Genome wide identification and functional characterization of strawberry pectin methylesterases related to fruit softening

Abstract

AbstractBackgroundPectin methylesterase (PME) is a hydrolytic enzyme that catalyzes the demethylesterification of homogalacturonans and controls pectin reconstruction, being essential in regulation of cell wall modification. During fruit ripening stage, PME-mediated cell wall remodeling is an important process to determine fruit firmness and softening. Strawberry fruit is a soft fruit with a short postharvest life, due to a rapid loss of firm texture. Hence, preharvest improvement of strawberry fruit rigidity is a prerequisite for extension of fruit refreshing time. Although PME has been well characterized in model plants, knowledge regarding the functionality and evolutionary property ofPMEgene family in strawberry remain limited.ResultsA total of 54PMEgenes (FvPMEs) were identified in woodland strawberry (Fragaria vesca‘Hawaii 4’). Phylogeny and gene structure analysis divided theseFvPMEgenes into four groups (Group 1–4). Duplicate events analysis suggested that tandem and dispersed duplications effectively contributed to the expansion of the PME family in strawberry. Through transcriptome analysis, we identifiedFvPME38andFvPME39as the most abundant-expressedPMEs at fruit ripening stages, and they were positively regulated by abscisic acid. Genetic manipulation ofFvPME38andFvPME39by overexpression and RNAi-silencing significantly influences the fruit firmness, pectin content and cell wall structure, indicating a requirement of PME for strawberry fruit softening.ConclusionOur study globally analyzed strawberry pectin methylesterases by the approaches of phylogenetics, evolutionary prediction and genetic analysis. We verified the essential role ofFvPME38andFvPME39in regulation of strawberry fruit softening process, which provided a guide for improving strawberry fruit firmness by modifying PME level.