitors. The differential regulation observed for HaHSP17.6a and HaHSP17.6b genes differs from previous observations on duplicated sHSP genes in plants. Plant Biology ISSN 1435-8603 Plant Biology 12 (2010) 13–22 ª 2009 German Botanical Society and The Royal Botanical Society of the Netherlands 13