Isolation and Characterization of Two Persimmon Xyloglucan Endotransglycosylase/Hydrolase (XTH) Genes That Have Divergent Functions in Cell Wall Modification and Fruit Postharvest Softening.

Ye Han,Jiangtao Suo,Jingping Rao,Kun Meng,Qiuyan Ban,Yali Hou

doi:10.3389/fpls.2016.00624

Ye Han, Jiangtao Suo + Show 4 more

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https://doi.org/10.3389/fpls.2016.00624

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Abstract

Fruit cell wall modification is the primary factor affecting fruit softening. Xyloglucan endotransglycosylase/hydrolase (XTH), a cell wall-modifying enzyme, is involved in fruit softening. In this study, two novel XTH genes (DkXTH6 and DkXTH7) were identified from persimmon fruit. Transcriptional profiles of both of the two genes were analyzed in different tissues of persimmon, and in response to multiple hormonal and environmental treatments [gibberellic acid (GA3), abscisic acid (ABA), propylene, and low temperature]. Expression of DkXTH6 was positively up-regulated during ethylene production and by propylene and ABA treatments, and suppressed by GA3 and cold treatment. In contrast, DkXTH7 exhibited its highest transcript levels in GA3-treated fruit and cold-treated fruit, which had higher fruit firmness. We found that DkXTH6 protein was localized in cell wall by its signal peptide, while cytoplasmic DkXTH7 protein contained no signal peptide. When expressed in vitro, the recombinant proteins of both DkXTH6 and DkXTH7 exhibited strict xyloglucan endotransglycosylase (XET) activity but no xyloglucan endohydrolase (XEH) activity. The recombinant protein of DkXTH6 showed a higher affinity with small acceptor molecules than the recombinant DkXTH7. Taken together with their opposing expression patterns and subcellular localizations, these results suggested that DkXTH6 might take part in cell wall restructuring and DkXTH7 was likely to be involved in cell wall assembly, indicating their special roles in persimmon fruit softening.

Highlights

Persimmon (Diospyros kaki L. cv Fuping jianshi) is rich in nutrition and has a unique flavor, but it softens and decays quickly, which affects badly its marketability (Zhang et al, 2012; Lv et al, 2014)
Two novel full-length sequences designated as DkXTH6 and DkXTH7 were isolated from persimmon fruit and submitted to GenBank with the accession numbers of KC511053 and KC541541, respectively
The DkXTH7 cDNA, 1105 bp, consisted a full-length open reading frame (ORF) of 807 bp (106–912 bp), and a deduced polypeptide of nearly 30.83 kDa, which comprised of 268 amino acids with a pI of 6.32

Summary

Introduction

Persimmon (Diospyros kaki L. cv Fuping jianshi) is rich in nutrition and has a unique flavor, but it softens and decays quickly, which affects badly its marketability (Zhang et al, 2012; Lv et al, 2014). Fleshy fruit softening is associated with significant biochemical changes in cell wall fractions (Vicente et al, 2007; Matas et al, 2009), usually resulting from cell wall polymer breakdown catalyzed by various cell wall enzymes, such as polygalacturonase, pectate lyase, β-galactosidase, cellulase, and xyloglucan endotransglycosylase/hydrolase (XTH; Cosgrove, 2005; Figueroa et al, 2008; Payasi et al, 2009). In the cell wall of most dicotyledons, xyloglucan is the major hemicellulosic polysaccharide, which can form skeletal networks with the cellulose fibrils to confer strength and rigidity on the wall (Schroder et al, 1998; Zhu et al, 2013). It has been demonstrated that there are two types of endotransglycosylase; integrational XET catalyzes a newly secreted xyloglucan molecule’s reaction with a previously formed wall-bound xyloglucan, while restructuring XET catalyzes a reaction between two preformed wall-bound xyloglucan molecules (Thompson and Fry, 2001)

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