FvMYB79 Positively Regulates Strawberry Fruit Softening via Transcriptional Activation of FvPME38

Strawberry is a soft fruit with short postharvest life, due to a rapid loss of firmness. Pectin methylesterase (PME)-mediated cell wall remodeling is important to determine fruit firmness and softening. Previously, we have verified the essential role of FvPME38 in regulation of PME-mediated strawberry fruit softening. However, the regulatory network involved in PME-mediated fruit softening is still largely unknown. Here, we identified an R2R3-type MYB transcription factor FvMYB79, which activates the expression level of FvPME38, thereby accelerating fruit softening. During fruit development, FvMYB79 co-expressed with FvPME38, and this co-expression pattern was opposite to the change of fruit firmness in the fruit of ‘Ruegen’ which significantly decreased during fruit developmental stages and suddenly became very low after the color turning stage. Via transient transformation, FvMYB79 could significantly increase the transcriptional level of FvPME38, leading to a decrease of firmness and acceleration of fruit ripening. In addition, silencing of FvMYB79 showed an insensitivity to ABA-induced fruit ripening, suggesting a possible involvement of FvMYB79 in the ABA-dependent fruit softening process. Our findings suggest FvMYB79 acts as a novel regulator during strawberry ripening via transcriptional activation of FvPME38, which provides a novel mechanism for improvement of strawberry fruit firmness.

Inhibitory Effects of CaCl2 and Pectin Methylesterase on Fruit Softening of Raspberry during Cold Storage

Quality of raspberry fruit experiences a rapid decline after harvest due to its vulnerable texture and high moisture content. Application of calcium chloride (CaCl2) combined with pectin methylesterase (PME) is efficient in delaying fruit softening. In this study, the effects of exogenous CaCl2 alone or in combination with PME on the structure of the cell wall, the molecular properties of pectin, and the amount of free water of raspberry during postharvest storage were investigated. The results showed that CaCl2 combined with PME treatment could maintain fruit firmness and inhibit weight loss. The treatment of CaCl2+PME maintained the cell wall structure via sustaining middle lamella integrity and reducing the activities of cell wall-degrading enzymes, such as polygalacturonase, pectin methylesterase, β-galactosidase, α-L-arabinofuranosidase, and β-xylosidase. In addition, CaCl2+PME treatment could effectively increase the content of chelate-soluble pectin (CSP) and develop a cross-linked structure between Ca2+ and CSP. Moreover, CaCl2+PME treatment was of benefit in maintaining free water content. CaCl2 in combination with PME treatment could be a promising method for inhibiting softening and maintaining the quality of postharvest raspberry during cold storage.

A Novel Method of a High Pressure Processing Pre-Treatment on the Juice Yield and Quality of Persimmon

This study investigates the effects of a high pressure processing pre-treatment (pre-HPP) on the juice yield of persimmon (Diospyros kaki L.) pulp and the pre-HPP plus HPP or thermal processing (TP) on microorganism inactivation and quality changes of the persimmon juice. The “Gongcheng” persimmon was selected with the highest juice yield (48.9%), and the pre-HPP set at 300 MPa/8 min increased the juice yield by 60% through an increasing pectin methylesterase (PME) activity of 25.03% and by maintaining polygalacturonase (PG) activity. For different processing modes, namely, pre-HPP plus HPP at 550 Mpa/5 min and pre-HPP plus TP treatment at 95 °C/5 min, both of the guaranteed microorganisms in the juice were below 2.0 lg CFU/mL; however, the persimmon juice treated by the pre-HPP plus HPP had higher contents of total phenol and ascorbic acid which were 16.07 mg GAE/100 g and 17.92 mg/100 mL, respectively, a lower content of soluble tannin which was 55.64 μg/mL, better clarity which was 18.6% and less color change where the ΔE was only 2.68.

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

Background Pectin methylesterase (PME) is one of pectin-modifying enzyme that affects the pectin homeostasis in cell wall and regulates plant growth and diverse biological processes. The PME genes have been well explored and characterized in different plants. Nevertheless, systematic research on the soybean (Glycine max L.) PME genes remain lacking. Results We identified 127 Glycine max PME genes (GmPME) from the soybean Wm82.a2.v1 genome, which unevenly distributed on 20 soybean chromosomes. Phylogenetic analysis classified the GmPME genes into four clades (Group I, Group II, Group III and Group IV). GmPME gene members in the same clades displayed similar gene structures and motif patterns. The gene family expansion analysis demonstrated that segmental duplication was the major driving force to acquire novel GmPME genes compared to the tandem duplication events. Further synteny and evolution analyses showed that the GmPME gene family experienced strong purifying selective pressures during evolution. The cis-element analyses together with the expression patterns of the GmPME genes in various tissues suggested that the GmPME genes broadly participate in distinct biological processes and regulate soybean developments. Importantly, based on the transcriptome data and quantitative RT-PCR validations, we examined the potential roles of the GmPME genes in regulating soybean flower bud development and seed germination. Conclusion In conclusion, we provided a comprehensive characterization of the PME genes in soybean, and our work laid a foundation for the functional study of GmPME genes in the future.

