Abstract

BackgroundFragaria vesca or ‘woodland strawberry’ has emerged as an attractive model for the study of ripening of non-climacteric fruit. It has several advantages, such as its small genome and its diploidy. The recent availability of the complete sequence of its genome opens the possibility for further analysis and its use as a reference species. Fruit softening is a physiological event and involves many biochemical changes that take place at the final stages of fruit development; among them, the remodeling of cell walls by the action of a set of enzymes. Xyloglucan endotransglycosylase/hydrolase (XTH) is a cell wall-associated enzyme, which is encoded by a multigene family. Its action modifies the structure of xyloglucans, a diverse group of polysaccharides that crosslink with cellulose microfibrills, affecting therefore the functional structure of the cell wall. The aim of this work is to identify the XTH-encoding genes present in F. vesca and to determine its transcription level in ripening fruit.ResultsThe search resulted in identification of 26 XTH-encoding genes named as FvXTHs. Genetic structure and phylogenetic analyses were performed allowing the classification of FvXTH genes into three phylogenetic groups: 17 in group I/II, 2 in group IIIA and 4 in group IIIB. Two sequences were included into the ancestral group. Through a comparative analysis, characteristic structural protein domains were found in FvXTH protein sequences. In complement, expression analyses of FvXTHs by qPCR were performed in fruit at different developmental and ripening stages, as well as, in other tissues. The results showed a diverse expression pattern of FvXTHs in several tissues, although most of them are highly expressed in roots. Their expression patterns are not related to their respective phylogenetic groups. In addition, most FvXTHs are expressed in ripe fruit, and interestingly, some of them (FvXTH 18 and 20, belonging to phylogenic group I/II, and FvXTH 25 and 26 to group IIIB) display an increasing expression pattern as the fruit ripens.ConclusionA discrete group of FvXTHs (18, 20, 25 and 26) increases their expression during softening of F. vesca fruit, and could take part in cell wall remodeling required for softening in collaboration with other cell wall degrading enzymes.

Highlights

  • Fragaria vesca or ‘woodland strawberry’ has emerged as an attractive model for the study of ripening of non-climacteric fruit

  • Strawberry fruit ripening is not accompanied by a burst of ethylene activity as seen in climacteric fruit, ethylene plays an important role in its ripening [8, 9]

  • FvXTHs identification Aiming to identify the complete set of Xyloglucan endotransglycosylase/hydrolase (XTH) family members in F. vesca, we searched the public database of the Hawaii 4 strawberry reference genome version 1.1

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Summary

Introduction

Fragaria vesca or ‘woodland strawberry’ has emerged as an attractive model for the study of ripening of non-climacteric fruit. It has several advantages, such as its small genome and its diploidy. Ripening has been well characterized in climacteric fruits such as tomato, where ethylene induces and controls the associated changes, which are due to the coordinated action of thousands of genes [2]. The cultivated strawberry, Fragaria x ananassa, has been a widely studied subject of non-climacteric fruit ripening [7,8,9]. The complex octoploid genome composition of the cultivated strawberry F. x ananassa complicates molecular dissection of its physiological processes [10], including the role of ethylene in fruit ripening. The diploid strawberry model system [11] is an enticing alternate system in which to study the molecular mechanisms of fruit ripening

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