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

Abstract

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 abundantexpressed 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.

Fruit softening correlates with enzymatic activities and compositional changes in fruit cell wall during growing in Lycium barbarum L.

“…Cx causes degradation of the cellulose matrix in the fruit cell wall. α‐Gal catalyses the hydrolysis of α‐galactosidic bonds, and galactooligosaccharides specially, and provides D‐galactose for glycolysis to participate in energy metabolism (Ross et al ., 1993; Castro & Morales‐Quintana, 2019; Xue et al ., 2020). Besides, α‐Gal, Cx, PG, β‐Gal and PEM activities were negatively correlated with fruit firmness (Fig.…”

Genome-wide identification of PME genes, evolution and expression analyses in soybean (Glycine max L.)

“…The dynamics of cell walls such as constructions, differentiations, maturations and degradations are crucial for regulating plant growth [ 1 , 2 ]. Pectin is one of the most abundant components of plant cell walls, which is associated with the porosity and hydration of the cell wall as well as the plant cell intercellular adhesion [ 3 , 4 ].…”

“…Pectin methylesterase (PME, EC 3.1.1.11), so-called pectinesterase, is a hydrolytic enzyme that catalyzes the de-esterification of methyl esterified galacturonic acid residues of pectin to generate carboxyl groups and release methanol and hydrogen ions in the cell wall [ 7 , 8 ]. A high level of PME often induces the loosening of the cell wall, whereas, low PME activity tends to form a rigid cell wall [ 2 ]. Early studies turned out that the PME activity was tightly linked to distinct plant developmental courses, including pollen tube elongation [ 9 , 10 ], seed germination [ 11 , 12 ], hypocotyl growth [ 13 , 14 ], fruit ripening and softening [ 2 , 15 , 16 ].…”

“…A high level of PME often induces the loosening of the cell wall, whereas, low PME activity tends to form a rigid cell wall [ 2 ]. Early studies turned out that the PME activity was tightly linked to distinct plant developmental courses, including pollen tube elongation [ 9 , 10 ], seed germination [ 11 , 12 ], hypocotyl growth [ 13 , 14 ], fruit ripening and softening [ 2 , 15 , 16 ].…”

“…In recent years, whole-genome sequencing technologies promoted the exploration of multiple gene families in diverse species [ 17 ]. Genome-wide identifications and characterizations of PME genes have been carried out in diverse plant species, including Arabidopsis [ 18 ], rice [ 19 ], maize [ 20 ], cotton [ 21 ], tomato [ 16 ] and strawberry [ 2 ]. For the gene structures, all the PME gene members contain the PME domains, and some of them meanwhile harbor the PME inhibitor (PMEI) domains [ 21 ].…”