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DEVELOPMENT AND HORMONE ACTION

Antisense Down-Regulation of the FaPG1 Gene Reveals an Unexpected Central Role for Polygalacturonase in Strawberry Fruit Softening^1,[W]

Departemento Biología Vegetal, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga, Spain (M.A.Q., S.P., F.P.-A., J.A.M.); Instituto de Investigación y Formación Agraria y Pesquera, Centro de Churriana, 29140 Málaga, Spain (J.A.G.-G., S.J.-B.); Departemento Genética, Universidad de Córdoba, 14071 Córdoba, Spain (A.M.-S.); and Departemento Bioquímica y Biología Molecular, Universidad de Córdoba, 14071 Córdoba, Spain (R.B.-P., J.L.C., J.M.-B.)

The strawberry (Fragaria x ananassa ‘Chandler’) fruit undergoes a fast softening during ripening. Polygalacturonase (PG) activity is low during this process, but two ripening-related PG genes, FaPG1 and FaPG2, have been cloned. Both genes were up-regulated during fruit ripening and were also negatively regulated by auxin. To further assess the role of FaPG1 on strawberry softening, transgenic plants containing an antisense sequence of this gene under the control of the 35S promoter (APG lines) were obtained. Sixteen out of 30 independent transgenic lines showed fruit yields similar to those of the control. Several quality parameters were measured in ripe fruits from these 16 lines. Fruit weight was slightly reduced in four lines, and most of them showed an increase in soluble solid content. Half of these lines yielded fruits significantly firmer than did the control. Four APG lines were selected, their ripened fruits being on average 163% firmer than the control. The postharvest softening of APG fruits was also diminished. Ripened fruits from the four selected lines showed a 90% to 95% decrease in FaPG1 transcript abundance, whereas the level of FaPG2 was not significantly altered. Total PG activity was reduced in three of these lines when compared with control fruits. Cell wall extracts from APG fruits showed a reduction in pectin solubilization and an increase in pectins covalently bound to the cell wall. A comparative transcriptomic analysis of gene expression between the ripened receptacle of the control and those of the APG fruits (comprising 1,250 receptacle expressed sequence tags) did not show any statistically significant change. These results indicate that FaPG1 plays a central role in strawberry softening.

² These authors contributed equally to the article.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: José A. Mercado (mercado{at}uma.es).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.138297

^* Corresponding author; e-mail mercado{at}uma.es.

Received March 9, 2009; accepted April 19, 2009; published April 24, 2009.