Down-regulation of an Auxin Response Factor in the tomato induces modification of fine pectin structure and tissue architecture

Abstract

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) alpha-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.

Ethylene control of fruit ripening: revisiting the complex network of transcriptional regulation

“…The auxin inhibitor p-Chlorophenoxyisobutyric acid mimics ACC treatment, confirming the antagonistic action of the two hormones during fruit ripening, and auxin delays tomato ripening by affecting a set of key factors, such as RIN, ethylene, and ABA (Su et al, 2015). Consistent with the role of auxin in fruit ripening, tomato fruit firmness was shown to be partly regulated by tomato Auxin Response Factor4 (SlARF4), a transcription factor known to mediate auxin responses Guillon et al, 2008;Sagar et al, 2013). More recently, SlARF2, a tomato auxin response factor, was described as an essential component of the regulatory network controlling fruit ripening.…”

SlARF4, an Auxin Response Factor Involved in the Control of Sugar Metabolism during Tomato Fruit Development

“…Moreover, the link between auxin biosynthesis or signaling and sugar accumulation in the fruit tissues has been highlighted by a number of studies (Pandolfini et al, 2002;Wang et al, 2009), though the mechanisms by which this hormone impacts sugar metabolism and therefore fruit quality remain poorly understood. Previous work demonstrated that DR12/ARF4, a member of the tomato ARF gene family of transcription factors, is involved in the regulation of fruit development; that is, transgenic tomato plants with decreased SlARF4 mRNA levels produced dark-green fruit at immature stages, with increased chlorophyll content, a larger number of chloroplasts, and unusual cell division at late stages of fruit development, as well as blotchy ripening and enhanced fruit firmness (Jones et al, 2002;Guillon et al, 2008). In further characterizing the role of this auxin transcriptional regulator, the current study addresses more specifically the impact of down-regulation of SlARF4 on sugar metabolism throughout fruit development.…”

Gene and Metabolite Regulatory Network Analysis of Early Developing Fruit Tissues Highlights New Candidate Genes for the Control of Tomato Fruit Composition and Development

“…cell volume, shape, and adhesion; Fig. 1) that affect visual aspect and major texture attributes of the fruit (Rose and Bennett, 1999;Cheniclet et al, 2005;Chaïb et al, 2007;Guillon et al, 2008). To get an insight into the regulation of the developmental and metabolic processes taking place in expanding fruit tissues, we analyzed at cytological, transcriptomic, and metabolic levels two major tomato fruit tissues, the mesocarp and the locular tissue, from the end of the cell division period to the end of the cell expansion period and combined these data.…”