Postharvest Biology and Technology 44 (2007) 254–259 Prickly pear polygalacturonase gene: cDNA cloning and transcript accumulation during ethylene treatment, cold storage and wounding Flor de F´ atima Rosas-C´ ardenas, Mar´ ıa Leonor Valderrama-Ch´ airez, Andr´ es Cruz-Hern´ andez, Octavio Paredes-L´ opez ∗ Departamento de Biotecnolog´ ıa y Bioqu´ ımica, Unidad Irapuato, Centro de Investigaci´ on y de Estudios Avanzados del IPN, Km 9.6 libramiento norte, Carretera Irapuato-Le´ on, Apartado Postal 629, CP 36500 Irapuato, Gto., Mexico Received 8 August 2006; accepted 10 December 2006 Abstract Polygalacturonase (PG; EC 3.2.1.6.9) has been the most widely studied cell wall hydrolase in fruit ripening. Degenerate oligonucleotides corresponding to conserved regions from reported sequences were used as primers for RT-PCR to amplify mRNA extracted from middle ripe fruit. Cloning and characterization of a cDNA OsPG showed a 282 bp product with a predicted sequence of 94 amino acids. The peptide exhibited a high identity with previously reported fruit PGs. Northern blot analysis of the messenger showed a 1.7 kb transcript induced during prickly pear ripening. It was found by Southern blot analysis that there is one copy of this gene. The OsPG mRNA expression is sensitive to ethylene, cold storage and wounding. © 2006 Elsevier B.V. All rights reserved. Keywords: Cell wall; Fruit ripening; Polygalacturonase; Prickly pear; Softening; Non-climacteric 1. Introduction Fresh or processed fruits are a very important source of vita- mins, minerals and carbohydrates. There is an increasing interest to improve the quality, nutrition and extend the variety of avail- able fruit. Fruit ripening is a dynamic developmental process and involves phenomena such as softening, which is the main fac- tor in determining the post-harvest deterioration of fruit crops (Tucker, 1993), and is associated with changes in cell wall composition due to the action of cell wall modifying enzymes (Fischer and Bennett, 1991; Barnavon et al., 2001). Pectins are a major class of cell wall polysaccharides, which are degraded during fruit ripening undergoing both depolymer- ization and solubilization (Hadfiel and Bennett, 1998). A wide range of cell wall hydrolases, such as endo PG and exo PG are known to catalyze pectin modification and disassembly of Abbreviations: DEPC, diethyl pyrocarbonate; PG, polygalacturonase ∗ Corresponding author. Tel.: +52 462 623 9641/74; fax: +52 462 624 5996. E-mail address: oparedes@ira.cinvestav.mx (O. Paredes-L´ opez). the cell wall (Brownleader et al., 1999; Nunan et al., 2001). The most studied and the best characterized of these enzymes are the polygalacturonases (PGs). An increase in its activity has been associated with fruit ripening, although the amount detected varies widely with species; for example the activity in tomato is about 50 times higher than in peach (Hadfiel and Bennett, 1998). PG activity has also been reported in lower lev- els in non-climacteric fruits such as strawberry, grape berry, and prickly pear (Redondo-Nevado et al., 2001; Nunan et al., 2001; Carrillo-L´ opez et al., 2002). PG cDNA was the first ripening related gene to be cloned from tomato. PG activity has long been known to increase dramati- cally during tomato fruit ripening (Fischer and Bennett, 1991). These studies have also shown that the increase in PG activity during ripening is preceded by augmented gene transcription. Although the presence of PG, pectin methylesterase, - galactosidase and cellulase in various climacteric fruits has been correlated with softening, reports of such activities and gene expression in non-climacteric fruit are scarce (Barnavon et al., 2001; Nunan et al., 2001; Carrillo-L ´ opez et al., 2002). Prickly pear represents an important resource for arid and semi-arid regions both as wild and cultivated plant populations 0925-5214/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2006.12.008