J. Plant Physiol. 161. 219 – 227 (2004) http://www.elsevier-deutschland.de/jplhp Cloning and analysis of a cDNA encoding an endo-polygalacturonase expressed during the desiccation period of the silique-valves of turnip- tops (Brassica rapa L. cv. Rapa) María del Carmen Rodríguez-Gacio 1 , Carlos Nicolás 2 , Angel J. Matilla 1 * 1 Departamento de Fisiología Vegetal, Facultad de Farmacia, Universidad de Santiago de Compostela, Campus Sur s/n. 15782-Santiago de Compostela, Spain 2 Departamento de Fisiología Vegetal, Facultad de Farmacia. Centro Hispano-Luso de Investigaciones Agrarias. Universidad de Salamanca, Plaza de los Doctores de la Reina s/n. 37007-Salamanca, Spain Received May 12, 2003 · Accepted August 24, 2003 Summary During zygotic embryogenesis of turnip-tops (Brassica rapa L. cv. Rapa), the polygalacturonase ac- tivity (PG; EC 3.2.1.15), measured as a decrease in viscosity of polygalacturonic acid, reached a high when the desiccation process in the seeded silique was triggered and the valves had lost more than 70–75 % of their moisture (45–50 DPA). The PG activity was not detected in any phases of develop- ing seeds. This work also characterizes a cDNA with an open reading frame of 1303bp and that co- des for a putative PG called Br PG1. This falls into the category of clade-B, which includes PG related to shattering and abscission processes. The deduced Br PG1 sequence predicted a 434-residue- long precursor protein (46.7kDa) with a transit peptide sequence 23 amino acids long. A molecular mass of 44.3 kDa was calculated for the mature form of Br PG1, which showed high sequence similar- ity to PGA1 (97%) of B. napus (X98373) and ADPG1 (87%) of Arabidopsis thaliana (AJ002532). All conserved amino acids at the catalytic site of PGs belonging to clade-B were preserved on Br PG1. This Br PG1 gene was specifically expressed in the silique valves of turnip-tops and was temporally expressed at the beginning of its desiccation. Key words: Brassica rapa – embryogenesis – germination – polygalacturonase – seed – silique-wall – turnip-tops Abbreviations: Br PG1 = polygalacturonase clone of turnip-tops. – CDTA = cyclohexane-diamine- tetracetic acid. – DPA = days post anthesis. – PVP = polyvinyl-pyrrolidone. – PG = polygalacturonase. – RT-PCR = reverse transcriptase polymerase chain reaction * E-mail corresponding author: bvmatilla@usc.es 0176-1617/04/161/02-219 $ 30.00/0