BcMF27 , a Pectin Methylesterase Gene, Regulates Pollen Development And Pollen Tube Growth in Brassica Campestris

Functional pollen grains are an essential ingredient of successful reproduction in flowering plants and are protected by outer walls. Pectin methylesterases (PMEs) modify pectin, a structural component of pollen intine. However, there are few studies on PMEs. Artificial microRNA (amiRNA) and overexpression technology was performed to investigate the function of pollen-specific PME gene, BcMF27, in pollen development. Knockdown of BcMF27 led to pollen wall collapse, 20% of which unknown material adhered to. Wall-collapsed pollen had abnormally thick intine outside of the germinal furrows. A portion of the cytoplasm was degraded in the remaining pollen with unknown material on the wall, in addition to a thick intine. Overexpression of BcMF27 resulted in 66.67% pollen wall disruption, causing an abnormally thick intine. In addition, functional interruption of BcMF27 gave rise to pollen tubes twisted in vitro. Taken together, BcMF27 contributes to the intine morphogenesis during pollen development and stabilizes pollen tube elongation. This research can promote knowledge of PMEs function and the molecular mechanism in pollen wall construction.

PME and CaCl2 vacuum infusion maintains the firmness and physicochemical characteristics of tomato fruits

Tomato is a fruit of great commercial importance and highly cultivated. However, postharvest losses represent one of the main problems of this crop and can be minimized as alternative techniques. Therefore, the objective of the present work was to maintain tomato firmness by applying calcium chloride-associated pectin-methylesterase (PME) by the vacuum infusion method. Tomatoes of cultivar IAP-6 were submitted to vacuum infusion with water, vacuum infusion with 5% calcium chloride and vacuum infusion with PME associated with 5% calcium chloride, fruits without infusion were used as control. Fresh mass loss, fruit firmness, peel color, soluble solids content, pH, total acidity, PME activity and calcium activity were evaluated. The experiment was carried out in a completely randomized design in a 4x5 factorial scheme with three replications for 12 days, evaluated every 3 days. The means were compared using the Tukey test (p <0.05). Data were analyzed graphically with confidence interval (CI p <0.05). Regarding the loss of fresh mass there was an increase over time in all treatments. The PME + CaCl2 5% treatment was the most suitable for reducing firmness loss, as well as presenting the smallest variation of PME activity, as well as low levels of organic acids. Therefore, vacuum infusion with PME + CaCl2 in tomatoes maintains acceptable firmness and physicochemical characteristics as well as CaCl2 infusion.

BcMF27, A Pectin Methylesterase Gene, Regulates Pollen Development and Pollen Tube Growth in Brassica Campestris

Functional pollen grains are an essential ingredient of successful reproduction in flowering plants and are protected by outer walls. Pectin methylesterases (PMEs) modify pectin, a structural component of pollen intine. However, there are few studies on PMEs. Artificial microRNA (amiRNA) and overexpression technology was performed to investigate the function of pollen-specific PME gene, BcMF27, in pollen development. Knockdown of BcMF27 led to pollen wall collapse, 20% of which unknown material adhered to. Wall-collapsed pollen had abnormally thick intine outside of the germinal furrows. A portion of the cytoplasm was degraded in the remaining pollen with unknown material on the wall, in addition to a thick intine. Overexpression of BcMF27 resulted in 66.67% pollen wall disruption, causing an abnormally thick intine. In addition, functional interruption of BcMF27 gave rise to pollen tubes twisted in vitro. Taken together, BcMF27 contributes to the intine morphogenesis during pollen development and stabilizes pollen tube elongation. This research can promote knowledge of PMEs function and the molecular mechanism in pollen wall construction.

The Right-Handed Parallel β-Helix Topology of Erwinia chrysanthemi Pectin Methylesterase Is Intimately Associated with Both Sequential Folding and Resistance to High Pressure

The complex topologies of large multi-domain globular proteins make the study of their folding and assembly particularly demanding. It is often characterized by complex kinetics and undesired side reactions, such as aggregation. The structural simplicity of tandem-repeat proteins, which are characterized by the repetition of a basic structural motif and are stabilized exclusively by sequentially localized contacts, has provided opportunities for dissecting their folding landscapes. In this study, we focus on the Erwinia chrysanthemi pectin methylesterase (342 residues), an all-β pectinolytic enzyme with a right-handed parallel β-helix structure. Chemicals and pressure were chosen as denaturants and a variety of optical techniques were used in conjunction with stopped-flow equipment to investigate the folding mechanism of the enzyme at 25 °C. Under equilibrium conditions, both chemical- and pressure-induced unfolding show two-state transitions, with average conformational stability (ΔG° = 35 ± 5 kJ·mol−1) but exceptionally high resistance to pressure (Pm = 800 ± 7 MPa). Stopped-flow kinetic experiments revealed a very rapid (τ < 1 ms) hydrophobic collapse accompanied by the formation of an extended secondary structure but did not reveal stable tertiary contacts. This is followed by three distinct cooperative phases and the significant population of two intermediate species. The kinetics followed by intrinsic fluorescence shows a lag phase, strongly indicating that these intermediates are productive species on a sequential folding pathway, for which we propose a plausible model. These combined data demonstrate that even a large repeat protein can fold in a highly cooperative manner.