JXB Advance Access published online on February 10, 2008
Journal of Experimental Botany, doi:10.1093/jxb/erm323
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RESEARCH PAPER |
Down-regulation of an Auxin Response Factor in the tomato induces modification of fine pectin structure and tissue architecture
1UR1268 Biopolymères Interactions Assemblages, INRA, F-44300 Nantes, France
2UMR990 Génomique et Biotechnologique des Fruits, INRA/INTP-ENSA Toulouse, Université de Toulouse, F-31326 Catsanet Toloson, France
* To whom correspondence should be addressed. E-mail: guillon{at}nantes.inra.fr
It has previously been shown that down-regulation of an auxin response factor gene (DR12) results in pleiotropic phenotypes including enhanced fruit firmness in antisense transgenic tomato (AS-DR12). To uncover the nature of the ripening-associated modifications affecting fruit texture, comparative analyses were performed of pectin composition and structure in cell wall pericarp tissue of wild-type and AS-DR12 fruit at mature green (MG) and red-ripe (RR) stages. Throughout ripening, pectin showed a decrease in methyl esterification and in the content of galactan side chains in both genotypes. At mature green stage, pectin content in methyl ester groups was slightly higher in AS-DR12 fruit than in wild type, but this ratio was reversed at the red-ripe stage. The amount of water- and oxalate-soluble pectins increased at the red-ripe stage in the wild type, but decreased in AS-DR12. The distribution of methyl ester groups on the homogalaturonan backbone differed between the two genotypes. There was no evidence of more calcium cross-linked homogalacturan involved in cell-to-cell adhesion in AS-DR12 compared with wild-type fruit. Furthermore, the outer pericarp contains higher proportion of small cells in AS-DR12 fruit than in wild type and higher occurrence of (1
5) 
-L-arabinan epitope at the RR stage. It is concluded that the increased firmness of transgenic fruit does not result from a major impairment of ripening-related pectin metabolism, but rather involves differences in pectin fine structure associated with changes in tissue architecture.
Key words: Auxin, cell wall, firmness, fruit, pectin, pericarp, tomato
Received 12 July 2007; Revised 25 October 2007 Accepted 9 November 2007
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