Journal of Plant Physiology 166 (2009) 1745—1754 Differential expression of the ornithine decarboxylase gene during carposporogenesis in the thallus of the red seaweed Grateloupia imbricata (Halymeniaceae) Pilar Garcı ´a-Jime´nez a , Federico Garcı ´a-Maroto b , Jose A. Garrido-Ca ´rdenas b , Cristina Ferrandiz c , Rafael R. Robaina a,Ã a Departamento de Biologı ´a, Facultad de Ciencias del Mar, Universidad de Las Palmas de Gran Canaria, Campus Universitario de Tafira, C.P. 35017 Las Palmas de Gran Canaria, Spain b Area de Bioquı ´mica, Universidad de Almerı ´a, Almerı ´a, Spain c Instituto de Biologı ´a Molecular y Celular de Plantas (UPV-CSIC), Campus de la Universidad Polite´cnica de Valencia, Avda. de los Naranjos s/n, E-46022 Valencia, Spain Received 19 February 2009; received in revised form 21 April 2009; accepted 22 April 2009 KEYWORDS Carposporogenesis; Differential expression; Ornithine decarboxylase; Polyamines; Red seaweed Summary This paper describes the cloning of the ornithine decarboxylase gene from a red seaweed, Grateloupia imbricata (Rhodophyta), the characterization of its expres- sion throughout the reproductive process, and demonstrates how polyamines are involved in seaweed reproduction. In addition, the data indicate that the basal perennial and non-spore-forming thalli behave physiologically and genetically differently from the distal reproductive tissue. The common polyamines putrescine, spermidine and spermine have been associated with carposporogenesis in red seaweeds. Ornithine decarboxylase (ODC, EC 4.1.1.17) produces the diamine putrescine from the non-protein amino acid, ornithine. ODC is predominant in the synthesis of polyamines in G. imbricata. The gene encoding the ornithine decarboxylase in G. imbricata was cloned by genomic polymerase chain reaction (PCR) using degenerate primers against conserved motives, followed by chromosome walking using inverse PCR (iPCR). The encoded protein (GiODC, accession # FJ223132) was very similar to other ODCs, bearing the characteristic conserved domain of pyridoxal-dependent decarboxylases. The expression of the GiODC gene was investigated by real-time PCR and in situ hybridization (ISH), and was observed to vary according to cystocarp differentiation. It was weakly transcribed in apical parts of fertile tissue where the cystocarps are located, while the transcript levels ARTICLE IN PRESS www.elsevier.de/jplph 0176-1617/$ - see front matter & 2009 Elsevier GmbH. All rights reserved. doi:10.1016/j.jplph.2009.04.018 Ã Corresponding author. Tel.:/fax: +34 9284529 04. E-mail address: rrobaina@dbio.ulpgc.es (R.R. Robaina).