Abstract
BackgroundFruit quality depends on a series of biochemical events that modify appearance, flavour and texture throughout fruit development and ripening. Cell wall polysaccharide remodelling largely contributes to the elaboration of fleshy fruit texture. Although several genes and enzymes involved in cell wall polysaccharide biosynthesis and modifications are known, their coordinated activity in these processes is yet to be discovered.ResultsCombined transcriptomic and biochemical analyses allowed the identification of putative enzymes and related annotated members of gene families involved in cell wall polysaccharide composition and structural changes during apple fruit growth and ripening. The early development genes were mainly related to cell wall biosynthesis and degradation with a particular target on hemicelluloses. Fine structural evolutions of galactoglucomannan were strongly correlated with mannan synthase, glucanase (GH9) and β-galactosidase gene expression. In contrast, fewer genes related to pectin metabolism and cell expansion (expansin genes) were observed in ripening fruit combined with expected changes in cell wall polysaccharide composition.ConclusionsHemicelluloses undergo major structural changes particularly during early fruit development. The high number of early expressed β-galactosidase genes questions their function on galactosylated structures during fruit development and storage. Their activity and cell wall substrate remains to be identified. Moreover, new insights into the potential role of peroxidases and transporters, along with cell wall metabolism open the way to further studies on concomitant mechanisms involved in cell wall assembly/disassembly during fruit development and storage.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0887-0) contains supplementary material, which is available to authorized users.
Highlights
Fruit quality depends on a series of biochemical events that modify appearance, flavour and texture throughout fruit development and ripening
Cell wall characterization The global sugar composition of cell wall prepared as an alcohol insoluble material (AIM) was analysed at each developmental and storage stage (Table 1)
Acetyl ester content decreased during the ripening stages from 1.5 % at 60DAF to 1.2 % of non-starch polysaccharides (NSP) at 2 months of cold storage (2 M)
Summary
Fruit quality depends on a series of biochemical events that modify appearance, flavour and texture throughout fruit development and ripening. Cell wall polysaccharide remodelling largely contributes to the elaboration of fleshy fruit texture. Apple (Malus domestica) fruit development involves a series of biochemical events determinant for qualitative traits, such as appearance, flavour and texture [1]. The relative content of the major cell wall sugars represented by galacturonic acid attributed to pectin, and glucose from cellulose and hemicelluloses increase during apple ripening [9, 10]. Galactose and arabinose content decreases during fruit expansion and further declines during ripening [10,11,12,13] This is due in part to β-galactosidases and α-arabinofuranosidases degradation of the galactan and arabinan side chains of the pectic rhamnogalacturonan I (RGI) [6, 14, 15]. Methyl ester substitutions of the homogalacturonan structural domain of pectins (HG) are partly removed by the action of pectin methylesterases (PME) during apple development [16, 17]
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