UNCORRECTED PROOF Journal : Large 425 Dispatch : 27-1-2014 Pages : 13 Article No : 2031 ¨ LE ¨ TYPESET MS Code : PLAA-D-13-00697 þ CP þ DISK 1 3 Planta DOI 10.1007/s00425-014-2031-4 ORIGINAL ARTICLE Differential expression of the brassinosteroid receptor-encoding BRI1 gene in Arabidopsis Lidia Hategan · Blanka Godza · Laszlo Kozma-Bognar · Gerard J. Bishop · Miklos Szekeres Received: 7 November 2013 / Accepted: 15 January 2014 © Springer-Verlag Berlin Heidelberg 2014 the wild phenotype, expression from the photosynthesis- associated CAB3 and the vasculature-specific SUC2 and ATHB8 promoters resulted in plants with varying morpho- genic defects. Our results reveal complex differential regu- lation of BRI1 expression, and suggest that by influencing the distribution and abundance of the receptor this regula- tion can enhance or attenuate BR signalling. Keywords Ectopic expression · Hormone susceptibility · Phytohormone · Reporter gene Abbreviations BR Brassinosteroid BL Brassinolide CS Castasterone DD Continuous dark LD Light–dark cycles LL Continuous light DAG Days after germination LUC Firefly luciferase GUS β-Glucuronidase Introduction Brassinosteroids (BRs) are polyhydroxylated steroid hor- mones that control plant development from germination to seed production (Clouse and Sasse 1998; Haubrick et al. 2006). The biologically active BRs castasterone (CS) and brassinolide (BL) are perceived by the plasma membrane-localized leucine-rich repeat receptor-like kinase BRASSINOSTEROID INSENSITIVE 1 (BRI1) (Li and Chory 1997), which then initiates a phosphoryla- tion/dephosphorylation-based signalling cascade that con- trols the transcriptional activity of BR-responsive genes. Abstract Brassinosteroid (BR)-regulated growth and development in Arabidopsis depends on BRASSINOS- TEROID INSENSITIVE 1 (BRI1), the BR receptor that is responsible for initiating the events of BR signalling. We analysed the temporal and spatial regulation of BRI1 expression using stable transgenic lines that carried BRI1 promoter:reporter fusions. In both seedlings and mature plants the tissues undergoing elongation or differentia- tion showed elevated BRI1 gene activity, and it could be demonstrated that in the hypocotyl this was accompanied by accumulation of the BRI1 transcript and its receptor protein product. In seedlings the BRI1 promoter was also found to be under diurnal regulation, determined primarily by light repression and a superimposed circadian control. To determine the functional importance of transcriptional regulation we complemented the severely BR insensitive bri1-101 mutant with a BRI1-luciferase fusion construct that was driven by promoters with contrasting specificities. Whereas the BRI1 promoter-driven transgene fully restored L. Hategan and B. Godza contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s00425-014-2031-4) contains supplementary material, which is available to authorized users. L. Hategan · B. Godza · L. Kozma-Bognar · M. Szekeres (*) Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, 6726 Szeged, Hungary e-mail: szekeres@brc.hu G. J. Bishop Division of Biology, Imperial College London, London SW7 1AZ, UK Present Address: G. J. Bishop East Malling Research, Kent ME19 6BJ, UK 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 Author Proof