Wrzaczek et al. BMC Plant Biology 2010, 10:95 http://www.biomedcentral.com/1471-2229/10/95 Open Access RESEARCH ARTICLE © 2010 Wrzaczek et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Research article Transcriptional regulation of the CRK/DUF26 group of Receptor-like protein kinases by ozone and plant hormones in Arabidopsis Michael Wrzaczek †1 , Mikael Brosché †1 , Jarkko Salojärvi 1 , Saijaliisa Kangasjärvi 2 , Niina Idänheimo 1 , Sophia Mersmann 3 , Silke Robatzek 3,4 , Stanisław Karpiński 5 , Barbara Karpińska 6 and Jaakko Kangasjärvi* 1 Abstract Background: Plant Receptor-like/Pelle kinases (RLK) are a group of conserved signalling components that regulate developmental programs and responses to biotic and abiotic stresses. One of the largest RLK groups is formed by the Domain of Unknown Function 26 (DUF26) RLKs, also called Cysteine-rich Receptor-like Kinases (CRKs), which have been suggested to play important roles in the regulation of pathogen defence and programmed cell death. Despite the vast number of RLKs present in plants, however, only a few of them have been functionally characterized. Results: We examined the transcriptional regulation of all Arabidopsis CRKs by ozone (O 3 ), high light and pathogen/ elicitor treatment - conditions known to induce the production of reactive oxygen species (ROS) in various subcellular compartments. Several CRKs were transcriptionally induced by exposure to O 3 but not by light stress. O 3 induces an extracellular oxidative burst, whilst light stress leads to ROS production in chloroplasts. Analysis of publicly available microarray data revealed that the transcriptional responses of the CRKs to O 3 were very similar to responses to microbes or pathogen-associated molecular patterns (PAMPs). Several mutants altered in hormone biosynthesis or signalling showed changes in basal and O 3 -induced transcriptional responses. Conclusions: Combining expression analysis from multiple treatments with mutants altered in hormone biosynthesis or signalling suggest a model in which O 3 and salicylic acid (SA) activate separate signaling pathways that exhibit negative crosstalk. Although O 3 is classified as an abiotic stress to plants, transcriptional profiling of CRKs showed strong similarities between the O 3 and biotic stress responses. Background Receptor-like/Pelle kinases (RLKs) are important compo- nents in the regulation of plant development, hormone signalling, abiotic, and biotic stress responses in plants. RLKs are serine-threonine protein kinases that typically contain a signal peptide, a variable extracellular domain, a transmembrane region, and a conserved intracellular protein kinase domain. The extracellular ligand-binding domain perceives signals and is commonly used to clas- sify RLKs into distinct subgroups [1]. The RLKs are one of the largest gene families in Arabidopsis with more than 600 members, [1-4], but only relatively few of them, mostly leucine-rich repeat RLKs (LRR-RLK), have been functionally characterized. CLAVATA1, a LRR-RLK, binds the small extracellular protein CLAVATA3 to regu- late meristem proliferation [5]. FERONIA (a member of a previously uncharacterized group of RLKs) is central to the regulation of male-female interactions during pollen tube reception in Arabidopsis [6] and in Brassica the S- locus Receptor Kinase and its ligand are critical determi- nants of self-incompatibility [7,8]. In Arabidopsis, ERECTA (a LRR-RLK) is a multifaceted regulator of development and physiological processes as well as envi- ronmental responses [9]. BRASSINOSTEROID INSEN- SITIVE 1 (BRI1, a LRR-RLK) binds the plant hormone brassinosteroid and dimerizes with BRI1-ASSOCIATED RECEPTOR KINASE 1/SOMATIC EMBRYOGENESIS * Correspondence: jaakko.kangasjarvi@helsinki.fi 1 Plant Biology Division, Department of Biosciences, University of Helsinki, FI- 00014 Helsinki, Finland † Contributed equally Full list of author information is available at the end of the article