BACKGROUND Pectin 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 of PME gene family in strawberry remain limited. RESULTS A total of 54 PME genes (FvPMEs) were identified in woodland strawberry (Fragaria vesca 'Hawaii 4'). Phylogeny and gene structure analysis divided these FvPME genes 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 identified FvPME38 and FvPME39 as the most abundant-expressed PMEs at fruit ripening stages, and they were positively regulated by abscisic acid. Genetic manipulation of FvPME38 and FvPME39 by overexpression and RNAi-silencing significantly influences the fruit firmness, pectin content and cell wall structure, indicating a requirement of PME for strawberry fruit softening. CONCLUSION Our study globally analyzed strawberry pectin methylesterases by the approaches of phylogenetics, evolutionary prediction and genetic analysis. We verified the essential role of FvPME38 and FvPME39 in regulation of strawberry fruit softening process, which provided a guide for improving strawberry fruit firmness by modifying PME level.

中文翻译：

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与水果软化有关的草莓果胶甲酯酶的全基因组鉴定和功能表征。

背景技术果胶甲基酯酶（PME）是一种水解酶，其催化高半乳糖醛酸聚糖的去甲基酯化并控制果胶的重建，这在调节细胞壁修饰中必不可少。在果实成熟阶段，PME介导的细胞壁重塑是确定果实硬度和软化的重要过程。草莓果实是一种柔软的水果，由于迅速失去了坚实的质地，因此具有较短的收获后寿命。因此，草莓果实刚度的收获前改善是延长果实刷新时间的前提。尽管在模型植物中已经很好地表征了PME，但是关于草莓中PME基因家族的功能和进化特性的知识仍然有限。结果在林地草莓（草莓草莓'夏威夷4号'）中共鉴定出54个PME基因（FvPMEs）。系统发育和基因结构分析将这些FvPME基因分为四个组（第1-4组）。重复事件分析表明，串联重复和分散重复有效地促进了草莓PME家族的扩大。通过转录组分析，我们确定FvPME38和FvPME39是果实成熟阶段表达最丰富的PME，并且它们受脱落酸的正调控。过表达和RNAi沉默对FvPME38和FvPME39的遗传操作显着影响果实的硬度，果胶含量和细胞壁结构，表明PME对草莓果实软化的要求。结论我们的研究通过系统发育，进化预测和遗传分析的方法对草莓果胶甲基酯酶进行了全球分析。