Abstract
Fruit softening is mainly associated with cell wall structural modifications, and members of the xyloglucan endotransglucosylase/hydrolase (XTH) family are key enzymes involved in cleaving and re-joining xyloglucan in the cell wall. In this work, we isolated a new XTH gene, DkXTH8, from persimmon fruit. Transcriptional profiling revealed that DkXTH8 peaked during dramatic fruit softening, and expression of DkXTH8 was stimulated by propylene and abscisic acid but suppressed by gibberellic acid and 1-MCP. Transient expression assays in onion epidermal cells indicated direct localization of DkXTH8 to the cell wall via its signal peptide. When expressed in vitro, the recombinant DkXTH8 protein exhibited strict xyloglucan endotransglycosylase activity, whereas no xyloglucan endohydrolase activity was observed. Furthermore, overexpression of DkXTH8 resulted in increased leaf senescence coupled with higher electrolyte leakage in Arabidopsis and faster fruit ripening and softening rates in tomato. Most importantly, transgenic plants overexpressing DkXTH8 displayed more irregular and twisted cells due to cell wall restructuring, resulting in wider interstitial spaces with less compact cells. We suggest that DkXTH8 expression causes cells to be easily destroyed, increases membrane permeability and cell peroxidation, and accelerates leaf senescence and fruit softening in transgenic plants.
Highlights
Fruit softening is mainly associated with cell wall structural modifications, and members of the xyloglucan endotransglucosylase/hydrolase (XTH) family are key enzymes involved in cleaving and rejoining xyloglucan in the cell wall
A new full-length sequence named DkXTH8 was amplified from persimmon (Diospyros kaki L. cv Fuping jianshi); the sequence has been deposited in GenBank under accession number KF318888
Previous works have reported that xyloglucan endotransglycosylase/hydrolase (XTH) are encoded by a large multigene family[9,10]
Summary
Fruit softening is mainly associated with cell wall structural modifications, and members of the xyloglucan endotransglucosylase/hydrolase (XTH) family are key enzymes involved in cleaving and rejoining xyloglucan in the cell wall. We suggest that DkXTH8 expression causes cells to be destroyed, increases membrane permeability and cell peroxidation, and accelerates leaf senescence and fruit softening in transgenic plants. Fruit softening occurs primarily through modifications to the cell wall as the result of cell wall polymer degradation catalyzed by diverse enzymes such as cellulase, polygalacturonase, β-galactosidase, pectate lyase, and xyloglucan endotransglycosylase/hydrolase (XTH)[1,2,3]. Xyloglucan, the major hemicellulose in the primary cell wall of dicotyledonous plants, comprises a network with cellulose microfibrils to provide strength to the cell wall[5,6], with xyloglucan endotransglucosylases/hydrolases (XTHs) functioning in xyloglucan metabolism through xyloglucan endotransglycosylase (XET) and/or xyloglucan endohydrolase (XEH) activities[7,8]. Correspondence and requests for materials should be addressed to J.R. (email: raojingpingxn@163. com) www.nature.com/scientificreports/
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