Higher expression of the strawberry xyloglucan endotransglucosylase/hydrolase genes FvXTH9 and FvXTH6 accelerates fruit ripening.

Fruit softening in 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 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 donor substrate. Interestingly, FvXTH9 showed activity of mixed-linkage glucan:xyloglucan endotransglucosylase (MXE) and cellulose:xyloglucan endotransglucosylase (CXE). The pH optimum of both FvXTH9 and FvXTH6 was 6.5. Prediction of the sub-cellular localization suggested localization to the secretory pathway, which was confirmed by localization studies in Nicotiana tabacum. Overexpression showed that F. × ananassa fruits infiltrated with FvXTH9 and FvXTH6 ripened faster and showed decreased firmness compare to the empty vector control pBI121. Thus, FvXTH9 and also FvXTH6 might promote strawberry fruit ripening by modification of cell wall components. This article is protected by copyright. All rights reserved.