Abstract
SummaryFruit softening in Fragaria (strawberry) is proposed to be associated with the modification of cell wall components such as xyloglucan by the action of cell wall‐modifying enzymes. This study focuses on the in vitro and in vivo characterization of two recombinant xyloglucan endotransglucosylase/hydrolases (XTHs) from Fragaria vesca, FvXTH9 and FvXTH6. Mining of the publicly available F. vesca genome sequence yielded 28 putative XTH genes. FvXTH9 showed the highest expression level of all FvXTHs in a fruit transcriptome data set and was selected with the closely related FvXTH6 for further analysis. To investigate their role in fruit ripening in more detail, the coding sequences of FvXTH9 and FvXTH6 were cloned into the vector pYES2 and expressed in Saccharomyces cerevisiae. FvXTH9 and FvXTH6 displayed xyloglucan endotransglucosylase (XET) activity towards various acceptor substrates using xyloglucan as the donor substrate. Interestingly, FvXTH9 showed activity of mixed‐linkage glucan:xyloglucan endotransglucosylase (MXE) and cellulose:xyloglucan endotransglucosylase (CXE). The optimum pH of both FvXTH9 and FvXTH6 was 6.5. The prediction of subcellular localization suggested localization to the secretory pathway, which was confirmed by localization studies in Nicotiana tabacum. Overexpression showed that Fragaria × ananassa fruits infiltrated with FvXTH9 and FvXTH6 ripened faster and showed decreased firmness compared with the empty vector control pBI121. Thus FvXTH9 and also FvXTH6 might promote strawberry fruit ripening by the modification of cell wall components.
Highlights
Plant cells are surrounded by a primary cell wall that consists of polysaccharides, proteins and sometimes lignin, and exhibits variability in composition and organization
Fruit softening in Fragaria is proposed to be associated with the modification of cell wall components such as xyloglucan by the action of cell wall-modifying enzymes
This study focuses on the in vitro and in vivo characterization of two recombinant xyloglucan endotransglucosylase/hydrolases (XTHs) from Fragaria vesca, FvXTH9 and FvXTH6
Summary
Plant cells are surrounded by a primary cell wall that consists of polysaccharides, proteins and sometimes lignin, and exhibits variability in composition and organization. The ripening-associated softening of fleshy fruit such as Fragaria (strawberry) is related to the selective modification of cell wall architecture (Prasanna et al, 2007; Fry, 2017a). Modifications in the cell wall structure are characterized by the solubilization of pectic polysaccharides and by a decrease in the polymer size of xyloglucan (Hayashi and Kaida, 2011; Paniagua et al., 2017). The alteration of linkages between the polymers, such as in the cellulose–hemicellulose interaction, in parallel with decreasing fruit firmness takes place (Brummell, 2006; Vicente et al, 2007). Strawberry fruit have a short post-harvest shelf life as a result of the dramatic reduction in firmness during ripening. Recent findings showed that strawberry softening is closely related to pectin metabolism (Paniagua et al, 2017). The middle lamella of the cortical parenchyma cells is extensively degraded throughout ripening in strawberry
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